Distinct neurophysiological mechanisms for manic and cycloid psychoses: evidence from a P300 study on manic patients

Pathologically asymmetrical P300 fields with right lateralized peaks were d escribed in core schizophrenia as an expression of left-temporal functional deficits, while higher than normal amplitudes were found in cycloid psycho sis. This latter finding appeared to be specific for cycloid psychosis and was explained by a generalized cerebral hyperarousal. Based on some psychop athological analogies with cycloid psychosis, and on the comparable pharmac ological treatment of the acute episodes, a group of 19 manic patients was investigated immediately after remission and clinical stabilization of an e pisode. Patients with psychotic features were excluded to avoid overlaps wi th cycloid psychosis. Patients showed normal P300 amplitudes and no patholo gical asymmetries of the field, but more posterior positive areas compared to age- and sex-matched controls. This indicates that the neurophysiologica l changes underlying mania are different from both core schizophrenia and c ycloid psychosis. Based on previous three-dimensional source location studi es, this finding indicates that disinhibition due to reduced frontal lobe a ctivity, and not hyperarousal, is the basic functional mechanism of manic d isorders.