Amygdala and Hippocampal Volumes in Adolescents and Adults With Bipolar Disorder

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Abstract
THE NEUROBIOLOGY of adolescent and adult bipolar disorder (BD) has received little study, although the identification of brain abnormalities associated with early onset and age-related disease progression could help to inform prevention and treatment strategies. Medial temporal lobe abnormalities have been implicated in the pathophysiology of BD by studies of localized lesions, seizure disorders, and neuropsychological test performance. Lesions in this brain region, especially those that produce seizure foci, are associated with episodic symptoms that range from inappropriate elation, grandiosity, distractibility, and hypersexuality to depression, excessive guilt, circumstantiality, and paranoia.1-4 Preclinical observation of the vulnerability of medial temporal structures to sensitization spawned a valuable heuristic model to conceptualize the increased rate of BD cycling as a consequence of the increasing accumulation of multiple, untreated affective episodes.5 The reduction of sensitization by anticonvulsants led to their successful implementation in the treatment of BD.5,6 In adult BD, the impaired recognition of facial affects and the inappropriate emotional biasing of cognitive functions have implicated disturbances in amygdala functioning.7-10 Verbal learning deficits during times of mania and euthymia in adults with BD,11-13 discordant monozygotic twins, and nontwin siblings14,15 implicate a trait deficit in hippocampal functioning.