Psychosis: when brains overrate new information
New evidence has emerged for the origin of psychosis. This is a mental condition where people lose touch with reality; they hear or see things that aren’t there, and develop irrational delusions. And although many people suffer from it, the underlying mechanism in the brain that causes these experiences isn’t known. But now scientists at the University of Cambridge have discovered that it may be down to how the brain processes new information. Phil Sansom and Chris Smith heard more from author Joost Haarsma...
Joost - Now, what we found in our study is that the brains of people who have recently had a psychosis cannot distinguish reliable from unreliable information to the same extent that healthy people do. And we, furthermore, also found that an important messaging system in the brain, called the dopamine system plays a really important role in distinguishing reliable from non-reliable information. And this latter finding is really crucial. As we know, from previous studies, that the dopamine system tends to be disturbed in psychosis.
Phil - What is this psychosis, exactly? So I can get it clear in my head. What does it lead to?
Joost - Psychosis is a term that doctors use to describe a collection of symptoms. Someone might start to hear voices inside of their head or see things visually that are not actually there. Patients often also start to form very unlikely and improbable beliefs that are often also very distressing. So for example, they might start to think that the secret services are out to get them. So it might induce some state of paranoia. And these symptoms, they are common in a wide range of psychiatric and neurological disorders. It happens in something like schizophrenia, as you mentioned before, but they're also common in Parkinson's disease, they can occur after taking certain drugs. And also it can occur after a prolonged sleep deprivation.
Phil - Now, how were you actually looking at people with psychosis to figure out what might be behind it?
Joost - We invited a group of individuals that recently had an episode of psychosis, and some of these people still struggled with some of the symptoms of it. We invited them over to come and do a few experiments where they needed to learn about new information, where we as experimenters varied whether it was reliable or not. And importantly, when they were doing this task, they were lying in something, what we call an MRI scanner, which is basically a big magnet. Then in combination with radio pulses allow neuroscientists like me to look inside the brain, and study how the brain actually takes to account its reliability
Chris - And Joost, how do you know that dopamine is involved? And what does it actually do?
Joost - In our study, we also had a separate group of people who are healthy, that we then gave a drug that alters how to dopamine system in their brain functions. So this is our route to our evidence. And what we think it actually does in the brain, when we learn about the world, we signal, these signals in the brain, what we call error signals, which basically tell us how wrong we were. And when we think we are wrong, that signal should be stronger. And we think that dopamine scales this signal up. So that signal then has more of an influence on how we change our mind in the future.
Chris - Would the hypothesis be, then, if you take a person and you block up, give drugs that block dopamine in the same way that we give these sorts of drugs to people who have psychosis, if you Rob the brain of that dopamine signal, do they become equally bad at judging the value? Cause they haven't got the dopamine there to judge the value of the misinformation.
Joost - So this is what we've done in our study with the healthy individuals, we gave them a drug that blocks at least certain dopamine receptors, and indeed, what we found in their brain, they're not able to take into account reliability of information anymore. And what we've done in a study as well, we also gave a drug that amplifies the dopamine system. And the evidence was a little bit less clear there. But if we amplify the dopamine system, all information seems to become more important.
Chris - Now people, when we treat them, who have psychosis, and we give them dopamine blocking drugs, these drugs often have horrible side effects. They cause movement disorders and many other manifestations because dopamine is a multipurpose neurotransmitter in the brain, isn't it? Does your research shed any light on how we might be able to be more targeted with our treatments, so we can help people with their psychosis, but not rob them of their other faculties.
Joost - I think that is rather difficult to do. I think it's in the nature of giving people certain drugs, that you tend to have very global effects in the brain. The thing that we looked at in the brain was a specific region in the brain. It's kind of, if you put your hands on your head and put them somewhere in the middle, it's in that part of the brain that we found this effect. But if you take a drug, it's going to have an effect on all other parts of the brain as well.
Chris - So this study adds understanding and corroboration of a theory. But at the moment we can't say that this is going to make the lot of someone who has psychosis any better.
Joost - I wouldn't be that pessimistic. If you are seeing a patient and a couple of months ago, they had a psychotic episode, until recently the only explanation a psychiatrist might say is that perhaps something is going wrong in your dopamine system. And that's why you had the psychosis, but it's not really an explanation. So it at least allows psychiatrists to give them a more full explanation of how it can be that a brain starts to form these beliefs that can be so distressing.