What are hallucinations?

10 January 2023


photo of an MRI scanner



This person says, what is a hallucination? What makes them happen? What's going on in the brain?


Leor - So hallucinations are sensory experiences that are not rooted in any external stimulus. So there is no outside event actually happening, but the person is experiencing maybe an auditory hallucination where they're experiencing voices and similarly there's visual hallucinations or tactile hallucinations. And it's interesting to think about why the brain hallucinates and what the brain looks like when it hallucinates. And actually, insome of the research that my colleagues and I have done, we've looked at what a hallucinating brain looks like in the brain scanner and we wanted to know whether a visual hallucination that you see looks the same to the brain as an auditory hallucination. And we had this hypothesis, this theory, that there would be one area in the brain that would be able to distinguish between real and unreal information. So basically, would it be able to distinguish between a hallucination and a real sensory perception. What we did find is that the brain, the hallucinating brain, looks exactly like the perceiving brain. And that's fascinating that the brain doesn't seem to actually distinguish for itself between a hallucination and a real event.

Chris - Goodness. So when people say that it really seemed real to them and they're unshakable in their belief, if you try and dissuade someone who's having a hallucination that it's not real, that's why they so strongly disbelieve you, because to them it really is exactly the same brain wiring firing off as when they're having that experience for real. Which is why it feels real to them.

Leor - Exactly.


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