New study links brain activity, learning and delusions
Delusions are odd beliefs about the world. They accompany a number of psychiatric illnesses, in particular schizophrenia. A major challenge is to understand delusions in terms of changes in brain function. A team of scientists from the University of Cambridge Behavioural and Clinical Neurosciences Institute, supported by a joint award from the Medical Research Council and the Wellcome Trust, have published new evidence linking delusions to the psychological processes and brain functions that underpin how we normally develop ‘beliefs’. The scientists believe that malfunction in a normal process called ‘prediction error’, which is crucial for establishing a rational view of events in the world, may be at least partly responsible for delusions.
When surprising things happen in the world, human beings try and work out their cause. This means that when the same events occur again, we are more capable of predicting what will happen and respond appropriately. This process involves updating our beliefs about the world, which is driven by the amount of surprise or ‘prediction error’ that we experience.
Dr. Philip Corlett and Dr. Paul Fletcher, working with colleagues in Addenbrooke’s Hospital in Cambridge as well as collaborators from University College London attempted to link prediction error to delusion formation. They measured the brain responses of healthy individuals to prediction errors and then transiently induced delusions in those same subjects with the anaesthetic drug ketamine, which at low doses can temporarily cause delusions. Dr Corlett’s study, published in the journal Archives of General Psychiatry (link to paper), showed that across subjects in the study, responses to prediction errors in the prefrontal cortex of the brain predicted the severity of delusions suffered by those same subjects when they were administered ketamine.
This study suggests that people with delusions might form their odd beliefs because they experience prediction errors when they shouldn’t, meaning that their world feels unexpected and surprising. Delusions are formed as a way of explaining away these inappropriate feelings of surprise.
Dr Corlett said, “We think that this is an important result because it provides us with a working model of delusion formation, which means that we might be able predict vulnerability to delusions in those at high risk of psychosis and improve their prognosis.”
