Motor asymmetry, a neurobiologic abnormality in the major psychoses.

A century after Kraepelin, clinical scientists still debate whether the major functional psychoses, schizophrenia and bipolar illness, are separate disease entities or fall on opposite ends of a spectrum of severe psychopathology. In a study of control of hand-muscle force, patients with schizophrenia and bipolar affective disorder exhibited opposite asymmetries, with greater right-hand dyscontrol in schizophrenia, and greater left-hand dyscontrol in bipolar disorder. This suggests that there is greater pathological involvement of the dominant hemisphere in schizophrenia and of the non-dominant hemisphere in bipolar disorder.