Psychopharmacology (2002) 163:36–41 DOI 10.1007/s00213-002-1120-4 ORIGINAL INVESTIGATION Andrea Zangara · R. J. R. Blair · H. Valerie Curran A comparison of the effects of a b-adrenergic blocker and a benzodiazepine upon the recognition of human facial expressions Received: 12 November 2001 / Accepted: 10 April 2002 / Published online: 29 June 2002 # Springer-Verlag 2002 Abstract Rationale: Accumulating evidence from neu- ropsychological and neuroimaging research suggests that facial expressions are processed by at least partially separable neurocognitive systems. Recent evidence im- plies that the processing of different facial expressions may also be dissociable pharmacologically by GABAer- gic and noradrenergic compounds, although no study has directly compared the two types of drugs. Objective: The present study therefore directly compared the effects of a benzodiazepine with those of a b-adrenergic blocker on theabilitytorecogniseemotionalexpressions. Methods: A double-blind, independent group design was used with 45 volunteers to compare the effects of diazepam (15 mg) and metoprolol (50 mg) with matched placebo. Partici- pants were presented with morphed facial expression stimuli and asked to identify which of the six basic emotions (sadness, happiness, anger, disgust, fear and surprise) were portrayed. Control measures of mood, pulse rate and word recall were also taken. Results: Di- azepam selectively impaired participants’ ability to recognise expressions of both anger and fear but not other emotional expressions. Errors were mainly mistak- ingfearforsurpriseanddisgustforanger.Metoprololdid not significantly affect facial expression recognition. Conclusions: These findings are interpreted as providing further support for the suggestion that there are dissocia- ble systems responsible for processing emotional expres- sions. The results may have implications for under- standing why ‘paradoxical’ aggression is sometimes elicited by benzodiazepines and for extending our psychological understanding of the anxiolytic effects of these drugs. Keywords Benzodiazepine · b-Blocker · Emotion · Emotional expression · Facial expression Introduction Facial expressions appear to be processed by at least partially separable neurocognitive systems (Adolphs et al. 1996; Blair et al. 1999). Neuropsychological and neu- roimaging studies have demonstrated the role of the amygdala in processing fearful expressions. Patients with lesions to the temporal lobe, including the amygdala, often fail to recognise fearful expressions (Adolphs al. 1994; Calder et al. 1996) though not always (Hamann et al.1996;FineandBlair2000).Functionalimagingstudies consistently report increased activation in the left amyg- dala to presentation of fearful expressions (Morris et al. 1996; Phillips et al. 1997). In addition, two neuroimaging studies have indicated that the amygdala is also involved inprocessingsadexpressions(Schneideretal.1995;Blair et al. 1999). As regards expressions of disgust, both basal ganglia and insula, but not the amygdala, have been implicated (Sprengelmeyer et al. 1996; Gray et al. 1997; Phillips et al. 1997). Patients with Huntingdon’s disease, which initially affects the basal ganglia and caudate nucleus, show impaired recognition of the expression of disgust (Sprengelmeyer et al. 1996; Gray et al. 1997). Moreover, recently a patient with an insula lesion has been reported, who showed selective impairment of identifying disgusted expressions (Calder et al. 2000). As regards angry expressions, there is neuroimaging evidence that the orbitofrontal cortex is involved in responding to this emotional signal (Sprengelmeyer et al. 1998; Blair et al. 1999). While current neuroimaging data suggests that the amygdala does not respond to angry expressions(Sprengelmeyeretal.1998;Blairetal.1999), A. Zangara · R.J.R. Blair · H.V. Curran ( ) ) Department of Psychology, University College London, Gower Street, London WC1H 6BT, UK e-mail: v.curran@ucl.ac.uk Tel.: +44-207-6791898 R.J.R. Blair Institute of Cognitive Neuroscience, Alexandra House, 17 Queen Square, London WC1N 3AR, UK H.V. Curran Psychopharmacology Laboratories, Sub-department of Clinical Health Psychology, University College London, Gower Street, London WC1H 6BT, UK