Depression, Affect and Cognitive Control

Dichter, Felder, and Smoski (2009) investigated limbic-prefrontal interactions in patients with major depressive disorder who were unmedicated by using a target detection task while they underwent fMRI scanning. There were seven fMRI runs, in which the first five runs consisted of a forced-choice target detection task (oddball task) in which in rare cases a target cue did appear that was embedded between changing blocks of neutral and sad pictures. The subjects were given the instruction to press a button with their right hand to all emerging stimuli as quickly as they could for every non target stimulus and with the other for a target stimulus. Behavioral performance was not different among patients and healthy control subjects.The imaging findings revealed that when both conditions were combined, there was no evidence of prefrontal hypo-activation in patients with depression. In contrast, differences among the groups were found related to target events that were embedded in sad or neutral blocks. In the neutral condition, the healthy control subjects exhibited more midfrontal and anterior cingulate cortex activation. In the patients with depression, more prefrontal activity was found in the case of sad embedded stimuli. It is suggested that prefrontal dysfunction in patients with depression might lead to an altered way in sad contexts than in either neutral or baseline contexts. The passive viewing runs showed that patients with depression had larger activation of the left amygdala. This is argued to be supportive of hyperactivity of the amygdala in patients with depression associated with sad pictures causes enhanced prefrontal activation to the target stimuli. Furthermore, the authors state that depressed patients need more cognitive effort to disengage from the sad pictures when responding to target cues (Dichter et al., 2009).