In Seven and a Half Lessons About the Brain, Lisa Feldman Barrett playfully addresses some common mysteries that surround the human brain. Published in 2020, her explanations shed light on the inner workings of the brain and how they impact feelings, behaviors, and relationships. Barrett argues that by understanding the basics of how your brain works, you can take a more active role in deciding how to think and behave. Her seven-and-a-half lessons explore how the brain evolved, how it’s organized, how it develops throughout our lifetimes, and how it works on its own and with other brains.
Barrett is a leading neuroscientist, researcher, and science writer. She is a professor of psychology at Northeastern University and is the Chief Science Officer for the Center for Law, Brain & Behavior at Harvard Medical School. She has written more than 260 peer-reviewed articles as well as the popular book How Emotions Are Made (2017). Barrett is known for making neuroscience accessible to a lay audience through myth-busting explanations of what we know (and don’t yet know) about the brain and the mind (the brain being the physical organ, and the mind being our individual patterns of thought and action).
Our guide explores Barrett’s seven-and-a-half lessons through four themes:
We also compare Barrett’s explanations of the brain to those of other experts, and we offer practical applications for the insights she shares.
Barrett begins with an explanation of how the brain is organized: not as a layered structure with specific parts and jobs, as has long been thought, but as a network of neurons (brain cells that receive and transmit information) that can all perform different tasks according to need. By understanding the brain’s organization, we can recognize the flexibility and resilience of the human brain and learn what makes it different from the brains of other animals.
Barrett argues that the way we traditionally think of the human brain is based on outdated research. There’s a popular belief that the human brain has three distinct parts, each with distinct functions: a brain core (or “lizard brain”), a limbic system, and a neocortex. The three-layer model of the brain has long been used as “proof” that the human brain is more evolved than other animal brains.
This model became popular in the mid-20th century when doctor Paul MacLean identified structural similarities and differences among the brains of different animals:
Barrett says that researchers debunked this model in the late 20th century, yet the general public still believes it to be true.
The Impact of the Three-Layer Brain Model
The myth of the three-layer brain was further popularized by books such as Simon Sinek’s Start With Why, where he puts forward a model for finding a person’s or organization’s purpose that mimics how the three-layer brain allegedly works. Sinek’s “Golden Circle” model consists of three concentric circles, each representing one of the core concepts in his theory:
1. The inner circle is the Why: the purpose that orients everything you do. It’s the core belief that motivates you to get out of bed in the morning. Why originates from and appeals to the limbic system—which, he argues, processes emotions and generates “gut feelings.”.
2. The middle circle is the How: the methods and practices that characterize you and that other people consider your strengths. How corresponds to both the limbic system, which handles decision-making, and the neocortex, which controls rational thought and language.
3. The outer circle is the What: the outputs you generate. It’s the tangible part of your organization or life and the easiest to identify. What appeals to the neocortex, which he argues is well-equipped to process factual information.
The problem is that this model relies on what brains look like to deduce what they can do. To combat this error, Barrett explains three truths about our brain’s structure and how it functions.
First, several parts of the brain are needed, for example, to breathe, to feel angry, or to make a plan. It’s not accurate to say that there’s one specific part of the brain that deals with a specific function. (Shortform note: The understanding that several parts of the brain collaborate to perform specific tasks also debunks the common myth that the left and right hemispheres have distinct functions. While books such as The Whole-Brain Child argue that the right side of the brain deals with emotions while the left deals with rational thought, this is inaccurate.)
Second, appearance and location aren’t the only determining factors of a neuron’s function. When researchers studied neurons (nerve cells) more closely, they found that neurons from animals and humans can look very different or be found in different parts of each brain, yet have similar genetic structures. Thus, different animals can have brain cores that look similar, for instance, but that doesn’t mean that they’re responsible for primitive, instinctual functions that we believe all animals share. Likewise, just because the outer layer of our brains (the neocortex) looks different from other animals’, it doesn’t mean that the animals lack the function that our neocortex plays.
(Shortform note: Researchers have found that a neuron’s development process can also determine its function. Looking at the development of fruit flies’ brains, they discovered that young neurons can have the same genetic information but trigger different genes within that information, resulting in widely different adult neurons. Researchers say this information has important implications for future studies of neurodevelopmental disorders, such as attention-deficit/hyperactivity disorder (ADHD), learning disabilities, and cerebral palsy.)
Third, most brains, including the human brain, a monkey’s brain, and a lizard’s brain, develop in the same order. According to Barrett, the difference is that they develop different parts for different lengths of time. For example, all mammals and reptiles have a cerebral cortex (part of the neocortex), but the human cerebral cortex spends more time developing so it becomes larger and more complex than that of a monkey or lizard.
(Shortform note: Even different species of our ancestors developed at different paces. For example, the brains of Australopithecus afarensis, a hominid that lived between 3.85 and 2.95 million years ago, were 20% larger than the brains of chimpanzees and took much longer to develop. Much like modern-day humans, their brains continued to develop during childhood, making them dependent on adults of the species for a longer time.)
Thus, Barrett argues that human brains aren’t more evolved than others, as the myth of the three-layer brain would have us believe. Our brains just evolved differently from other animals, in a specific trajectory that made us who we are today—good at reading books, but bad at sleeping with our eyes open to stay aware of our surroundings, like guinea pigs. (Shortform note: Not only did our brains not evolve more than others’, they might also have not evolved as differently as we think. For example, some evidence shows that monkeys also have some ability to use symbolic reasoning, albeit to a much lesser degree than humans. Some other species, such as dogs and primates, also have the “human” ability to read emotions.)
Rather than a simple and static three-layer structure, Barrett says the brain is a complex and active web of neurons. Put simply, neurons are the messengers of the brain. They take in information and transmit electrical impulses to each other to communicate what is happening and how the body should react. For example, if you touch a hot stove, the neurons in your brain would receive that data and instantly tell your body to pull your hand back.
Barrett goes on to explain that neurons form clusters and share information with each other. We can imagine these clusters as a group of people talking. Some of the neurons in those clusters communicate with other clusters in the vicinity (like neighbors chatting in the front yard). Some clusters are bigger and more powerful than others (such as people who have a public forum or social influence). And some clusters communicate with other clusters across the brain, not just the ones nearby (as in email, a phone call, or on social media). In this way, the entire brain shares information and participates in shaping your experiences and behaviors.
(Shortform note: It might seem from this description that neurons are the only stars of the brain show, but there are other important cells in the brain that allow neurons to do their work: glial cells. Their name comes from the Greek word for glue, which makes sense because they help neurons build connections with each other to share information. In addition, they identify and destroy injured neurons so new ones can crop up.)
As we’ve seen, brains are made up of neurons that get together to form clusters and share information. Barrett says that, as the foundational element of brains, neurons give brains two important characteristics: plasticity and complexity.
1. Plasticity
Plasticity refers to the brain’s capacity for constant change. Neurons continuously learn new information, age, die, and get replaced. This doesn’t mean that the information those neurons contained disappears, though. Other neurons preserve that information in case you need it in the future.
Similarly, neural connections that aren’t getting used become less agile while those that are exercised often become stronger, just like your muscles. That’s why you have a hard time remembering and using any information you only heard once. But if you go back to the information several times, that connection will become stronger and easier to retrieve and apply.
Neurons can also learn to perform new tasks if necessary. They don’t naturally have one specific job. Instead, they can all perform a range of different tasks but end up performing the specific functions we need them to do. For example, Barrett explains that if a person loses one of their senses, such as their eyesight, the neurons that process visual input can quickly learn to process other sensory input. This is why a blind person’s sense of touch is heightened, which helps them read braille.
You can think of your brain as an orchestra and neurons as the individual musicians. Plasticity gives musicians (neurons) the ability to learn new music and play more than one instrument (just as neurons are capable of having more than one job). But if they stop practicing, they become rusty.
Plasticity Helps Overcome Trauma
Sufferers of post-traumatic stress often use some neural connections more than others because traumatic memories stored in the brain can be triggered very easily. Even if the context they’re in is very different from the one where the trauma took place, the brain already recognizes a similarity and goes into fight-or-flight mode as soon as the traumatic memory resurfaces. This makes it hard to separate the current context from the traumatic context, and therefore triggers reactions that are inappropriate for the current situation.
Each time a trigger makes a traumatic memory resurface, it strengthens that neural connection. However, by intentionally making small behavioral changes and finding new ways to think about triggers of traumatic memories, PTSD sufferers can rewire their brain to make those traumatic neural connections less active. Over time, those neural connections will weaken and make room for more constructive ones.
Some behavioral changes people can make to weaken traumatic neural pathways are:
Practicing new ways of thinking about the memory and intentionally bringing those new associations to mind.
Making room for traumatic feelings instead of avoiding them.
Proactively deciding how to act when triggers happen instead of acting by default.
2. Complexity
Complexity refers to the capacity of neurons and clusters to organize into different information-sharing patterns and respond to new needs by changing those patterns as needed. For example, there are specific neurons and clusters in your brain that allow you to navigate your city or town every day. If you use public transportation, there are several clusters that help you find your way to the right stop, pick the right bus, and get off at the right station. If you move to a different neighborhood, those clusters will reorganize themselves to help you learn the streets and stops in your new surroundings.
Barrett argues that complexity is a crucial characteristic that we rely on for day-to-day survival:
Referring back to your brain’s “orchestra,” complexity allows it to adapt to changes quickly and easily. For example, if the orchestra’s conductor changes, or one of the musicians is ill, they can adapt to the new conductor’s style or find a substitute for the musician and carry on with the show.
(Shortform note: Complexity is a powerful skill that Artificial Intelligence still lacks, and as such it’s a differentiator in how machines and human brains process information. For example, scientists explain that when you look at an object from a different angle, you’re still able to recognize that it’s the same object. Not so for machines, which might see the back of an object and no longer recognize it as being the same. This is because our brains' patterns can reorganize themselves quickly to understand new information, which AI cannot do—yet.)
Turning from the brain’s organization to its functions, Barrett argues that the brain’s most important job isn’t thinking, it’s allostasis. Allostasis refers to the process of managing the body’s energy budget so it can survive and reproduce. All of its other functions (such as thinking) are secondary.
The Brain’s Most Important Function
While Barrett argues that the brain’s single most important job is managing the body’s energy budget, in The Body Keeps the Score, Bessel van der Kolk breaks down the brain’s primary role into several tasks, including:
Signaling when your body needs essentials such as food, water, rest, shelter, safety, and sex
Interpreting the world around you to point you in the right direction to find and satisfy those essential needs
Creating the energy and initiating the actions to achieve those tasks
Warning you of dangers and opportunities you may encounter as you pursue those tasks
Adapting and responding to changing circumstances along the way
To better understand how allostasis (the brain’s process of energy budgeting) works, it helps to know how it has affected our brain’s evolution. Primitive organisms evolved to require more energy, so their energy-budgeting cells had to evolve to keep up with their needs.
Barrett explains that, before brains existed, primitive creatures had energy-budgeting cells that kept track of their energy needs. These cells signaled to the rest of the body when it needed to eat (or move to find food), or rest—whichever would preserve its energy best in that moment.
During the Cambrian period (starting about 541 million years ago and lasting for about 56 million years), primitive animals started needing more energy and the process of budgeting energy became more complex, so those energy budgeting cells clustered together to form a brain. Barrett explains that this evolution was due to two main factors that made energy budgeting more challenging:
1. Some primitive creatures began hunting, which meant they now had to hunt for food and escape predators. They began developing more sophisticated senses to detect danger and opportunity and to make decisions that directly impacted their energy budgets, such as whether to move (and expend energy) to try and catch prey (to gain energy) or escape danger.
(Shortform note: Hunting continued to impact our brains well after the Cambrian period. Around 2.6 million years ago, as the populations of large animals dwindled, early humans needed to exercise more skill to catch smaller and more agile prey. (Think about the difference it would make to catch a large and conspicuous mammoth versus a quick-moving hare with primitive tools.) Scientists believe that this change demanded more of human brains, which triggered a period of growth where brains got much larger—possibly to accommodate those new skills.)
2. Primitive creatures began evolving into more complex organisms with more organs and internal systems. The more complex an organism is, the more complex its energy budgeting becomes because each organ and system has specific energy requirements that need to be satisfied.
(Shortform note: In Your Inner Fish, Neil Shubin sheds light on one of the reasons complex organisms have higher energy requirements. Early Precambrian creatures were made of the same type of “glue” (collagen and proteoglycan) that allows human body cells to stick together to build materials and organs. However, more evolved organisms require this glue to be a mix of molecules that differs depending on the organ it’s forming—for instance, a bone versus an eye. Without the molecule mix attaching cells to each other, bodies couldn’t be formed. This requires more energy in order to create the right “glue” and assign it to the right body part or system.)
Barrett says that your own sophisticated sensations and movements are also the result of your brain performing allostasis. Your sensory experience is actually a combination of external data from your environment and internal data from inside your body. Your brain then combines this information with memories of similar situations to motivate you to make a change that helps manage the body’s energy budget.
For example, your brain senses heat from the sun on your skin (an external sensation) and a rise in your body temperature (an internal sensation), and it tells your body to produce sweat to regulate your temperature. Your brain has to make millions of reactions like these all day, and it has to do them efficiently to stay alive. If you spend too much time in the sun without drinking water and cooling your skin with sweat, you could die. So, Barrett argues, the pressure is on for your brain to make the right call quickly.
Barrett explains that this is where the third source of information comes into play: the brain’s memories of what you’ve done before when you encountered similar information. Before it fully processes the external and internal information it receives, it searches its memory for previous situations where the environment and your body felt similarly. It recalls what it did in that situation and triggers an action for today. This allows your brain to be one step ahead and make decisions quickly and efficiently.
All of this happens before the brain has time to contrast the real sensory data with the experience it created for you. Barrett says this is why you feel less thirsty immediately after drinking water, even though that water won’t reach your bloodstream until 20 minutes later. Your brain knows you’ll be satisfied in a little while, so it creates the experience of quenched thirst.
Help Your Brain Create More Manageable Sensations
Understanding how the brain creates your experiences can help you manage sensations better, especially challenging ones. We tend to think that when we hurt ourselves, like when you stub your toe, a message travels from your toe to the brain alerting it of the pain. However, it’s actually your brain noticing that you stubbed your toe and creating pain to alert you to what happened so you can ice it or avoid walking on it.
You can leverage this mechanism by “teaching” your brain what sensations to expect and whether to be concerned by them or not. For example, pregnant women who are preparing for labor are often taught to refer to pain during labor as intensity and contractions as surges so they can visualize the sensation in a less negative and more manageable way.
Barrett says that, sometimes, the experience your brain constructs turns out to be inaccurate, so you perceive something different from reality. For example, let’s say your brain senses that the sun is down (an external sensation) and your energy is low (an internal sensation). When it compares that data to the historical data in its memory, it comes to the conclusion that you need to eat, so it signals your body to search for food. But the reality might be that you’re tired, not hungry.
However, the brain has the chance to realize it jumped to the incorrect conclusion by contrasting the experience it created with the sensory data. Barrett says that this is what we call learning: The brain makes a mistake, realizes it, and adjusts its database of historical data so it can make a better decision the next time it encounters similar information. By making an intentional effort to learn, you can help your brain make better decisions in the future. For example, if you notice that you eat a snack every day right before bedtime, it might be a good idea to check whether you’re actually just tired. Instead of reaching for food, you might need to just go to bed.
How to Teach Your Brain
It’s easy to become trapped in the decisions your brain makes automatically. To avoid getting trapped in incorrect patterns of behavior and help your brain learn, there are two strategies you can deploy: reflection and visualization.
Reflection: Observe your actions and decisions as impartially as possible. Ask yourself why you reacted the way you did and whether you skipped over important information that might have been useful. For example, imagine that you regularly get upset with a coworker but aren’t sure why. By reflecting, you might notice that the coworker reminds you of someone else, and that memory is triggering your negative reactions rather than what the coworker does.
Visualization: When you notice a pattern you want to change, use visualization to train your brain to follow a different pattern. For example, through visualization, you can walk your brain through different situations with that coworker where, instead of getting upset, you remind yourself of why you’re feeling triggered and pause before reacting. Then, when you face the coworker again, your brain will be trained to react in a different way.
So far we've explored the brain's hardware—its neurons, networks, and functions—but each individual's brain develops differently, based on a combination of their genes and their environment. According to Barrett, brain development depends on the interaction between the genetic information already present in the brain and the environment it develops in, and this interaction has great implications for the healthy development of children’s brains.
Barrett explains that after birth, a baby’s brain develops according to its genetic coding and the physical and social environment. Genes help develop the basic infrastructure of the brain while environmental input triggers brain plasticity to develop certain neural connections more or less strongly.
Barrett identifies two specific processes that take place in the newborn’s brain as genes and the environment interact:
(Shortform note: Compared to other animals, a human baby’s brain is woefully unprepared for the world—for example, while other animals can almost immediately start walking, the human brain remains fetus-like for at least two years. Babies are born with immature brains because a full-grown human brain would not make it through the birth canal. As a result, babies rely on their environment to help complete their development. Scientists argue that this fosters human intelligence because human adults need to care for the survival of helpless members of their families, which makes their own brains develop uniquely human skills of survival.)
According to Barrett, the environment—especially the quality of the baby’s caregivers—is essential during this process. While the baby’s brain is developing, caregivers perform energy budgeting tasks for them, such as feeding them, helping them sleep, and comforting them when they’re distressed. This allows the brain to spend more energy tuning and pruning. Conversely, children who don’t receive adequate physical and social support from their environment have difficulties developing their brains. This happens in situations where there is poverty or neglect, for example.
Crucial Tasks of a Caregiver
It might be overwhelming for parents or caregivers to consider the responsibility they have in shaping a child’s brain. But child development specialists suggest focusing on three key tasks (after meeting the child’s needs for food, sleep, and comfort):
Encourage the child’s innate curiosity by paying attention to what catches their interest and helping them explore and learn about the world.
Understanding the stages of development a child will go through to give them the kind of stimulus they will benefit from at each stage.
Helping the child learn to manage anxiety and stress—both of which place a heavy load on their energy budgets.
Although our brains (physical organs) share a basic architecture, each one gets tuned and pruned according to its environment, producing widely different minds (individual patterns of thought and action). This is similar to the way two college students might buy the same laptop with the same basic capabilities (brain), but they each load certain programs onto their laptops (and delete others) based on what they are studying (since their needs and culture will be different). One student might have more money and more expensive software and accessories, while the other might use the free or cheap ones (since their conditions and environment will vary as well). As a result, the two computers will appear very different once you boot them up, just like our minds.
Barrett claims that this capacity for brain variation is the result of our brain’s plasticity and complexity, as neurons and neural clusters change to meet environmental needs. This flexibility makes humans adaptable to different environments, aiding in our evolution and survival as a species. As individuals, it also allows us to alter our minds by exposing ourselves to new stimuli and learning intentionally.
(Shortform note: Evolution might help explain why the same human brain can produce a wide range of different minds. As Barrett says, brain variation helps our species’ survival. In fact, evolutionary biologists argue that each type of personality has distinct evolutionary benefits that allow humans to survive and thrive in specific situations. For example, extroverted minds are often more successful at finding a mate, while introverted minds are often more successful at creating stable families. Minds with neurotic tendencies are especially adept at detecting dangers, while agreeable minds are especially adept at picking up on the emotional states of others and creating harmony within a community.)
As we saw in Part 3, the brain requires input from our environment to properly develop. Long after it’s done developing, however, the brain continues to solicit information from other brains to perform daily tasks. This is what makes us social animals, and Barrett claims it has profound effects on our well-being.
Barrett explains that our brains are constantly collaborating with each other in four key ways:
1. Our interactions with other people encourage our neurons’ tuning process to strengthen certain neural connections over others. This process is particularly intense when we’re newborns, but it continues throughout life. For example, when you interact often with a person who speaks a different language, you might learn to speak some words in their language to communicate more easily with them.
(Shortform note: Anthropologists found another way that brains collaborate and impact each others’ well-being: They argue that our brain’s reliance on interaction is one reason for long human lifespans. Since young humans are dependent on their environment and the people around them, interacting with them to help them develop gives older humans a reason to stay active and healthy longer.)
2. Our internal bodily functions have a regulating effect on the people around us, Barrett says. Brains coordinate with brains around them, matching breathing and heartbeat patterns, especially when we’re in intense interactions (whether they’re positive or negative). This can have a calming effect, for example, or help you collaborate with others more effectively.
(Shortform note: You don’t even need to be in the same room with someone for your brains to synchronize. A study found that the brains of online gamers playing together from different places can get on the same brain wave frequency. In fact, the more able they are to sync up their brains, the better their performance as a team in the game.)
3. Our conscious actions impact others’ energy budgets and well-being. For example, Barrett claims that saying something comforting to a person in distress can help them relax and require less energy to bring themselves back to a neutral state. On the other hand, acting in a threatening way can trigger their danger response and increase their energy load.
(Shortform note: In How Emotions Are Made, Barrett explains that our influence on others’ emotional states can extend to impact their physical health. For example, if someone is causing you anxiety, your brain can interpret it as a physical danger and generate cortisol to help you be alert. That unnecessary cortisol can trigger inflammation in the body, making you ill and thus turning an anxiety-inducing social encounter into physical illness.)
4. Our brains collaborate to create a shared social reality, which includes all of the sociocultural elements that structure our life and don’t rely on physical reality. For example, we agree on national borders, the value of products and currencies, the authority of certain figures, and the power of laws.
Humans are able to create social reality because we have the following abilities:
(Shortform note: Some scientists believe that our capacity to create social reality has made the world more complicated than our brains were prepared for. By using our skills, we’ve made our environment a lot more complex—such as creating government systems, political parties, and elections that millions of people vote in. But our brains are still essentially the same brains that early humans used to live in tribes of around 150 people, and they revert to using the same tools to deal with increasingly complicated problems. For example, we revert to cognitive biases that helped us survive millions of years ago, such as tribalism, but that limit our capacity to handle today’s challenges.)
Barrett claims that the ways our brains collaborate make us a social species, which improves our day-to-day lives. For example, people who have supportive relationships live longer than those who constantly feel lonely. (Shortform note: Other social species, such as some primates and dolphins, also have better health outcomes when their social networks are strong. When they’re isolated or face social stress, however, they suffer from stress, reduced health, and a shorter average lifespan.)
Since we impact each other’s well-being as a social species, Barrett notes that we also have the following responsibilities:
1. We have to make a conscious effort to empathize with people who are different from us. If we don’t make a deliberate effort to do this, our brains default to collaborating and syncing up with people we already understand and agree with.
Empathy is a skill that comes naturally to us, but with limitations, such as who we’re able to empathize with. It’s also a complex skill that needs to be practiced throughout life and that children need to be taught. If you’re a parent or caretaker, you can help your children develop empathy by teaching these skills, which Daniel Siegel and Tina Payne Bryson list in The Whole-Brain Child:
Seeing another person’s perspective: Help your child practice this skill by frequently asking questions about how someone else might feel and why someone may have reacted in a certain way.
Interpreting nonverbal communication: Help your child learn to read nonverbal cues by encouraging her to notice other people’s body language, and explaining the emotions it reflects.
Making amends: Teach your child that there are times when she needs to perform a follow-up action to make things right after a conflict, and help her to determine the appropriate action.
2. We have to find a balance in the conflict between individual rights and the impact we have on each other’s energy-regulating functions. For example, the exercise of individual freedom of speech might have a negative effect on people if our speech causes them stress, which affects the energy-regulating capacity of their brain.
(Shortform note: One way you can keep other people’s actions from having a negative impact on your energy budget and well-being is to make a conscious effort to resolve all conflicts before ending your day. Researchers found that people who worked through arguments on the same day before going to sleep could keep their stress hormone levels from piling up day after day, effectively flushing cortisol out of their system each day to stay healthy.)
3. We have to understand the risks of social reality. Although we generally agree on aspects of social reality like borders and currency, disagreements happen and can be problematic, or even deadly, such as in wars over boundary disputes between nations. Also, some social realities are harmful, such as racism.
(Shortform note: This is perhaps the hardest responsibility to take on because social reality relies on the belief that others experience the world in the same way we do. When we find evidence that others disagree with our social reality or want to change it, we instinctively turn to our families or core social groups that do share our social reality to affirm what we believe. This is why challenging negative social realities is difficult and frequently causes conflict.)
The way our brains collaborate makes us a social species, which improves our day-to-day lives but also comes with responsibilities.
Barrett stresses the importance of empathizing with people who are different from us. Describe an experience when you spent time with someone with a different background, belief system, or culture. What was that like? For example, were you uncomfortable, or was it enjoyable?
Continuing with that experience, identify a few ways that you and that person are alike.
If you were to have more of these experiences (spending time with someone different from you), how might that shape you as a result of your brain’s plasticity (the capacity to learn and improve skills) and complexity (the ability to adapt to new conditions)?