Our brains are uniquely complex information processors, yet most people know little about how they work. When we understand how our brains have evolved to function, we can work with our brains’ natural impulses and tendencies to improve our thinking and learning in all aspects of our lives.
John Medina argues that our brains have evolved to increase our chances of survival by achieving these three core functions:
He takes the reader step-by-step through 12 rules that he says help fulfill these core functions. We’ve grouped these rules into five categories that correspond to recurring themes among them:
Medina argues that our environment has shaped our brain development throughout our evolution and continues to influence the way our brain works today. He proposes two rules that underpin this theory:
Medina explains that our brains evolved in response to changes in both our physical bodies and our environments. Each of these influences led to the development of our unique human abilities.
When we evolved to walk on two legs instead of four, our bodies could send more energy to our brains because walking on two legs is more efficient. In addition, when we adapted to environments ranging from jungles to savannahs and beyond, our brains had to prove flexible enough to respond to the different survival pressures.
(Shortform note: Research supports Medina’s theory that walking on two legs freed up energy for brain development—recent studies show that chimpanzees use much less energy when they walk on two legs instead of four. Scientists also largely agree that our brains developed in response to environmental changes but often disagree about which changes had the most impact—some researchers believe that the most brain development occurred during highly variable climactic periods, while others think it happened more during stable periods, which were most conducive to thriving human life.)
Medina argues that in response to these influences, we developed three uniquely human characteristics:
Medina explains that while our brains all fulfill the same basic functions, the neural structure of every brain is unique to every individual. This is why every person has an individual array of talents and skills.
Neurons are the cells that carry out the brain’s functions. They allow the brain to absorb information.Our brains create neural paths—connections between neurons that shape our thoughts and emotions—each time we’re exposed to new things. Because everyone has unique, individual experiences, everyone develops a unique neural network, which means everyone develops their own, individual way of reacting to and understanding the world.
(Shortform note: Researchers note that experiences early in life have more of an effect on neural growth than experiences later in life. For example, experiences with language early in life influence a person’s language skills later in life. Studies show that, if someone is regularly exposed to multiple languages as an infant, they’re more likely to be bilingual later on. And children who learn two languages to fluency typically develop a larger left brain hemisphere.)
The first category described how fundamental natural processes influence the brain. In this category, Medina explores more deeply how aspects of our individual environments and lifestyles influence our brain functions. He writes that exercise, sleep, and stress are three key aspects of our lives which affect our cognition, brain health, and learning.
Medina argues that our brain function is highly influenced by whether or not we exercise, and that more exercise results in more brain power.
According to Medina, our ability and desire to exercise is baked into our biology. As we’ve mentioned before, humans had to contend with intense environmental conditions, and constant motion was necessary for survival.
Exercise boosts cognition by increasing blood flow to the brain. When we exercise, our bodies create new blood vessels, which allow blood to circulate more efficiently. This brings more oxygen-rich blood to the brain.
The oxygen serves two functions: It feeds our brain cells—helping neurons stay young and operational—and it removes harmful toxins. Increasing the flow of oxygen, then, immensely helps the brain carry out its essential functions, including cognitive abilities like memory, focus, and problem solving.
(Shortform note: Most people benefit when they get increased levels of oxygen to their brain, but some suffer from the opposite problem: too much oxygen to the brain, which can hurt memory function. This can happen in people with mild cognitive impairment (MCI), when their bodies pump excess blood to their brains in an attempt to make up for their reduced cognitive function, which ironically exacerbates that reduced function. Researchers have found that for adults with MCI, exercise helps regulate their blood flow, reducing the excess flow to their brains and improving cognition.)
Medina argues that even though exercise has proven benefits, the structures of contemporary life often prevent exercise: Many jobs necessitate sitting down for large portions of the day, and school requires kids to sit for hours at a time as well. Medina contends that it’s because of these sedentary lifestyles that many people suffer cognitive decline, particularly as they age.
Medina thus encourages you to find ways to incorporate exercise into your daily routines, even if it’s not what you’re used to. For instance, he recommends walking on a treadmill while working.
(Shortform note: According to a recent study, sitting for long periods of time is associated with the thinning of the MTL, a part of the brain that forms new memories. Over time, MTL thinning can lead to cognitive decline and dementia.)
Medina notes that just as we benefit from exercise, we benefit from regular rest: sleep. Sleep is an essential function of the brain which allows us to learn—and when we don’t get enough sleep, our cognitive abilities suffer.
Our sleep, and the quality of that sleep, is determined by biological processes. We’re wired to stay awake and go to sleep in predictable cycles. If these cycles are disrupted, we can get less sleep than we need and our cognition can suffer.
These biological processes differ from person to person, causing some people to be early risers (who wake up early and go to sleep early), some to be late risers (who wake up late and go to sleep late), and some to be somewhat in-between. He notes that finding a work and sleep schedule that best fits your sleep type will help you function better.
(Shortform note: While everyone has their own chronotype (the technical term for sleep type), people’s chronotypes follow a pattern based on age. Children typically have early chronotypes, which get progressively later in adolescence, and peak around the age of 20. Then, chronotypes get progressively earlier again (though men’s chronotypes are typically slower to change than women’s).)
Medina argues that stress interferes with our brain’s ability to learn because we haven’t evolved to handle it over a long period of time.
Medina notes that there are two kinds of stress: short-term stress (acute stress) and long-term stress (chronic stress).
Stress evolved as a survival response, since early humans faced a number of immediate dangers on a regular basis. He argues that people have evolved to manage acute stress well, because this is the type of stress that helps us avoid imminent threats. However, he argues that we haven’t evolved to handle chronic stress well.
Medina explains that chronic stress can degrade memory because it sends excessive amounts of the hormone cortisol to the hippocampus, which can disconnect neural networks. This causes memory loss and can prevent new cells from being created—and thus hurt your ability to form new memories and learn new information.
(Shortform note: Studies have noted two particularly significant impacts stress can have on learning: It damages the ability to retrieve information, which makes testing difficult, and damages the ability to change memories based on new information, which makes it difficult to build on pre-existing knowledge.)
According to Medina, understanding our brain’s responses to sensory stimuli helps our learning, work performance, and happiness. Medina writes that we learn best when we use more than one sense, that vision is the most important sense, and that we’re hardwired to respond to music.
In this chapter, Medina contends that using more than one sense at a time improves our learning.
Medina argues that our brains evolved to absorb and make sense of numerous sources of information at the same time, and have developed that capacity so effectively that they actually work best when doing so. We can see this in the fact that our brains better understand and react to different senses when using more than one:
(Shortform note: That senses activate and improve one another is dramatically illustrated in the phenomenon of synesthesia, a condition in which a person’s senses are activated by each other in unexpected ways. For example, a person with this condition (it’s estimated that 1 in 90 people has it) might see the color blue when she hears the number three. Though uncommon, synesthesia is a clear demonstration that our senses are hard-wired to work together.)
Medina writes that because our brains are more highly activated and are functioning more optimally when processing multiple senses at once, we can absorb information best when we use more than one sense to do so. Research backs this up: When people learn new information in several ways—for example, learning a language by reading it, listening to it, and watching a movie in it—they retain that information better and for longer.
(Shortform note: Many educators are aware of the efficacy of multisensory learning as a way to improve cognition, and they incorporate techniques based on it into their lessons. For example, teachers may have students who are learning letters to write them out using their hands in shaving cream while saying them out loud—thus engaging the senses of vision, hearing, and feel to help them learn.)
Medina argues that vision leads and influences all the other senses, shaping our perception of the world and influencing our learning and memory.
He notes that about half of the brain is dedicated to perceiving and interpreting vision. Because it takes up so much more space in the brain than other senses, vision can overrule other sensory input. Thus, if we receive contradictory information from multiple senses, vision tends to win out.
(Shortform note: The tendency of vision to override other senses, even when inaccurate, is called the Colavita visual dominance effect. While most people experience this effect, research shows that people with autism spectrum disorder may experience the reverse—in one study, hearing overrode vision for autistic subjects, even though vision overrode hearing for subjects without ASD. This “reverse Colavita effect” shows that, despite established patterns, many people process information differently.)
Medina notes that vision’s dominance also extends to learning and memory. We remember just about anything better when there’s a visual component, so Medina recommends using visual aids to improve learning. Importantly, he notes that visual aids do not include text, which the brain processes differently than pictures.
(Shortform note: Experts advise that in addition to using visual aids to help teach, educators be sure to explain the context for those visual aids—exactly how an aid relates to the information the students are learning, what elements are important, and what elements are irrelevant. For example, if you use Civil-War-era props when studying that time period, analyze how each one sheds light on the habits of people at that time.)
Medina argues that playing and listening to music can notably improve cognition. He describes several areas of cognitive function that may be positively affected by participating in or listening to music.
Music leads to improved auditory skills. Medina cites several studies noting that musicians score higher on tests involving identifying subtle differences between sounds—including in speech.
(Shortform note: A recent study shows that piano lessons help children to differentiate between pitches, an important part of language processing.)
Music leads to improved language skills. Studies show that children who study music see improvements in language skills, both spoken and written.
(Shortform note: Since music helps language processing, it also helps children learn how to read and learn language. Studies show that music lessons may even be more effective than additional reading lessons.)
Music leads to improved social skills. Infants exhibit improved social skills when participating in music, such as increased smiling, laughing, and waving to others.
(Shortform note: Studies show that, for children with poor social skills, taking group music lessons improves prosocial behaviors like sharing and helping others. Children also show more positive attitudes toward their peers.)
Music leads to improved emotional skills. According to Medina, studies show that children who played musical games during school have increased empathy for others, as opposed to children who played non-musical games or no games at all. Practiced musicians are also better at detecting emotion in others’ voices.
(Shortform note: Research shows that music education helps children to recognize emotions in images and texts, and can help children to express their emotions.)
Medina argues we can improve our learning and performance by understanding how the brain pays attention, keeps focus, and creates and retrieves memories.
Medina argues that the better we’re able to focus on something, the better we’re able to learn it and remember it. This is because when we pay attention to more than one thing—when we multitask—we divert our attention from any one task over and over again. Each time we divert our attention and then subsequently refocus our attention, we have to reacquaint ourselves with the task—we have to recall where we left off, the details, our plans for our next steps, and so on. This takes an enormous amount of brain power and results in inefficiencies. Thus, by attempting to focus on two tasks at once, you lessen your ability to complete either. Medina advises that you can be more productive and focused, then, by completing one task at a time.
How to Stay Focused, Instead of Multitasking
As Medina notes, when you multitask, you lose your focus, since your attention is redirected again and again. If you frequently multitask and struggle to pay attention to a single task, here are a few recommendations:
Pick a few times of day to check email, messages, and/or social media. These all pose frequent distractions, so it can be helpful to determine specific times to check these instead of refreshing them throughout the day.
Remove distractions from your environment. If you still find yourself checking your phone, your email, or social media frequently, try moving your phone to a different room and blocking distracting websites.
If your environment is still distracting, leave it. If your workspace has numerous distractions and you need to focus intently on a project, pick a different space with less distractions.
Do the most difficult, or most important, task of your day first. By doing this, you complete the most focus-intensive work of your day early, so there’s less pressure to finish it later.
Medina writes that we can strengthen our memories through repetition, and therefore boost our learning.
To form memories, and therefore, to learn from experiences, the brain goes through a complex process that starts with encoding, which is when our brain processes and stores sensory information.
There are two major types of encoding, automatic and effortful processing, based on how easy or difficult it is to make a memory.
Automatic processing is encoding that requires very little conscious effort, usually involving visual stimulus. For example, when you see a memorable movie, your brain will encode it automatically and details of the movie will effortlessly enter your memory.
Effortful processing, on the other hand, requires conscious attention to form a memory. For example, when you study for a test, your brain uses effortful encoding. Effortful encoding can be challenging and requires numerous repetitions before you can easily remember what you learned.
What Happens When Encoding Is Disrupted?
The importance of encoding can be seen when the process is disrupted—for example, when the hippocampus, the area of the brain that encodes short-term memories into long-term ones, is damaged. Hippocampus damage can occur through injury or conditions like Alzheimer’s disease.
When someone’s hippocampus doesn’t function properly, that person develops anterograde amnesia, meaning they can remember very short-term memories but can’t form long-term memories. Thus, while a person with a properly functioning hippocampus might be able to remember their trip to a new bakery a week later, a person with a damaged hippocampus might only remember it for a few minutes.
Medina offers several techniques you can use to strengthen effortful processing and create accurate long-term memories.
(Shortform note: One way to give memory meaning, which Barbara Oakley suggests in A Mind for Numbers, is to create a “memory palace.” To do this, imagine a place that you know well—for example, your childhood home. Then fill it with images representing the concept you want to remember. For example, to remember that grocery list, you might imagine a chicken on the staircase or a bag of spinach in the hall.)
(Shortform note: Research suggests that repeating information without breaks in between is hardly better than not repeating information at all. But if you don’t have time to repeat information periodically over the course of several hours or days, repeating with short breaks in between can be helpful.)
(Shortform note: If you’re an educator, one way you can use this memory-boosting technique is to quiz students often. This is because it makes students apply what they learned, and consider their interpretations of the information, right after they learn it.)
At the end of the book, Medina explores how gender and our instinctive desire to explore influence how our brains function.
Medina argues that our biological gender affects how we think, learn, and interact with others. He explores this idea in how it relates to behavior and in how it relates to cognition.
Medina describes numerous behavioral differences between men and women, which he believes affect social and professional relationships. Some research shows that women and girls are generally better at verbal communication than men and boys. Medina notes that this is likely because women tend to use both hemispheres of the brain when speaking and processing verbal information, whereas men tend to use just one.
Gendered Conversational Styles in the Workplace
Linguist Deborah Tannen has found that gendered conversational patterns can benefit men in workplace situations: For example, women may downplay their own contributions, and men may compete to have theirs heard, so people may think their male colleagues have more interesting ideas than their female colleagues. Men may also be seen as more confident than women in the workplace.
Even if gendered conversational styles don’t unfairly benefit men, they can still cause general misunderstandings. For example, men tend to raise issues directly, while women tend to do so indirectly—and if people aren’t on the same page about how to raise an issue, they’re likely to misunderstand each other.
Medina also notes several cognitive differences between men and women, which he argues affect both thought processes and cognitive health.
One cognitive difference is that men and women tend to respond to stress differently. Research suggests that, when responding to stress, men focus on the general overview of a situation, while women focus on the details.
(Shortform note: Research also shows that men respond to stress with a “fight-or-flight” response, while women respond with a “tend-and-befriend” response. This means that, when faced with a stressful situation, men are likely to either confront or avoid it, while women are likely to look for comfort.)
Men and women also tend to be susceptible to different psychological health issues. Men may be more susceptible to intellectual disabilities, schizophrenia, antisocial behavior, alcoholism, and drug addiction. On the other hand, women may be more susceptible to depression, anxiety, and anorexia.
(Shortform note: Most researchers believe that a combination of biological and cultural factors explain why men and women are susceptible to different mental disorders. Men and women have different hormones, which impact our mental health. Yet aspects of culture that affect gender, like discrimination and gender roles, can also cause harm to mental health. Scientists note that much more research is needed to better understand how biology and culture can create different mental health outcomes for men and women.)
Medina argues that we have an instinctive, strong desire to explore that drives us to learn about the world throughout our lives.
Medina notes that babies are born with intense curiosity and demonstrate early use of the scientific method. Babies are able to explore and test their surroundings. Their explorations roughly follow the steps of the scientific method: They observe, form hypotheses, experiment, and draw conclusions. We can see this in their earliest attempts to imitate others, which teach them about cause-and-effect and prompt them to run experiments: If I clap, will Mom clap back? As they get older, they test out objects with their hands, mouths, eyes, and so on, to figure out what the object is made of and what it can do. And finally, they discover that other people have different desires than them, and they test these desires by pushing boundaries—learning from an early age how to cooperate within a society.
(Shortform note: Others have spotted the similarities between a child’s exploration and the scientific method, some going so far as to say not only are children small scientists, but that scientists are merely big children. In fact, they point out that the inventor of the modern scientific method, John Dewey, was inspired to outline the steps of the method by watching how children play.)
Brain Rules was written by molecular biologist John Medina to explain 12 essential cognitive functions that shape the way we react to and interact with the world. Medina wrote the book for the vast majority of people who know little about the brain, to help them figure out how to use the brain’s natural instincts, desires, capabilities, and tendencies to improve their memory, ability to learn and solve problems, and other cognitive skills.
John Medina is a developmental molecular biologist and an affiliate professor of bioengineering at the University of Washington School of Medicine. His research focuses on the genetics of psychiatric disorders and the genes involved with human brain development.
Connect with John Medina:
Brain Rules was published in 2011 by Pear Press. Through that publisher, Medina has published several follow-ups to Brain Rules, including Brain Rules for Baby, Brain Rules for Aging Well, Brain Rules for Work, and Attack of the Teenage Brain!
John Medina summarizes some of the most important aspects of neuroscience known to researchers as of 2009. In doing so, he built on centuries of study in the field.
In ancient Greece and ancient Egypt, people believed that the heart, not the brain, controlled the mind—the way people thought about and reacted to events. Ancient Rome was the first culture to believe that the brain controlled thoughts, as first theorized by the physician Galen. It took hundreds of years for scientists to develop more advanced brain science: Notably, in 1664, Thomas Willis wrote Anatomy of the Brain, which introduced the term “neurology” and described neurological issues like epilepsy and paralysis. In 1837, scientist J.E. Purkinje introduced the term “neuron,” and in 1878, William McEwen conducted the first neurosurgery.
Developments came much quicker in the 20th century with the advent of technology. In 1929, Hans Berger invented the electroencephalography (EEG), which measures the brain’s electrical activity. Just a few years later in 1932, Lord Edgar Douglas Adrian and Sir Charles S. Sherrington discovered how neurons communicate with one another and won the Nobel Prize.
We now have many technologies to study the brain and its electrical activity, and we know more about the structure of the brain. These strides in knowledge provide the basis for Medina’s 12 brain rules—without knowing the functions of the different parts of the brain or how to examine it, we wouldn’t know very much about how the brain works.
Medina notes that each of the 12 brain rules is supported by peer-reviewed research that has been replicated. This focus on accuracy, according to Medina, helps to dispel many false ideas about the brain’s effects on behavior. If Medina’s book is about brain rules, we can call these false ideas “brain myths.”
One brain myth that Medina counters is that we all have individual “learning styles.” Learning styles is a popular theory that everybody learns best with one of their senses: There are visual learners, auditory learners, and kinesthetic learners (people who learn best when they can physically engage with what they’re learning). This theory is widely accepted by educators, but research does not support it. It may even cause harm in teaching, because students may try to avoid learning through methods that don’t match their “learning style.”
Another brain myth is that we only use 10% of our brains at once. This theory probably emerged sometime in the early 1900s, and is now widely accepted. However, brain scans show that we use almost all of our brains at all times, even during simple activities.
Medina notes that part of the reason so many people believe brain myths is that people don’t understand many of the underlying principles of how the brain works. By supporting each of his brain rules with peer-reviewed, replicated research, Medina sets out to dispel myths and inform readers of how the brain’s functions shape how we learn and understand the world.
Brain Rules was a success: It hit the New York Times best-seller list in 2009, an ebook was published in 2011, and an audiobook was published in 2014.
In November 2021, Medina presented a lecture at the National Conference of State Legislatures, an association representing the legislative bodies of the U.S. states. Medina gave advice on how to better listen and cooperate with one another, using research based on his neuroscience work. This lecture for a nonpartisan political organization indicates that Medina has developed influence as an expert on using neuroscientific principles in daily life.
USA Today gave Brain Rules a positive review, with critic Bruce Rosenstein writing that Medina’s writing style and voice make a potentially challenging topic pleasurable to read.
Reviews on websites like Amazon and Goodreads are largely positive, commenting on Medina’s lively voice and the new insights they’ve learned about the brain and daily life.
One common criticism was that the book was largely sharing intuitive, uninteresting ideas (for example, that it’s hard to pay attention to boring information). Some also found the book superficial, and others found that the principles weren’t directly applicable or actionable in their lives.
Medina synthesizes research about complex concepts and presents them to the reader simply and directly. He clearly explains each of his concepts, using interesting examples and humor, and is informed about how both science and culture inform the development of the brain.
There are, however, occasionally inaccurate concepts reported in Brain Rules, and some areas have seen new scientific developments since its publication 10 years ago.
The organization of Brain Rules is simple and straightforward: Medina outlines a single rule in each chapter. This is easy to follow and intuitive, and Medina also uses the organization to his advantage by threading in ideas from earlier chapters in later chapters of the book.
In this guide, we’ve reorganized the structure of Brain Rules by sorting the 12 rules into five categories organized by common themes.
Within each chapter, we’ve summarized the information to focus on the most important takeaways, removing tangential points and occasionally abbreviating scientific detail unimportant to understanding Medina’s main ideas.
When necessary, we’ve also provided commentary providing corrections or updates to scientific concepts. Other commentary provides more in-depth information on Medina’s concepts, ideas for incorporating Medina’s principles into one’s life, and scientific and cultural ideas related to the brain rules.
Our brains are uniquely complex information processors, yet most people know little about how they work. By learning about core brain functions, we can improve our thinking and learning in all aspects of our lives.
Today, our lives are at odds with how our brains are designed to function. We evolved to travel throughout dangerous outdoor environments, but the sedentary lives many people now lead don’t align with how our brains function best. We also experience much more stress than we’re built to, and don’t always engage our senses to the fullest extent. Throughout Brain Rules, Medina addresses how current norms, like classrooms where children remain seated or jobs with high stress levels, work against our brains. By learning about our brain functions, we can make the most of our cognitive capabilities.
John Medina is a molecular biologist with a focus on psychiatric disorders. Medina wrote this book in order to help the public understand how brains work, and how the functions of the brain affect how we interact with the world. To develop this idea, Medina argues that our brains have evolved to increase our chances of survival by achieving these three core functions:
He takes the reader step-by-step through 12 rules that he says each help fulfill these core functions. We’ve grouped these rules into five categories that correspond to recurring themes among them:
By learning about brain functions in each of these areas, we can begin to understand how the brain works and how to carry this knowledge into our daily lives.
The first category focuses on how natural processes have shaped the brain. Medina describes two rules that fall under this category:
These two rules affect how we approach the world and allow us to learn from changes and problems in our lives.
For the first rule, Medina starts at the beginning of the human race.
In this chapter, Medina discusses how the physical adaptations of the human body helped our brains to develop in the advanced way that led to our species’ unique intelligence. He says that this specialized evolutionary process led to the development of three uniquely human characteristics: the ability to imagine, the ability to embrace variety, and the ability to cooperate.
By understanding the evolution of the brain and how it led to these characteristics, we can learn how brain evolution has allowed us to thrive.
According to Medina, one particular advance played a major role in our brain evolution: the ability to walk on two legs instead of four, which happened when we migrated from forests to grasslands and needed to travel long distances to get food and water.
Not only did walking on two legs allow us to cover more ground quickly, but it’s also a less energy-intensive method of moving around, and thus allowed our bodies to devote more resources to our brain development than our basic bodily functions.
Another Theory for Why Humans Walk on Two Legs
Medina and many contemporary scientists believe that walking on two legs allowed for crucial brain development—and there’s research that backs it up, including that chimpanzees use much less energy when they walk on two legs than when they walk on four, suggesting that the brain could use that spared energy.
The same research suggests another plausible theory that Medina does not address, which is that we evolved to walk on two legs to make it easier to carry food. Researchers also found some support for this theory, because chimpanzees often walk on two legs when carrying important food.
Medina argues that as we evolved, we developed the ability to think rationally, which allowed us to deal with difficult, changing, or complex circumstances. This led to the development of three human capabilities that form the basis for society and culture: imagination, the ability to adapt to variation, and cooperation.
One key characteristic of humans that sets us apart from other species is our imaginative capability, which allows us to engage in symbolic reasoning, or the ability to make meaning from things that aren’t inherently meaningful. For example, when you look at a cloud and think it’s shaped like a turtle, you’re using symbolic reasoning.
Symbolic reasoning has allowed for the development of many central aspects of human existence, like written language, artistic expression, mathematics, and science. It’s also enabled us to develop societies and culture, which required the ability to imagine ways of life that didn’t already exist: for example, agriculture, towns & cities, and formal education.
Can Animals Use Symbolic Reasoning?
While Medina argues that symbolic reasoning is a uniquely human ability, other researchers have found evidence that monkeys use it too. One study examined whether capuchin monkeys were able to engage with symbolic reasoning by testing their ability to understand the concept of exchanging currency for goods. When the researchers presented tokens representing food to the monkeys, the monkeys understood that taking a token would enable them to get food, suggesting that they’re able to use symbolic reasoning to some extent.
However, they had more trouble determining how valuable a token was—for example, the monkeys didn’t have a preference between a token representing one Cheerio and a token representing four pieces of Parmesan cheese, even though four pieces of cheese would be more valuable to them. The researchers concluded, then, that the monkeys’ ability to use symbolic reasoning was less developed than humans’ ability. So while symbolic reasoning itself may not be exclusively human, the advanced way that we use symbolic reasoning is unique.
Our unique evolution also led to another specifically human characteristic: our acceptance of variation and change, which was necessary because early humans had to deal with great instability.
As humans evolved, the climate began to change rapidly. While early humans lived in hot, humid environments, later humans had to deal with a climate that constantly changed from hot to cold. We’ve mentioned that early humans migrated from forests to grasslands. They did this, in part, to find new sources of food in an ever-changing climate. Once there, they not only had to adjust to a new environment but also contended with the species already living there. Many of these species were stronger than humans.
In response to these massive changes in our environments, our brains developed the ability to quickly solve problems and to learn from past mistakes. We evolved the ability to retain memories and to make decisions based on those memories. As a result, we now have brains well-equipped to adapt to new environments and respond to new situations.
Theories About Climate Change and Brain Evolution
Medina’s argument that climate change spurred human brain evolution is supported by research. However, the studies supporting this theory are recent, and scientists have differing views on how climate change affected brain development.
Researchers have found that the two most significant periods of early human evolution coincided with periods of climate change. While this shows that there’s a correlation between climate change and human evolution, scientists have different views on what that correlation might be. For example, some scientists believe that most brain development occurred during periods when the climate varied between wet and dry and between hot and cold (this matches Medina’s belief). Others believe that most brain development occurred during “wet” periods of climate change, when the climate was most conducive to thriving human life. They believe that the abundance of resources in these periods allowed humans to develop more complex cultures.
While scientists draw different conclusions on how climate change impacted human brain development, they largely agree that it shaped our ability to respond to change in some way.
Another key human characteristic Medina outlines is the ability to cooperate with one another.
Since humans are not as strong as many other animals, we had to develop the ability to work with one another in order to survive. Humans developed an essential skill to make this possible: the ability to imagine what others may be thinking or feeling.
People ascribe motivations and feelings to one another, and even sometimes to animals and objects. Because we can “read” people’s emotions, we can communicate and solve complex problems with one another. Medina suggests that symbolic reasoning may have developed so we could imagine people’s thoughts and feelings.
Do Animals Cooperate and Read Emotions?
While Medina writes that the ability to cooperate and read emotions are uniquely human features, other researchers have found these skills in animals. They hypothesize that other species evolved these abilities because cooperation can bolster the health of a species.
For example, researchers have found evidence that dogs and primates are able to detect emotions in others, both in their own species and in humans. This indicates that these species use this skill to strengthen social ties.
So while cooperation and the ability to read emotions are essential human characteristics, other animals possess them to some degree as well.
While our brains all fulfill the same basic functions, the structure of every brain is unique to every individual. This is why every person has an individual array of talents and skills.
In this chapter, Medina explores how this came to be. He discusses how neurons shape the functions of our brain, and how each person ends up with a set of neurons that are unique to them. He then explores how we can use this information to structure our schools and businesses to function more efficiently.
Neurons are the cells that carry out the brain’s functions, including allowing the brain to absorb information. When our brains receive information, our neurons process it by sending messages to each other in the form of electrical signals or chemicals. This is how the brain has thoughts, creates memories, and learns new concepts.
(Shortform note: Neurons communicate with each other by sending electric signals to the brain, then converting them into chemicals to transmit the messages to one another.)
The process of developing neural connections occurs differently in every person. As a result, everyone’s brain ends up with its own unique set of neural connections.
The average adult has 10,000 points of connection between neurons. Some of these connections are created through genetics and control things like our bodily functions and our ability to learn languages. But many of these connections are created through experiences, and then influence the way we understand the world.
When we’re exposed to new things, our brains adapt and incorporate the information into our neural networks. Because everyone’s individual experiences are unique, our brains develop unique ways of reacting to and understanding the world.
Experiences Shape Neural Growth Most in Childhood
Researchers note that experiences early in life have more of an effect on neural growth than experiences later in life.
For example, experiences with language early in life influence a person’s language skills later in life. Studies show that, if someone is regularly exposed to multiple languages as an infant, they’re more likely to be bilingual later on. And children who learn two languages to fluency typically develop a larger left brain hemisphere.
Early experiences can also increase the likelihood of developing mental disorders. Attention deficit/hyperactivity disorder (ADHD) is one mental disorder that’s often shaped by early experience: Research shows that problems during pregnancy, birth complications, premature birth, and a dysfunctional home during childhood are all associated with the later development of ADHD.
To illustrate how everyone’s brains are unique, Medina discusses studies that show how people store information in different parts of their brains. For example, two people may store their language ability in different regions from one another. This uniqueness shows the flexibility of our brains and accounts for our ability to adapt to new circumstances and environments.
(Shortform note: This illustrates that, even if a cognitive function is usually processed by one part of the brain, individuals may store it differently. Most people store language on the left side of their brain. However, some people also store language on both sides of the brain, or only on the right side.)
Medina argues that we can redesign institutions like schools and workplaces to suit everyone’s unique brain wiring. Since most schools and workplaces are standardized in structure, they don’t fit all individuals. For example, while most students are expected to read by the 1st grade, not all children have the ability to do so yet.
Medina recommends a couple of methods of individualized instruction to address this issue. To help suit school to individual students, Medina recommends smaller class sizes. This would help teachers learn students’ different learning styles. Another technique for individualized instruction is to use a “flipped classroom” where students review lectures at home before doing supervised homework at school.
Are Small Class Sizes and Flipped Classrooms Effective?
Medina recommends small class sizes as a way to encourage individualized learning, but findings on their effectiveness are mixed. A set of studies showed that while small class sizes improved reading skills, they did not improve math skills. This mixed effectiveness might be because schools have to hire a large number of teachers in order to create small classes, which might lead them to lower their hiring standards so that some of those teachers may not be well-qualified. Studies show that while small class sizes can encourage individualized instruction, it’s more important for students to have great teachers.
On the other hand, studies show that flipped classrooms can be very effective. Students in flipped classrooms often see improvements in their memory of important concepts, critical thinking, and engagement with course materials.
For workplaces, Medina believes that employees should advocate for changes that will help them individually, such as schedule flexibility. Medina also recommends that managers pay close attention to the strengths and weaknesses of their employees, and assign tasks and projects based on their abilities.
Individualized Workplaces
Many professionals agree with Medina’s ideas for workplaces that accommodate workers’ individuality, as they can help both employees and managers.
Flexible work schedules are helpful for employees because they can adapt their schedules to their lifestyles, and they’re helpful for managers because their employees are happier and more productive.
Likewise, tasks assigned based on strengths are helpful for employees because they can do work they like, and they’re helpful for managers because their employees are more likely to do strong work.
Medina described symbolic reasoning and cooperation as two special features of human behavior. Everybody makes use of these skills in their daily lives, whether they think about it or not.
Think of a time when you were working with others, and you had to “read” someone else’s emotions or motivations to get effective work done. (For example, if you’re proposing ideas for a project with a coworker, you might have to read their emotions to assess whether they like your proposals.) What did you think that person was feeling or thinking?
Why did you think this is what the other person felt or thought?
How accurate were your assumptions about your collaborator’s thoughts or feelings?
Based on this experience, how will you approach “reading” someone else’s thoughts and feelings in the future?
The first category described how fundamental natural processes influence the brain. In this category, Medina describes how aspects of our individual environments and lifestyles influence our brain functions. Medina writes that exercise, sleep, and stress are three key aspects of our lives which affect our cognition, brain health, and learning.
Medina argues that our brain function is highly influenced by whether or not we exercise, and that more exercise results in more brain power. He explores why we've evolved to exercise frequently, how exercise benefits our brains, and how sedentary lifestyles harm them. He then describes several important truths that illustrate exercise’s importance.
According to Medina, our ability and desire to exercise are baked into our biology. As we’ve mentioned before, humans had to contend with intense environmental conditions, and constant motion was necessary for survival. For example, when early humans migrated from shrinking rainforests into vast, dry savannahs, they had to walk and run long distances to find food and shelter and to fend off hostile wildlife. Early humans traveled as much as 12 miles a day. Our bodies are still designed to exert such high levels of energy.
Did We Evolve to Exercise or to Conserve Energy?
Daniel Lieberman, a professor of human evolution and biology at Harvard University, argues that rather than evolving to exercise, we evolved to conserve energy. Conserving energy was important during times of limited food supplies, and allowed early humans to use more energy for physical activity when they needed to, like if they were hunting for food or fleeing a predator. This is why today, many people now would rather relax than go for a run.
Lieberman does agree, however, that hunter-gatherers were more active than people now and that they walked several miles every day. He also agrees that walking regularly has major health benefits. So while Medina and Lieberman disagree on whether we’ve evolved to exercise or to conserve energy, both would agree that our brains benefit from regular exercise.
Given that we’ve evolved to exercise, we reap not only physiological but also mental benefits from physical activity. Exercise boosts cognition by increasing blood flow to the brain. When we exercise, our bodies create new blood vessels, which allow blood to circulate more efficiently. This brings more oxygen-rich blood to the brain.
The oxygen serves two functions: It feeds our brain cells—helping neurons stay young and operational—and it removes harmful toxins. Increasing the flow of oxygen, then, immensely helps the brain carry out its essential functions, including cognitive abilities like memory, focus, and problem solving.
Exercise May Benefit Those With Memory Loss in an Unexpected Way
Most people benefit when they get increased levels of oxygen to their brain. However, some people suffer from the opposite problem: too much oxygen to the brain, which can hurt memory function. This can happen in people with mild cognitive impairment (MCI), when their bodies pump excess blood to their brains in an attempt to make up for their reduced cognitive function, which ironically exacerbates that reduced function.
One study found that for adults with MCI, exercise helped regulate their blood flow, which reduced the excess flow to their brains. Participants in the study saw improved scores on cognitive tests when they exercised.
Medina argues that even though exercise has proven benefits, the structures of contemporary life often prevent exercise, which has detrimental effects on our brains. Contemporary life has led to sedentary lifestyles: Many jobs necessitate sitting down for large portions of the day, and school requires kids to sit for hours at a time as well. Because of these sedentary lifestyles, many people suffer cognitive consequences, particularly as they age.
(Shortform note: According to a recent study, sitting for long periods of time is associated with the thinning of the MTL, a part of the brain that forms new memories. Over time, MTL thinning can lead to cognitive decline and dementia.)
Medina encourages finding ways to incorporate exercise into daily routines, even if it’s not what you’re used to. For instance, he recommends walking on a treadmill while working.
(Shortform note: Since Brain Rules was published, many people have begun using treadmill desks. Like Medina, many people believe that treadmill desks can help incorporate light exercise into your work day.)
It’s clear that we’ve evolved to be physically active, and our brains respond well to physical activity. But how much can exercise actually benefit our lives? Medina establishes several truths that determine how much exercise can impact our lives.
Researchers have found that exercise can lead to heightened cognitive capabilities in older people. Studies consistently show that older people who exercise have better skills in many different areas, including long-term memory, problem-solving, and the ability to think abstractly, when compared to older sedentary people. They are also at far less risk for cognitive issues like dementia and Alzheimer’s disease.
Exercise Reduces The Risk of Cognitive Diseases
Studies support Medina’s assertion that exercise reduces the risk of dementia and Alzheimer’s disease. Research shows that people who exercise in mid-life cut their risk of developing dementia later in life by 30%, and Alzheimer’s by 45%. Older people who exercise regularly also see these cognitive benefits: One study showed that, in a group of over 700 people with the median age of 82, those who exercised the least were over twice as likely to develop Alzheimer’s as those who exercised the most.
Studies show that people who live sedentary lifestyles can regain cognitive abilities through exercise. Medina notes that researchers found improvements in the cognitive abilities of older people after exercise had been introduced in their lives in as little as four months. Studies show that children, too, develop stronger cognitive abilities when they routinely exercise, and that those increased abilities lessen if they stop exercising.
Research Shows How Exercise Improves Cognitive Skills
Since Brain Rules was published, more research has bolstered Medina’s assertion that exercise can help people regain cognitive abilities, particularly older people. A recent study of sedentary older people with mild cognitive impairment found that those who began a program of regular aerobic exercise saw benefits in executive function, planning, and decision-making. (A control group who did light stretches instead of aerobic exercise also saw improved memory and thinking, but the researchers thought that aerobic exercise helps these capacities more in the long run.)
Medina says that research indicates aerobic exercise is the most beneficial type of exercise for cognitive health. It also indicates that people don’t need to do too much of it to see rewards. He notes that 30 minutes of aerobic exercise two to three times a week has been shown to be effective, and that adding strength training can provide a boost to the already-strong cognitive benefits. In other words, just going on a brisk walk twice a week can benefit your cognitive health.
Aerobic Exercise Spurs Growth in a Crucial Part of the Brain
According to a 2014 study, regular aerobic exercise can increase the size of the hippocampus, the part of the brain most responsible for verbal memory and learning. Notably, other forms of exercise—resistance training, balance, and muscle toning—didn’t cause hippocampus growth. So if you want to improve your brain power, aerobic exercises like walking, running, or swimming are best.
Aerobic exercise can also help to alleviate mental disorders. Since exercise helps to regulate brain chemicals, physical activity can lessen symptoms of mental health disorders such as anxiety and depression. Medina notes, though, that while exercise can be a supplement to medical treatments of mental health disorders, it is not a substitute.
How Exercise Can Improve Depression and Anxiety Symptoms
While it does not substitute professional mental health treatment, exercise can help to improve symptoms of depression and anxiety. One reason exercise for this is that exercising over a long period of time helps neurons to grow and make connections, improving how you feel in your day-to-day life and calming depression symptoms. Exercise also promotes the production of several brain chemicals that can reduce anxiety.
Using exercise to help manage depression and anxiety symptoms has the potential to help many people, considering the prevalence of both conditions. Depression and anxiety are exceedingly common: In the United States, about 8% of adults have struggled with depression, while about 19% of adults report having a chronic anxiety disorder.
While more research needs to be done, researchers have found that exercise can improve children’s academic performance. Medina notes that there have been few studies on how children’s cognitive performance improves when exposed to frequent exercise. But he notes that the existing studies suggest their schoolwork and classroom behavior improves, especially their focus.
Exercise Improves Abilities in Math and Reading
Reflecting Medina’s assertion that exercise improves childrens’ cognition, studies suggest that children who regularly exercise see improved academic performance, particularly in math and reading. This is likely because exercise improves executive function, which allows us to focus and use our memories and is an essential cognitive capability for these two subjects.
In the previous chapter, Medina discussed the cognitive benefits of activities that can wear you out. Just as we benefit from exercise, we benefit from regular rest: sleep. Sleep is an essential function of the brain which allows us to learn—and when we don’t get enough sleep, our cognitive abilities suffer. In this section, Medina describes the biological processes that set our sleep schedules, the positive effects that sleep has on our learning ability, and the negative effects that a lack of sleep can bring.
Our sleep, and the quality of that sleep, is determined by biological processes. We’re wired to stay awake and go to sleep in predictable cycles. If these cycles are disrupted, we can get less sleep than we need and our cognition can suffer.
The process that keeps us awake is called the circadian arousal system, or Process C. The process that keeps us asleep is called the homeostatic sleep drive, or Process S. These two processes are constantly active and fighting against one another, leading to a predictable pattern of waking and sleeping—generally for about eight hours of sleep at night and about 16 hours of wakefulness during the day. Researchers William Dement and Nathaniel Kleitman found that the process of waking and sleeping is governed internally by these processes, rather than by external factors like whether it’s light or dark outside.
Light Does Affect Our Sleep Cycles
While Medina notes that our sleep cycles aren’t affected by whether it’s light or dark outside, other evidence shows that light has a significant effect on our sleep patterns.
Our internal clocks are controlled by a part of the brain that responds to light and dark signals. So, when we see light, our brains release hormones telling us to be alert, and when we’re in darkness, our brains release hormones that start the sleep process. As a result, exposing yourself to artificial light at night, such as a cell phone or TV, can make it difficult to sleep.
However, despite its importance to our sleep instincts, scientists agree that light isn’t the only reason we have consistent sleep cycles. We’ll discuss later in the chapter how Process C and Process S often make us sleepy in the middle of the day.
While everyone’s sleep schedule is controlled by these processes, the timing of the processes is unique to each individual. Medina identifies three different types of sleepers, based on when in the day they naturally function best: He calls them larks (early risers), owls (“night owls”), and hummingbirds (who are in-between the two).
Early risers tend to wake up around 6:00 AM, and peak in energy and focus by noon. They get sleepy as the day goes on, and might want to go to sleep around 9:00 PM. They form about 10% of the population. Night owls are the opposite of early risers, tending to wake up after 10:00 AM, peaking in energy in the evening, and likely going to sleep around 3:00 AM. They also form about 10% of the population.
The remaining 80% are “hummingbirds,” or in-between sleepers. These sleepers aren’t as strongly biased toward the morning or the evening as early risers or night owls. However, all in-between sleepers will still show tendencies toward one or the other—a lark-ish hummingbird might wake up at 7:30 AM every day and feel sleepy by 10:30 PM, or an owl-ish hummingbird might get up at 9:30 AM and go to sleep at 1:00 AM.
Chronotypes Change With Age
While everyone has their own chronotype (the technical term for sleep type), people’s chronotypes follow a pattern based on age. Children typically have early chronotypes, which get progressively later in adolescence, and peak around the age of 20. Then, chronotypes get progressively earlier again (though men’s chronotypes are typically slower to change than women’s).
Chronotype, then, explains why teenagers like to go to sleep late and get up late—it’s not laziness. In fact, a “night owl” chronotype is so typical of teenagers that some researchers believe that the end of adolescence is determined by when one’s chronotype begins shifting earlier. Since most people’s chronotype gets progressively later until their early 20s, adulthood would then begin when their chronotype lateness peaks around the age of 20.
Because everyone has their own sleep type, our society’s often-inflexible working hours cause many people to sleep poorly. In American society, for example, many people’s work schedules require them to work from early morning to early evening.
This works for larks, since it allows them to go to bed early and wake up early. But, if you’re a night owl, you might find that your sleep type runs against the standards of contemporary society. As a result, owls might accumulate a “sleep debt,” meaning they lose sleep so consistently that it’d take a long time to catch back up again, and can suffer cognitive difficulties as a result.
How to Catch Up on Sleep
Many people live with sleep debt, often caused by demanding work schedules that don’t align with our chronotypes. If you accumulate a sleep debt over a long period of time, it can be hard to catch up, since you can’t solve it by getting one good night’s sleep. According to research, it could take up to nine days to fully catch up on a sleep debt.
If you have a sleep debt, here are a few recommendations for getting sufficient sleep:
Increase your sleep time gradually until you regularly feel well-rested.
Maintain a consistent sleep schedule.
Keep a sleep diary, so you can see if you have any disruptive sleep patterns.
Take short afternoon naps.
And if sleep loss is causing you difficulty in your day-to-day life, talk to your doctor.
To compensate for mismatches between sleep type and working hours, Medina suggests that you set your schedule to match your sleep type if you’re able. He also recommends that companies match employees’ schedules to their sleep types.
(Shortform note: Research suggests that, when employers match employees’ schedules to their chronotypes, employees are less fatigued, more honest, and happier.)
He also recommends that you take a mid-afternoon nap when possible. A nap at this time of day can create cognitive benefits, because Process S and Process C (the hormonal processes that send us to sleep and keep us awake) reach the same level in the mid-afternoon and each requires a lot of energy at that time, which makes us feel sleepy. Medina recommends that businesses and schools give employees or students a half-hour break in mid-afternoon or at least refrain from scheduling meetings or presentations during the “nap window.”
(Shortform note: A study NASA conducted on astronauts shows the effectiveness of taking a midday nap. Compared to astronauts who didn’t nap, astronauts who took a 26-minute-nap in the middle of the day were up to 54% more alert and improved their work by up to 34% more.)
Learning is the cognitive process most affected by sleep. Medina writes that there are a number of possible reasons for this. One is that during the stage of deep sleep called slow-wave sleep, we replay what we’ve learned over the past day, potentially helping to solidify our memories. If we’re awakened during this stage of sleep, then we’ll likely have memory trouble the next day, leading to difficulty retaining new information.
(Shortform note: In addition to deep sleep, rapid eye movement (R.E.M.) sleep, which is the phase of sleep when your brain is active and you dream, is also important for developing and retaining memories.)
Another reason sleep helps with learning is that during sleep, the brain cleans up toxic molecules that accumulate over the course of the day, creating better conditions for learning.
(Shortform note: A 2013 study provides strong evidence for this theory. Researchers found that brain cells shrink during sleep. This opens up space between neurons and allows fluid to flow more easily through the brain, so the brain can flush toxic materials.)
Medina has explained that exercise and sleep are two factors that can benefit our cognitive health. He then turns his attention to another environmental influence: stress, which can hurt our cognitive health. He argues that stress interferes with our brain’s ability to learn because we haven’t evolved to handle it over a long period of time. Medina defines stress, distinguishes between acute and chronic stress, describes the cognitive (and physical) effects of stress, and discusses how stress can cause problems at home and at work.
Stress can be hard to define because no single situation is stressful for everyone. Additionally, from a scientific perspective, all kinds of physiological arousal cause similar reactions in the body, whether it’s a stressful response or a pleasurable response. As a result, scientists can have a hard time distinguishing between physical manifestations of stress and other kinds of excitement.
Medina cites researchers Jeansok Kim and David Diamond, who came up with three criteria to determine if someone is experiencing stress:
How to Shift From Stress to Excitement
You can use the similarities between stress and excitement to adopt a positive attitude in anxiety-inducing situations. Instead of trying to “calm down,” which is incredibly difficult when your body is in a state of stress, shift your mindset to excitement. This is an easier response because you can improve your mood without changing your physical responses.
To shift from stress or anxiety to excitement, researchers recommend you begin thinking of “threats” as “opportunities.” For example, if you’re nervous about an upcoming job interview, try thinking of it as an opportunity to further your career.
Medina notes that there are two kinds of stress: short-term stress (acute stress) and long-term stress (chronic stress). If you’re driving and swerve to avoid an oncoming vehicle, you’d experience acute stress. On the other hand, if you experience heavy traffic every day, causing you to be habitually late to work, you’ll experience chronic stress.
Stress evolved as a survival response, since early humans faced a number of immediate dangers on a regular basis. He argues that people have evolved to manage acute stress well, because this is the type of stress that helps us avoid imminent threats. However, he argues that we haven’t evolved to handle chronic stress well.
The reason chronic stress is a problem is that the body isn’t meant to deal with stress hormones over a long period of time. When we have a stress response, our bodies produce the hormones adrenaline and cortisol, which give a burst of intense energy and focus the body on the immediate threat. If this happens over a long period of time, these hormones can depress the health and growth of neurons, and can even disable the gene that creates these cells.
How Acute and Chronic Stress Affect Our Bodies and Minds
In addition to hormonal changes, acute stress causes other changes in the body that are intended to help us deal with immediate threats but that can cause harm when stress becomes chronic, affecting our ability to think and learn.
Acute stress causes muscle tension, because tensing our muscles guards us against injury. This is effective if we’re in a situation where injury is possible, but muscle tension over a long period of time is detrimental. For example, prolonged muscle tension can cause migraines and tension headaches, causing us physical pain and affecting our ability to focus, think, and learn. To improve muscle tension caused by stress, experts recommend relaxation techniques and participating in relaxing, pleasurable activities.
Acute stress also affects the gastrointestinal system. When we face a stressful situation, our digestive system slows or stops so our bodies can focus on the stressor. If we experience chronic stress, digestion can be slowed over a longer period of time, causing discomfort and pain. Notably, our digestive systems contain many neurons which are in constant communication with the brain and can affect our mood, meaning that persistent digestive problems can impede us mentally and emotionally. Because of the link between the gut and the brain, experts have found that mental health treatments like cognitive behavioral therapy, relaxation therapy, and hypnosis can help ease persistent digestive problems.
Medina discusses the negative cognitive effects that chronic stress can cause. Long-term stress can be particularly harmful to memory and our ability to solve problems.
Medina writes that short-term stress can actually improve memory. This is because the hippocampus, which stores memories, has a lot of receptors for the hormone cortisol, which is a hormone that your body produces during acute stress. Thus, during times of acute stress, you can retrieve information and solve problems more effectively because of the additional cortisol. Medina postulates that our brains have developed in this way because of the evolutionary need to remember how to respond to stressful situations and to think on our feet.
However, chronic stress can degrade memory because it sends excessive amounts of cortisol to the hippocampus, which can disconnect neural networks. This causes memory loss and can prevent new cells from being created—and thus hurt your ability to form new memories.
Ways to Lower Cortisol Levels
Studies show that elevated cortisol can be particularly harmful to memory in older adults. One study of over 4,000 older people found that those with the highest cortisol levels had lower brain volume than other participants, and found that they performed worse on memory tests.
If you have a stressful life, there’s a good chance you have high cortisol levels—and therefore, that you might be at risk for memory loss later in life. To lower your stress and cortisol levels, try finding more ways to relax and enjoy yourself. For example, try watching a comedic TV show—studies show that watching funny videos can lower cortisol levels.
Because of its profound effects on memory, chronic stress can severely hinder learning. Studies show that adults with chronic stress perform worse than low-stress adults on tests related to memory, math, language, focus, and the ability to use pre-existing knowledge to solve new problems.
(Shortform note: Studies have noted two particularly significant impacts stress can have on learning: It damages the ability to retrieve information, which makes testing difficult, and damages the ability to change memories based on new information, which makes it difficult to build on pre-existing knowledge.)
Chronic stress can also contribute to clinical depression, which harms many important cognitive functions. These include not only memory and language, already established to be harmed by stress, but also spatial awareness, problem-solving & abstract reasoning, and quantitative reasoning.
(Shortform note: Scientists believe that the relationship between stress and depression is “bidirectional”, meaning that just like stress can cause depression, depression can cause stress. If you find yourself slipping into a stress-depression cycle, medical professionals recommend talking with supportive family and friends, making small lifestyle changes (like getting sufficient sleep and making time for yourself), and consulting with a professional if these steps don’t help.)
Medina argues that the physiological effects of stress, including cardiovascular disease and immune system problems, can affect our ability to learn at school or to perform at work. Those who suffer physical symptoms of stress, especially those whose immune systems are weakened, may need to take more time off from work or school than a low-stress person. Their ability to keep up with class material, or effectively fulfill the requirements of their job, would then be lessened. In this sense, physiological symptoms of stress can also set us back cognitively.
(Shortform note: The physiological effects of chronic stress can harm your ability to go about your day-to-day life in the long term, so experts recommend managing sources of chronic stress. To do this, identify what causes of stress in your life can be changed—for example, frequently being late to work or spending less time with friends than you’d like. Then, limit the amount of stress you deal with in a given day by planning your days in advance, and start doing relaxing or pleasurable activities when you can.)
Medina describes two environments—at home and at work—where people are likely to experience chronic stress, causing damage to relationships, health, and productivity.
Stress in our home lives, often caused by frequent conflicts in the home, can be ongoing and damaging to children. Kids have strong reactions to their parents or caregivers fighting, such as physical tension or yelling at their parents to stop.
These responses indicate that arguments among caregivers make children reach their stress limit. If these conflicts are ongoing, the negative impacts of stress on children can be long-lasting, potentially leading to poor academic performance, increased rates of teenage pregnancy, and higher likelihood of poverty.
How to Help Reduce Children’s Stress at Home
Medina writes that conflict between caregivers causes children stress, but many other factors can lead to stress in childrens’ home lives: for example, moving to a new town, loss of a loved one or pet, or high expectations from family members. In addition to the reactions Medina describes, a child experiencing chronic stress in the home might also display behavioral changes like acting out or spending more time alone.
To help reduce stress in a child’s life, try listening to and acknowledging the child’s feelings about the source of stress, ensuring they have a consistent sleep schedule and healthy eating habits, and maintaining routines. Even if you can’t remove the source of stress, like if you’re moving to a new house, these strategies can help children cope with stressful situations.
Work, too, can be a major site of stress. All jobs have moments of stress, but some jobs can become overwhelming. Workplace stress occurs when there’s a great deal expected of an employee, but the employee has little control over the quality of their work.
A job that causes frequent boredom for an employee also causes stress. Yet a completely unpredictable job is also stressful, so the happy medium would be a reliable job that offers some variety.
Finally, stress at home can cause stress at work, and vice versa. This is called a “work-family conflict”. Stress begins at home or at work, which then causes stress in the other space, leading to a vicious cycle of unabating stress in both areas of your life.
The Benefits of Leaving Stressful Work
Many workers agree with Medina that work can be stressful, and some respond by leaving their jobs. Workers who do so often cite unpredictable scheduling, inflexible time off, workplace conflicts, and lack of benefits as reasons. Stressful jobs can cause you to feel tired, irritable, unmotivated, and can cause sleep loss—and leaving a job can help to ease these symptoms of stress.
Experts advise that as long as you have sufficient savings or will be able to quickly find a new job, leaving a stressful job can help your overall mental health and can allow you to find work that’s more fulfilling.
Everyone experiences stress in their life sometimes. Now that you have some more knowledge about the causes and effects of stress, think about what you do when you experience stress.
Reflect on a time when you experienced chronic stress. For example, you could have been falling behind on deadlines at work, or you could have been in the middle of a difficult conflict with a loved one. How did this stress affect you, mentally and physically?
What steps did you take to counteract this stress?
How would you address this stressful situation differently now? Or if you’d address it the same way, why do you think your approach was effective?
The previous category focused on how our brains respond to our environments. This category focuses on the brain’s perception of sensory information. Medina writes that we learn best when we use more than one sense, that vision is the most important sense, and that we’re hardwired to respond to music. According to Medina, understanding our responses to sensory stimuli helps our learning, work performance, and happiness.
In this chapter, Medina contends that, because we evolved to live in a multi-sensory world, using more than one sense at once improves our learning. He describes how we take in sensory information, why our senses improve when we combine them, and how using multiple senses benefits learning specifically. He also shares ideas for incorporating multi-sensory learning into your life.
When we process sensory information, our brains take us through three steps: sensing, routing, and perceiving. These steps allow us to take disparate sensory information and combine it into a logical whole.
The first step is sensing, or the absorbing of sensory input. When you, for example, stand in an amusement park, you’ll see the rides and gift shops, hear shouts, and smell funnel cakes. Your senses take in this information and send it to the brain to be converted into electrical signals between neurons.
The second step is routing, when the brain sends these signals to the parts of the brain pertaining to each sense.
The third step is perceiving, when the brain makes sense of those signals. There are two ways the brain processes the sensory input: assembling and interpreting. Your brain first assembles the different types of stimuli you’ve absorbed into a full picture. It then interprets this picture by adding meaning. It remembers similar experiences you’ve had in the past and connects your current experiences to those memories, so you know how to react. Interpreting is subjective, since it relies on individual experience. Therefore, no two people will perceive a stimulus in the same way.
How Sensory Processing Can Go Wrong
Medina describes how our brains have evolved to sense, route, and perceive information, but he doesn’t discuss what happens when people have difficulties with sensory processing.
Some people who suffer brain damage have issues with sensory processing. Most commonly, this can manifest as a loss of sensory perception: For example, a brain injury might leave someone unable to process smell or taste. Less commonly, a brain injury can lead to hypersensitivity, meaning that everyday sensory stimuli feel overwhelming. This can make it difficult for a person to interact with the world: If background noise overwhelms someone, for instance, they’ll have a difficult time determining what to focus on in a noisy environment.
Others are born with difficulties processing sensory information. Sensory processing disorder (SPD) causes people to be unable to cope with everyday sensory stimuli: A pair of jeans might be painful to the touch, or the sound of a car starting could cause intense anxiety. Many children have SPD, which causes them difficulty in their education and social development. Researchers have found evidence that the brains of children with SPD are significantly different from those without SPD: The parts of the brain that integrate visual, auditory, and tactical processing are abnormal, leading to difficulties integrating sensory information.
There are numerous treatments that can help those with sensory processing issues. If someone’s hypersensitive to sensory information, whether because of brain damage or a condition like SPD, therapy can help them improve their sensory processing, as can reducing troublesome stimuli in their environments. If necessary, medications can also help with sensory integration.
Because the environments we live in have multiple, simultaneous sensory stimuli, our brains evolved to absorb and make sense of numerous sources of information at the same time. Since our senses have evolved to work together in this way, when we use one sense, others are automatically activated.
Medina describes a few studies that provide evidence for this phenomenon. In one, researchers found a connection between sight and sound by showing subjects silent videos of people speaking. When watching these videos, the auditory centers of their brains lit up, in addition to the visual centers. This indicates that sight influences sound: When we see an image associated with sound, like talking, our brains automatically engage our sense of hearing.
Further, Medina notes that one sense can even improve another. One study Medina describes shows this phenomenon in action. Researchers showed subjects a flickering light that gradually grew dimmer. When a sound was paired with the flickering, they were able to see the light flickering for much longer.
Many People Can “Hear” Motion
Medina describes how our senses work together, to the extent that they can activate and improve one another. While most people’s senses activate each other in predictable pairings, like taste with smell, some people’s senses go a step further: People with synesthesia experience senses paired with unexpected senses. For example, they might associate numbers and letters with specific colors, or sounds might have taste.
Synesthesia is relatively uncommon, occurring in 1 in 90 people. However, research shows that one particular type of synesthesia is more common: “hearing motion”. In one study, 20% of participants heard sounds when they were shown moving images, even though no sounds were actually present. These results parallel the study Medina mentioned, where the auditory centers of participants’ brains lit up when viewing silent videos of speech. While not everyone experiences synesthesia, the prevalence of “hearing motion” indicates how our senses are hard-wired to work together.
Medina argues that because we’ve evolved to process multiple senses at once, our brains learn and absorb information best when it involves more than one sense. Studies show that people who learn using multiple senses retain information better than those who used only one sense—even 20 years after first learning the information.
In addition to remembering information better, multisensory learners also showed much greater problem-solving skills than single-sense learners. Some researchers think this is because the brain retains memories better when you use elaborative processing, which is committing information to memory using multiple techniques. For example, if you remember a recipe, you probably did more than just read it. You likely remember it because you engaged the senses of smell, touch, and taste by cooking it.
If you’re learning or teaching something new, then, it can be helpful to use multiple senses. For example, if you’re learning a new language, you could reinforce it by watching films in that language, in addition to reading and speaking it. Using only one sense, on the other hand, can make learning more difficult. Listening to a lecture, for instance, might leave you less likely to retain information than watching a documentary, since it only involves auditory stimuli.
Teaching Reading With Multiple Senses
Since multisensory learning helps to retain information over time, many educators use it when teaching children important skills. Reading is one skill that can benefit from multisensory learning, and there are several techniques for engaging the senses of touch, sight, and sound during reading lessons:
Tactile writing. Have students write words using their hands in a soft material, like sand or shaving cream. As they write the words, instruct them to sound out each letter.
Tapping out words. Have students tap out each sound of a word using their thumb and fingers—for example, for the word “dog,” tap the thumb to the forefinger on “d,” the thumb to the middle finger on “o,” and the thumb to the ring finger on “g.” Then they can put the sounds together.
Reading together. While a student reads a book, read it aloud with them. You can also ask them to interact with the book by underlining or circling words—for example, they could circle all the verbs, or underline words they don’t know.
Medina gives several recommendations for incorporating multisensory learning in education and business. If you’re giving a presentation at work or in school, Medina recommends making it a multimedia presentation. For example, Medina, as a college professor, would use the same scent in his classroom during both a lecture and the subsequent test. The practice led students to perform better. Businesses that are training employees can also use this technique to improve the employees’ memory of the new information.
(Shortform note: Some of the best teachers in the United States frequently use multisensory learning techniques. Among recent winners and finalists of the National Teacher of the Year awards, some strategies teachers use include having students create advertisements to understand scientific concepts, or using musical concepts to help students understand complex literature. These teachers’ success shows that multisensory learning is a great way to engage a class and help them learn concepts.)
Medina also recommends retailers engage in sensory branding, which pairs scents with sales, as using the right scents has been shown to motivate people to make purchases. For example, if you run a candy store, you could fill the store with scents of chocolate and caramel to encourage people to buy more candy.
(Shortform note: While using scent can improve a brand’s sales, using even more senses in branding can be even more effective. For example, a brand could create a signature sound (hearing), use a distinctive logo (sight), and partner with restaurants (taste).)
In the previous chapter, Medina discussed how the brain interprets sensory information. In this chapter, Medina focuses on arguably the most important sense: vision. He argues that vision leads and influences all of the other senses, shaping our perception of the world and influencing our learning and memory.
Medina describes how the brain processes visual information, including how it can go awry, and how it stays dominant despite its faults. Because of vision’s dominance, he also explains how we can use visual aids to improve our learning.
While it’s easy to think that seeing is simple and straightforward, it’s actually a complicated, energy-consuming process. In order to understand all of the sights around us, the brain needs to take many steps to process this visual information.
Seeing begins when visual information passes through the retina, the part of the eye that processes visual information. The visual stimuli then go on a complicated journey through the brain: from the optic nerve to the thalamus, which distributes sensory information across the brain, then from the thalamus to the visual cortex, which processes visual information, and then on to the brain’s interpretive regions.
The information eventually forms into two different streams of visual information: the ventral stream, which determines what object the visual information represents and what color it is, and the dorsal stream, which determines where the object is located and if it is moving.
Because of how complicated this process is, about half of the brain is dedicated to vision—more than any other sense. Medina notes that there’s a reason the brain jumps through so many hoops to see the world accurately. Out of all the senses, vision helps us understand the world around us the most, so the brain takes extra effort to see clearly.
How Does Blindness Affect the Brain?
Medina explains that visual processing is so complex that about half of the brain is devoted to it. Yet many people are born without the ability to see but still live full lives. This is because, according to research, the brain’s visual processing center adapts to strengthen other senses.
Researchers have found that the visual cortex has the same structure and fulfills many of the same functions in blind people as in sighted people—but does so for hearing and touch. For example, in sighted people, the visual cortex allows for the ability to understand where objects are in space. In blind people, the visual cortex does the same, but through the senses of hearing and touch (for example, understanding how far away a person is by listening to the sound of their voice).
Researchers discovered this by giving sighted and blind people tasks involving touch or hearing, and monitoring their brains as they completed the tasks. The blind subjects’ visual cortexes lit up during these tasks more than the sighted subjects’, indicating that the visual cortex is equally essential in blind people as in sighted people—though it’s unable to process visual information, it makes up for it by making other senses much stronger.
Because visual stimuli fall on the retina in two dimensions, the brain has had to adapt to interpret a two-dimensional representation of a three-dimensional world. Sometimes, this means the brain has to make educated guesses about what it’s seeing. These guesses show up as minor hallucinations that we experience every day.
For example, the brain constantly fills in blind spots. A region of the eye called the optic disk has no cells that perceive sight, so that area of our vision is technically blank. However, the brain prevents us from perceiving these blind spots. Medina notes that researchers believe that the brain either makes a guess and fills in the blind spot, or it simply ignores the blind spot.
When Guesses Go Wrong: Optical Illusions
The brain’s importance in interpreting optical information and giving us daily hallucinations is especially clear when it comes to optical illusions—when our brain thinks we see something that isn’t really there. Examples are when we look at a black-and-white grid and think we see shades of gray, or when we look at a mural on a wall that looks 3-dimensional but isn’t.
These types of visual deceptions are often caused by the intricate wiring of your eye, in which nerves in different areas of your retina perceive light and motion with different sensitivities. They can also be caused by expectations of your brain, as when you’re accustomed to interpreting larger objects as close to you and smaller objects as farther from you, which can lead you to see a 2-dimensional illustration as 3-dimensional.
Another everyday hallucination is the merging of two visuals. Because we have two eyes, we receive different visual information in each eye. The brain then creates a single visual from the two eyes. It guesses what the most accurate image is based on past visual experiences. These two hallucinations represent how the brain processes visual information: Instead of simply receiving full, accurate images, the brain sorts through incomplete and conflicting information, and reconstructs it in order to create a complete image.
(Shortform note: In 2015, researchers found the place in the brain that integrates visual input into one image. A group of neurons in the visual cortex, called V1, process the visual information from each eye. Immediately following, another group of neurons in the visual cortex, called V2, convert them into one image. This shows that the conversion of two images into one occurs very early in visual processing.)
Because it takes up so much more space in the brain than other senses, vision can overrule other sensory input. Vision shapes how we see the world more than other senses, so if we receive contradictory information from multiple senses, vision tends to win out. For example, if you eat candy that comes in an assortment of colors, you might think that they all have different flavors, even if they’re all the same.
(Shortform note: The tendency of vision to override other senses, even when inaccurate, is called the Colavita visual dominance effect. While most people experience this effect, research shows that people with autism spectrum disorder may experience the reverse—in one study, hearing overrode vision for autistic subjects, even though vision overrode hearing for subjects without ASD. This “reverse Colavita effect” shows that, despite established patterns, many people process information differently.)
The dominance of vision over other senses seems to be written into our DNA. Medina writes that, throughout human history, the senses of vision and scent have struggled for genetic dominance. Vision has taken the upper hand. Medina notes that our smell-related genes have lost genetic dominance at a consistent rate, leaving vision to lead the pack of the senses.
(Shortform note: Medina cites extensive evidence that visual dominance is ingrained in our brains, even being dominant in our DNA. However, some have argued that the dominance of vision may be overstated, arguing that vision is seen as dominant only because it’s been researched more than other senses, and because vision is culturally dominant in Western societies. Such critics say that more research is needed to determine whether vision is conclusively dominant or if other senses may be equally dominant.)
Medina notes that vision’s dominance also extends to learning and memory. We remember just about anything better when there’s a visual component, so Medina recommends using visual aids to improve learning. Importantly, he notes that visual aids do not include text, which the brain processes differently than pictures.
Medina notes that the best visual aids for learning often involve motion. Our brains evolved to detect motion, since many early threats to our survival were predators that moved quickly. As a result, we have a keen eye for moving images. Using videos or animation in presentations, then, can be an extra-effective way to use visual aids.
Other aspects of images that capture our attention are color and placement. For example, a brightly colored image placed next to important text will draw our attention, and likely help us remember the text.
How to Teach With Visual Aids
Many educators agree with Medina that using visual aids is a strong teaching method, especially if the visual aid includes motion, memorable colors, and/or strategically places images near important content. However, there are numerous ways to approach teaching with visual aids. Some strategies to help ensure that teaching with visual aids is effective include:
Explain the context for visual aids. Visuals can’t just stand on their own without context—students need to know how an image relates to what they’re learning. To help provide context for a visual aid, you can explain why you selected the image, how it connects to the course material, and what you want your students to learn from the visual aid. For example, if you use Civil-War-era props when studying that time period, analyze how each one sheds light on the habits of people at that time.
Discuss visual aids as a class. Once the students understand the visual aid, ask them to discuss what they’ve learned from it. For example, if you show a documentary in a history class, you could ask them how seeing re-enactments of a historical event affects how they think about the event, and if it challenged their pre-existing knowledge. This further helps students understand the visual aid, and to develop their thoughts about the course material.
The previous chapter focused on how the human brain prioritizes the sense of vision. This chapter focuses on an aspect of the sense of hearing: music. Medina argues that playing and listening to music can notably improve cognition.
Medina discusses the definition of music, the numerous cognitive benefits of music, how music can create hormonal changes that lead to shifts in mood, the positive effects of music therapy, and misperceptions about music’s effects on cognition.
While music is an integral part of most people’s day-to-day lives and exists in all cultures, researchers haven’t pinned down a single, concrete definition of it. Music is different across cultures, and what sounds like unpleasant noise to one culture may be beautiful music to another.
Medina does observe that all music has at least some common features: tempo, changes in frequency, and timbre (the tone or “color” of a sound). Music also frequently inspires movement, such as dancing.
How Do Experts Define Music?
Ethnomusicologist Patrick Burke has a broad definition of music: It’s whatever sound people call music. While many people believe music is a “universal language,” people view music differently across cultures, meaning that it’s hard to pin down a single, concrete definition of music.
However, Burke does note that all cultures practice music in some way. So even if the diversity in how cultures practice music makes it hard to define, it’s still a part of all of our lives.
Medina describes several areas of cognitive function that may be positively affected by participating in or listening to music.
Music leads to improved auditory skills. Medina cites several studies noting that musicians score higher on tests involving identifying subtle differences between sounds—including in speech.
(Shortform note: A recent study shows that piano lessons help children to differentiate between pitches, an important part of language processing.)
Music leads to improved language skills. Studies show that children who study music see improvements in language skills, both spoken and written. At 10 years old, children who have been practicing musical instruments for at least three years often see improvements in their vocabulary.
(Shortform note: Since music helps language processing, it also helps children learn how to read and learn language. Studies show that music lessons may even be more effective than additional reading lessons.)
Music leads to improved social skills. Infants exhibit improved social skills when participating in music. Medina cites a study where infants in a parent/child music class, involving tasks like playing with instruments, developed strong social skills such as increased smiling, laughing, and waving to others. Their stress levels were also lower than infants who did not participate in this class.
(Shortform note: Studies show that, for children with poor social skills, taking group music lessons improves prosocial behaviors like sharing and helping others. Children in these lessons also show more positive attitudes toward their peers.)
Music leads to improved emotional skills. According to Medina, studies show that children who played musical games during school have increased empathy for others, as opposed to children who played non-musical games or no games at all. Practiced musicians are also better at detecting emotion in others’ voices.
(Shortform note: Research shows that music education helps children to recognize emotions in images and texts, and can help children to express their emotions.)
Medina cites several reasons why music boosts our cognition.
Music improves our speech skills because music and speech share regions of the brain: The brain needs a strong sense of rhythm and pitch to understand both music and speech. As a result, playing or listening to music improves our language skills.
(Shortform note: Some researchers believe that, because of its shared neural pathways with language processing, studying music may be more important for verbal communication than studying phonics. Since music training can help language processing so much, music training may help prevent literacy and language disorders in children.)
Music improves our emotional and social skills because it increases the production of hormones that increase pleasure, lower stress, and stimulate social bonds. Collaborative musical performance, like performing with a band or a choir, also encourages social skills because it requires cooperation and nonverbal communication.
(Shortform note: Research shows that listening to or participating in music stimulates the areas of our brain that govern social engagement, even if we do it alone. This is because music releases endorphins in the brain, pleasurable hormones that are also released when we socialize with others. So while engaging musically with others is a better way to improve social skills, participating in music alone is still helpful.)
Because of the benefits of music, particularly its ability to improve your mood by stimulating hormones, medical professionals often use music as a form of therapy. In music therapy, music is played to patients to improve their recovery from physical, mental, or emotional injury. Medina notes that music therapy can help patients who have experienced injuries or traumas that affect cognitive functions, such as speech, memory, and focus.
Music Therapy for Mental Health
Music therapy is a common method for treating mental health issues. Here are a few ways that music therapists work with patients who are struggling with their mental health:
Studying Lyrics. By discussing song lyrics, patients can make connections to their own experiences and emotions, without needing to discuss sensitive information.
Songwriting. Songwriting can help patients to understand and express their feelings.
Listening to Emotional Music. Therapists can play music that matches their patients’ emotions, and can gradually alter the mood of the music. This can help patients reach more positive emotions.
Musical Improvisation. When working with a group, improvising music with instruments can foster connection and collaboration and can help patients express their feelings.
Though Medina describes many cognitive benefits of music, he does argue that some benefits people commonly associate with music education are not based on evidence.
Some people believe music education is associated with higher test scores in reading and math. Medina writes that, based on studies showing the relation between music education and reading and math ability, people may see small improvements in these abilities. However, they’re probably not enough to make a major difference. Music-trained people also don’t seem to have higher IQs than others.
Though Medina notes that the popular argument that music is “good for your brain” is overstated, it does not negate the many cognitive benefits that music has. For example, music seems to improve spatiotemporal reasoning, or the ability to envision the relationship between objects and space—an important skill for professions like architecture and engineering.
How Can Music Best Benefit Cognition?
Most researchers agree with Medina that music education doesn’t have a direct correlation to improved academic performance. Some studies show that music education for children confers no cognitive benefits. The researcher who conducted the study argued that, because of the lack of evidence for improved academic performance from music education, arts education advocates should focus on the social, cultural, and artistic benefits of musical education.
However, other research shows that music education can help childrens’ cognition, but only if they’re actively engaged in the class and making music. Studies show that the benefits of listening to music are negligible, but playing musical instruments with others improves childrens’ neural processing.
More research is needed to determine the exact benefits of music education. But it seems likely that music education that involves active participation can help children cognitively, and at the very least socially.
Because vision is the most dominant sense, visual aids can help us learn new information.
Describe a time when a visual aid helped you learn or remember information. For example, maybe a documentary helped you remember a historic event, or images in a presentation at work helped you learn a new concept.
Why do you think this visual aid helped you learn?
In the future, how can you use visual aids to help learn new information?
The previous category focused on how the brain integrates sensory information. This category focuses on a more conscious process: thinking. Medina argues we can improve our learning and performance by understanding how the brain’s thought processes work. This category discusses how the brain pays attention and how the brain creates and retrieves memories.
Medina argues that the better we’re able to focus on something, the better we’re able to learn it and remember it. In this chapter, he explores how we pay attention, what piques our attention, and why multitasking doesn’t work.
At any given time, there are millions of sensory neurons carrying messages to your brain, each competing for your attention. But only a few capture it. Stimuli direct our attention and help us to determine what is most important to focus on at any given moment. If our brains didn’t direct our attention to specific stimuli, so many things would be competing for our attention that it’d be difficult to focus on any one.
To pay attention, our brains go through a process controlled by three neural networks, which are activated consecutively.
Selective Attention
The process of paying attention, controlled by the alerting, orienting, and executive networks, is activated through selective attention. Selective attention allows us to narrow our attention to one thing at a time, even in an environment filled with stimuli. For example, if you’re in a coffee shop, your alerting network will kick into gear if you hear the barista call your name, but you won’t register the conversations of patrons around you.
Because of selective attention, we’re able to filter out unimportant information and focus on what’s relevant to us—if we didn’t have selective attention, our alerting network would ping back and forth between numerous sounds and images, without letting us focus on any one.
Emotionally charged stimuli capture our attention. Medina argues that this is a result of human evolution, because emotions like fear and sexual arousal are important for survival.
If you want to capture someone’s attention, Medina thus recommends using emotion as a “hook” to draw them in. For example, many advertisers and marketers use emotion to sell products and services. For example, advertisements often show happy people using their products. If you’re giving a presentation, play to your audience’s emotions to pull them in, instead of just relaying facts.
How Emotion Affects Our Attention
A recent study shows how emotion in storytelling grabs our attention. Researchers showed participants an episode of a television show, while scanning their brains to measure their attention. They found that the participants’ brains all showed similarly high levels of attention during emotionally engaging moments (for example, when a character was solving a mystery). During less emotionally stimulating scenes, their attention fell.
This study shows how people’s attention naturally focuses and drifts off, and echoes Medina’s assertion that emotional stimuli consistently make people pay attention.
Medina writes that multitasking is impossible when we do tasks that require our full focus. For example, you can’t read a book and watch a movie at the same time and keep full attention on both of them. On a higher-stakes level, it’s impossible to fully concentrate on driving if you’re also sending a text message.
Multitasking doesn’t work because it’s like subjecting yourself to a series of interruptions, and interruptions prevent you from sustaining focus on any one activity. Medina explains what interruptions do to our attention by outlining the steps that attention follows:
By attempting to focus on two tasks at once, you lessen your ability to complete either. You can be more productive and focused, then, by completing one task at a time.
How to Stay Focused, Instead of Multitasking
As Medina notes, when you multitask, you lose your focus, since your attention is redirected again and again. If you frequently multitask and struggle to pay attention to a single task, here are a few recommendations:
Pick a few times of day to check email, messages, and/or social media. These all pose frequent distractions, so it can be helpful to determine specific times to check these instead of refreshing them throughout the day.
Remove distractions from your environment. If you still find yourself checking your phone, your email, or social media frequently, try moving your phone to a different room and blocking distracting websites.
If your environment is still distracting, leave it. If your workspace has numerous distractions and you need to focus intently on a project, pick a different space with fewer distractions.
Do the most difficult, or most important, task of your day first. By doing this, you complete the most focus-intensive work of your day early, so there’s less pressure to finish it later.
The previous chapter discussed how we pay attention, and how our attention can be diverted. This chapter describes the results of paying attention: forming memories. Medina writes that we can strengthen our memories through repetition, and therefore boost our learning.
Medina primarily focuses on declarative memories, or memories that you have to actively think about to retrieve. Nondeclarative memories are the opposite. (For example, remembering the names of your kindergarten classmates would be declarative memories, while remembering your own first name would be a nondeclarative memory.)
Medina discusses why humans need memory, and how the brain creates, stores, and retrieves memories. He also describes several techniques for building strong memories through different types of repetition, and he suggests strategies for building strong memories in school and at work.
Medina writes that memory is essential to human survival. Early humans lived among species that were physically stronger than us. Having strong memories gave us a mental advantage over any other species. As humans evolved, memory allowed us to remember important facts about our environments, like where to find food or where predators lived.
Medina argues that memory is one of the key characteristics that makes us human, because it enables us to retain information and learn from experience. For example, we need memory to use spoken and written language, a uniquely human ability.
The Evolution of Memory
Many forms of memory evolved over time, leading to progressively more complex animal life. Researchers have determined seven types of memory that modern animals have, growing gradually more complex. The most complex, the social-subjective system, belongs only to humans.
The social-subjective system allows us to form societies, learn facts, and participate in organized social interactions with one another. This system allows us to have autobiographical memory, or memories about our individual lives and identities, and knowledge of the cultures we live in.
To form memories, and therefore learn from experience, the brain goes through a complex process. Medina writes that the most important part of making a memory is encoding, which is how our brain processes and stores sensory information. Encoding happens in the first few seconds of having an experience.
When we take in new information, each of our senses processes it at the same time. For example, imagine purchasing a danish from a new bakery in your neighborhood. You’d see the display case of baked goods, you’ll hear the sounds of the customers and employees, you’ll feel the pastry you’ve been handed, and you’ll smell and taste the danish you’ve purchased. Each of these senses is processed by different areas of the brain, so all of this information is converted into electrical signals by neurons in their respective areas.
After encoding, the brain then stores the different pieces of information in the areas that they’ve been processed in. Instead of the memory of the bakery entering one particular spot in your brain, then, the various sensory information you’ve processed in the bakery will be dispersed all over the brain.
What Happens When Encoding Is Disrupted?
The importance of encoding can be seen when the process is disrupted—for example, when the hippocampus, the area of the brain that encodes short-term memories into long-term ones, is damaged. Hippocampus damage can occur through injury or conditions like Alzheimer’s disease.
When someone’s hippocampus doesn’t function properly, that person develops anterograde amnesia, meaning they can remember very short-term memories but can’t form long-term memories. Thus, while a person with a properly functioning hippocampus would be able to remember their trip to a new bakery a week later, a person with a damaged hippocampus might only remember it for a few minutes.
Not all encoding is the same. There are two major types of encoding, automatic and effortful processing, which determine how easy or difficult it will be to retrieve a memory.
Automatic processing is encoding that requires very little conscious effort, usually involving visual stimulus. For example, when you see a memorable movie, your brain will encode it automatically.
Effortful processing, on the other hand, requires conscious attention to form a memory. For example, when you study for a test, your brain uses effortful encoding. Effortful encoding can be challenging and requires numerous repetitions before you can easily remember what you learned.
“Chunking” Can Help Effortful Processing
In A Mind for Numbers, Barbara Oakley describes chunking, a strategy for forming and retaining memories. A “chunk” is a group of related ideas that you sort together in your mind to create meaning from your memories. Oakley notes that we can hold only a limited amount of working (or short-term) memories at a time—about four chunks of information. Automatic processing helps us chunk a lot of information without us noticing, but sometimes chunking requires effortful processing. Oakley suggests some strategies for chunking more efficiently to build stronger memories.
One chunking technique you can use is to simplify concepts you’re learning to the extent that you could easily explain them to someone that knows nothing about the topic. This helps you thoroughly understand the concept, helping to firmly commit the concepts to memory.
Another technique is to chunk from the “bottom-up”: Learn the information, then learn the concepts behind the information, then learn the context surrounding the information. These steps give you a full picture of the information you want to learn, helping to cement it in your memory.
By trying either of these strategies, you’ll improve your effortful processing and have an easier time committing difficult information to memory.
Just as there are two primary types of encoding, there are two different types of memory: working memory (or short-term memory) and long-term memory. Short-term memories are usually accurate, but long-term memories can be filled with false information.
Working memories are temporary memories that have been stored for immediate use. Short-term memory retrieval is straightforward: When you search for a memory, you’re able to find it and review it accurately.
Long-term memories are a small number of memories that are stored for an extended period of time. Long-term memory retrieval is more complicated. We likely remember bits and pieces of the long-past event or information, and then fill in the gaps based on what they think makes sense. This can lead to a memory that’s filled with false information. Even if a memory is important to you, it can become difficult to remember accurately if you don’t think or talk about it often.
“Knowledge Collapse” Occurs Before Creating Long-Term Memories
Medina describes the difficulties of retrieving long-term memories. Barbara Oakley expands on this in A Mind for Numbers, where she discusses one particular pitfall of long-term memory.
This pitfall is called knowledge collapse. As you learn more about a subject, your neurons will sometimes have to rearrange themselves in order to store the new information. This can temporarily wreak havoc on retrieving your long-term memories about the subject: As restructuring occurs, it becomes suddenly difficult to remember information you thought you solidly knew.
However, this is a temporary problem, as this restructuring ultimately helps you learn new and complex information. If you experience knowledge collapse, instead of stressing and giving up, keep up with your learning until your brain has integrated the new information.
To strengthen effortful processing and to create accurate long-term memories, we need to repeat the information, starting soon after the event occurs. Effortful processing can be difficult and long-term memory can be unreliable. If you don’t use repetition to create strong, reliable memories, then you’ll have difficulty learning from your memories.
Medina describes several repetition strategies that can help us create strong memories. One strategy is to use a complex process to give meaning to your memories. When information has a lot of meaning, it becomes much easier to remember. For example, if you need to memorize a shopping list, it would help you to think about what you need each item for. You’ll have an easier time remembering the items than if you tried to memorize them without context.
(Shortform note: One way to give memory meaning, which Barbara Oakley suggests in A Mind for Numbers, is to create a “memory palace.” To create a memory palace, imagine a place that you know well—for example, your childhood home. Then fill it with images representing the concept you want to remember. If you’re trying to remember your grocery list, for example, you could imagine a dozen eggs sitting on the shelf of the kitchen, bottles of hand soap on the bathroom counter, and detergent in the laundry room.)
Another strategy is to repeat information over an extended period of time. Spacing out repetition of information is more effective than trying to cram it all in at once. Rather than repeating information 15 times in a row, then, Medina would recommend repeating it once a day for 15 days.
(Shortform note: Research suggests that repeating information without breaks in between is hardly better than not repeating information at all. But if you don’t have time to repeat information periodically over the course of several hours or days, repeating with short breaks in between can be helpful. For example, if you have a test in an hour and want to remember a vocabulary word, you could repeat it frequently with 10-second breaks in between.)
Another strategy is to reflect and interpret a memory right after it’s formed. This is useful if you have an experience you immediately know you want to remember. Right after an event occurs or you learn new information, discuss the facts of it with someone else. Once you’ve talked about the facts, then discuss your personal interpretation of the event or information.
(Shortform note: If you’re an educator, one way you can use this memory-boosting technique is to quiz students often. This is because it makes students apply what they learned, and consider their interpretations of the information, right after they learn it.)
In addition to using strategies for forming memories, you can use strategies for retrieving long-term memories. One strategy is to put yourself in the same circumstances you first learned the information in. This is called context-dependent learning: People recall information better in the same situation in which they first encoded it. For example, if you learned a concept in your backyard, you could return to your backyard to reinforce it. Or if you were listening to a particular song, you could play that song again while you review.
State-Dependent Learning
In the same way that you can better recall information in the same place you were when you learned it, you can also better recall information when you’re in the same mood or physical state. This is called state-dependent learning.
One study showed that people who learn information while drunk remember it better while drunk, while those who learn information sober remember it better sober. This shows how the physical state you’re in affects what you remember.
If you want to create strong memories, try recreating the state you’re in when you first learned them. For example, if you were in a good mood when you first learned a piece of information, try thinking of happy memories to recreate that same mood.
How well we remember information affects our success in important areas of our lives, especially school and the workplace. Because of this, Medina suggests several techniques to strengthen memories in school and at work.
One strategy is for schools to repeat material several times over the course of a day, instead of having hour-long classes for each subject. According to Medina, frequent repetitions would encourage strong memory encoding. For example, a student might have 25 minutes of English, 25 minutes of math, and 25 minutes of history, which would be repeated three times.
(Shortform note: Repeating information in intervals helps to remember concepts, so it’s recommended that students repeat what they learned after class, in the evening, and before the next class. This suggests that Medina’s idea would be an effective model for learning: It provides class time to reinforce concepts, so students could retain information better and spend less time studying.)
Another strategy is for schools and businesses to repeat key information over the course of several years. Long-term repetitions can help to cement information in your long-term memory. In schools, Medina suggests reviewing course material periodically. For example, students would review basic algebra once a year from the seventh grade to the eleventh grade. In businesses, Medina suggests offering classes that provide reviews of important skills. For example, a marketing professional would be able to take classes to refresh their knowledge on social media, digital marketing, and writing skills.
(Shortform note: Research shows that learning information over a long period of time can help cement it. A study of foreign language students showed that they remembered words better when they learned and repeated them over the course of 56 days than when they learned them over 28 days. This suggests that Medina’s idea of repeating information over an extended period of time could help students retain information.)
Medina argues that we can strengthen our memories through repetition. A few of the techniques Medina suggests include repeating information over an extended period of time, giving meaning to information, reflecting on and discussing information soon after you learn it, and putting yourself in the same situation as when you first learned the information.
Think of a time when you used one of the strategies Medina recommends, such as playing scales every day when learning to play an instrument (repetition), or creating acronyms when studying for a test (making meaning). How effective was the strategy?
Why do you think this strategy was effective, or ineffective?
In what situations would you use that strategy in the future? If you wouldn’t use this strategy again, pick another strategy Medina describes, and explain why you would use that strategy in the future.
In the previous category, Medina described some of the brain’s fundamental cognitive processes. In this category, Medina describes two more aspects of our lives that influence our thinking and learning: gender and exploration.
In this chapter, Medina discusses factors with more contested effects on the brain: sex and gender. Medina discusses evidence of differences in brain structure, behavior, and cognitive differences between men and women. He argues that, though more research is needed, gender affects how we think, learn, and interact with others.
(Shortform note: Since the publication of Brain Rules, science has shown much more evidence that male and female brains aren’t notably different, and that behavioral and cognitive differences between men and women are primarily influenced by social expectations. Examples will be included throughout the chapter guide to provide more context on Medina’s findings.)
Medina notes that there are observable differences in the brains of men and women. For example, various regions of male and female brains have different sizes. The frontal and prefrontal cortex, which deal with decision-making, are larger in women. The limbic system, on the other hand, is larger in men. This system contains the amygdala, which controls the generation and memory of emotions.
Males and females also have different brain chemicals. Serotonin, which regulates emotions, is much higher in men than women. While male and female brains have differences, these differences don’t necessarily affect how men and women behave. This is because, according to Medina, neuroscientists have not found a definitive link between brain structure and behavior.
Brain Structure Doesn’t Strongly Influence Behavior
Although Medina suggests otherwise, recent research indicates that gendered differences in brain structure are unlikely to shape how we behave. Researchers have noted differences in behavior among men and women and differences in brain structure—most notably that male brains are typically 10-15% larger than female brains. However, when they compared differences in brain structure with differences in behavior among study participants, they found that brain structure did not have a statistically significant impact on behavior.
Medina describes numerous behavioral differences between men and women, which he believes affect social and professional relationships. Some research shows that women and girls are generally better at verbal communication than men and boys. Medina notes that this is likely because women tend to use both hemispheres of the brain when speaking and processing verbal information, whereas men tend to use just one.
Male and female children also form relationships differently, a pattern that extends into adulthood. Girls tend to bond by talking frequently, while boys bond through physical activities. And while girls prefer to form a consensus with another in social groups, boys prefer a social hierarchy with a distinct “leader”. When these styles of relationships persist into adulthood, they can cause social and professional difficulties. For example, a woman with a “masculine” leadership style may be seen as “bossy,” harming her ability to advance in the workplace. On the other hand, a man who does not try to compete with his colleagues may be seen as weak or unmotivated.
Gendered Conversational Styles in the Workplace
Linguist Deborah Tannen has found that gendered conversational patterns can benefit men in workplace situations: For example, women may downplay their own contributions, and men may compete to have theirs heard, so people may think their male colleagues have more interesting ideas than their female colleagues. Men may also be seen as more confident than women in the workplace.
Even if gendered conversational styles don’t unfairly benefit men, they can still cause general misunderstandings. For example, men tend to raise issues directly, while women tend to do so indirectly—and if people aren’t on the same page about how to raise an issue, they’re likely to misunderstand each other.
Tannen recommends that managers acknowledge that their employees may have different conversational styles, and that these are often influenced by their gender. By understanding how conversational styles differ, they can determine how to communicate best with their employees, how to ensure participation in meetings, and how to understand their employees properly.
Medina notes that gendered communication and relationship styles are a general pattern, and that individual men and women often don’t adhere to them. He also notes that boys and girls are treated differently from one another from an early age. This suggests, then, that social differences between boys and girls at least partially result from cultural gender norms.
(Shortform note: Recent research from cognitive neuroscientist Gina Rippon bears this out. Rippon believes that male and female brains aren’t meaningfully distinct, but that the practice of treating boys and girls differently can shape their behavior—and since their brains are developing, their neural pathways.)
Medina also notes several cognitive differences between men and women, which he argues affect both thought processes and cognitive health.
One cognitive difference is that men and women tend to respond to stress differently. Research suggests that, when responding to stress, men focus on the general overview of a situation, while women focus on the details.
(Shortform note: Research also shows that men respond to stress with a “fight-or-flight” response, while women respond with a “tend-and-befriend” response. This means that, when faced with a stressful situation, men are likely to either confront or avoid it, while women are likely to look for comfort.)
Men and women also tend to be susceptible to different psychological health issues. Men may be more susceptible to intellectual disabilities, schizophrenia, antisocial behavior, alcoholism, and drug addiction. On the other hand, women may be more susceptible to depression, anxiety, and anorexia.
(Shortform note: Most researchers believe that a combination of biological and cultural factors explain why men and women are susceptible to different mental disorders. Men and women have different hormones, which impact our mental health. Yet aspects of culture that affect gender, like discrimination and gender roles, can also cause harm to mental health. Scientists note that much more research is needed to better understand how biology and culture can create different mental health outcomes for men and women.)
Because of the cognitive differences between men and women, Medina believes that teachers and managers should make adjustments to address gender.
In school, Medina recommends trying out same-sex classes. Because boys and girls typically have different social styles, he believes that same-sex learning environments would make participation more equal. Boys could participate competitively, and girls could participate with consensus, without either of these social styles coming into conflict.
(Shortform note: Many advocates for single-sex schools believe, like Medina, believe that single-sex schools can effectively accommodate differences in boys’ and girls’ learning. However, author Juliet A. Williams believes that there is little evidence that single-sex schools provide better educational experiences than co-ed schools, and they can actually have detrimental effects because they reinforce gender stereotypes.)
At work, on the other hand, Medina recommends pairing men and women together in teams. This is because men tend to remember the big picture of situations better, while women tend to remember the details better. Medina believes these two modes of thinking could complement each other in the workplace.
(Shortform note: One study found that workplace teams with even proportions of men and women come up with better ideas than teams with an uneven gender balance. The researchers found that this is because, when a person is in the minority in a group based on their gender, they’re less confident and less likely to share ideas. Equal representation of genders in a team seems to solve this problem.)
Brain Rules has discussed numerous aspects of cognitive science and development, ultimately painting a picture of some of the brain’s most important functions and how they impact our lives.
In the final chapter, Medina trains his focus on a particularly important function: exploring, which helps us understand our environments and learn from our experiences. Medina argues that we have an instinctive, strong desire to explore that drives us to learn about the world throughout our lives. He says that this desire is innate, and as such, we can observe this trait even in babies. He discusses how exploring plays a major role in early childhood development, and how we can continue to explore and learn throughout our lives.
Medina notes that babies are born with intense curiosity and demonstrate early use of the scientific method. Babies are able to explore and test their surroundings. Their explorations roughly follow the steps of the scientific method: They observe, form hypotheses, experiment, and draw conclusions.
Almost as soon as they’re born, newborns can imitate others. If you stick your tongue out at a baby, they’re likely to stick their tongue out in return. The baby might find that imitating something can lead to a specific result. This makes them test their hypothesis. For example, if you wave to a baby frequently, they’ll likely start waving back. Eventually, they wave at you first because they expect a wave in return. If you do wave back, they’ll learn that their hypothesis was correct.
At around 12 months, babies experiment with objects they encounter. Babies experiment with objects because they want to learn more about them. If a baby gets a new toy, for example, they might throw it, kick it, shake it, and put it in their mouth.
At around 18 months, babies learn object permanence. Object permanence is the ability to recognize that, even if you can’t see something, it doesn’t mean it disappeared. Developing object permanence enables babies to understand their environments. Babies often learn this through experiments—Medina uses a baby repeatedly covering and uncovering an object as an example.
They also discover that others have different wants and needs from them. Babies also discover around this age, through experiments, that others have different desires than them. Once they learn that other people want different things from them, babies and toddlers start to test the limits of others’ desires. For example, toddlers disobey their parents to test their limits, and to see how their parents will react to unwanted behavior. Through these tests, babies learn to understand the extent of others’ desires, which helps them to cooperate with others.
(Shortform note: Others have spotted the similarities between a child’s exploration and the scientific method, some going so far as to say not only are children small scientists, but that scientists are merely big children. In fact, they point out that the inventor of the modern scientific method, John Dewey, was inspired to outline the steps of the method by watching how children play.)
Later Stages of Development
Medina describes how children explore, from imitating in infancy, to experimentation at 12 months, to object permanence and learning others’ feelings at 18 months. Though Medina stops there, children learn to explore in even more ways throughout childhood. These are the next steps of exploration, from 3-4 and 5-6 years old:
At 3-4 years old, children ask questions about the world around them. At this age, children have developed language and stronger motor skills, and they use them to explore their curiosity about the world around them. They tend to ask lots of questions of parents and teachers—for example, “why is the sky blue?” or “why do dogs bark?”
They’ll also continue to experiment with the world around them, and start to share their findings with others. For example, if a child plays in the dirt and finds a worm there, they might tell a friend that they found out where worms live.
At 5-6 years old, children begin to use critical thinking and creativity in their experiments. At this age, children are just as curious but have developed more cognitive skills, so their experiments become more sophisticated. They can reach concrete answers to their questions through experimentation, and apply that knowledge in the future.
For example, a child coloring with crayons might discover that red and yellow blended together make orange. They show it to a friend, and they talk about what might happen when they put other colors together. Coloring all over a piece of paper, they find out that red and blue make purple, and that yellow and blue make green. From this observation and experiment, they’ll have learned about mixing colors, and they use this knowledge to draw pictures.
While a massive amount of learning occurs during infancy and early childhood, we all learn throughout our lives. Medina writes that, while scientists used to believe the brain’s capacity for learning diminished over time, they now know that the brain’s capacity for learning stays strong as we age.
Brains also continue to change in response to new experiences. This is an evolutionary necessity. The ability of the brain to process new experiences helps us to realize when we’ve made dangerous errors and to learn not to repeat them.
Medina emphasizes that people never stop wanting to learn. While bad educational experiences can blunt the desire to learn, Medina believes that the drive to learn is strong and persists despite obstacles.
You Can Learn Later in Life, But You Have to Practice
Many people assume that the capability to learn and remember information decreases with age. However, research echoes Medina’s assertion that your brain remains flexible as you age. Though some skills are still much easier to acquire in childhood, older adults actually have some learning advantages: Compared to children, adults have more developed skills in discipline and critical thinking.
To keep your memory and ability to learn sharp as you age, it’s important to stay physically fit, which helps brain health, and to practice using your memory. Some older adults assume their memory is bad, so they avoid using their memories in day-to-day life—for example, using a recipe for a dish they cook frequently. This can actually hurt the ability to form new memories and learn new information, so it’s important to frequently jog your memory as you get older.
Medina believes that people naturally love to learn, and that people can continue learning well into their adult lives.
What’s an interest of yours you’d like to learn more about? This can be a topic you want to learn about, like U.S. history or jazz music, or a new hobby or skill you want to pursue, like playing tennis or taking a dance class.
How will you go about learning it?
How do you think it’ll improve your life to learn something new?