Amygdala Function in Major Depressive Disorder (MDD)

Studies link dysfunction in brain regions like the amygdala with clinical depression. Identifying functional abnormalities is a step toward greater understanding and treatment of MDD. 15 unmedicated depressed men and women (Hamilton Depression > 18) and 15 age and gender matched control subjects participated. Subjects underwent fMRI scanning on a Siemens Allegra 3T scanner. BOLD functional images were acquired while subjects performed a task shown to activate the amygdala in normal subjects. The tasks consisted of two conditions—requiring either the matching of (MvR) or identification of (IdvR) emotional faces. We analyzed the results of activation patterns within the groups and between groups. Signal changes were specifically evaluated in our region of interest (ROI), the amygdala. Results revealed activation in the amygdala and BA47, a frontal region involved in emotion regulation, within depressed and control groups. There were no significant between-group differences in MvR. Results from amygdala ROI analysis showed no differences in percent activation during MvR, but significant differences (Control > Depressed) were found in IdvR. The variance in amygdala ROI values in MvR was significant, but anxiety did not account for this as there was no difference between anxious (n=6) and nonanxious (n=9) depressed subjects in this region. However, other regions like the insula and BA47 showed differential activation between the anxious and non-anxious depressed subjects. Our data support more subtle differences in amygdala functioning in depressed subjects than previous reported. Most prior studies involved medicated patients, which may explain such differences. Anxiety symptoms produced differences suggesting a decrease in regulatory control over somatic symptoms in these patients. Future larger studies might reveal further differences in unipolar depression subgroups from controls.