Being left-handed, I have done a bit of reading on the topic. So I have known for a while that one of the causes of left-handedness is the presence of higher than normal levels of testosterone in utero. If there is a high level of testosterone during certain stages of brain development, hemisphere dominance can change, and left-handedness can be a result.
A new study by Simon Baron-Cohen shows high levels of steroid hormones in utero for children who later show signs of autism. Testosterone is, of course, a steroid hormone. This made me wonder if there is a correlation between left-handedness and autism.
Not only is there, but we have known about it since 1983.While the general population shows 37% non-right handed dominance (meaning left-handedness or various forms of ambidexterity; left-handedness alone is about 18%), that number is almost twice as high in people with autism: 62%. This is pretty much a complete inversion of neurotypicals' handedness. More recent papers all suggest people with autism may be three times more likely to be left-handed.
Of course, autism is not the only condition strongly associated with left-handedness. Dyslexia is as well. And so are many mental disorders. Equally, about half of lefties are clearly neurotypical (not autistic, dyslexic, etc.), so it's important to understand that while the presence of left-handedness may indicate non-neurotypical neural architecture, it does not necessarily do so.
Still, the correlation between high testosterone levels and left-handedness and the correlation between high steroid levels (including testosterone) and autism points toward Baron-Cowan's theory of autism as a more male brain. Now, given that I subscribe to the "intense world theory" of autism (at least for myself and my son), I have to wonder if there is a relationship between these high steroid levels and neurohyperactivity.
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