Salience and psychosis

Dr. Shitij Kapur is a psychiatrist-neuroscientist at the University of Toronto. He is articulate and creative. Among a number of contributions to a better understanding of psychosis, he has recently proposed a model of psychosis that focuses on the concept of ‘salience’.

Salience, in this model, is defined as a determination, by the brain, as to the relevance, to the person (organism), of any mental experience. Some mental experiences are significant, others are not. The latter can be ignored.

Experiences that are salient, on the other hand, are added to our conceptual framework, our understanding of the world, our beliefs about what is happening.

The heart of Kapur’s model is the idea that psychosis arises from a relative inability of the brain to determine salience. The brain can’t tell the differences between relevant and irrelevant information. There are obvious implications of this inability on the resulting conceptual frameworks, our belief systems.

Let’s look at a simple example. Walking down the street I notice a man sitting in a car, smoking a cigarette. A moment later a woman walks past the car, stops and answers a call on her cell phone. I think nothing of it; no salience to me.

But suppose I couldn’t tell if those two events were salient or not and I assumed, therefore, that they might be. This could start me off a train of thought and speculation. To begin, if these experiences are salient, there must be some reason, related to me, that the man is in the car as I walk by. Was he there to watch me? Was it the man in the car who called the woman? If so, are they working together to spy on me? As you can see, I am well on my way to paranoid delusional system, a belief system that is based on fundamentally flawed ‘evidence’; evidence that is flawed because I am unable to determine salience.

It is interesting that Kapur’s model proposes that psychotic experiences, delusion beliefs in this case, are actually formed in exactly the same way as non-psychotic beliefs. The only difference is that delusions incorporate experiences (information) that are not actually relevant (salient).

One clinical implication is that the person who has formed the delusional belief is as sure that it is true as they are about any non-psychotic belief they hold. Why shouldn’t they be; the belief was formed through the same process.