Early stimulus processing in dysthymia and anhedonia.

Previous event-related brain potential (ERP) research has found that dysthymic subjects differ from control subjects during later stages of information processing. An important issue that emerges from this literature is whether differences found in these ERP components, typically associated with cognitive processing, can be attributed to earlier differences in basic perceptual processing. This study was undertaken to determine whether early processing deficits are apparent in dysthymic persons. Responses of dysthymics (n = 23) were compared with those of anhedonic (n = 15) and normal control (n = 17) subjects. ERPs were recorded while subjects heard tones at 55, 65, 75, 85, and 95 dB. Overall, N1-P1 and N1-P2 components of the ERP increased in a strong linear fashion as stimulus intensity increased. Dysthymics did exhibit a smaller N1-P2 response than normal subjects, which suggests the presence of difficulties in initial perceptual processing.