Why Do We Hallucinate?

Researchers say the idea that hallucinations take place due to the brain’s tendency to interpret the world using prior knowledge and predictions.

19:01 15 October 2015

Scientists at Cardiff University have conducted a study to examine whether the brain creates images of the world that contribute to the development of psychosis. The research, which was published in the journal Proceedings of the National Academy of Sciences, assessed the mental health of 18 people who were showing very early signs of psychosis.

 

The patients together with 16 healthy volunteers were asked to make a sense of vague black and white images. There was a larger performance improvement in people with early signs of psychosis compared to the healthy control group.

 

The University of Cambridge's Naresh Subramaniam said: "These findings are important because, not only do they tell us that the emergence of key symptoms of mental illness can be understood in terms of an altered balance in normal brain functions.

"Importantly, they also suggest that these symptoms and experiences do not reflect a 'broken' brain but rather one that is striving - in a very natural way - to make sense of incoming data that are ambiguous."

 

One of the study's authors, Dr Christoph Teufel, from Cardiff University, said: "Vision is a constructive process - in other words, our brain makes up the world that we 'see'.

 

"It fills in the blanks, ignoring the things that don't quite fit, and presents to us an image of the world that has been edited and made to fit with what we expect."

 

Prof Paul Fletcher of the University of Cambridge said: "Having a predictive brain is very useful - it makes us efficient and adept at creating a coherent picture of an ambiguous and complex world.

 

"But it also means that we are not very far away from perceiving things that aren't actually there, which is the definition of a hallucination."