Memory template comparison processes in anhedonia and dysthymia

Anhedonic subjects, potentially at risk for psychopathology because of a deficient ability to experience pleasure, have demonstrated a large N200 component in the event-related brain potential (ERP). The present experiment attempted to determine the psychological significance of this finding in light of Näätänen's (1990) distinction between N2a and N2b subcomponents. Anhedonics were contrasted with controls and dysthymics, an at-risk group reporting depression. Across groups, N2a was larger when a tone mismatched a longer run of preceding identical tones. Thus, an involuntary mismatch process appears to be intact in both at-risk groups. However, the three groups produced distinct N2bs as a function of stimulus sequence. The N2b finding for anhedonics is consistent with Knight's (1984, 1992) model of early stimulus processing deficits in schizophrenia.