What both halves of your brain don’t say about you

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There are hundreds of personality quizzes online that claim to tell you, based on criteria ranging from your preference in paints to your stated ability to remember names and faces, whether the right or left half of you. your brain is dominant. Left-brained people, quizzes will tell you, are logical and excellent at language and math; right-brained people are more imaginative, emotionally intelligent, and good at spatial reasoning. There’s just one problem: that’s not how the brain works.

“Popular science enthusiasts kind of took this idea and used it, and it’s just become entangled in popular culture now, and it’s not going to go away. But that’s not true, ”says neuroradiologist Jeff Anderson. He would know – he is the main author of a 2013 study from the University of Utah who used MRI scans to analyze brain activity across the hemispheres.

Despite this enduring belief, there is no such thing as being “right brain” or “left brain”. Whether you are someone who tends more towards creativity or logic has nothing to do with one hemisphere of your brain dominating the other. But the real science of how the two halves of our brains work together is sometimes stranger than fiction.

Specialized brain regions

The human brain is divided into two hemispheres, the left and the right. In all vertebrate animals, the right hemisphere controls the left side of the body and vice versa. (Although the the jury is still absent why.) And scientists have long known, from the behaviors of brain-damaged patients, that different areas of the brain do different things.

Several nineteenth-century neurologists, for example, noted the presence of lesions in the left frontal lobes of several patients with speech disorders. Broca’s area, the brain’s language center, has been named after the most famous scientist (but not the first) to document this connection.

But Paul Broca struggled with his discovery because the very suggestion that the left and right halves of the brain function differently disrupted the idea that nature tends towards perfect symmetry, says Peggy Mason, a neuroscientist at the University of Chicago. . “Today we know it’s just a fact, that the left hemisphere is primarily responsible – it does not function on its own – but is primarily responsible for learning and producing language,” she says.

The two hemispheres are connected by a dense highway of nerves that runs down the middle of the brain. Called the corpus callosum, this highway is what allows the two halves of the brain to communicate with each other. From the early to mid-20th century, some physicians attempted to control seizures in their severely epileptic patients by surgically severing the corpus callosum – and thereby disrupting the electrical impulses traveling from one hemisphere to the other. The procedure, which is still sometimes practiced today, has reduced seizures. But its side effects have revealed unexpected truths about how the two halves of the brain work together.

In the 1960s, California Institute of Technology neuropsychologist Roger Sperry and doctoral student Mike Gazzaniga worked with four so-called “split-brain” patients who had undergone this surgery. They found subtle but surprising differences in the way patients treated the world around them.

In experience, Sperry and Gazzaniga gave the patients a spoon to hold in their right hand and asked them to identify the object without looking. Because the right hand is controlled by the left hemisphere of the brain, which contains Broca’s area for language processing, patients had no problem explaining what they were holding. However, when they held a pencil with their left hand (controlled by the right half of the brain without Broca), patients could no longer identify what it was. Meanwhile, patients reproduced drawings better with their left hand than with their right hand, indicating that the right brain plays an important role in spatial reasoning.

“If you have a focal lesion in the right or left hemisphere, you will have deficits in these areas,” says Gazzaniga, now director of the SAGE Center for the Study of Mind at the University of California at Santa Barbara. “What was shocking was to see not a deficit but simply a disconnect – one party didn’t know what the other was doing. It was a surprising breakthrough.

A core of truth

The work of Sperry and Gazzaniga revealed the importance of different hemispheres of the brain for different activities and the role of the corpus callosum in sharing information between hemispheres. However, their research quickly saw misinterpretations in the general public: Some have postulated that creative people should have right brains, and logical people should have left brains. This theory, in Gazzaniga’s words, is “just plain wrong”.


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Researchers like Anderson have shown that not only are personality unrelated to different halves of the brain, but people don’t really have right or left brains to begin with. “The idea that we have dominants on the left and dominants on the right, and that [this] is linked to the personality, is categorically wrong. This has never been supported in the neuroscience community. Neuroscientists don’t believe this and never have.

However, Anderson, who is now a neuroradiologist in Oregon and an associate professor at the University of Utah, notes that “often when you even have something that maybe isn’t correct in popular culture, it sometimes there is a kernel of truth and it is worth looking at it from a more rigorous point of view.

In their 2013 study, Anderson and colleagues performed statistical analyzes of more than 1,000 brain scans. “In each individual, there would be stronger connections in the left hemisphere and others in the right hemisphere. And it varied on a connection-to-connection basis, ”he says. “People had roughly equal mixes of the two. When you average it it was not the case that an individual would tend to have stronger connections overall in the left hemisphere.

Ultimately, he says, “What we’ve learned is that there are some really important differences between the left hemisphere and the right hemisphere. It’s just that they have nothing to do with personality or whether the cognitive strategy is more logical or free-spirited or creative.

It’s also worth noting that laterality is also unrelated to having one half of the brain dominating the other (i.e., left-handed people don’t have right brains). Likewise, there is no set of personality traits or skills that go with being right-handed or left-handed. While there are differences in brain scans between left-handed and right-handed people in terms of how their brains work, says Silvia Paracchini, a neurogeneticist who studies the origins of laterality at the Institute of Neural and Behavioral Sciences of the University of St. Andrews. For example, among strongly left-handed people, more use parts of their right brain for language processing. These differences are, however, quite small.

While researchers have shown the limits of how our brain’s hemispheres influence our lives, Anderson understands the appeal of such ideas. “People are infinitely fascinated with themselves and our friends, and these subtle differences in the way we think about the world are really important and meaningful to people. When you offer a listicle or online quiz it tells us something about ourselves, we are drawn to it. It’s irresistible, ”he says. “It’s always a way of thinking about people and ranking them in an interesting or useful way. You just have to take it with a huge grain of salt.

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