In contrast, prior studies have found evidence that novelty P3 or P3a is increased in anxiety disorders. Patients having an anxiety disorder (primarily social phobia or panic disorders; n = 22) showed an abnormally large early P3 potential with a frontocentral topography resembling P3a (Bruder et al., 2002), and patients having a post-traumatic stress disorder (n = 24) showed larger P3 to novel sounds at frontal sites when compared to controls (Kimble et al., 2000). The opposite P3a or novelty P3 abnormality in depressive and anxiety disorders suggests a possible relation to specific symptom features. This is supported by the findings of Partiot et al. (1993), who measured ERPs during a simple go/no-go reaction-time task and found that a subgroup of depressed patients with retarded and blunted affect had reduced frontal P3a amplitude when compared to a subgroup with anxious–agitated symptoms. We did not, however, find evidence of a relation between amplitude of novelty or target P3 and severity of depression or anxiety ratings in patients. This suggests that the diagnostic category or subtype of depression is more closely related
