In 1950, two researchers noticed something that didn’t quite add up. Hector Chevigny, a writer who had lost his sight in adulthood, and psychologist Sydell Braverman were studying the psychological lives of blind people when they stumbled upon an intriguing pattern: schizophrenia, a serious mental illness affecting people across virtually every known society, appeared to be entirely absent in people who had been blind from birth.The observation sat largely ignored for decades, held back by limited understanding of the disease and a lack of patient data. Then, in the early 2000s, large national health databases allowed researchers to follow entire populations from birth into adulthood, and the pattern held up.The most rigorous evidence comes from a 2018 whole-population study tracking nearly half a million children born in Western Australia between 1980 and 2001. Of those, 1,870 developed schizophrenia, but not one of the 66 children with cortical blindness did.That sample of blind children is small, but the pattern holds across more than 70 years of evidence: not a single congenitally blind person with schizophrenia has ever been reported. The protection seems to be specific to cortical blindness, which is caused by damage to the brain’s visual cortex.People who lose their sight later in life, or whose blindness is caused by damage to the eyes rather than the brain, can still develop the condition. This makes it clear that blindness itself isn’t the deciding factor. Something specific about the visual brain is.This might seem odd. Schizophrenia is most commonly associated with hearing voices or holding unusual beliefs, not with vision. But the explanation lies not in what people see, but in how the brain uses vision to make sense of the world.
Fascinating and new to me. You learn something every day.
Text and cropped image from The Conversation, where there is more explanatory text. Via Neatorama.
The entire body of evidence may be convincing, but the "most rigorous" evidence is hardly so. The probability that among 66 randomly selected children from the population there would be no instances of schizophrenia is more than 70%.
ReplyDeleteConservatively using a population of 400,00, I calculated a probability of
(1–(1870/400000))^66 = about 0.74.
Small sample size.
ReplyDeleteClaude says "This is not statistically significant.
Expected cases in 66 children, given the base rate of ~1,870/500,000 (0.37%), is about 0.25. Observing zero has a probability of roughly 78% under the null hypothesis (Poisson, λ ≈ 0.25). That is nowhere near significance.
For a zero-count finding in 66 people to reach p < 0.05, the expected count would need to exceed ~3, meaning the background rate would have to be roughly 12x higher than schizophrenia's actual prevalence in that cohort."
There's also the possibility that the mental illness that would have been schizophrenia manifests as some other narrowly defined condition instead because the blind person's brain has developed differently.
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