Endorphin release from social laughter to support social bonds

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Finnish and British research reveals how the endorphin release induced by social laughter may be an important pathway that supports formation, reinforcement, and maintenance of social bonds between humans.

The results were obtained by researchers from Turku PET Centre, the University of Oxford and Aalto University .

Social laughter led to pleasurable feelings and significantly increased release of endorphins and other opioid peptides in the brain areas controlling arousal and emotions. The more opioid receptors the participants had in their brain, the more they laughed during the experiment.

“Our results highlight that endorphin release induced by social laughter may be an important pathway that supports formation, reinforcement, and maintenance of social bonds between humans. The pleasurable and calming effects of the endorphin release might signal safety and promote feelings of togetherness. The relationship between opioid receptor density and laughter rate also suggests that opioid system may underlie individual differences in sociability,” says Professor Lauri Nummenmaa from Turku PET Centre, the University of Turku.

“The results emphasise the importance of vocal communication in maintaining human social networks. Other primates maintain social contacts by mutual grooming, which also induces endorphin release. This is however very time consuming. Because social laughter leads to similar chemical response in the brain, this allows significant expansion of human social networks: laughter is highly contagious, and the endorphin response may thus easily spread through large groups that laugh together,” says Professor Robin Dunbar from the University of Oxford.

The study was conducted using positron emission tomography (PET). The participants were injected with a radioactive compound binding to their brain’s opioid receptors. Radioactivity in the brain was measured twice with the PET camera: after the participants had laughed together with their close friends, and after they had spent comparable time alone in the laboratory.

The research was funded by the Academy of Finland and the European Research Council.

Abstract
The size of human social networks significantly exceeds the network that can be maintained by social grooming or touching in other primates. It has been proposed that endogenous opioid release following social laughter would provide a neurochemical pathway supporting long-term relationships in humans (Dunbar, 2012) yet this hypothesis currently lacks direct neurophysiological support. We used positron emission tomography (PET) and μ-opioid-receptor (MOR) specific ligand [11C]carfentanil to quantify laughter-induced endogenous opioid release in 12 healthy males. Before the social laughter scan, the subjects watched with their close friends laughter-inducing comedy clips for 30 min. Before the baseline scan, subjects spent 30 min alone in the testing room. Social laughter increased pleasurable sensations and triggered endogenous opioid release in thalamus, caudate nucleus, and anterior insula. In addition, baseline MOR availability in the cingulate and orbitofrontal cortices was associated with the rate of social laughter. In a behavioral control experiment, pain threshold — a proxy of endogenous opioidergic activation — was elevated significantly more in both male and female volunteers after watching laughter-inducing comedy vs. non-laughter inducing drama in groups. Modulation of the opioidergic activity by social laughter may be an important neurochemical pathway that supports formation, reinforcement, and maintenance of social bonds between humans.

Authors
Sandra Manninen, Lauri Tuominen, Robin Dunbar, Tomi Karjalainen, Jussi Hirvonen, Eveliina Arponen, Riitta Hari, Iiro P Jääskeläinen, Mikko Sams, Lauri Nummenmaa

University of Turku material[/link]
Journal of Neuroscience abstract


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