Journal Article

Perceiving is believing: a Bayesian approach to explaining the positive symptoms of schizophrenia

Frith, Chris D., Fletcher, Paul C.

2009

Overview

Key Points Hallucinations (false perceptions) and delusions (bizarre beliefs) are characteristic symptoms of schizophrenia and other psychotic illnesses. In order to understand how disturbances in brain function may give rise to these complex symptoms, we require cognitive neuroscientific models of the normal processes that are involved in perception and belief. Existing models treat perception and belief separately, leading to a need for a two-factor theory proposing that both are deranged in schizophrenia. We suggest that recent advances invoking Bayesian theory in cognitive neuroscience offer a way of considering perception and belief as arising from the same process: error-dependent updating in a hierarchical Bayesian structure. Within the framework of this Bayesian model, one can consider both hallucinations and delusions as emerging owing to disruptions in the same updating mechanism, without the need to posit coincident deficits in two separate systems. According to this model, disruptions in prediction-error firing from lower-level systems in the hierarchy require higher-level systems to reject and change inferences in order to accommodate this error signal. At lower levels this may lead to false perceptions but, if it continues, new and more bizarre beliefs will emerge because of a continued sense that the world is not well predicted or modelled by previous beliefs. Hallucinations and delusions are striking features of schizophrenia that have been difficult to explain. Fletcher and Frith discuss cognitive theories of the positive symptoms of schizophrenia and describe how abnormalities in error-dependent learning could underlie both hallucinations and delusions. Advances in cognitive neuroscience offer us new ways to understand the symptoms of mental illness by uniting basic neurochemical and neurophysiological observations with the conscious experiences that characterize these symptoms. Cognitive theories about the positive symptoms of schizophrenia — hallucinations and delusions — have tended to treat perception and belief formation as distinct processes. However, recent advances in computational neuroscience have led us to consider the unusual perceptual experiences of patients and their sometimes bizarre beliefs as part of the same core abnormality — a disturbance in error-dependent updating of inferences and beliefs about the world. We suggest that it is possible to understand these symptoms in terms of a disturbed hierarchical Bayesian framework, without recourse to separate considerations of experience and belief.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: Adult and adolescent clinical studies / Animal Genetics and Genomics / Bayes Theorem / Behavior modification / Behavioral Sciences / Biological and medical sciences / Biological Techniques / Biomedical and Life Sciences / Biomedicine / Brain / Brain - pathology / Brain - physiopathology / Care and treatment / Cognition & reasoning / Cognition - physiology / Diagnosis / Dopamine / Electrodiagnosis. Electric activity recording / Hallucinations / Hallucinations and illusions / Humans / Investigative techniques, diagnostic techniques (general aspects) / Medical sciences / Medical screening / Methods / Models, Neurological / Nervous system / Neurobiology / Neurosciences / Patients / Perception - physiology / Perceptions / Physiology / Psychology. Psychoanalysis. Psychiatry / Psychopathology. Psychiatry / Psychoses / review-article / Risk factors / Schizophrenia / Schizophrenia - physiopathology / Schizophrenic Psychology