# People Born Blind Are Mysteriously Protected From Schizophrenia



## David Baxter PhD (Feb 14, 2020)

*People Born Blind Are Mysteriously Protected From Schizophrenia*
by Shayla Love, _VICE
_Feb 11, 2020

It was something Tom Pollak had heard  whispers about—an odd factoid, referred to now and again, usually with  bewilderment: *No person who was born blind has ever been diagnosed with  schizophrenia.
* 
Over the past 60 some years, scientists around the world have been writing about this mystery. They've analyzed past studies, combed the wards of psychiatric hospitals, and looked through agencies that treat blind people, trying to find a case. 

As time goes on, larger data sets have emerged: In 2018, a study  led by a researcher named Vera Morgan at the University of Western  Australia looked at nearly half a million children born between 1980 and  2001 and strengthened this negative association. Pollak, a psychiatrist  and researcher at King's College London, remembered checking in the  mental health facility where he works after learning about it; he too  was unable to find a single patient with congenital blindness who had  schizophrenia. 

These findings suggest that _ something_ about congenital  blindness may protect a person from schizophrenia. This is especially  surprising, since congenital blindness often results from infections,  brain trauma, or genetic mutation—all factors that are independently  associated with greater risk of psychotic disorders.

 More  strangely, vision loss at other periods of life is associated with  
higher risks of schizophrenia and psychotic symptoms. Even in healthy  people, blocking vision for just a few days can bring about  hallucinations. And the connections between vision abnormalities and  schizophrenia have become more deeply established in recent years—visual  abnormalities are being found before a person has any psychotic  symptoms, sometimes predicting who will develop schizophrenia. 

But the whispered-about fact persists: Being born blind, and perhaps  specific types of congenital blindness, shield from the very disorders  vision loss can encourage later in life. A myriad of theories exist as  to why—from the blind brain's neuroplasticity to how vision plays an  important role in building our model of the world (and what happens when  that process goes wrong). Select researchers believe that the ties  between vision and psychotic symptoms indicate there's something new to  learn here. Could it be that within this narrowly-defined phenomenon  there are clues for what causes schizophrenia, how to predict who will  develop it, and potentially how to treat it? 

In 2004, 13 healthy people were blindfolded for 96 hours, and 10 of them reported having visual hallucinations between their first and second day in the dark. 

One subject, a 29-year-old woman, saw a green face with big eyes when  she was standing in front of where she knew there was a mirror—though  she couldn’t see it. Another 24-year-old man, by the end of the second  day, was having difficulty walking because of all the hallucinations  that appeared to be in his way. He reported seeing "mounds of pebbles,  or small stones...and between them was running a small stream of water."  By the end of the study, he reported seeing "ornate buildings of  white-green marble" and "cartoon-like figures." 

 We've known for a  long time about the link between vision loss and hallucination. Charles  Bonnet syndrome, first described in 1760, is a disorder in which people  lose their vision and then start to experience  hallucinations. These kinds of mental conjurings don't necessarily come  with mental illness, though people with schizophrenia have been  regularly shown to also have issues with their sight.

Having  unusual eye movements, problems with the retinas, unusual blink rates,  and other visual aberrations makes it more likely for a person to be  diagnosed with schizophrenia. 

One study found that those vision problems start _ before _a person has their first psychotic episodes, not after.

 Yet  this association falls away among people born without sight. Pollak and  Phil Corlett, an associate professor of psychiatry and psychology at  Yale University, have a theory about why—which they published late last year in the journal _ Schizophrenia Bulletin. _It's rooted in the hypothesis that one of our brain's most important jobs is to make predictions about the world. 

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This view of the brain argues that rather than perceiving the world  around us in real time, our brains create a model of what’s out there, predict  and simulate what we experience, and then compare our predictions to  what’s actually happening—using any errors to update or change the model  in our minds. The accuracy of your past predictions are crucial for the  accuracy of your overall model—it's what you're comparing new inputs  to, and how you're making any adjustments.

 This is where  vision comes in. Vision gives us a lot of information about the world  around us, and is an important sense that helps link together other  sensory cues, like sound and touch, Pollak said. If the way a person  sees the world is off, it can make it harder to predict, correct errors,  and build a model of the world that makes sense. And when people have  problems with their vision, the brain has to make more predictions to  explain them. On the other hand, if you couldn’t see anything, you  wouldn’t build up those false representations of the world around  you—which could lead to problems in thinking later on. 

This might help researchers explain all those issues in vision and  sensory processing early in life seen in people with schizophrenia. 

In a 2006 study  by Elaine Walker at Emory University, she analyzed home movies of  people diagnosed with schizophrenia when they were children. A lot of  the children were more clumsy in the videos, like dropping a ball more  frequently during catch, stumbling more often, or tilting to the left  side. It suggests there's some sort of disconnect with the way they’re  sensing and interacting with the world. When children of mothers who  have schizophrenia show visual dysfunction  when they’re young, it can predict if they develop schizophrenia when  they’re older. Children who end up with schizophrenia, both with and without  a family history, have more problems with their eyes compared to  children who develop non-psychotic diseases or other mental illnesses.

 A  person who was born blind doesn't have the visual inputs to help shape  their model of the world. They have to build it with their other  senses—a model of the world that Pollak and Corlett argue could be more  stable. 

“The idea we’re trying to get at is, there must be something  different in the representation and the stability of the internal world  in congenitally blind people,” Pollak said. “And that stability, in a  way, is keeping itself protective against the kind of mistakes and false  inferences that you get in schizophrenia and psychotic disorders.” 

 The  hallucinations, delusions, and bizarre behavior in people with  schizophrenia are well known. But Steve Silverstein, a psychiatrist at  the University of Rochester, said that he and others view those symptoms  as side effects, not the cause of the disease. Actually, schizophrenia  could be more rooted in cognitive deficits—disturbances in perception,  attention, memory, language, or learning. 

 Around 2010, Silverstein read _ Blind Vision—_a  book by scientists Zaira Cattaneo and Tomaso Vecchi, on the cognitive  abilities and experiences of blind people. “I was struck by how many of  the compensations that the brain seems to make, or the skills that blind  people develop, seem to be the exact opposite of what you find in  schizophrenia,” he said. 

 Silverstein doesn’t disagree with  Pollak and Corlett’s predictive brain theory, but thinks that the answer  may be more far-reaching: that prediction is just one way a  congenitally blind person's brain has advantages over a schizophrenic  brain. He thinks that being blind strengthens the brain in various  ways—and in the very same ways that it is weakened when someone has  schizophrenia.

To take one example, there’s something called _ selective attention_  when it comes to listening, which is the ability to stay attentive to  one source of auditory information—say, when you’re at a party and  listening to one person without letting the sounds from the rest of the  room distract you. In a lab setting, researchers test selective  attention by playing one noise into your left ear and a different one  into your right, asking you to pay attention to one and not the other. 

People with schizophrenia have been shown to have problems with  selective attention, Silverstein said, and meanwhile people who were  born blind are better at this task than sighted people. When compared to  sighted people, congenitally blind people are also better at hearing  different pitches, telling pitches apart, and telling where sounds come  from. People with schizophrenia are the opposite: They usually have  difficulty with listening accuracy, and process speech abnormally. Not  being able to properly figure out where sounds are coming from could  lead to someone thinking that their own voice is coming from somewhere  else, and contribute to delusional thinking. 

 It's a compelling  list that goes on and on: Blind people are better than sighted ones on  reaction time to both sound and touch; schizophrenia patients show  deficits in these areas. Blind people have better working memories, and  people with schizophrenia can have impairments in memory. Congenitally  blind people are also impervious to the rubber hand illusion,  when a person feels like an inanimate object is part of their own body  (the experiment is typically done using a rubber hand). It could mean  that blind people have more stability when it comes to their bodily  representation.

“I would say there are probably about 20 ways that people who are born  blind are better, on average, than people in the general population,”  Silverstein said. “And it’s in those same areas where people with  schizophrenia tend to have more cognitive problems.” (He's even made a chart, published in one of his papers.) 

"If you're born blind, your brain basically from an early age takes  over the visual part of the brain to do other things," Silverstein said.  "And that's thought to be the reason why some of these auditory,  attentional, and body-representation skills are a little more developed  in people who were born blind than other people." Another result of  blindness is that brain regions are talking to each other more, in ways  they don’t in sighted people—some brain-imaging studies have seen that.  People with schizophrenia, meanwhile, tend to have many fewer of these  connections. 

 A concrete  explanation for why congenital blindness protects from schizophrenia is  still up for grabs—whether the protection comes from predicting the  world, having a more connected brain, or relying on other senses. 

 There’s a lot that needs to be fleshed out. For example, there is more than one kind of congenital blindness. _ Cortical _blindness is caused by an issue in the part of the brain that processes vision, whereas _ peripheral_  blindness is a problem in the eyes instead—but the visual part of the  brain is okay. While there are still no reported cases of people with  congenital cortical blindness, there might be a few people who were born  blind with peripheral blindness who did develop schizophrenia. (Some of  the cases are several decades old, or the person has other serious  diseases, so saying for sure is tough.) 

Congenital blindness doesn’t seem to protect against any other mental  illness, so it’s not a safeguard overall. Congenitally blind people  have been reported to have had eating disorders and arachnophobia—a  person can have those disorders without ever having seen their bodies or  a spider). And if a person is born both deaf _ and _blind, it doesn’t seem to offer protection either—that comes with higher risks for psychosis. 

 There’s  a disease called Usher syndrome, in which people are born deaf and lose  their vision early in childhood; it’s been associated with  schizophrenia and psychosis. Silverstein said that it’s unclear why  adding deafness to the mix removes the protection that blindness seems  to offer. “One possibility is that blindness by itself presents a  surmountable challenge to cope with the environment and thereby fosters  compensatory sensory, perceptual, and cognitive changes that lead to a  surprisingly high level of functioning,” Silverstain wrote in a 2013 paper.  “Deafblindness, on the other hand, may so seriously restrict the  opportunity for environmental interaction that it also stunts the  development of cognitively based coping strategies.”

But in the end, it's this extreme specificity that's most intriguing. It  could lead to a different approach to thinking about psychosis, Corlett  said. The development of the visual system could be looked at more  closely, along with people’s visual predictions. It could open up some  basic research avenues to help gain more fundamental understanding of  schizophrenia: “What's the relationship between those really basic  visual perceptual mechanisms and the onset of symptoms?” Corlett asked.  We've made very little progress in our understanding of psychosis in  particular, but also in psychiatry more broadly, in terms of how these  symptoms are created in the brain. I think anything that gives us  inspiration, anything that might give us a bit of leverage is really,  really welcomed.”

In the U.S., work with schizophrenia patients has been heavily  focused on cognitive tasks, like memory, Corlett said, but maybe  cognitive training should include more focus on sensory factors and  perception. Perhaps early visual training, along with cognitive  training, could potentially help. And instead of a blood test, perhaps  one day there could be an eye test for people to assess if they’re at  high risk for psychosis. 

 Another thing to consider, which  Silverstein has written about, is having people at risk for  schizophrenia increase their reliance on their non-vision senses, to see  if that enhances their functioning. 

It's not a novel approach: to go looking for where a disease _ doesn’t _exist,  in order to learn something more about it. In the 1980s and 1990s,  there were people who were commonly exposed to HIV, but never developed AIDS.

Studying those people  led to a deeper understanding of risks, and what protective factors  they may have had. It was a long-standing medical mystery that people  with sickle-cell anemia were somehow protected from getting malaria. The same gene  that causes abnormal red blood cells in sickle cell anemia is  protective against malaria—offering a window into how malaria works in  the body. 

 It can be difficult to study, especially for rare  diseases, where you have to wait for natural cases to arise. But it can  be a unique place for clues. “I often joke that it’d be interesting to  study people like Keith Richards or Ozzy Osbourne: Why they haven't been  ravaged by opiate addiction in the same way or similar addiction,”  Corlett said. “_ What is it about these people that led them not to manifest illnesses?_ has been traditionally a very useful way of exploring what it means to be at risk and what it means to have pathophysiology.”

 With  schizophrenia and blindness, Silverstein said we’re not there yet, and  probably not close. That said, he doesn’t think that we should ignore  it. 

 “At this point, I don’t think I’d go so far as to say it's  promising,” Silverstein said. “The word I’d use is intriguing. “In some  ways, this is one of the most interesting observations in a long time in  schizophrenia research. Because it’s the only thing that seems to be  protective against schizophrenia. I think there’s something here and  this should be looked into much more.”


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