[intro] If you start reading pop-psychology listicles, you might come across this statement: Supposedly, no one who was born blind has ever been diagnosed with schizophrenia.

We saw this so-called "fact," too, and it seemed so bizarre that we almost immediately dismissed it. After all, schizophrenia is a mental illness with symptoms including delusions, disordered thinking, and hallucinations.

How is that closely related to being blind? Well, surprisingly, there is some truth behind this idea. In the nearly 70 years they've been looking- and despite the fact that is should happen statistically- researchers have found no known cases of someone with a certain kind of blindness also being diagnosed with schizophrenia.

It sounds unlikely, but some evidence suggests these conditions are more closely related than you might think. In fact, some scientists think this kind of blindness may even prevent people from developing schizophrenia in the first place. First, it's worth noting that this research has only looked at small, limited sample sizes and is only based on correlations.

That doesn't mean these studies aren't useful, but it does mean it's too early to say anything for sure- especially since we still don't know what causes schizophrenia. That being said, some researchers have made pretty interesting observations here. Their work is specifically focused on congenital or early cortical blindness, which we'll call CCB for short.

This is a condition someone has at birth or develops in infancy, and it's blindness caused by a dysfunction in the brain's occipital visual cortex. So if someone became blind as an adult or was born blind because of something about their eyes, these studies don't apply. At first glance, it might not seem like this condition has anything to do with schizophrenia.

But once you look at how the brain might cause schizophrenia's symptoms, the possible connection becomes a lot more clear. Take visual hallucinations, for example. They're relatively common in people with schizophrenia, and some evidence suggests they could happen when someone has trouble integrating information from their senses- especially their sense of sight.

The idea is that the brain would have trouble getting the visual information it receives to line up with what it's getting from the other senses. And because of that- or in an effort to compensate- it could end up producing hallucinations. Of course, if someone had never gotten any visual input- like, say, if they had CCB- this couldn't happen.

There would be nothing to overwhelm the brain, so this process couldn't be triggered. This isn't the only connection scientists have noticed, though: They've also seen a similar relationship with auditory symptoms. People with schizophrenia tend to score lower on measures of auditory processing, and they frequently report having hallucinations- two things that are likely related to the brain's auditory cortex.

It's too early to say that these cortex conditions cause those symptoms, but some experiments have found a correlation between the two. In one published in 2017, for example, participants with schizophrenia who had experienced auditory hallucinations tended to have thinner auditory cortexes than those who hadn't. But where does CCB come in?

Well, many folks with this kind of blindness have spent their lives relying more on their sense of hearing, so they tend to have a greater auditory perception than average. And brain scans have revealed structural changes that reflect that. Most notably, their auditory cortexes have likely expanded.

So even if someone with CCB was born with a thinner auditory cortex or was at risk of developing one, having to rely on their hearing could have strengthened that brain region. And that could lower their risk for developing auditory hallucinations. Relationships like this one have even been observed on a larger, more brain-wide scale- although the consequences there are still a bit fuzzy.

In any case, though, this research is all based on correlation, which means we can't conclusively say CCB prevents schizophrenia. But one thing we can say is that these studies are still significant. They're super interesting on their own, and on a larger scale, they can teach us more about how conditions like schizophrenia affect the brain- and how we could treat them.

Based on this kind of research, scientists have suggested that people at high risk for schizophrenia might benefit from some kind of cognitive training at a young age- training that works on things like sensory or perceptual skills. We don't know if that would be able to prevent the condition from happening, but it would hopefully improve someone's quality of life. Ultimately, this is another example of how our brains are full of surprises, and how seemingly-unrelated systems are connected.

And by studying relationships like this, there's a lot we can learn. If you want to learn more about schizophrenia and how it might be different than what you've heard, you can watch our episode about it after this. And as always, thanks for watching this episode of SciShow Psych! [outro]