Summary: Researchers uncover how laughter releases endorphins in the brain.

Source: University of Turku.

Finnish and British researchers have revealed how laughter releases endorphins in the human brain. The more opioid receptors the participants had in their brain, the more they laughed during the experiment.

The recent results obtained by researchers from Turku PET Centre, the University of Oxford and Aalto University have revealed how social laughter leads to endorphin release in the brain, possibly promoting establishment of social bonds.

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.

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

Source: Lauri Nummenmaa – University of Turku
Image Source: NeuroscienceNews.com image is in the public domain.
Original Research: Abstract for “Social Laughter Triggers Endogenous Opioid Release in Humans” by Sandra Manninen, Lauri Tuominen, Robin Dunbar, Tomi Karjalainen, Jussi Hirvonen, Eveliina Arponen, Riitta Hari, Iiro P. Jääskeläinen, Mikko Sams and Lauri Nummenmaa in Journal of Neuroscience. Published online May 23 2017 doi:10.1523/JNEUROSCI.0688-16.2017

Abstract

Social Laughter Triggers Endogenous Opioid Release in Humans

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.

SIGNIFICANCE STATEMENT

Social contacts are of prime importance to humans. The size of human social networks significantly exceeds the network that can be maintained by social grooming in other primates. Here we used positron emission tomography to show that endogenous opioid release following social laughter may provide a neurochemical mechanism supporting long-term relationships in humans. Participants were scanned twice; following 30-minute social laughter session, and after spending 30 minutes alone in the testing room (baseline). Endogenous opioid release was stronger following laughter versus baseline scan. Opioid receptor density in the frontal cortex predicted social laughter rates, Modulation of the opioidergic activity by social laughter may be an important neurochemical mechanism reinforcing and maintaining social bonds between humans.

“Social Laughter Triggers Endogenous Opioid Release in Humans” by Sandra Manninen, Lauri Tuominen, Robin Dunbar, Tomi Karjalainen, Jussi Hirvonen, Eveliina Arponen, Riitta Hari, Iiro P. Jääskeläinen, Mikko Sams and Lauri Nummenmaa in Journal of Neuroscience. Published online May 23 2017 doi:10.1523/JNEUROSCI.0688-16.2017

Endorphins (contracted from “endogenous morphine”^{[note 1]}) are endogenous opioid neuropeptides and peptide hormones in humans and other animals. They are produced by the central nervous system and the pituitary gland. The term “endorphins” implies a pharmacological activity (analogous to the activity of the corticosteroid category of biochemicals) as opposed to a specific chemical formulation. It consists of two parts: endo- and -orphin; these are short forms of the words endogenous and morphine, intended to mean “a morphine-like substance originating from within the body”.^[2] The class of endorphin compounds includes α-endorphin, β-endorphin, γ-endorphin, σ-endorphin, α-neo-endorphin, and β-neo-endorphin. The principal function of endorphins is to inhibit the transmission of pain signals; they may also produce a feeling of euphoria very similar to that produced by other opioids.

Endorphins are naturally produced in response to pain, but their production can also be triggered by various human activities. Vigorous aerobic exercise can stimulate the release of endorphins in the bloodstream, leading to an effect known as a “runner’s high”.^[9][10] Laughter may also stimulate endorphin production; a 2011 study showed that attendees at a comedy club showed increased resistance to pain.