Visual event-related potentials and depression in the elderly

Event-related potentials (ERPs) were recorded during a visual discrimination task from nine elderly individuals (mean=68.1 years), diagnosed as having major depressive disorder, and nine age-matched controls (mean=68.0 years). During the task, subjects pressed a switch to targets (the number 9) and ignored background (the number 6) and novel stimuli (random designs). Novel and target stimuli were both interspersed infrequently in the sequence of background stimuli. Scalp electrical activity was recorded from midline frontal (Fz), central (Cz), and parietal (Pz) sites. Depressives were characterized by lengthened response times and increased number of errors across the session. Speed of response was also found to vary directly with clinical status. Additionally, ERP correlates of depression in the elderly were found: N1 was more prolonged for target than non-target stimuli in the depressed group; P2 was larger for all conditions; N2 was uniformly small across the scalp, whereas the controls showed small N2 amplitudes only at Fz; large P3s appeared in trials following the novel stimuli in the depressed but not in the control group. These results are interpreted in terms of the symptomatology associated with depression (i.e., distractability, impaired short-term memory or concentration, indecisiveness) and possible age-related changes in the ERP scalp distribution.