Event-related potentials (ERPs) to hemifield presentations of emotional stimuli: differences between depressed patients and healthy adults in P3 amplitude and asymmetry.

Depression may involve dysfunction of right parietotemporal cortex, a region activated during perception of affective stimuli. To further test this hypothesis, event-related brain potentials (ERPs) were measured in a paradigm previously shown to produce ERP asymmetries to affective stimuli over parietal sites in healthy adults. Pictures of patients with dermatological diseases showing disordered or healed facial areas before (negative) or after (neutral) surgical treatment were briefly exposed for 250 ms to either the left or right hemifield. ERPs of 30 unmedicated, unipolar depressed patients and 16 healthy adults, all right-handed, were recorded from 30 electrodes. A principal components analysis extracted factors which closely corresponded to distinctive ERP components previously reported for this task (N1, N2, early P3, late P3, slow wave). Significant effects of emotional content, i.e. enhanced amplitudes to negative than neutral stimuli, were found for early and late P3. Control subjects showed significant hemispheric asymmetries of emotional processing for late P3 (peak latency 460 ms), with the largest emotional content effects over the right parietal region. In striking contrast to control subjects, depressed patients did not show an increase in late P3 for negative compared to neutral stimuli over either hemisphere and had smaller late P3 amplitude than control subjects. Patients did, however, show larger early P3 (peak latency 330 ms) to negative than neutral stimuli. Results suggest intact early discrimination but abnormal late appraisal of affective content in depression, which may arise from selective inhibition of right parietal regions integral for perceiving and evaluating emotional stimuli.