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 described in core schizophrenia as an expression of left-temporal functional deficits, while higher than normal amplitudes were found in cycloid psychosis. This latter finding appeared to be specific for cycloid psychosis and was explained by a generalized cerebral hyperarousal. Based on some psychopathological analogies with cycloid psychosis, and on the comparable pharmacological treatment of the acute episodes, a group of 19 manic patients was investigated immediately after remission and clinical stabilization of an episode. Patients with psychotic features were excluded to avoid overlaps with cycloid psychosis. Patients showed normal P300 amplitudes and no pathological asymmetries of the field, but more posterior positive areas compared to age- and sex-matched controls. This indicates that the neurophysiological changes underlying mania are different from both core schizophrenia and cycloid psychosis. Based on previous three-dimensional source location studies, this finding indicates that disinhibition due to reduced frontal lobe activity, and not hyperarousal, is the basic functional mechanism of manic disorders.