The neuropsychology and neuroanatomy of bipolar affective disorder: a critical review

Objectives: To present a comprehensive review of the existing neuropsycholo gical and neuroinlaging literature on bipolar affective disorder. This revi ew critically evaluates two common conceptions regarding the neuropsycholog y of bipolar disorder: 1) that, in contrast to schizophrenia, bipolar affec tive disorder is not associated with general cognitive impairment independe nt of illness episodes, and 2) relative right hemisphere (RH) dysfunction i s implicated in bipolar illness patients, supported by reports of relativel y greater impairment in visuospatial functioning, lateralization abnormalit ies, and mania secondary to RH lesions. Methods: The major computerized databases (Medline and PSYCInfo) were consu lted in order to conduct a comprehensive, integrated review of the literatu re on the neuropsychology and neuroanatomy of bipolar disorder. Articles me eting specified criteria were included in this review. Results: In a critical evaluation of the above notions, this paper determin es that: 1) while there is little evidence for selective RH dysfunction, si gnificant cognitive impairment may be present in bipolar illness, particula rly in a subgroup of chronic, elderly or multiple-episode patients, suggest ing a possible toxic disease process, and 2) the underlying functional corr elate of these cognitive deficits may be white matter lesions ('signal hype rintensities') in the frontal lobes and basal ganglia, regions critical for executive function, attention, speeded information processing, learning an d memory, and affect regulation, While this hypothesized neural correlate o f cognitive impairment in bipolar disorder is speculative, preliminary func tional neuroimaging evidence supports the notion of frontal and subcortical hypometabolism in bipolar illness, Conclusions: The etiology of the structural brain abnormalities commonly se en in bipolar illness, and their corresponding functional deficits, remains unknown. It is possible that neurodevelopmental anomalies may play a role, and it remains to be determined whether there is also some pathophysiologi cal progression that occurs with repeated illness episodes. More research i s needed on first-episode patients, relatives of bipolar probands, and with in prospective longitudinal paradigms in order to isolate disease-specific impairments and genetic markers of neurocognitive function in bipolar disor der.