Lateralization of emotional expression under a neuroleptic drug

Sixteen student volunteers were administered placebo and 50 mg of chlorpromazine (CPZ) in tablet form, on separate occasions, two hours before testing. Whilst volunteers related pleasant and unpleasant personal life events, the frequency and intensity of expressions on the left and right sides of the face were rated by independent observers. Subsequently the valence of the narration was also rated. Similar to a previous study facial expressions during negative emotions were expressed more often and intensely in the left face but positive emotions were bilaterally represented. CPZ neutralised the emotion on both sides of the face, irrespective of whether it was positive or negative. However, because negative emotions were almost completely lateralised to the left face the drug's effect on this emotion was most pronounced on this side. Independent ratings of the narration of the life events showed CPZ made them more pleasant. It is suggested that emotional arousal increases the asymmetry of behaviours when these are unilaterally represented or controlled. CPZ may equalize the symmetry of behaviour by reducing emotional arousal rather than by blocking all behaviour.