The Japanese journal of neuropsychology

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ArticleTitle	Hallucinations and delusions: the price we pay for our creative brains
Language	E
AuthorList	Chris Frith
Affiliation	Wellcome Trust Centre for Neuroimaging at University College London, UK; Neils Bohr project, CFIN, University of Aarhus, Denmark
Publication	Japanese Journal of Neuropsychology: 24 (1), 18-29, 2008
Received
Accepted
Abstract	How can a brain abnormality cause hallucinations (false perceptions) and delusions (false beliefs)? The reason is that our brain is not simply a passive recorder of what happens in the world. Our brain uses prior knowledge and expectation to construct models of the physical world. On the basis of these models our brain can predict the crude signals produced by our senses. By testing these predictions and noting the prediction errors our brain can update and improve its models. By acting upon the world we can explore our models and test our predictions even more thoroughly. In these terms there is no difference in principle between perceptions and beliefs: both depend upon a process of updating models of the world on the basis of new evidence with Bayes' theorem providing the underlying computational mechanism. Many hallucinations and delusions can be explained as the consequence of faulty evidence being used to generate models of the world. The mechanism by which we use evidence to discover about the physical world of objects can also be used to discover about the mental world of ideas in the minds of others. However, when modelling other people's minds the process becomes more complex, since, in a true interaction, each person in the dialogue is trying to model the mind of the other. For success in such interactions it is not sufficient to model what is in the other's mind. We must also model what the other thinks is in our mind (closing the loop). The hallucinations and delusions associated with schizophrenia are largely the result of over-activity in the mechanisms used to model the mental worlds of other minds. These symptoms are the price we pay for our creative brains, but without such creativity we would never be able to share ideas with other minds.
Keywords	hallucinations, delusions, schizophrenia, Bayes, perception, action, interatcion, hidden states