Amygdala Morphometry in Affective Disorders

To the Editor: In their interesting review article on hippocampal and amygdala volumetry, Stephanie Campbell, Ph.D., and coworkers (1) reported that inclusion of the amygdala with the hippocampus obscures volumetric findings. However, besides the technical argument, there are other strong points why the amygdala and hippocampus should not be measured as a single structure. Besides the studies mentioned in the review, there are even more reports of increased amygdala volumes in depressive (2, 3) and other (4) affective disorders. Thus, including possibly increased amygdala and decreased hippocampal volumes within one measurement obviously decreases the sensitivity of a method. Besides, the basolateral amygdala is a functionally and anatomically distinct structure (5) that is assessable in a reliable way with modern magnetic resonance imaging technology (6) and should therefore not be mixed up with the hippocampus.

Furthermore, the authors point out that clinical variables, such as duration of illness or presence of abuse, may account for much of the variance of the volumetric findings, whereas factors such as slice thickness or other scan parameters were not so important. However, another confounding clinical factor that might be even more important is medication. There is evidence that psychotropic medication might affect the volume not only of the amygdala (7) but also of the hippocampus (8). Thus, medication should be controlled when we measure amygdala or hippocampal volumes in affective and other neuropsychiatric disorders.