A functional MRI study of verbal fluency in adults with bipolar disorder and their unaffected relatives.

BACKGROUND: Individuals with a history of bipolar disorder demonstrate abnormalities of executive function, even during euthymia. The neural architecture underlying this and its relationship with genetic susceptibility for illness remain unclear.
METHOD: We assessed 18 remitted individuals with bipolar disorder, 19 of their unaffected first degree relatives and 19 healthy controls using functional magnetic resonance imaging (fMRI) and a paced verbal fluency task with two levels of difficulty.
RESULTS: Bipolar patients made significantly more errors in the easy level of the verbal fluency task than their relatives or controls. Analysis of variance of fMRI data demonstrated a significant main effect of group in a large cluster including retrosplenial cortex and adjacent precuneate cortex (x=7, y=-56, x=15). All three groups showed deactivation in these areas during task performance relative to a neutral or rest condition. Group differences comprised a lesser amount of deactivation in unaffected relatives compared with controls in the easy condition [F(2, 55)=3.42, p=0.04] and in unaffected relatives compared with bipolar patients in the hard condition [F(2, 55)=4.34, p=0.018]. Comparison with the control group indicated that both bipolar patients and their relatives showed similar deficits of deactivation in retrosplenial cortex and reduced activation of left prefrontal cortex.
CONCLUSIONS: Bipolar disorder may be associated with an inherited abnormality of a neural network incorporating left prefrontal cortex and bilateral retrosplenial cortex.