Differential hemispheric asymmetries in depression and anxiety: a reaction-time study.

Several lines of evidence suggest impaired right hemisphere function in depression. In order to further investigate this phenomenon, simple reaction times (RTs) to lateralized visual stimuli were studied in patients with mild unipolar depression, in patients with chronic anxiety, and in medical patients free of psychiatric symptoms. The results showed a marked slowing of RTs to left visual field (right hemisphere) stimuli in depressed patients. Anxious patients showed a trend toward an opposite asymmetry, with slower responses to right field (left hemisphere) stimuli. In the nonpsychiatric group no visual field differences were present. The results are discussed in light of two alternative interpretations: depression may engage the right hemisphere's mechanisms, interfering with its functioning at a premotor level, or it may influence the regulation of performance by arousal and vigilance mechanisms lateralized to the right hemisphere, possibly operating at an earlier sensory stage.