Left temporal deficit of P300 in patients with schizophrenia: effects of task.

P300 is often, but not always, observed to be more reduced over left than right temporal lobes in patients with schizophrenia. The possibility that task differences contribute to the inconsistency in the literature was explored in this study. ERPs were collected from 17 right-handed men with schizophrenia (DSM-IIIR) and 11 right-handed healthy male community controls, performing three auditory oddball tasks - respond to a target tone by: (1) counting; (2) pressing a response button with the right index finger; or (3) pressing a response button with the left index finger. Although patients with schizophrenia had smaller and later P300 amplitudes than controls, they did not have smaller P300s over the left temporal scalp (T3) than over the right (T4). P300 recorded over the left (C3) and right (C4) motor cortices indicated sensitivity to responding hand, with greater negativity being associated with contralateral button pressing. Failure to find P300 asymmetry is not related to the presence or absence of a button pressing task, or the hand used for button pressing. Rather, P300 asymmetry may be related to structural neuroanatomical asymmetries.