“Although it has taken years to be certain, because not all studies have shown the same results, there is now fairly good agreement that the frontal cortex (which is associated with decision-making and controlling impulsive behavior) shrinks in size when bipolar disorder is allowed to progress. This is basically the same result which has been seen in severe forms of depression which remain untreated.”
“Researchers are homing in on regions of the brain which act differently in people with bipolar disorder compared to those without the illness. Evidence is growing quite strong that a region of the brain called the medial prefrontal cortex is underactive in people with bipolar disorder even when they are having no symptoms at all.”
“In general the picture which seems to be developing here is that people with bipolar disorder are working harder with their emotional centers when doing basic thinking work, compared to those without the illness. This may be some form of compensation for decreased activity in more frontal regions of the brain.”
“. . . It seems like nearly every single person with bipolar disorder I see is unusually creative or intelligent or charismatic or something. Quite a few have been really profoundly intelligent to the point where I have trouble keeping up with their minds.”
For more: PsychEducation
Also recommended:
Bipolar in Order: Advocating for the Mentally Ill 