Event-related potential based evidence of cognitive dysfunction in patients during the first episode of depression using a novelty oddball task.

Studies using event-related potentials (ERP) to investigate cognitive dysfunction associated with depression have generated variable findings. The differences among reported results are typically attributed to the disparity of the samples. To eliminate the effects of factors such as medication and comorbidity with other psychiatric disorders, first-episode unmedicated patients suffering from depression were recruited in this study. Both depressed patients and matched controls performed an auditory novelty oddball task and ERPs were recorded. The depression group exhibited an increased P2 to standard tones. For the target tones, depressed subjects showed reduced N2 at anterior regions and reduced target P3 in the right hemisphere. In response to novel stimuli, there was a reduced amplitude of the novelty P3 component at the fronto-central region in depressed patients. Our findings suggest that patients with depression in the initial stages show an impaired ability in voluntary and involuntary attention and exhibit frontal lobe and right-hemisphere dysfunctions.