BRAIN EVENT-RELATED POTENTIALS TO COMPLEX TONES IN DEPRESSED-PATIENTS- RELATIONS TO PERCEPTUAL ASYMMETRY AND CLINICAL-FEATURES

Brain event-related potentials (ERPs) to probe tones in a dichotic com plex tone test were recorded from right-handed depressed patients (n = 44) and normal subjects (n = 19) at homologous sites over left and ri ght hemispheres (F3, F4; C3, C4; P3, P4; O1, O2). There were no differ ences between groups in N1 or P2 amplitude, but patients had smaller P 3 amplitude than did normal subjects. Depressed patients failed to sho w either the left ear advantage or behavior-related hemispheric asymme try of P3 seen for normal subjects. Depressed patients also showed les s difference in hemispheric asymmetry between same and different judgm ents. These findings indicate that the abnormal behavioral asymmetry f or dichotic pitch discrimination in depressed patients reflects a redu ction in hemispheric asymmetry and is related to relatively late stage s of cognitive processing.