81. A cognitive, perceptual, and motor study of hemispheric asymmetry in the major psychoses

Studies have demonstrated asymmetric hemispheric dysfunction in patients with schizophrenia and bipolar disorder. However, few studies have compared directly the dysfunction in schizophrenia to that of bipolar disorder, and few have studied hemispheric asymmetries across modalities, which could address regional specificity of lateralized hemispheric dysfunction. We assembled a battery of assessments designed to measure lateralized hemispheric function of the following modalities: sensory information processing and arousal (dichotic listening, chair identification, consonant-vowel-consonant test), memory (Warrington recognition memory test), and motor (hand force instability, velocity scaling, reaction time). To date, 19 right-handed male patients with schizophrenia (N 5 11) and bipolar disorder (N 5 8) have been assessed to determine whether differences in lateralized performance appear across multiple modalities. Effect sizes between diagnostic groups were large for L-R (left minus right) scores for chair identification and velocity scaling and medium for hand force instability. In measures purported to reflect dopaminergic tone (velocity scaling and hand force instability), schizophrenia patients showed diminished right hemispheric function relative to the left, whereas bipolar patients showed diminished left hemispheric function relative to the right. In a measure purported to reflect hemispheric arousal (chair identification), the reverse was true: schizophrenia patients showed diminished left hemispheric function relative to the right, whereas bipolar patients showed diminished right hemispheric function relative to the left. These findings support the literature demonstrating a hemispheric imbalance in schizophrenia and bipolar disorder. They also suggest the possibility that the hemispheric dysfunction in psychosis is complex and may be related to either increased activity in one hemisphere or decreased activity in the other hemisphere. They also indicate that there may exist different mechanisms of hemispheric control, one responsible for motor activity and another for arousal.