Emotional and working memory in treatment resistant depression: an fMRI study

1.1 Abstract Neurocognitive deficits and mood-congruent biases have been reported in depression, although there are inconsistencies which may be related to the population studied. We investigated the neural basis of working and episodic memory, including the encoding and retrieval of emotional memories in patients with treatment resistant depression (TRD) on the basis that this population may be more homogeneous and likely to display neurocognitive deficits than an undifferentiated depressed group. Using functional magnetic resonance imaging (fMRI) we compared the behavioural and BOLD signal response of 30 healthy volunteers and 27 medicated TRD patients using the working memory n-back task and an emotional encoding and retrieval pictures task. There was no difference in behavioural performance on the memory tasks. During the n-back task the TRD patients showed a reduced activation of the dorsolateral prefrontal cortex compared to the controls. In the emotional memory task, the TRD group had less activation of the posterior cingulate cortex whilst encoding both positive and neutral images, and reduced anterior cingulate cortex activation whilst retrieving positive images compared to neutral. Whilst retrieving images irrespective of valence, the TRD group demonstrated an increased activation of the posterior insula compared with controls. The decreased activation of the prefrontal cortex during the n-back task was demonstrated here in a treatment resistant population. This study also suggests there is an alteration in the functioning of the cingulate and insular cortex in the encoding and retrieval of positive emotional memories in this group of patients with TRD. Further study is needed to determine whether there is alteration of negative emotional memory processing and what relationship this has to the degree of depression or a failure to respond to treatment.