Recently, Velakoulis et al1 reported very interesting morphometric findings in a large sample of patients with different psychotic disorders. While patients with chronic schizophrenia displayed bilateral hippocampal volume reduction, patients with first-episode schizophrenia had only left hippocampal volume reduction and patients with schizophreniform disorder did not display hippocampal volume reduction at all. In contrast, patients with first-episode nonschizophrenic psychosis displayed amygdala enlargement. Velakoulis et al stress the possibility that increased amygdala volumes might be a nonspecific marker for the presence of a major affective syndrome rather than a diagnostic endophenotype of a specific nosological entity like, for example, major depression or schizophrenia. We want to support this notion and stress that amygdala enlargement has been reported in quite different neuropsychiatric entities ranging from unipolar and bipolar depression2,3 to dysthymia in epilepsy,4 generalized anxiety disorder,5 or psychosis in epilepsy.6 Amygdala volume reduction, on the other hand, has been reported in entities such as borderline personality disorder,7 patients with epilepsy and aggression,8 patients with schizophrenia,9 or, in fact, patients with depression.10 Like often in psychiatric research, these findings seem to be contradictory and thus frustrating at first glance. However, if a dimensional rather than a categorical approach is chosen, all these findings might be integrated based on the assumption that the amygdala volume status might reflect the dominant mode of emotional information processing. Psychopathological features such as depressed mood, anhedonia, lack of drive, phobic anxiety, and rumination might characterize a mode of emotional information processing that is associated with enlarged amygdala volumes, whereas symptoms like emotional instability, dysphoria, irritability, aggression, and psychotic anxiety might go along with reduced amygdala volumes. Patients with the diagnosis of major depression following DSM-IV or International Statistical Classification of Diseases, 10th Revision criteria might present with symptoms from both poles and thus turn out to have enlarged, normal, or reduced amygdala volumes depending on the composition of the specific sample. This hypothesis might explain why a categorical approach, which is generally chosen in most studies in psychiatry, might result in contradictory findings, whereas a dimensional approach might be able to integrate many seemingly contradictory findings.
Tebartz van Elst L, Ebert D, Hesslinger B. Amygdala Volume Status Might Reflect Dominant Mode of Emotional Information Processing. Arch Gen Psychiatry. 2007;64(2):251-252. doi:10.1001/archpsyc.64.2.251