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  • Robb G. Best

The Left-Handed Brain

What do Babe Ruth, Marie Curie, David Bowie, Barack Obama, and Oprah have in common, other than fame? No, that’s not the start of a riddle; there’s a simple, non-trick answer. They’re all left-handed.

Today, left-handed people make up roughly ten percent of the population. Modern science has yet to explain what causes left-handedness in humans, although we have weeded out some of our earlier theories, such as “being a witch.” Still, the idea that lefties are in some way untrustworthy has persisted across cultures and centuries (famously, the Latin word for “left” comes from the word “sinister”). As late as the 1960’s, American public schools forced left-handed children to write with their right hand.

What gives? Perhaps it’s a classic case of a majority failing to understand a minority, and coming to fear them instead. Interestingly, even today, neuroscience experiments commonly exclude left-handed subjects, in the hopes of eliminating variables. In a 2014 article in Nature Reviews Neuroscience, Roel Willems and his colleagues argue that this is a real problem.

Not only is it never a great idea to systematically exclude 10% of the population from your samples, the article explains that left-handed brains are worth studying for their own merits. “According to the textbooks, facial recognition takes place in the right half of the brain,” it notes. However, in 2009 studies, Willem’s team had discovered “the same process takes place in both halves of the brain in the case of left-handed people, but with the same final outcome.” In other words, there appear to be noticeable neurological differences between lefties and the rest of us—maybe not a pact with the devil that grants them sinister magic powers, but something.

Could this include a greater degree of creativity? It’s hard to say. While it’s easy to conjure an impressive list of artsy southpaws, the sheer number of famous creative types throughout history also allows a high degree of selection bias. Besides, “creativity” as a trait covers so much ground, and involves so many variables, with often such subjective results, that it is very difficult to judge in a laboratory setting. However, some studies do suggest that left-handed students may have a slight edge on their peers when it comes to the decidedly analytical task of solving difficult math problems.

And researchers may be making some headway on the origins of left-handedness—or rather, left-finnedness. Scientists at the University of Konstanz are looking at brains and genes of the lake-dwelling Perissodus microlepis, an African species of a cichlid fish. Many of these fish are pretty consistent in choosing a direction to attack their prey from. These cichlids are not the only non-human animal to show a preference for either their left or right side—both great apes and birds do the same—but here, it is easy to notice.

In those fish with a strong directional leaning, the biologists found an asymmetric Tectum Opticum, a brain region that enables vision. That is to say, fish’s favored side had slightly better developed eyesight.

The cichlids with a preference also seemed to display asymmetric gene behavior; that is to say, the genes in the corresponding brain hemisphere were more active than in the other. This held true for at least 140 genes, but the one with the biggest difference appeared to be the synuclein gamma alpha (sncga) gene. In a way, it makes sense, because the sncga expresses most clearly in the habenula, a brain region that is asymmetric in any vertebrate. This could suggest that hand preference is tied to the fundamental physiology of the brain.

Of course, scholars are reluctant to draw broad conclusions about our lives from a study built on tiny fish. Still, it could be an interesting window into a centuries-old question. “We hope that our results also will contribute to further our understanding of handedness in humans," says biologist and study co-author Dr Ralf Schneider. In that case, maybe it’s time to give those fish some math problems...

#biology #brainchemistry