Brain imaging and psychiatric disorders (schizophrenia)

Since psychiatric disorders most probably result from abnormalities of brai n function rather than structure the new functional brain imaging technique s are of enormous importance in the study of psychiatric patients, Three ma in approaches have been adopted. First, the pattern of brain activity has b een observed in patients while at rest or when experiencing particular symp toms. The presence of negative features such as poverty of speech and socia l withdrawal tend to be associated with reduced activity in the frontal cor tex, while patients experiencing hallucinations tend to show over-activity in sensory association cortex. Second, the pattern of brain activity has be en observed while patients performs tasks designed to engage particular bra in systems. Abnormal patterns of activity have been observed when patients perform complex problem solving tasks and when they are engaged in auditory imagery. Third, brain imaging has been used to examine hypotheses about th e mechanisms underlying particular symptoms. For example, some symptoms, su ch as delusions of control, may arise from a failure of self-monitoring whi ch results in sensations steming from the patients own actions being respon ded to as unexpected events of external origin. The observation of over-act ivity in relevant brain areas is consistent with this hypothesis. This over -activity may result from disconnections between frontal regions concerned with generating actions and posterior regions concerned with analysis of th e sensory consequences of these actions.