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For more than 100 years, scientists have observed that the two hemispheres of the brain appear to differentially contribute to emotion. Most of the observations on the asymmetrical contributions of the hemispheres to emotional phenomena have come from the study of patients with unilateral brain lesions or epilepsy. For example, Jackson (1880) noted that when the emotion of fear “occurs at the onset of a paroxysm... the first spasm is usually on the left side of the body." Goldstein (1939) noticed that patients with left hemisphere damage were more likely to display what has been termed the catastrophic-depressive reaction compared with patients showing comparable right hemisphere damage. More recently, a large number of studies have appeared that compared the emotional reactions of patients with unilateral right and left hemisphere lesions. In the first systematic comparison of such patient groups, Gainotti (1972) confirmed that left hemisphere-damaged patients were more likely to display catastrophic and depressive reactions compared with a matched group of right brain-damaged patients.

These early observations have catalyzed interest in the hemispheric substrates of affective behavior in non-neurological populations. Using noninvasive methods to make inferences about patterns of regional brain activation, investigators began to study hemispheric differences during experimentally aroused emotion and in individuals selected to differ in dispositional affective tendencies. Although many studies have appeared that use behavioral methods to make inferences about asymmetric hemispheric activation during emotion, all suffer from the …