Bipolar disorder: Anomalous brain asymmetry associated with psychosis

Objective: Anomalous cerebral asymmetry in schizophreniform disorders has b een described, but its presence in psychotic mood disorders has not been es tablished. Measures of cerebral asymmetry may distinguish patients with psy chotic mood disorders from those with nonpsychotic mood disorders and from comparison subjects. To test this hypothesis, the authors examined function al cerebral asymmetry by using a metric based on magnetic source imaging. M ethod: A total of 33 subjects participated. Nine were patients with bipolar I disorder and a negative history of psychotic symptoms during mood disord er episodes, 12 were patients with bipolar I disorder and a positive histor y of psychotic symptoms during mood disorder episodes, and 12 were nonpsych iatric comparison subjects. Equivalent current dipole generators in both he mispheres were estimated for the 20-msec-latency somatosensory evoked field (M20) component produced by stimulation of the contralateral median nerve. Results: The comparison subjects demonstrated asymmetry in anterior-poster ior equivalent current dipole locations of the M20 (right anterior to left) , and the bipolar subjects with no history of psychosis were similarly asym metric. The bipolar subjects with a history of psychosis during mood episod es, however, demonstrated a reversal of cerebral asymmetry of the M20 (left anterior to right). Conclusions: Cerebral lateralization of the M20 distin guished bipolar subjects with psychosis from those without psychosis and co mparison subjects. The M20 is generated in area 3b of the postcentral gyrus . These findings suggest anatomical displacement of the postcentral gyrus i n psychotic disorders and support the hypothesis that anomalous cerebral as ymmetry is a feature of psychotic disorders generally, including psychotic mood disorders.