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

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.

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.

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.

Bipolar disorder may be associated with an inherited abnormality of a neural network incorporating left prefrontal cortex and bilateral retrosplenial cortex.