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Left-Handedness and Genius

Despite stunning scientific advances in genetics, nanotechnology and robotics (to name a few), many neurologic phenomena remain unexplained. Take hand dominance. Scientists have been struggling for centuries to explain why, unlike animal populations whose right vs. left limb dominance always follows a 50/50 distribution, nearly 90% of the human population is right-handed. Although the answer is still blurry, the history of how neuroscientists arrived at it–including a dissection of Einstein’s brain–is fascinating.

As a preliminary matter, it is well understood that the brain-body relationship is criss-crossed. In other words, the left-brain controls punches thrown with the right hand, and the right-brain controls those thrown with the left. This is why those who suffer a stroke or a tumor on one side of the brain suffer paralysis on the opposite sides of their bodies. However, the analogy breaks down beyond the motor cortex (a relatively small portion of the brain), such as when it comes to thought and personality. So it cannot be said that left-handed folks are right-brain thinkers, and vice versa.

So what do we know about the connection between hand dominance and thought/personality, if anything? Our knowledge began with the dissections performed by French neurosurgeon Paul Broca in the nineteenth century. The first dissection was of a patient who’d passed away after suffering from speech problems and eventually the loss of motor control on the right side of his body. The operation revealed a large lesion on the patient’s left frontal cortex, likely due to a tumor. The second dissection was of a patient who ended up in Broca’s office after a fall, unable to utter more than a few words, and died a few weeks later. His brain also evidenced a dramatic lesion on its left side. Broca concluded that for most individuals, the speech center of the brain was located on the left-side.

Broca’s studies led to an explosion of neuroscientific theories, including the eventual “Distribution of Manual Asymmetry” by Marian Annett, which theorized that the strong focus on speech, a primarily left-brain function, was responsible for humanity’s overwhelming right-handedness.

Eventually, even Albert Einstein’s brain was dissected, and the results were both fascinating and congruent with many of the theories that had been espoused regarding brain structure. Specifically, Einstein’s brain was notable due to its unusual anatomical symmetry that suggested above-normal connectivity between hemispheres and regions.  Einstein also had a relatively small Broca’s area (responsible for speech), and a very large inferior parietal lobe (responsible for mathematical thought). In some ways, it resembled the brain structure of some Schizophrenic brains that had been studied in the past, which in turn lined up with Einstein’s signature thought processes, which were fused with grandiose imagery, movement and scenarios. It confirmed that brain structure (a.k.a. neuroanatomy) is intimately connected to brain function, and suggested that the line between insanity and genius may be extraordinarily thin, and structural. 

So what does all of this tell us about left-handedness? First and foremost, the precise neurologic origin and associated explanation for left-handedness has not yet been triangulated. But as of now, it is clear that left-handedness suggests a structural difference in the brain, which may enable distinctive cognitive processes and perspectives. This is congruent with the high incidence of left-handedness in the population of CEOs and visionaries, as often, the key to creativity and problem-solving (and therefore, success) is looking at things in ways that the majority of the population doesn’t.

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