EFFECTS OF MEDICATION HISTORY ON MIDLATENCY AUDITORY-EVOKED RESPONSESIN SCHIZOPHRENIA

The recovery cycle of the P1 component of the auditory evoked potentia l (50-70 ms latency) has been reported as abnormal in both unmedicated and medicated patients with schizophrenia when a paired stimuli proto col is used to examine recovery. However, findings have been mixed whe n a stimulus train protocol is used. This study examined the effects o f medication history on P1 abnormalities in schizophrenia assessed by a stimulus train protocol. Auditory evoked potentials were recorded fr om 14 normal controls, 14 neuroleptic naive patients with schizophreni a and 14 previously medicated patients in response to binaural clicks presented at three stimulus rates: 1/s, 5/s and 10/s. Neuroleptic naiv e patients showed a smaller P1 at the baseline rate (1/s) and greater recovery (less amplitude suppression) at faster rates than did normal controls or previously medicated patients. Additional analyses suggest ed that this latter effect was not due to smaller baseline P1 amplitud es. Greater recovery in neuroleptic naive patients was not associated with clinical symptomatology contrary to previous findings of the auth ors for a mixed sample of neuroleptic naive and previously medicated p atients. Medication status appears to account for some of the variabil ity in P1 abnormalities in schizophrenia although identification of th e underlying mechanism responsible requires further study.