The peculiarities of the left-handed brain

About 10% of humans preferentially use their left hand for writing and all other routine tasks. They are left-handed people. Scientists have long been interested in the differences between the brain right-handed and left-handed people. So far, the observations are contradictory and no clear difference emerges. The samples tested, only a few hundred left-handers, are too small. An international team of researchers, under the direction of Max-Planck Institute for Psycholinguistics, compared the brains of 31,864 individuals, including 3,062 left-handed. On the brain images, they compared 8,681 points across the cortex to compare asymmetries between the brain right-handed and left-handed people.

Cerebral asymmetries specific to left-handers

The human brain is asymmetric, each hemisphere is specialized in different functions. For example, it is the left hemisphere that controls the hand of right-handers and the right that controls the hand. left-handers. But this also concerns other functions such as language. In 95% of right-handed people, the right hemisphere dominates the language, but this is only the case for 70% of left-handed people according to the authors of the study. How closely is left-handedness related to brain asymmetry? This is what the researchers wanted to know. They also looked at the roles of certain genes already known to be associated with awkwardness.

Analyzing all these brains was no easy task. ” It took about three out of twelve months of treatment computers running in parallel Recalls Zhiqiang Sha, a post-doctoral fellow who worked on the project. From all these hours of calculation, scientists have derived interesting information. They identified ten regions where there is a difference in asymmetry between right-handed and left-handed people. These ten regions are located throughout the cerebral cortex and are characterized by a layer of matter thicker gray, and therefore more connections between neurons, in the right hemisphere in left-handed people than in right-handed people. It sticks because in left-handers, it is the right hemisphere that controls the movements of the dominant hand. ” This is the first time that specific areas of brain anatomy have been confidently linked to left-handedness. », Explains Clyde Francks, director of this research.

Differentiate the brain of a left-hander from that of a right-hander?

In the brain regions of language, structural asymmetries are associated with genes involved in awkwardness. More precisely, six genes have been identified, one of which NME7 which is also responsible for the position of the organs on the right or left of the body. Despite the large number of images analyzed, scientists were unable to identify a clear marker that can differentiate the brain from a right-hander to that of a left-hander at a glance.