background Episodic memory impairment is considered to be a cognitive core deficit of Major Depressive Disorder (mdd). It is currently unknown whether this deficit already plays a role in the early course of mdd and whether this deficit is a state or a trait marker of mdd.
aim To answer this question, we probed the neural correlates of episodic memory formation in patients with a first episode of mdd, patients recovered from a first episode of mdd and healthy controls. We specifically aimed at exploring the potential role of the amygdala in forming episodic memories with emotionally neutral content, because there is some evidence that the amygdala exhibits hyperactive responses even to neutral stimuli in depressed subjects.
methods Using event-related fmri, we performed an associative memory task with neutral stimuli while subjects underwent scanning and analysed the data with respect to behavioral performance and neural activity underlying successful versus unsuccessful encoding of stimuli and their appropriate context.
results Both patient groups showed similarly stronger subsequent memory effects in the amygdala when compared to controls. We did not find any differences in memory performance nor hippocampal activity between groups, but there were several anterior and posterior brain regions that show more activity during the depressed state.
conclusion The state related increase in brain regions shown to serve mnemonic processes can best be interpreted in the light of compensatory activity during acute depression. Our amygdala findings provide initial evidence for a neurocognitive trait factor of mdd, which in the early course may be a more important factor than hippocampal dysfunction known to account for memory impairment seen later in the course of mdd.