Effects of diazepam on facial emotion recognition

Objective: There have been few studies of the pharmacologic modulation of facial emotion recognition. The present study aimed to replicate and extend the finding that recognition of facial anger was selectively impaired by diazepam. The hypothesis was that, in comparison with placebo, diazepam would impair the recognition of facial anger in healthy volunteers, but not the recognition of 5 other basic emotions: happiness, surprise, fear, sadness and disgust. Design: A randomized, counterbalanced, double-blind, placebo-controlled, within-subjects comparison of diazepam with placebo. Setting: A university psychopharmacology research unit. Participants: Healthy male (n = 6) and female (n = 22) volunteers, aged 18-45 years. Procedures: Subjects were tested on 2 tasks following the administration of diazepam, 15 mg, and placebo on separate occasions. In the first "multimorph" task, images of facial expressions were morphed to produce continua between the neutral and full expressions of 6 basic emotions. Accuracy and identification thresholds were assessed for stimuli in which the intensity of expression gradually increased. In the second "emotional hexagon" task, facial expressions were morphed between pairs of emotions. Single images were presented, and accuracy and speed of response were assessed. Results: Diazepam produced broad impairments in response accuracy, recognition thresholds and response speed on the facial emotion tasks that were not limited to angry expressions. Conclusions: The present study found that diazepam, 15 mg, impaired facial emotion recognition, but not selectively. In the emotional hexagon task, a reaction-time analysis suggested that the identification of facial anger might be differentially sensitive to variations in stimulus duration, complicating the interpretation of this paradigm.