When P300 parameters were used in patients with depressive disorder, there were conflicting reports as to whether patients displayed reduced P300 amplitude. In depressed patients, half of the studies resulted in reduced amplitude compared with healthy controls (Roth et al. 1986). In patients with anxiety disorder, several studies have suggested that P300 amplitude is reduced compared with healthy controls (Boudarene and Timsit-Berthier 1997; Bauer et al. 2001). Although P300 could have clinical value as a diagnostic tool for psychiatric disorders, it is widely accepted that the clinical value of scalp P300 has been impeded by unsatisfactory test–retest reliability and the existence of overlapping activities in scalp electroencephalography.
