The novelty P3 source was localizable to the midline frontocentral region along the longitudinal fissure and was markedly reduced in depressed patients when compared to healthy controls. Previous work suggests that this reduction reflects a deficit in an early attentional response to novelty, rather than in the later cognitive evaluation of these stimuli. However, the novelty P3 reduction was restricted to the earliest phase of the source at the vertex. In contrast, the subsequent, frontal portion of the midline source, characterizing both target and novel stimuli in this task, was not reduced.
