Prefrontal hypoactivation during working memory in bipolar II depression.
BACKGROUND
Patterns of abnormal neural activation have been observed during working memory tasks in bipolar I depression, yet the neural changes associated with bipolar II depression have yet to be explored.


METHODS
An n-back working memory task was administered during a 3T functional magnetic resonance imaging scan in age- and gender-matched groups of 19 unmedicated, bipolar II depressed subjects and 19 healthy comparison subjects. Whole-brain and region-of-interest analyses were performed to determine regions of differential activation across memory-load conditions (0-, 1- and 2-back).


RESULTS
Accuracy for all subjects decreased with higher memory load, but there was no significant group × memory load interaction. Random-effects analyses of memory load indicated that subjects with bipolar II depression exhibited significantly less activation than healthy subjects in left hemispheric regions of the middle frontal gyrus [Brodmann area (BA) 11], superior frontal gyrus (BA 10), inferior parietal lobule (BA 40), middle temporal gyrus (BA 39) and bilateral occipital regions. There was no evidence of differential activation related to increasing memory load in the dorsolateral prefrontal or anterior cingulate cortex.


CONCLUSIONS
Bipolar II depression is associated with hypoactivation of the left medio-frontal and parietal cortex during working memory performance. Our findings suggest that bipolar II depression is associated with disruption of the fronto-parietal circuit that is engaged in working memory tasks, which is a finding reported across bipolar subtypes and mood states.
Department of Psychiatry & Biobehavioral Sciences,UCLA Semel Institute for Neuroscience & Human Behavior,Los Angeles,CA,USA.
J O
JO
Brooks
Department of Psychiatry & Biobehavioral Sciences,UCLA Semel Institute for Neuroscience & Human Behavior,Los Angeles,CA,USA.
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N
Vizueta
Department of Psychiatry & Biobehavioral Sciences,UCLA Semel Institute for Neuroscience & Human Behavior,Los Angeles,CA,USA.
C
C
Penfold
Department of Psychiatry & Biobehavioral Sciences,UCLA Semel Institute for Neuroscience & Human Behavior,Los Angeles,CA,USA.
J D
JD
Townsend
Department of Psychiatry & Biobehavioral Sciences,UCLA Semel Institute for Neuroscience & Human Behavior,Los Angeles,CA,USA.
S Y
SY
Bookheimer
Department of Psychiatry & Biobehavioral Sciences,UCLA Semel Institute for Neuroscience & Human Behavior,Los Angeles,CA,USA.
L L
LL
Altshuler
D000328:Adult; D001714:Bipolar Disorder / Q000503:physiopathology*; D001921:Brain / Q000503:physiopathology; D001931:Brain Mapping / Q000379:methods; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D017397:Prefrontal Cortex / Q000503:physiopathology*; D015203:Reproducibility of Results
working memory