background Valence-specific memory enhancement is one of the core cognitive functions that causes and maintains major depressive disorder (mdd). While previous neuroimaging studies have elucidated the neural underpinnings of this emotional enhancement effect in depressed patients, this study aimed at detecting processing biases that are maintained throughout remission while patients were in an euthymic mood state.
aim First, we investigated valence-specific memory enhancement in remission from depression with fmri. The focus laid on investigating activity within prefrontal cortex (pfc) and medio temporal lobe (mtl). Additionally, we investigated tissue integrity and structural connectivity in md using diffusion tensor imaging (dti).
method Medication-free female patients remitted from depression (mean hdrs = 5.3) in comparison with healthy controls (each n = 14) were scanned during encoding of positive, neutral and negative words in a direct subsequent free recall memory paradigm using event-related fmri (1.5T scanner, standard epi-sequence, optimized for mtl activations). Secondly, standard DTI was performed interleaved with the fmri experiment.
results The two groups did not differ in memory performance and showed no neural differences during successful encoding of neutral or negative words. However, during successful encoding of positive words, patients exhibited a larger recruitment of a set of areas, comprising cingulate gyrus, right inferior- and left medialfrontal gyrus as well as the right amygdala. Moreover, the dti analysis of the mean diffusivity showed lower density in md compared to healthy controls in right and left superior medial gyrus and (small-volume corrected) within the right amygdala.
conclusion Female mdd patients in clinical remission exert greater neural recruitment of memory-related brain regions when successfully encoding positive words, suggesting that neural biases away from positive information do not entirely normalize. These neural activation differences may sensitize former mdd patients to future relapses. This functional effect may be related to structural differences within the frontal and mtl regions.