Hemispheric specialization for emotional expression

It has been hypothesized that the left hemisphere is specialized for positive, and the right for negative, emotional expression. If this hypothesis is correct, the affected hemisphere should be inactive while the opposite, intact hemisphere mediates the abnormal emotional reaction. To help determine if such hemispheric emotional specialization exists, we reviewed videotapes of emotional reactions following unilateral intracarotid amobarbital injections and measured the interval from drug effect to emotional expression. Mean emotional response onset time was 30.2 seconds for positive (laughter) reactions, which were most frequent after right hemispheric anesthesia. Mean onset time was 6.0 seconds for negative (crying) reactions which occurred only after barbiturization of the left hemisphere. Since these onset times are shorter than the period of hemispheric inactivation, results support the hypothesis of left hemisphere specialization for positive, and the right for negative, emotional expression.