P300 in major depressive disorder.

This study presents evidence of differences in the P3 (P300) component of the event-related potential (ERP) between major depressed patients and normal controls. ERPs were collected to visual stimuli in a modified continuous performance task. For each subject, the peak of the P3 (also N2 and P2) component was identified for four different electrode sites and three trial types (target, background, and unexpected). P3 amplitude was significantly smaller in the depressed group to target, but not to background stimuli. P3 latency differences were for the most part nonsignificant. Recent evidence suggests that P3 amplitude may not only reflect higher level cognitive functions, but also some degree of emotional involvement for the subject. It is suggested that a decrease in task involvement could account for the smaller P3 in depressives.