Studies examining P3 subcomponents in depressed patients could therefore provide new information concerning the specific nature of their cognitive deficit and the underlying neurophysiologic mechanisms. In a study recording ERPs during two-stimulus tonal and phonetic oddball tasks (Bruder et al., 2002), we used principal components analysis (PCA) to identify and measure overlapping P3 subcomponents in patients having a depressive disorder alone (n = 58), an anxiety disorder alone (n = 22), comorbidity of these disorders (n = 18), and healthy controls (n = 49). An early P3 subcomponent (peak latency 315 ms) was larger in patients having an anxiety disorder alone when compared to depressed patients or healthy controls. Depressed patients having a comorbid anxiety disorder tended to have a smaller early P3 than healthy controls, but those having a depressive disorder alone did not. The timing and frontocentral topography of this early P3 subcomponent resembled that seen for P3a. A later positive subcomponent (peak latency 400 ms) with a parietal maximum did not differ between patients having a depressive disorder alone and controls, but was larger in depressed patients having a comorbid anxiety disorder when compared to the other groups.
