That is not how your brain works

By | March 5, 2021

Lisa Feldman Barrett writes:

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.

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. Most neurons have multiple jobs, not a single psychological purpose. 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.

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. 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. (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.

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.

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.

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. [Continue reading…]

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