Full transcript
0:00Here's a strange thing to consider.
0:01There is a mental illness that affects
0:03roughly one in a hundred people. It
0:05doesn't care about your age, background,
0:06or diet. It shows up at roughly the same
0:09rate across most of human civilization
0:11and is one of the most robustly
0:13replicated findings in all of
0:15psychiatry. I'm talking about
0:16schizophrenia. And yet, as far as we
0:19know, no person born blind has ever been
0:22diagnosed with schizophrenia. Now,
0:23that's the kind of finding that seems
0:25too neat, too strange, but it keeps
0:27appearing across different countries,
0:29decades, and research groups who weren't
0:31looking for it. The pattern is
0:32consistent enough that psychiatrists had
0:35to take it seriously, which meant
0:36neuroscientists had to actually try to
0:39explain it. And the explanation says
0:41something quite profound about what
0:43brains are actually for. Here's the key
0:45idea. Your brain isn't a camera. It
0:48doesn't just passively receive sensory
0:50information and report back what it
0:52found. What it's actually doing is
0:53closer to forecasting. It holds this
0:56running model of the world built from
0:58everything you've ever experienced, and
1:00it uses that model to predict what's
1:03about to happen. The sights, the sounds,
1:05the feeling of the phone in your hand
1:07right now. Your brain has already
1:09guessed all of that before the signals
1:11even arrive. Most of the time the
1:13predictions are good enough that you
1:14never notice. The info comes in, matches
1:17the model, and you get on with your day.
1:19However, when there's a mismatch, that's
1:21when your brain pays attention. The
1:22error signal fires and the model
1:24updates. In schizophrenia, something in
1:26that process goes wrong. The error
1:28signal fires when it shouldn't. The
1:30model updates in response to things that
1:32aren't there. That becomes a
1:34hallucination or delusion. If you've
1:36never had visual input from day one,
1:38your brain never builds a visual
1:40predictive model in the first place, and
1:42thus, no forecast to get wrong.
1:45Researchers think this might be why
1:47people born blind don't get
1:49schizophrenia. The predictive system of
1:51a sighted brain simply doesn't exist in
1:54the same form. This protection seems to
1:56be specific to early blindness because
1:59losing your vision as an adult has the
2:01opposite effect. Late-onset visual
2:03impairment is associated with higher
2:05rates of psychosis-like symptoms, which
2:07makes sense. Your brain spent decades
2:10building a detailed visual model of the
2:12world, and now that visual input went
2:14dark. The forecaster kept working, but
2:16the data stopped arriving. What I find
2:19so fascinating about all of this is what
2:21it implies about the connection between
2:23our senses and the brain. We tend to
2:25think of mental illness as something
2:26that lives purely inside the brain.
2:28Chemicals, genetics, neural circuitry.
2:31And it is those things. But this
2:33suggests that the sensory experience you
2:34have or don't have, from the very
2:36beginning of your life, shapes your
2:38brain's architecture in ways that reach
2:40way beyond just perception. One of the
2:42most debilitating psychiatric conditions
2:44known to medicine may be held at bay by
2:47the simple fact of never having seen the
2:49world at all. Make of that what you
2:51will. If you like science we're sharing
2:52like this, then follow us everywhere at
2:54Today I Learned Science at TILscience.