Hallucinations and delusions - what's going on in the brain?

26 September 2010

Interview with

Professor Paul Fletcher, Department of Psychiatry, Cambridge University

Kat -  So if you could tell us a little bit about what fMRI can actually tell us about what's going on in the brain and what it can't actually tell us yet?  I think some people think it's maybe a magic mind reading machine.  Where are we at the moment with this technology?

Paul -   Well, as we were just hearing from Dr. Gallant,  fMRI is a way of looking at which different bits of the brain respond when people are asked to do things or when they're having particular experiences.  From my perspective, it's very interesting because we can start to look at the areas of the brain that become active when somebody's experiencing quite unpleasant symptoms that co-occur with mental illnesses.  So for example, a hallucination where somebody is perceiving something that isn't actually there; for example hearing a voice when there's nobody around or seeing something that isn't there. Or delusions where they believe very strange things, often very unpleasant things such as their neighbour is trying to kill them or something.  And fMRI offers us a way of putting them into the scanner and looking at how their brain is behaving in this sort of setting.

 MRI machine

Kat -   So, how are you actually doing this in practical terms?  What's your research involving?

Paul -   Well the first thing is, I'm not actually terribly interested in trying to map the hallucination to the brain.  I think that would be a lovely thing to do, but the problem is, if you lie somebody in the scanner, and they're having hallucination, you can get them to indicate when the hallucination occurs, and you can watch what changes in the brain are occurring, but you don't actually know whether those changes are the course of the hallucination which would be very interesting, or whether they're actually a consequence.  For example, if I'm hearing a voice, my brain will respond to that voice even though it's not causing that voice. Or there may be a compensation; so, a hallucination would be very unpleasant and that the changes we see in the brain might actually be a result of somebody trying to suppress the unpleasant thoughts and connotations.  So I'm much more interested in trying to use functional imaging to try and test particular cognitive or psychological models of how the hallucination occurs, what computations in the brain may be disturbed as a prelude to hallucinations or delusions.

Kat -   So you're trying to sort of strip out some of these variables.  How are you actually doing that?

Paul -   Well, we're taking as our starting point an acknowledgement that actually, pretty much all of us live in a fantasy world where we are hallucinating quite a lot of the time.  We're creating our own reality.  The reason being that if we were to try and sample all of our neural inputs at once, all of the sensations that are impinging on our brain, we would be totally paralysed by information.  And a consequence of that is we start to take shortcuts and we start to process the world, not so much as a result of what is there, but of what we expect to be there.  And I think we can think of our brains as being a very delicate balance between what we're predicting to see, or hear, or feel, and what we're actually experiencing through our neural apparatus. And my belief is that we can start to understand some of the symptoms of mental illness by looking at this balance and by acknowledging that there's a very important signal in the brain that almost pervades all neural firing which is the mismatch between what we expect and what we've got, the so-called 'prediction error.'  And so, what we can do is look at how prediction error firing in the brain occurs in people with and without hallucinations and see if that is disordered in some way.  For example, do they appear to show surprise or prediction error by things that should actually be highly predictable or contrarily, do they show an absence of prediction error when there should be something surprising occurring.  So we can use imaging to test this and in so doing, try and understand the basis of these experiences.

Kat -   So I understand that you're using a drug called ketamine to try and make people hallucinate.  My friend have this when he broke his leg.  Doctors gave it to him and he said that the doctors were fine putting his leg back together, but they were all talking backwards.  What can that tell us about hallucinations in the scanner?Ketamine

Paul -   Well, the big advantage of ketamine is that you can control it.  You can control the dose that somebody gets.  You can infuse it, you can keep them at a particular level for a certain amount of time, and you can watch how their brain responds.  You're not reliant on the chance and randomness of normal hallucinatory experiences.  So we use ketamine as a way of producing very temporarily these experiences and seeing what it does to the brain as a way of trying to understand how the hallucinations or delusions might arise in the context of mental illness.

Kat -   And so, what do we think about what is going on in mental illness when people are having these hallucinations and delusions?  What's actually going on in their brain?  What have you found out so far?

Paul -   Well what we seem to be finding is that people with these experiences are actually getting false signals in their brain that the world around them has become surprising, and is sort of baffling their expectations.  They can have very strong expectations about what they're about to see or hear, and even if what they do see or hear actually fulfils those expectations, nevertheless, their brain is telling them that it is wrong.  And so consequently, they have to keep changing their predictions, rebuilding their models of the world, trying to understand the world in new, and evermore often bizarre ways.  And I think there's good evidence emerging across our work and a series of other studies elsewhere that this may be a fundamental deficit in certain mental illnesses.

Kat -   And so, really briefly to touch on this, we sometimes hear about some great creative artists, very creative people who are also judged to be mentally unstable or mentally unwell, do you think maybe that some people who are extremely creative are slightly unhinged in this way that their hallucinations are maybe coming to the surface more?

 Van Gogh's Skull with a Burning Cigarette

Paul -   I think that's a very interesting point and certainly, people have played with that idea.  My own feeling is that up to a point, the sorts of processes that might be deranged in hallucinations and delusions, up to a point, actually, having a slight derangement in those could be advantageous because it might lead you to look at the world in very new, and salient, and original ways that might actually give you insights that perhaps you wouldn't normally get by just predicting the world and it always fulfilling your predictions.  So I think there may be a link there, but I have yet to actually draw it and so, I wouldn't want to speculate too much.

Kat -   Absolutely fascinating then, a line between genius and madness.  That was Cambridge University's Professor Paul Fletcher.

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