background Recently, the frequently found increased memory sensitivity for negative stimuli in acutely depressed patients has been associated with an over-activation of the amygdala- hippocampus and/or amygdala-caudateputamen system.
aim To investigate whether these behavioral memory biases and associated neural overactivations are maintained when being remitted from depression.
methods We investigated medicationfree patients remitted from maximal three episodes of depression (mean hdrs=4.9) in comparison with healthy controls (each n=14) using event-related fmri (1.5T scanner, standard epi-sequence, optimized for mtl activations). Subjects were scanned during encoding of positive, neutral and negative words in a direct subsequent free recall memory paradigm.
results There were no behavioral differences in subsequent memory performance between patients and controls. A general comparison of neural activity (whole brain: p<0.001 uncorrected) for later remembered and later forgotten words confirmed previous findings of engagement of left amygdala and bilateral hippocampus in emotional memory formation in both groups. An interaction of group x valence x memory gave rise to significant effects in left amygdala and right caudate-putamen (p<0.001 small volume corrected). Inspection of the contrast estimates suggests that the interaction in the left amygdala mainly arose from a larger subsequent memory effect to negative words in the patient group.
conclusion Even in clinical remission formerly depressed female patients still show neural processing biases during memory formation for negative words. These neural activation differences may sensitize former mdd patients to future relapses. Implications will de discussed in relation to the cognitive bias theories on the one hand and the other trait-related fmri findings presented during this symposium.