Abnormal cerebral laterality in bipolar depression: convergence of behavioral and brain event-related potential findings.

Cerebral laterality in bipolar and unipolar major depression was compared using visual half-field and dichotic listening measures of perceptual asymmetry. The results replicate our prior finding of abnormal laterality in bipolar depressed patients on a visuospatial test. Bipolar patients (n = 11) failed to show the left visual field (right hemisphere) advantage for dot enumeration seen for both unipolar patients (n = 43) and normal controls (n = 24). Bipolar patients performed significantly poorer than unipolar patients on normal controls for left visual field, but not right visual field stimuli. An electrophysiological correlate of abnormal visual field asymmetry in bipolar depression was found in brain event-related potentials recorded during audiospatial and temporal discrimination tasks. Bipolar patients had smaller N100 amplitudes for test stimuli in the left than right hemifield, whereas unipolar patients and normals did not. The origins of left hemifield deficits in bipolar depression are discussed in terms of right-sided dysfunction of an arousal/attentional system involving temporoparietal and possibly frontal regions.