By guest blogger Lucy Foulkes

When you see someone laughing hysterically, do you often find yourself laughing too? Laughter is usually extremely contagious. In fact, we are up to 30 times more likely to laugh with someone else than when alone. It’s a powerful bonding tool: we enjoy seeing other people happy, we enjoy laughing with them, and this brings us closer together.

But is this equally true for everyone, or is laughter more contagious for some people than others? For a paper in Current Biology, a team of researchers at UCL, led by Elizabeth O’Nions and César F. Lima, has investigated whether adolescent boys at risk of psychopathy are less likely to find laughter catching.

Psychopathic personality traits include reduced levels of empathy and guilt and a tendency to manipulate. Youths under the age of 18 who show these traits are at increased risk of developing psychopathy in adulthood. If it’s true that these young people find other people’s laughter less contagious or enjoyable than normal, that might contribute to their difficulty in forming close, loving relationships.

The researchers scanned the brains of three groups of boys aged 11-16. One group was “typically developing” – they didn’t show any problem behaviour and weren’t at risk of developing psychopathy. Boys in the other two groups all showed high levels of antisocial behaviour (e.g. violence, theft, destruction of property), and in one group they also showed the personality traits that put them at risk of psychopathy. While their brains were scanned, all the boys listened to audio recordings of laughter. They didn’t have to do anything other than listen to the clips.

The researchers found that both groups of antisocial boys showed reduced brain activity when listening to the clips of laughter, compared to the typically developing boys. The reduced activation was seen in the supplementary motor area – a region that’s important for helping us prepare to make movements and that previous research has shown is more active when we join in with others’ laughter. In addition, the boys at risk of psychopathy showed reduced activity in a part of the brain called the anterior insula, which among other things is involved in processing sounds and linking actions to emotional feelings, and is also known to be activated by hearing other people laughing. So, when listening to the clips, the boys at risk of psychopathy showed the least activation in areas of the brain that process the contagious and enjoyable aspects of others’ laughter.

After the scan, the boys listened to the clips again and rated how much they wanted to join in with the laughter in each recording – this was a subjective measure of how contagious they found the clips. The boys at risk of psychopathy had the least desire to join in, as compared with boys in the other groups. Importantly, the antisocial boys not at risk of psychopathy reported wanting to join in with the laughter just as much as the typically developing group, suggesting that a reduced interest in shared laughter was specific to those with callous, manipulative personality traits.

Individuals with psychopathic traits often bully, hurt and manipulate other people, and do not seem to care about developing close, intimate friendships. This research gives one reason why. For most people, laughing with others is a powerful way of bonding, but this doesn’t seem to be the case for young people at risk of psychopathy. We don’t know whether this muted response to laughter comes first, or whether it’s a consequence of having traits like a lack of empathy; future research that tracks children from a young age might help to figure this out.

Most previous research has focused on how those at risk of psychopathy process other people’s negative emotions. For example, these individuals don’t tend to feel guilty when they make people upset, and find it more difficult to recognize when other people are afraid. This laughter research is an extra piece of the puzzle, showing that they might respond less to other people’s happiness, too. Together, this reduced responsiveness to the emotional experiences of those around them, both good and bad, may help explain the troubling social behavior seen in young people at risk of developing psychopathy.

—Reduced Laughter Contagion in Boys at Risk for Psychopathy

Post written by Dr Lucy Foulkes (@lfoulkesy) for the BPS Research Digest. Lucy is currently working as a postdoctoral research associate in Prof Sarah-Jayne Blakemore’s lab at the Institute of Cognitive Neuroscience on the MYRIAD project – a Wellcome Trust-funded project assessing the feasibility of teaching mindfulness in schools, and the ways in which mindfulness might promote mental health and resilience in adolescents.