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Book Summary: The Neuroscience of You – How Every Brain Is Different and How to Understand Yours

The Neuroscience of You (2022) is an accessible primer to the human brain that explores how our individual quirks arise. Packed with practical tests and cutting-edge insights into why you think differently from others, it invites you to take a closer look at your brain and discover what makes it unique– and how to understand others and their quirks better.

Book Summary: The Neuroscience of You - How Every Brain Is Different and How to Understand Yours

Content Summary

Genres
Introduction: Discover how every brain is wired differently, and what this means for our behavior.
Brains that specialize in different functions interpret the world in varied ways.
Your brain’s lopsidedness affects how you process information.
Your brain is a unique neural cocktail, and its ingredients shape your personality.
Experience creates lenses through which we filter the world.
Summary
About the author
Table of Contents
Overview
Review/Endorsements/Praise/Award
Video and Podcast
Read an Excerpt/PDF Preview

Genres

Psychology, Science, Medicine, Medical, Self Help, Biology, Neuroscience, Brain, Mental, Popular Science

Introduction: Discover how every brain is wired differently, and what this means for our behavior.

What makes us who we are?

Everyone’s brain is structurally different– even the brains of identical twins conjoined at birth– and these structural differences matter. They shape how we see the world, and how we decide to operate in it. It affects whether we’re thrill seekers, how good we are at picking up languages, and even how we feel about karaoke.

Despite their importance, the biological differences in our brains are rarely discussed. The field of neuroscience has been dominated by a one-size-fits-all approach for over a century. What we know about brains is usually informed by scientists who focus on how brains work on average, glossing over our individual differences. But this is a missed opportunity to understand ourselves, other people, and the brain more deeply.

In this summary, we’ll draw upon the cutting-edge insights of neuroscientist Chantel Prat, who researches how brains differ, and why small differences in our brains can cause big differences in our characters.

You’ll discover how our brain’s lopsidedness affects how we approach problems, that our neurochemical cocktail determines how extraverted we are, and why it is that brains see colors differently. Ready? Let’s zoom into the inner workings of your brain and discover what makes you you.

Brains that specialize in different functions interpret the world in varied ways.

Have you ever heard of The Knowledge?

It’s the test required to be a taxi driver in London, and it’s one of the most famously difficult exams in the world. The test demands that you memorize London’s 20,000 windy streets and every business or landmark on each street. The test weeds out over half the people who take it— even if they’ve studied for it for years. It’s a truly herculean task!

A landmark study in 2000 showed that drivers who successfully acquired The Knowledge of London’s streets have a larger-than-average tail of the hippocampus, the region of the brain that is associated with spatial memory. In other words, by repeatedly asking their brains to perform specific tasks– like memorizing London, a complex and disorganized system– the taxi drivers actually changed their brains’ physicality.

Studying the cabbies’ brains led to another important discovery: though the tail of the hippocampus grows as they study for The Knowledge, the top of the hippocampus was actually smaller than average. Researchers then compared the brains of the taxi drivers to those operating in a similar environment: London bus drivers. They found that the taxi drivers had superior spatial memory to the bus drivers, but they had worse short-term memory and visual memory.

What this head-to-head comparison shows us is that there’s a cost to specialization. Certain enhancements of one type of memory will crowd out brain regions that are performing other jobs. After all, there’s only so much room in any given brain! Now, it’s not just that specialization leads your brain to perform certain functions better at the expense of other functions. What ends up happening is that brains that specialize in different functions end up interpreting the world in different ways– which is what Dr. Prat’s book is all about.

To begin to break down why that is, it’s helpful to think of our brains as finite information-processing machines operating in an essentially infinite environment. And in order to do its job effectively of keeping you alive in the big bad universe, your brain has to process the infinite environment into manageable pieces. In other words, it’s constantly filtering, and filling in the missing blanks with what it thinks is probably happening. It’s a bit like being given a stack of blurry photographs and being asked to make a movie with them. You have to decide which images are important and how to connect the dots to make a coherent video when there is missing information.

And because brains are structurally different and shaped by different experiences, they’ll process information in varying ways. One brain will deal with its inherent limitations differently than another, by relying on the computations and functions at which it’s more adept in order to figure out what is happening. And this is a major factor in why we have so much variation in worldviews and behaviors!

Now let’s take a closer look at how specific features of our brains will lead us to operate in varied ways in the real world. We’ll start with how the degree of our brain’s lopsidedness affects how we solve problems.

Your brain’s lopsidedness affects how you process information.

Imagine the human brain for a moment. It’s about three pounds, and it looks something like a large walnut, with two largely independent hemispheres connected at the core.

Now, this isn’t a very unique brain design. We can find divided brains throughout the animal kingdom, within all vertebrate animals.

What’s peculiar to humans is that our brains are, on average, remarkably lopsided, with the left hemisphere tending to be larger. This cerebral asymmetry is actually what makes us particularly good at complex speech and analytical tasks. But some of us are more lopsided than others, and it’s these variations of degree that make a difference in how we approach problem solving.

You might have heard analytical people described as left-brained, and creative people are considered right-brained. There’s a grain of truth to this, but it’s a bit more complicated than that. In reality, your strengths aren’t determined by which hemisphere is the “boss” of your brain— rather, it’s the degree to which your brain is lopsided that affects what types of mental computations you rely on more than others when faced with ambiguous information. This structural difference is a major reason why humans can have widely different interpretations of the same input.

It’s true that the left hemisphere is, in most people, optimally structured for analytical processes— it accomplishes its various functions with a “divide and conquer” approach by executing specialized computations that don’t interact with one another. If someone has a highly lopsided brain, they tend to rely more on computations associated with the left hemisphere. What this looks like in everyday life is that lopsided-brained people tend to solve problems by focusing on its specific details. It’s a bit like building a picture of a forest by processing one tree at a time.

In contrast, the right hemisphere is structured in a way that makes it better equipped to integrate different types of information into a coherent whole. So it builds a picture of a forest with a big-picture approach– it looks at something vertical and brown and says “Hmm, I know I’m in a forest, so this is most likely a tree.” In other words, it relies on wider context to make inferences about a given situation.

Now, all brains have forest and tree capabilities. Both approaches are vital to the many complex tasks we humans perform on a daily basis, so we’ve gotten really good at both over our evolutionary history. But if your brain is more lopsided, you’re more likely to focus on specific details to solve problems, and people with more balanced brains tend to consider the wider context over the specific details.

So, how lopsided is your brain? There are a few quick-and-dirty ways of approaching this question.

First, consider these everyday tasks: Brushing your teeth. Writing with a pen. Eating with a spoon. Opening a box. Holding the top of a broom handle as you sweep.

Now ask yourself if you would perform these tasks only with your dominant hand. Or would you feel comfortable switching between hands for at least some of these tasks?

How about looking into a microscope or the viewfinder of a camera: do you have an eye that you prefer?

If you could only imagine performing these tasks with your dominant hand and your dominant eye, then your brain is likely more lopsided. If you’re more comfortable switching between right and left hands, and right and left eye, your brain is likely more balanced.In the next section, we’ll turn our attention to the smallest parts of our brain features– the neurotransmitters, which are the chemicals that your neurons need to communicate– and dive into why such tiny parts can have a huge impact on us.

Your brain is a unique neural cocktail, and its ingredients shape your personality.

Ah, coffee. What would life be without it?

There’s a reason caffeine is the most popular drug in the world. In fact, a life without coffee would be a life with less pleasure! That’s because caffeine increases the availability of the neurotransmitter dopamine, the chemical that the pleasure circuits in your brain use to communicate.

Now consider this: what if someone else’s baseline levels of dopamine exceed the boost you get from your morning shot of espresso? In other words, what if they feel generally more pleasure than you? Or the other way around: someone else’s highest feelings of pleasure might be how you feel before you’ve had your morning cup of joe.

Anyone who’s experienced depression knows well how a brain with a lower level of feel-good chemicals can have a fundamentally different experience of the world than someone with higher levels. But dopamine levels profoundly affect our personalities and behaviors, whether we have depression or not.

Dopamine circuits play a big role in decision-making because they’re nudging you through the world in a way that will bring about the most amount of pleasure possible. In effect, differing levels of dopamine from brain to brain will affect how strongly one is motivated toward different behaviors. One key way this plays out in our personalities is in how introverted or extraverted we are.

Extraverted people are those who tend to “turn outward” and seek mental stimulation from external stimuli. Introverted people, on the other hand, often prefer their own thoughts and feelings to the outer world and tend to “turn inward.” You probably have a good idea of where you fall on this continuum.

Converging research demonstrates that dopamine is at least partially responsible for our introversion or extraversion because of how dopamine rewards our brains. It turns out that when unexpected rewards happen to extraverts, their brains actually release more dopamine than in their introverted counterparts. Another way of putting it is: if life were a video game, then extraverts get more pleasure points every time they’re positively surprised. So this makes them extra motivated to seek out outside stimulation.

So what does different susceptibility to dopamine look like in practice? Well, extraverts consistently rate themselves as more optimistic and happier than introverts. They’re also more likely to seek novelty and are more motivated to learn– and it’s no wonder, since external stimulation brings them extra pleasure.

You may be wondering if it’s simply better to be an extravert. It’s true that introversion has been linked to anhedonia and depression. But, despite extraverts experiencing more pleasure, there are also downsides to this design feature. For one thing, additional susceptibility to dopamine makes it more difficult for extraverts to override temptation for things that are bad for us. Extraversion has been linked with obesity and addiction, for example.

Now, let’s zoom back out for a moment and give your right hemisphere some big-picture context to consider. Dopamine is just one neurotransmitter of hundreds that drive the way you think, feel, and behave. Others include oxytocin, serotonin, and cortisol– and they’re all interacting with each other in a delicate balance. If varied levels of just one of these can affect your experience of the world so profoundly, it’s no wonder that the unique mixology of our neural cocktails creates such starkly different individuals!

In the last two sections, we discussed how the brain features of lopsidedness and neurochemistry affect our behavior. Now, in the final section, we’ll explore how our life experiences shape our brains. We’ll discover how our past life creates the lens through which we see the present.

Experience creates lenses through which we filter the world.

Who here remembers The Dress?

No, not one worn by Marilyn Monroe, Princess Diana, or Monica Lewinsky.

The Dress was a viral image that took the internet by storm in 2015. It’s a photograph of a striped dress that about half the population saw as blue and black, and the other half as white and gold. If you don’t know what I’m talking about, look up “The Dress” on Wikipedia. What colors do you see?

Dr. Prat posits that The Dress went viral because it’s a very stark example of how our brains create alternate versions of reality. It’s fascinating to discover that even something as basic as the colors of a static image are open to interpretation!

Even when told that the “actual” colors of The Dress in the photograph are blue and black, the people who see it as white and gold usually cannot see its true colors unless the lighting of the image is altered. As it turns out, the reason for this is at least partially due to our life experiences.

The lighting in the viral image is ambiguous, so our brain relies on a shortcut to make sense of the incomplete data it’s faced with. This results in brains with different past experiences making different assumptions about the source of the light, which in turn affects how the brain perceives the colors of The Dress.

If you’re seeing The Dress as white and gold, your brain is assuming that The Dress is in shadow and that the light is coming from behind. Research suggests that this is likely because you’re more familiar with natural lighting and that you’re an early riser. On the other hand, if you’re seeing The Dress as black and blue, your brain is assuming the lighting is coming from the front, probably through an artificial source. This perception correlates with people who tend to be night owls and have more experience with artificial lighting.

Our brains are shaped so profoundly by previous experience due to a process called Hebbian learning. In a nutshell, the theory of Hebbian learning states that when our brains learn something new, neurons are activated and connected with other neurons. At first these connections are weak, but they grow stronger every time the experience repeats, so the process becomes more intuitive. It’s what people mean when they say “neurons that fire together, wire together.”

Hebbian learning influences your brain over your lifespan and allows you to make shortcuts that are critical to your survival, so that you can make split-second inferences without processing an event as new every time. That would be time-consuming and exhausting. Hebbian learning is also at play when we learn skills like driving, that are difficult at first but become more and more automatic over time. But experience-based shortcuts can also lead us into some problematic territories that can be difficult to correct, such as biases.

A telling example of this has been demonstrated many times: people are more likely to assume an ambiguous object is a gun when presented next to a Black person’s face than a white person’s face. This mental shortcut arises without a correlation to someone’s actual experiences with Black people and guns, especially considering that gun ownership is common across many demographics in the United States.

So where do these biased mental shortcuts come from, if not from direct experience? Well, if your brain does not have direct experiences with something in real life– or some people– then it’s more likely that its database entry on a given topic is based on what it sees on television or in fictitious depictions. In this way, systemic biases can quite literally shape the way your brain perceives the world.

Changing your brain’s perception isn’t as simple as just becoming aware of your biases. Remember, those who see The Dress as white and gold can’t flip their perception just because they discover it’s actually blue and black. Instead, correcting your brain’s shortcuts is more likely to occur if you expose yourself to diverse and real-world experiences, and become more intentional about the types of narratives you feed your mind.

Summary

The key message in this summary is: Small differences in our brains that we’re either born with or adapt to create big differences in our thoughts, behaviors, emotions, and abilities. Just consider that the DNA blueprints that underlie chimp and human brains differ by only 5 percent– but that 5% allows humans to send complex messages in split-seconds across the globe, while the chimp’s day is occupied with finding food and picking nits.

Or on a much subtler level, think about how differently you feel in the morning versus in the evening. The changes in neurochemical signaling throughout the course of just twelve hours can cause a significant difference in how you’re experiencing the world. The point is: our differences matter, and a neuroscience that looks into them can provide a window into the self.

About the author

Chantel Prat is a professor at the University of Washington with appointments in the departments of Psychology, Neuroscience, and Linguistics; with affiliations at the Institute for Learning and Brain Sciences, the Center for Neurotechnology, and the Institute for Neuroengineering. She is a recipient of the Tom Trabasso Young Investigator Award from the Society for Text and Discourse and a Pathway to Independence Award from the National Institutes of Health. Prat also speaks internationally at events like the World Science Festival. She is featured in the documentary film I Am Human. Her studies have been profiled in media ranging from Scientific American, Psychology Today, and Science Daily to Rolling Stone, Popular Mechanics, Pacific Standard, Travel + Leisure, and National Public Radio.

Chantel Prat | Website
Chantel Prat | Twitter @ChantelPratPhD
Chantel Prat | LinkedIn

Table of Contents

Preface: From My Brain to Yours ix
Introductions: The Neuroscience of You 101 1

Part 1 Brain Designs 39
Chapter 1 Lopsided: The Two Sides of Your Brain’s Story 43
Chapter 2 Mixology: The Chemical Languages of the Brain 81
Chapter 3 In Sync: The Neural Rhythms That Coordinate Flexible Behavior 121

Part 2 Brain Functions 153
Chapter 4 Focus: How Signals Compete to Control Your Mind 157
Chapter 5 Adapt: How Your Brain Learns to Understand the Environment You Inhabit 183
Chapter 6 Navigate: How Knowledge Creates Road Maps and Why We Don’t Always Use Them to Guide Our Decisions 213
Chapter 7 Explore: How Curiosity and Threat Compete to Shape Behaviors at the Edges of Knowing 257
Chapter 8 Connect: How Two Brains Get on the Same Wavelength 287

Acknowledgments 323
Notes 327
Index 353

Overview

From University of Washington professor Chantel Prat comes The Neuroscience of You, a rollicking adventure into the human brain that reveals the surprising truth about neuroscience, shifting our focus from what’s average to an understanding of how every brain is different, exactly why our quirks are important, and what this means for each of us.

With style and wit, Chantel Prat takes us on a tour of the meaningful ways that our brains are dissimilar from one another. Using real-world examples, along with take-them-yourself tests and quizzes, she shows you how to identify the strengths and weakness of your own brain, while learning what might be going on in the brains of those who are unlike you. With sections like “Focus,” “Navigate,” and “Connect,” The Neuroscience of You helps us see how brains that are engineered differently ultimately take diverse paths when it comes time to prioritize information, use what they’ve learned from experience, relate to other people, and so much more.

While other scientists focus on how “the” brain works “on average,” Prat argues that our obsession with commonalities has slowed our progress toward understanding the very things that make each of us unique and interesting. Her field-leading research, employing cutting-edge technology, reveals the truth: Complicated as it may be, no two brains are alike. And individual differences in brain functioning are as pervasive as they are fundamental to defining what “normal” looks like. Adages such as, “I’m not wired that way” intuitively point to the fact that the brains we’re piloting, educating, and parenting are wonderfully distinct, explaining a whole host of phenomena, from how easily a person might learn a second language in adulthood to whether someone feels curious or threatened when faced with new information. This book invites the reader to understand themselves and others by zooming in so close that we all look gray and squishy.

Review/Endorsements/Praise/Award

“Move over, outer space—this book is a dazzling tour through inner space. Chantel Prat has a rare, remarkable gift for making neurons sing and dendrites dance, and she’s written the smartest, clearest, and funniest book I’ve ever read about the brain.”
—Adam Grant, #1 New York Times bestselling author of Think Again, and host of the TED podcast WorkLife

“Prat wants to help readers understand their brain…. She does so in a friendly, personable voice that makes the complexities of the brain accessible…. A highly readable, entertaining, and authoritative book. Recommended for all non-specialists interested in how the brain works.”
—Library Journal (starred)

“Numerous candidly written footnotes add comedic flair to the narrative, which will be appreciated by readers eager but intimidated to learn how and why their brains generate thoughts, feelings, and decision-making patterns….. [Prat] shines a positive light on how the brain operates from the inside out and from the outside in. An informal, highly accessible tour of neuroscience for general readers.”
—Kirkus

“Prat… covers the nature of the human brain in her lively and informative debut…There are lots of funny footnotes as well as cutting-edge research—on nematode nervous systems, for example—and her informal tone goes a long way in making her subject both understandable and enjoyable. This work of popular science sets itself apart.”
—Publishers Weekly

“In The Neuroscience of You, Chantel Prat pulls off the nearly impossible feat of writing a book that is authoritative, personal, technically astute and charming. Prat offers a profound thesis: that there is wonder and beauty in understanding the variation in how brains function. Prat teaches us that these differences should not be fuel for division, but rather, the object of fascination, appreciation, and celebration.”
—C. Brandon Ogbunu, Yale University, Ideas contributor for Wired Magazine

“Smart, funny, irreverent… reading this book is like downloading a PhD in neuroscience in one exuberant sitting. It’s a must read for any budding neuroscientists out there, and anyone else who wants to know how our brains work and why it matters.”
—Anna Lembke, author of New York Times bestseller Dopamine Nation: Finding Balance in the Age of Indulgence

“We’re all the same: human beings. At the same time, we’re all different individuals. In her marvelous, accessible, often funny and always informative book, Chantel Prat reconciles this seeming paradox. Read this book; you’ll understand — and admire — your species and your brain as never before. And you’ll have a hell of a lot of fun getting there!”
—David P. Barash author most recently of Threats: Intimidation and its Discontents

“Neuroscientists emphasize how most brains work, but finally here’s a book that emphasizes how your brain works! Chantel Prat artfully describes why and how our brains differ – skillfully interweaving accessible facts about genetics, environment, and brain science to help explain what makes you uniquely YOU! The book is a joy, the footnotes are hilarious, and the topic is of central importance to all those interested in human uniqueness, cognitive science, and how much we share and differ from the rest of humanity.”
—Patricia K Kuhl, cognitive neuroscientist, Member of the National Academy of Sciences, and author of The Scientist in the Crib

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Chapter 1

Lopsided

The Two Sides of Your Brain’s Story

If I were to show you a picture of your brain, the first thing you’d probably notice is that it looks like a big walnut (no offense), with two largely independent halves, or hemispheres, connected by a high-speed core. As strange as this might sound, it isn’t a very unique brain design. In fact, all vertebrate animals have brains that are divided down the middle, and they have probably been engineered this way for hundreds of millions of years.

What makes human brains remarkable in this design space is how lopsided we are, on average. Differences in the size, shape, and patterns of connectivity in our left and right hemispheres leave us far from symmetrical. And as you’ll learn in this chapter, these structural differences shape the way each side processes the information it receives.

However, contrary to the popular notion of the “left-brained” analytical person and the “right-brained” creative type, the most striking distinction between human brains isn’t which hemisphere is “in charge” of things. Instead, differences in our characteristic ways of thinking, feeling, and behaving are driven by our degree of lopsidedness, or how big the differences between our two hemispheres are. And so, this book about the differences between brains will begin with a discussion of the fundamental divide within them. But before we get into the nitty-gritty details about how your brain looks, let’s talk about why evolution might have landed on the different options in the first place. The idea, in essence, boils down to specialization.

The costs and benefits of brain specialization

To better understand the pros and cons of having a more lopsided or balanced brain design, let’s imagine that your brain is a team made up of two people. If both members of your team are well rounded, and have comparable skill sets, it would be easiest, and most equitable, to distribute tasks between them randomly. On the other hand, if one member of your team has incredibly strong verbal skills, while the other is an excellent graphic designer, your team would perform better as a whole if the tasks were systematically assigned to the individual best qualified for the job.

Job assignment in the brain works a bit like this. If the two hemispheres were truly identical to each other, there would be no rhyme or reason to which functions they might come to perform. But as soon as they start to differ-even a little bit-an opportunity is created for one hemisphere to be better suited for certain types of jobs than for others. When this happens, the assignment of jobs across hemispheres becomes more systematic. And as the jobs that a particular brain region is asked to do become more similar to one another, that region can adapt, developing a more specialized structure that allows it to perform the particular type of tasks it’s involved in even better.

I assume that the benefits of specialization are somewhat self-explanatory. If everything else were equal, many people would rather have an extremely talented graphic designer on their team than one with average skills. But what if that graphic designer was bad at everything else? If your whole team were made up of people with non-overlapping skills, what would happen if someone needed help or called in sick? One of the measurable costs to specialization in the brain is that the refinement process by which an area becomes specialized makes it better and better suited for doing fewer and fewer things.

Stefan Knecht and colleagues demonstrated this increased vulnerability associated with lopsidedness in a study that looked at language laterality-a term neuroscientists use to describe the extent to which any of your brain’s functions come to depend more on one hemisphere than the other. To do so, they first measured changes in blood flow in the two hemispheres when 324 volunteers named pictures in the lab. Then they selected 20 participants who had different patterns of laterality for speech, with approximately equal numbers of people who relied on their left or right hemispheres uniquely, or on both, for speech production.

Next, to study their vulnerability to brain injury, the research team used a tool called transcranial magnetic stimulation, or TMS for short. TMS uses magnetic fields to safely, and temporarily, stimulate different regions of the brain noninvasively. And if you stimulate one area over and over for a long enough time, it runs out of gas-creating an effect called a “virtual lesion.” If you’ve ever gotten a blind spot after seeing a bright light, you’ve experienced a similar phenomenon.

As expected, when Knecht and colleagues created virtual lesions in the hemisphere that a person’s speech was dependent on, their participants got significantly slower at the language task they were asked to perform. However, the more balanced a person’s speaking profile was-that is, the more both of their hemispheres were involved in the act of speaking-the less their behavior was affected when only one side of the brain was fatigued using TMS. The effect is kind of like benching different members of your team and measuring the dip in productivity that results. The more balanced brain designs, like the well-rounded teams, were more resilient to the injury of any single player.

But even for the majority of us who are lucky enough to make it through life without damaging too many brain cells, there are still prices to pay for brain specialization. One of them relates to how our hemispheres become different in the first place. Though I spent a decent amount of time in “Introductions” explaining how evolution has worked to cram as much brainpower as possible into our heads, the mechanisms that cause our hemispheres to become specialized may be an exception to this rule. According to the Right-Shift theory proposed by Marian Annett, the human propensity to be lopsided may be driven by a genetic variation that shrinks parts of the right hemisphere. According to Annett, our brains evolved this type of handicapping system as a way of refining job assignment in the brain. Consistent with her theory, Annett’s results suggest that people who have more “balanced” brains might not be as skilled at the more newly evolved human functions-like language-but they are also using more of the real estate in the right halves of their skulls, which you’ll learn is important for many other things, like visuospatial skills. On the other hand, she argues that highly lopsided people are less likely to have deficits in language-related skills but are more likely to struggle with the types of jobs that typically get assigned to the right hemisphere, like visuospatial tasks.

And there’s one other thing I’d like you to keep in mind when considering the costs and benefits of the specialization of our two hemispheres. As you’ll learn in this chapter, one of the ways your brain becomes specialized is by using highly experienced processing centers called modules. These modules are singularly focused on the task they’ve been given, and don’t consider input from other brain areas while they are doing their jobs. The result of this is that a more specialized brain tends to process the world by piecing together specific details rather than taking the whole picture into account. In other words, as a brain moves from being more balanced to more lopsided, its processing shifts from focusing on the more global, “forest-level” features to focusing on more specific, “tree-level” details. We’ll talk more about the specifics of this in the second half of the chapter. First, let’s get to work figuring out how lopsided you are.

Assessing laterality

One of the best ways to determine how lopsided your brain is, is to measure a bunch of different functions in each hemisphere separately. If your left and right hemispheres do them equally well, your brain is likely more balanced, but if one hemisphere tends to take the lead on these functions, your brain is probably more lopsided.

We’ll start with one of the most obvious asymmetries to observe in most people-our hand preference. Those of you who work with your hands for a living, or have suffered an injury that prevents you from doing so easily, are likely already aware of how much skill goes into precision hand movements. The rest of you might be largely oblivious to one of the most important benefits that our genetic differences from chimps created-our long thumbs. The fact that we can press our thumbs to the tips of each finger with precision levels of force allows us to execute movements ranging from removing an eyelash from someone’s cheek to hitting a nail on the head with a hammer. And these common tasks probably require a lot more brainpower than you think.

In fact, the neural circuitry that controls the movement of your hands is so large that it creates a U-shaped bulge in your brain called the hand knob. With a bit of training, you’d be able to identify your hand knob when looking at a picture of your walnut-shaped brain. It sits near the top of your motor cortex, a strip of brain that runs from temple to temple (about where a pair of glasses would fall if you rested them atop your head), and controls the movement of all of your body parts. In most people, you can even figure out whether they’re left- or right-handed by comparing the size of the two knobs in each hemisphere. And this is how we’re going to start the process of reverse-engineering your brain.

Though most people identify as either right- or left-handed, handedness is not a binary category. Instead, we each fall on a continuum ranging from extremely right-handed to extremely left-handed. Figuring out where you fall along this axis is the first step to understanding how lopsided your brain is. To start, I’ll give you a questionnaire I adapted based on the Edinburgh Handedness Inventory. This simple checklist, which asks about how you use your two hands for everyday tasks, is by far the most common tool used by neuroscientists to measure handedness.

To get an idea of where you fall along the handedness axis, answer each of the ten items below based on everyday activities that you might engage in with either your left or right hand. For each action, answer on a scale ranging from +2 to -2: If your preference for this activity is so strongly right-handed that you wouldn’t ever use your left hand, answer +2; if you prefer to use your right hand for this activity, but may occasionally use the left as well, answer with a +1; if you are truly indifferent, and use both hands equally well and equally frequently to accomplish this task, answer with 0; if you prefer to use your left hand for this activity, but may occasionally use the right as well, answer with a 1; and finally if your preference for this activity is so strongly left-handed that you wouldn’t ever use your right hand, answer with -2. The only time you should leave a question blank is if you have no experience with the activity in question (and if you’ve never held a broom, or a toothbrush, I’ll do my best not to judge you, since it’s antithetical to my goals for writing this book).

  1. Handedeness Assessment
  2. Writing with a pen or pencil.
  3. Hammering.
  4. Throwing (most commonly a ball but any object will suffice).
  5. Holding the match when striking a match.
  6. Holding a toothbrush when brushing your teeth.
  7. Using scissors to cut.
  8. Cutting with a knife (without a fork, such as when chopping food for cooking).
  9. Eating with a spoon.
  10. The upper hand when holding a broom to sweep. (If it’s been a while, grab a broom-sweep for science!)
  11. Opening the lid of a box.

Now, let’s calculate your handedness index. To figure out your “average” response, add the answers to each of the ten questions together and divide their sum by ten. To check your math, the result should fall within the -2 (strongly and consistently left-handed) to +2 (strongly and consistently right-handed) range. The closer you are to the extreme ends of this distribution, the more lopsided your brain is. Those of you who scored closer to the middle (between -1 and +1), the mixed-handers, likely have more balance in the capabilities of your two hemispheres. Still, you probably identify as right- or left-handed based on your answers to the first few questions. As you move from the top to the bottom of the scale, the precision required to execute the movements generally decreases, opening up the possibility for a less-skilled hemisphere to do a “good enough” job.

So, what does your degree of handedness tell me about how lopsided your brain is? The first thing to note is that the motor cortex in the left hemisphere of your brain controls the right half of your body, and vice versa. If you are strongly right-handed, it is likely that the motor cortex in your left hemisphere, particularly around the hand knob, is bigger. The reverse is true for the much smaller percentage of the population that is extremely left-handed. We’ll talk about the broader implications of what this means for how you work in a bit. For now, let’s check out some other functions, to see whether your brain is consistently more balanced or lopsided in its job assignments.

For starters, let’s check in with your feet. Although our feet are much less skilled than our hands, most lopsided people will also exhibit a preference for using one foot over the other when executing skilled movements. Which foot do you usually kick with? When going up stairs, which foot do you typically lead with? What if I asked you to put the tip of your toe on a quarter? Would you instinctively pick one foot over the other? Most people will find these foot skills more interchangeable than the hands, but if you answered each of these questions consistently with one foot, it provides further evidence that skills are unevenly distributed in your two hemispheres.

Now, let’s switch to an even more subtle function-the difference between how you use your two eyes. Though both eyes carry information about the world to the brain, some of us rely more on information coming in from one eye than the other. And here’s a fun fact-most people have a preference for information coming in from their right eye! We might go about assessing your eye dominance like we did handedness-by asking questions like which eye would you use to look into a microscope, or the viewfinder of a camera? But we can also measure this a bit more objectively with the following “sighting” experiment: Find an object about eight to twelve feet away from you and hold one of your index fingers up in front of it. With both eyes open, you might have the experience that you can “see through” your finger, or you might feel like you see two fingers (depending on where you’re focusing), but do your best to focus on the object and position your finger so that it is in a straight line between you and the object. Now, close your left eye. What happened? If your finger now looks like it is solidly blocking the object, you are right-eye dominant. If your finger now looks like it is off to the side of the object, try closing your right eye. Is it lined up now? If so, you are left-eye dominant. As long as you’ve picked something sufficiently far away, if your finger doesn’t line up when you close either eye, you’ve got mixed-eye dominance.

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