Happy Holidays. In this special issue we are reprinting our top stories of the past year. This article first appeared online in our “Mind” issue in March, 2021.
The 21st century is a time of great scientific discovery. Cars are driving themselves. Vaccines against deadly new viruses are created in less than a year. The latest Mars Rover is hunting for signs of alien life. But we’re also surrounded with scientific myths: outdated beliefs that make their way regularly into news stories.
Being wrong is a normal and inevitable part of the scientific process. We scientists do our best with the tools we have, until new tools extend our senses and let us probe more deeply, broadly, or precisely. Over time, new discoveries lead us to major course corrections in our understanding of how the world works, such as natural selection and quantum physics. Failure, therefore, is an opportunity to discover and learn.1
Brains don’t work by stimulus and response. All your neurons are firing at various rates all the time.
But sometimes, old scientific beliefs persist, and are even vigorously defended, long after we have sufficient evidence to abandon them. As a neuroscientist, I see scientific myths about the brain repeated regularly in the media and corners of academic research. Three of them, in particular, stand out for correction. After all, each of us has a brain, so it’s critical to understand how that three-pound blob between your ears works.
Myth number one is that specific parts of the human brain have specific psychological jobs. According to this myth, the brain is like a collection of puzzle pieces, each with a dedicated mental function. One puzzle piece is for vision, another is for memory, a third is for emotions, and so on. This view of the brain became popular in the 19th century, when it was called phrenology. Its practitioners believed they could discern your personality by measuring bumps on your skull. Phrenology was discredited by better data, but the general idea was never fully abandoned.2
Today, we know the brain isn’t divided into puzzle pieces with dedicated psychological functions. Instead, the human brain is a massive network of neurons.3 Most neurons have multiple jobs, not a single psychological purpose.4 For example, neurons in a brain region called the anterior cingulate cortex are regularly involved in memory, emotion, decision-making, pain, moral judgments, imagination, attention, and empathy.
LIZARD BRAIN: Why does the tale linger that our instincts stem from a part of our brain inherited from reptilian ancestors? Because if bad behavior stems from our inner beasts, then we’re less responsible for some of our actions.Galina Gala / Shutterstock
I’m not saying that every neuron can do everything, but most neurons do more than one thing. For example, a brain region that’s intimately tied to the ability to see, called primary visual cortex, also carries information about hearing, touch, and movement.5 In fact, if you blindfold people with typical vision for a few days and teach them to read braille, neurons in their visual cortex become more devoted to the sense of touch.6 (The effect disappears in a day or so without the blindfold.)
In addition, the primary visual cortex is not necessary for all aspects of vision. Scientists have believed for a long time that severe damage to the visual cortex in the left side of your brain will leave you unable to see out of your right eye, assuming that the ability to see out of one eye is largely due to the visual cortex on the opposite side. Yet more than 50 years ago, studies on cats with cortical blindness on one side showed that it is possible to restore some of the lost sight by cutting a connection deep in the cat’s midbrain. A bit more damage allowed the cats to orient toward and approach moving objects.
Perhaps the most famous example of puzzle-piece thinking is the “triune brain”: the idea that the human brain evolved in three layers. The deepest layer, known as the lizard brain and allegedly inherited from reptile ancestors, is said to house our instincts. The middle layer, called the limbic system, allegedly contains emotions inherited from ancient mammals. And the topmost layer, called the neocortex, is said to be uniquely human—like icing on an already baked cake—and supposedly lets us regulate our brutish emotions and instincts.
Myth number one is that specific parts of the human brain have specific psychological jobs.
This compelling tale of brain evolution arose in the mid 20th century, when the most powerful tool for inspecting brains was an ordinary microscope. Modern research in molecular genetics, however, has revealed that the triune brain idea is a myth. Brains don’t evolve in layers, and all mammal brains (and most likely, all vertebrate brains as well) are built from a single manufacturing plan using the same kinds of neurons.
Nevertheless, the triune brain idea has tremendous staying power because it provides an appealing explanation of human nature. If bad behavior stems from our inner beasts, then we’re less responsible for some of our actions. And if a uniquely human and rational neocortex controls those beasts, then we have the most highly evolved brain in the animal kingdom. Yay for humans, right? But it’s all a myth. In reality, each species has brains that are uniquely and effectively adapted to their environments, and no animal brain is “more evolved” than any other.
So why does the myth of a compartmentalized brain persist? One reason is that brain-scanning studies are expensive. As a compromise, typical studies include only enough scanning to show the strongest, most robust brain activity. These underpowered studies produce pretty pictures that appear to show little islands of activity in a calm-looking brain. But they miss plenty of other, less robust activity that may still be psychologically and biologically meaningful. In contrast, when studies are run with enough power, they show activity in the majority of the brain.7
Another reason is that animal studies sometimes focus on one small part of the brain at a time, even just a few neurons. In pursuit of precision, they wind up limiting their scope to the places where they expect to see effects. When researchers instead take a more holistic approach that focuses on all the neurons in a brain—say, in flies, worms, or even mice—the results show more what looks like whole-brain effects.8
Pretty much everything that your brain creates, from sights and sounds to memories and emotions, involves your whole brain. Every neuron communicates with thousands of others at the same time. In such a complex system, very little that you do or experience can be traced to a simple sum of parts.
Myth number two is that your brain reacts to events in the world. Supposedly, you go through your day with parts of your brain in the off position. Then something happens around you, and those parts switch on and “light up” with activity.
Brains, however, don’t work by stimulus and response. All your neurons are firing at various rates all the time. What are they doing? Busily making predictions.9 In every moment, your brain uses all its available information (your memory, your situation, the state of your body) to take guesses about what will happen in the next moment. If a guess turns out to be correct, your brain has a head start: It’s already launching your body’s next actions and creating what you see, hear, and feel. If a guess is wrong, the brain can correct itself and hopefully learn to predict better next time. Or sometimes it doesn’t bother correcting the guess, and you might see or hear things that aren’t present or do something that you didn’t consciously intend. All of this prediction and correction happens in the blink of an eye, outside your awareness.
If a predicting brain sounds like science fiction, here’s a quick demonstration. What is this picture?
If you see only some curvy lines, then your brain is trying to make a good prediction and failing. It can’t match this picture to something similar in your past. (Scientists call this state “experiential blindness.”) To cure your blindness, visit lisafeldmanbarrett.com/nautilus and read the description, then come back here and look at the picture again. Suddenly, your brain can make meaning of the picture. The description gave your brain new information, which conjured up similar experiences in your past, and your brain used those experiences to launch better predictions for what you should see. Your brain has transformed ambiguous, curvy lines into a meaningful perception. (You will probably never see this picture as meaningless again.)
Predicting and correcting is a more efficient way to run a system than constantly reacting in an uncertain world. This is clear every time you watch a baseball game. When the pitcher hurls the ball at 96 miles per hour toward home plate, the batter doesn’t have enough time to wait for the ball to come close, consciously see it, and then prepare and execute the swing. Instead, the batter’s brain automatically predicts the ball’s future location, based on rich experience, and launches the swing based on that prediction, to be able to have a hope of hitting the ball. Without a predicting brain, sports as we know them would be impossible to play.
What does all this mean for you? You’re not a simple stimulus-response organism. The experiences you have today influence the actions that your brain automatically launches tomorrow.
The third myth is that there’s a clear dividing line between diseases of the body, such as cardiovascular disease, and diseases of the mind, such as depression. The idea that body and mind are separate was popularized by the philosopher René Descartes in the 17th century (known as Cartesian dualism) and it’s still around today, including in the practice of medicine. Neuroscientists have found, however, that the same brain networks responsible for controlling your body also are involved in creating your mind.10 A great example is the anterior cingulate cortex, which I mentioned earlier. Its neurons not only participate in all the psychological functions I listed, but also they regulate your organs, hormones, and immune system to keep you alive and well.
Modern research in molecular genetics has revealed that the triune brain idea is a myth.
Every mental experience has physical causes, and physical changes in your body often have mental consequences, thanks to your predicting brain. In every moment, your brain makes meaning of the whirlwind of activity inside your body, just as it does with sense data from the outside world. That meaning can take different forms. If you have tightness in your chest that your brain makes meaningful as physical discomfort, you’re likely to visit a cardiologist. But if your brain makes meaning of that same discomfort as distress, you’re more likely to book time with a psychiatrist. Note that your brain isn’t trying to distinguish two different physical sensations here. They are pretty much identical, and an incorrect prediction can cost you your life. Personally, I have three friends whose mothers were misdiagnosed with anxiety11 when they had serious illnesses, and two of them died.
When it comes to illness, the boundary between physical and mental is porous. Depression is usually catalogued as a mental illness, but it’s as much a metabolic illness as cardiovascular disease, which itself has significant mood-related symptoms. These two diseases occur together so often that some medical researchers believe that one may cause the other. That perspective is steeped in Cartesian dualism. Both depression12 and cardiovascular disease13 are known to involve problems with metabolism, so it’s equally plausible that they share an underlying cause.
When thinking about the relationship between mind and body, it’s tempting to indulge in the myth that the mind is solely in the brain and the body is separate. Under the hood, however, your brain creates your mind while it regulates the systems of your body. That means the regulation of your body is itself part of your mind.
Science, like your brain, works by prediction and correction. Scientists use their knowledge to fashion hypotheses about how the world works. Then they observe the world, and their observations become evidence they use to test the hypotheses. If a hypothesis did not predict the evidence, then they update it as needed. We’ve all seen this process in action during the pandemic. First we heard that COVID-19 spread on surfaces, so everyone rushed to buy Purell and Clorox wipes. Later we learned that the virus is mainly airborne and the focus moved to ventilation and masks. This kind of change is a normal part of science: We adapt to what we learn. But sometimes hypotheses are so strong that they resist change. They are maintained not by evidence but by ideology. They become scientific myths.
Lisa Feldman Barrett (@LFeldmanBarrett) is a professor of psychology at Northeastern University and the author of Seven and a Half Lessons About the Brain. Learn more at LisaFeldmanBarrett.com.
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Lead image: hand draw / Shutterstock