Working memory in recurrent brief depression: an fMRI pilot study

Background: We examined women with recurrent brief depression (RBD) with and without episodes of hypomania with an n-back working memory paradigm to assess how working memory load affects the neurological network corresponding to working memory for these groups.

Method: Participants (n=33) were medication-free and mostly euthymic while performing a 1-back and a 2-back task in the fMRI scanner. Differential activation results between the tasks were assessed globally and within seven predefined regions of interest associated with working memory activation. The patient groups were compared with healthy women and matched for age, handedness, and length of education.

Results: Poor task modulation was observed in both RBD groups in the prefrontal cortex (BA9) in the 1-back task and activation during the 2-back task, particularly in a subgroup with a history of brief hypomanic episodes (RBD-H) compared with the subgroup without such episodes (RBD-O). Task modulation in the right parahippocampal gyrus (BA27) distinguished the RBD-O group, and task modulation in the right insula clearly distinguished the RBD-H group.

Limitations: Small sample size and recruitment of most patients through media that may induce a selection bias towards better-functioning subjects.

Conclusion: The observed lack of deactivation within the right insula has also been reported in patients with bipolar I disorders. Activation differences in BA9 and the parahippocampal region between RBD patients with and without a history of hypomania suggest different functional hypersensitivity of early limbic regions and ability to sustain attention and working memory, respectively, possibly identifying functional differences between the two subgroups.