Differential neural correlates of autobiographical memory recall in bipolar and unipolar depression

Objectives: Autobiographical memory (AM) recall is impaired in both bipolar depression (BD) and major depressive disorder (MDD). The current study used functional magnetic resonance imaging (fMRI) to investigate differences between healthy controls (HCs) and depressed participants with either BD or MDD as they recalled AMs that varied in emotional valence. Methods: Unmedicated adults in a current major depressive episode who met criteria for either MDD or BD and HCs (n=16/group) underwent fMRI while recalling AMs in response to emotionally valenced cue words. Control tasks involved generating examples from a given category and counting the number of risers in a letter string. Results: Both participants with BD and those with MDD recalled fewer specific and more categorical memories than HC participants. During specific AM recall of positive memories, participants with BD showed increased hemodynamic activity in the ventrolateral prefrontal cortex, posterior cingulate cortex, anterior insula, middle temporal gyrus, parahippocampus, and amygdala relative to MDD and HC participants, as well as decreased dorsolateral prefrontal (DLPFC) activity relative to MDD participants. During specific AM recall of negative memories, participants with BD manifested decreased activity in the precuneus, amygdala, anterior cingulate, and DLPFC along with increased activity in the dorsomedial PFC relative to MDD participants. Conclusions: While depressed participants with BD and MDD exhibited similar depression ratings and memory deficits, the brain regions underlying successful AM recall significantly differentiated these patient groups. Differential amygdala activity during emotional memory recall (particularly increased activity in participants with BD for positive AMs) may prove useful in the differentiation of individuals with MDD and BD experiencing a depressive episode.