title: Naltrexone increases negatively-valenced facial responses to happy faces in female participants.
abstract: Positive social cues, like happy facial expressions, activate the brain's reward system and indicate interest in social affiliation. Facial mimicry of emotions, which is the predominantly automatic and unconscious imitation of another person's facial expression, has been shown to promote social affiliation. It has been demonstrated repeatedly that the opioid system is vital to social affiliation in rodents, but there is less evidence in humans. We investigated whether a 50mg administration of naltrexone, an opioid antagonist with highest affinity for the mu-opioid system, modulates emotional mimicry. A passive viewing task with dynamic facial expressions was used in a randomized placebo controlled between-subjects design. Mimicry was measured with electromyography (EMG) on three facial muscles, the corrugator supercilii and the depressor jaw muscle, associated with negatively-valenced emotions, and the zygomaticus major, which is activated during smiling. The results demonstrate an increase of negatively-valenced facial responses (corrugator and depressor) to happy facial expressions after naltrexone compared to placebo, consistent with lowered interest in social interaction or affiliation. Our findings provide evidence for a role of the opioid system in modulating automatic behavioral responses to cues of reward and social interaction, and translate to rodent models of the mu-opioid system and social affiliation.
authors: Department of Experimental Psychology, Utrecht University, Utrecht, The Netherlands. Electronic address: I.M.Meier@uu.nl.
authors: Isabell M
authors: IM
authors: Meier
authors: Department of Experimental Psychology, Utrecht University, Utrecht, The Netherlands.
authors: Peter A
authors: PA
authors: Bos
authors: Applied Cognitive Science and Experimental Neuropsychology Team, Department of Psychology, University of Cape Town, Cape Town, South Africa.
authors: Katie
authors: K
authors: Hamilton
authors: Department of Psychiatry and Mental Health, Groote Schuur Hospital, MRC Unit on Anxiety & Stress Disorders, University of Cape Town, Cape Town, South Africa.
authors: Dan J
authors: DJ
authors: Stein
authors: Department of Experimental Psychology, Utrecht University, Utrecht, The Netherlands; Department of Psychiatry and Mental Health, Groote Schuur Hospital, MRC Unit on Anxiety & Stress Disorders, University of Cape Town, Cape Town, South Africa; Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, South Africa.
authors: Jack
authors: J
authors: van Honk
authors: Applied Cognitive Science and Experimental Neuropsychology Team, Department of Psychology, University of Cape Town, Cape Town, South Africa.
authors: Susan
authors: S
authors: Malcolm-Smith
mesh_terms: D000328:Adult; D004576:Electromyography; D005149:Facial Expression; D005152:Facial Muscles / Q000187:drug effects / Q000502:physiology; D000066499:Facial Recognition / Q000187:drug effects; D005260:Female; D006240:Happiness; D006801:Humans; D007100:Imitative Behavior; D009271:Naltrexone / Q000008:administration & dosage / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors*; D012938:Social Perception; D055815:Young Adult
chemical_list: D009292:Narcotic Antagonists; D017450:Receptors, Opioid, mu; D009271:Naltrexone
keywords: EMG; Mu-opioid system; Naltrexone; Negatively-valenced facial responses; Social affiliation