Selective impairment in the recognition of anger induced by diazepam

Rationale: Facial expressions appear to be processed by at least partially separable neuro-cognitive systems. Given this functional specialisation of expression processing, it is plausible that these neurocognitive systems may also be dissociable pharmacologically. Objective: The present study therefore compared the effects of diazepam (15 mg) with placebo upon the ability to recognise emotional expressions. Methods: A double blind, independent group design was used to compare the effects of diazepam and matched placebo in 32 healthy volunteers. Participants were presented morphed facial expression stimuli following a paradigm developed for use with patients with brain damage and asked to name one of the six basic emotions (sadness, happiness, anger, disgust, fear and surprise). Results: Diazepam selectively impaired subjects' ability to recognise angry expressions but did not affect recognition of any other emotional expression. Conclusions: The findings are interpreted as providing further support for the suggestion that there are dissociable systems responsible for processing emotional expressions. It is suggested that these findings may have implications for understanding paradoxical aggression sometimes elicited by benzodiazepines.