Why do some people use their left hand? MRI Brain Scans Are Now Providing Answers

Why do some people use their left hand_ MRI Brain Scans Are Now Providing Answers

I was not shocked to find that there are more than 43 million videos on TikTok featuring ink-smeared lefties slamming on doors, playing their guitars sideways, and utterly failing with the ice-cream scooper. Instead, I made the decision that it might be more intriguing to investigate the precise reasons why an estimated 10% of the world’s population possesses the trait of left-handedness.

As it turns out, there is some recent research on that topic, made possible by the wonders of MRI technology and a vast archive of brain scans. Late last year, a study led by the Max Planck Institute for Psycholinguistics pinpointed the precise location in the human brain where left-handedness manifests. Or more specifically, the study showed that left-handed people’s brains are typically less symmetrical than those of their right-handed counterparts.

Handedness-associated cortical thickness asymmetries. (A) Group average differences of cortical thickness asymmetry between 28,802 righthanders and 3,062 left-handers shown for the whole cortex, without a threshold for significance. Red color indicates a lower asymmetry index in left-handers (weaker average leftward or stronger average rightward asymmetry in left-handers compared to right-handers). Blue indicates a higher asymmetry index in left-handers (stronger average leftward or weaker average rightward asymmetry in left-handers compared to right-handers). (B) Regional clusters with significant group average differences of cortical thickness asymmetry between 28,802 right-handers and 3,062 left-handers.

An multinational team of researchers precisely measured the thickness and surface areas of the cerebral cortexes of 28,802 righties and 3,062 lefties using data from the UK Biobank. The mapping process took three months and required the co-operation of 12 clusters of computer servers.

The findings, which were reported in the Proceedings of the National Academy of Sciences, showed that there were 10 different regions of the brain with different average asymmetries between righties and lefties. Furthermore, these regions were dispersed across the whole surface of the brain rather than being confined to a single region. This is the first time that specific regions of the structure of the brain have been clearly connected to handedness, according to researcher Clyde Francks.

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The researchers suggest that handedness has an evolutionary component connected to a time in human history when communication was more gesture-based because some of these fascinating areas were connected to language.

Functional annotation of regions that show altered asymmetry in left-handedness. Functional annotation based on meta-analyzed fMRI data for clusters showing altered surface area asymmetry (A) and cortical thickness asymmetry (B) in left-handedness. (Left) Coactivation maps for the handedness-associated clusters derived from the “decoder” function of Neurosynth (higher z-scores indicate greater coactivation). (Right) Cognitive terms associated with the coactivation maps for handedness-associated clusters.

According to additional studies, being left-handed was something of a double-edged sword for early humans, giving them an advantage in warfare but a disadvantage in cooperative situations. According to one explanation, the tension between those two factors may be to blame for the persistent rarity of left-handed people in various communities.

All 10 of the differentiating brain regions in the Max Planck study tended to be larger in the right hemisphere for lefties. The researchers believe they have absolutely not discovered a technique to forecast whether someone would be left-handed solely by looking at their brain because the differences turned out to be quite small—a question of averages that could only be noticed over big data sets.

In other words, despite being a solace to the poor guy on TikTok who just dumped a scoop of rocky road all over his lap, our brains are much more similar than they are different.

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