Limbic changes identified by imaging in bipolar patients.

The hippocampus and amygdala are key limbic regions for memory formation and emotion modulation that are potentially involved in the cognitive and affective symptoms of bipolar disorder. Here we discuss the most consistent MRI literature in bipolar disorder, focusing on the role of the hippocampus and amygdala. In child and adolescent patients, a unique pattern of abnormalities has begun to emerge, with volume deficits in the hippocampus and amygdala already detectable early in the illness course. In adults, it is unclear whether hippocampal volumes are abnormal, whereas the amygdala is reported to be larger and hyperactive to external emotional stimuli. However, available findings are often conflicting, and most studies suffer from limitations. Future longitudinal magnetic resonance studies should focus on juvenile patients; first-episode, drug-free patients; and unaffected family members. Jointly with genetic, postmortem, and neuropsychological studies, these studies will be extremely valuable in separating state from trait brain abnormalities and further characterizing the pathophysiology of bipolar disorder.