“Left, right, wrong” (Brain hemisphere dominance)

One of the enduring ideas about the human brain is that its hemispheres determine someone’s personality and cognitive skills. Those who are organized and good at math are considered left-brained, while those who are intuitive and artistic are labeled right-brained. Not sure where that leaves me, given my less than stellar grades in both algebra and drawing classes.

As it turns out, however, the idea of persons being either left-brained or right-brained dominant lacks a scientific grounding.

True, the brain is divided into left and right hemispheres, which are responsible for different tasks. But just because there are functions that take place in one hemisphere, that does not mean this drives personalities or cognitive abilities.

For one thing, not all cognitive abilities are specific to either left or right. Short-term memory depends on the frontal lobe, which is housed in both hemispheres. Also, long-term memory (if I’m recalling correctly) is maintained by neural connections that run throughout the brain.

Then there are abilities like vision processing that localize in one hemisphere for the benefit of the other side.

But let’s get back to the abilities that localize in one hemisphere, such as language on the left and music on the right. It is these delineations that likely gave birth to the left-brained, right-brained myth. However, researchers in a 2013 study examined subjects’ MRI scans and deduced there was no scientific basis for the notion of hemisphere-dominant cognitive styles. When performing tasks, the subjects showed activity in either the left or right side, but none of them demonstrated a pattern of being consistently dominant in one hemisphere.

Another reason for this myth is a misunderstanding of the results achieved by neuroscientist Michael Gazzaniga and neurobiologist Roger Sperry when they were doing doctorate research. Sperry discovered that slicing the connective fibers of monkeys’ brains resulted in the right side of the brain seeming not knowing what the left side was doing. This suggested the fibers may serve as communication wires between the two hemispheres.

Gazzaniga found a similar effect in epilepsy patients when these fibers were severed to prevent seizures from spreading through the brain. When one of his patients who had had this surgery was shown a picture that only his left hemisphere could process, the patient was able to identify it. But when trying to process the image with his right hemisphere, the patient could only point at the picture, and was unable to name it.

Gazzaniga theorized that both hemispheres usually process an image, but that only the left can articulate what it is. Even though this research suggests the two hemispheres communicate with each other to help us execute cognitive tasks, popular culture has embraced an opposite idea that the hemispheres are segregated, and that this determines what kind of person we are and what kind of abilities we possess.

As to the difference between a neuroscientist and a neurobiologist, I don’t know. My left hemisphere is misfiring today.



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