Long before modern brain imaging technologies illuminated the neurophysiological mechanisms that make laughter contagious, William James (1842-1910) observed, "We don't laugh because we're happy, we're happy because we laugh." Although philosophers and psychologists have speculated about the role that laughter plays in social bonding for eons, until recently, there was relatively little empirical evidence that explained why laughter is contagious for most of us. Or, the neural reasons some people are immune to the laughter contagion. That said, in the past few months, researchers have finally pinpointed some neuroscience-based answers to the million-dollar question: "Why is laughter contagious?"

Monkey Business Images/Shutterstock
Source: Monkey Business Images/Shutterstock

Recently, two separate clinical studies investigated the brain mechanisms of genuine, contagious social laughter from different angles. The first study, "Social Laughter Triggers Endogenous Opioid Release in Humans," was published May 28, 2017, in the Journal of Neuroscience. The second study, "Reduced Laughter Contagion in Boys at Risk for Psychopathy," was published online September 28, 2017, in the journal Current Biology

In the first paper, Sandra Manninen and colleagues from the PET Centre in Finland along with researchers from the University of Oxford and Aalto University used positron emission tomography to identify that social laughter leads to endogenous opioid (endorphin) release in specific brain regions. The more opioid receptors a participant had in these regions of his or her brain, the more he or she was prone to contagious laughter.

Before the laughter-gauging brain scans, study participants observed their close friends laughing out loud as they watched comedy clips for 30 minutes. In a separate baseline experiment, the same participants spent 30 minutes alone in a sterile, laughter-free laboratory setting. Contagious social laughter was found to stimulate endorphin release in the thalamus, caudate nucleus, and anterior insula (AI). 

In a statement, Lauri Nummenmaa, who directs the Human Emotion Systems Laboratory at the University of Turku, said: "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." 

Co-author, Robin Dunbar, professor of evolutionary psychology at the University of Oxford, added, "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."

The authors conclude: "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."

Social Laughter Is Less Contagious in Boys at Risk for Psychopathy

 © 2017 Elizabeth O’Nions et al. Published by Elsevier Ltd. September 28, 2017

Neural Responses to Laughter Across All Participants and Differences Between Groups. (A) Responses to genuine laughter versus rest across all participants, N = 93, p < 0.001 peak level uncorrected, family-wise error (FWE) corrected (p < 0.05) at cluster level. (B) Responses to genuine laughter (versus rest) in typically developing (TD) boys versus boys with disruptive behavior and high callous-unemotional (DBHCU) traits.

Source: © 2017 Elizabeth O’Nions et al. Published by Elsevier Ltd. September 28, 2017

Another recent study from University College London (UCL) on contagious laughter corroborates that "human laughter engages brain areas that facilitate social reciprocity and emotional resonance, consistent with its established role in promoting affiliation and social cohesion." The UK researchers also found a link between the anterior insula and contagious laughter. 

However, this study identified that boys who were at risk of developing psychopathy—as marked by high levels of callous-unemotional traits coupled with disruptive social behavior—were less likely to join in with social laughter amongst friends than their "typically developing" peers. They also displayed less anterior insula activity. 

For this study, senior author Essi Viding, professor of developmental psychopathology at UCL, and her team recruited 62 boys aged 11 to 16 who exhibited disruptive behaviors and/or callous-unemotional traits along with a control group of 30 boys who did not display these traits.

Then, the UCL researchers used fMRI neuroimaging to observe brain activity as each boy listened to (1) genuine social laughter, (2) fake laughter, and (3) crying sounds. During these three auditory samples, boys were asked to rate "How much does hearing the sound make you feel like joining in and/or feeling the emotion?" and "How much does the sound reflect a genuinely felt emotion?" on a scale of one to seven. 

Most notably, the researchers found that boys whose disruptive behavior was coupled with callous-unemotional traits were much less likely to respond to genuine laughter. They also displayed significantly less brain activity in the anterior insula and supplementary motor area. 

Although contagious laughter may not register in some boys to the same degree it does with other children, this doesn't necessarily mean these boys are automatically destined to become antisocial. Rather, the researchers hope their latest findings on the neurophysiology of contagious laughter will lead to earlier interventions and more effective treatments for adolescent boys who may be at risk for psychopathy.

References

Caruana, Fausto. "Laughter as a Neurochemical Mechanism Aimed at Reinforcing Social Bonds: Integrating Evidence from Opioidergic Activity and Brain Stimulation." Journal of Neuroscience 37, no. 36 (September 6, 2017): 8581-8582. DOI: 10.1523/JNEUROSCI.1589-17.2017

Manninen, Sandra, Lauri Tuominen, Robin Dunbar, Tomi Karjalainen, Jussi Hirvonen, Eveliina Arponen, Riitta Hari, Iiro P. Jääskeläinen, Mikko Sams, and Lauri Nummenmaa. "Social Laughter Triggers Endogenous Opioid Release in Humans." Journal of Neuroscience (May 23, 2017): 0688-16. DOI: 10.1523/JNEUROSCI.0688-16.2017  

O’Nions, Elizabeth, César F. Lima, Sophie K. Scott, Ruth Roberts, Eamon J. McCrory, Essi Viding. "Reduced Laughter Contagion in Boys at Risk for Psychopathy." Current Biology (Published online September 28, 2017) DOI: 10.1016/j.cub.2017.08.062

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