A recent study published in the journal Current Biology examines how children at risk of psychopathy respond to laughter. The research was led by Essi Viding, a professor of developmental psychopathology at University College London in the United Kingdom.

As the Prof. Viding explains, “Psychopathy is an adult personality disorder. However, we do know from longitudinal research that there are certain children who are at a higher risk for developing psychopathy.”

Such children exhibit two main personality traits: they are likely to be disruptive and show “callous-unemotional traits.”

In the new study, the researchers screened for these traits and hypothesized that the children displaying them would also be somewhat “immune” to the social contagion that accompanies laughter. They looked at this hypothesis on both a behavioral and a neural level.

Prof. Viding explains the motivation for the study in the context of existing research, saying, “Most studies have focused on how individuals with psychopathic traits process negative emotions and how their lack of response to them might explain their ability to aggress against other people.”

“This prior work is important,” she adds, “but it has not fully addressed why these individuals fail to bond with others. We wanted to investigate how boys at risk of developing psychopathy process emotions that promote social affiliation, such as laughter.”

Studying laughter contagion in children

To do so, Prof. Viding and team examined the behavioral and neural response to laughter in 32 boys aged 11 to 16 who displayed callous-unemotional traits and disruptive behavior, as well as in 30 boys with disruptive behavior but who scored low for unemotional traits.

The scientists also examined 31 control children who did not display any psychopathy risk factors. These were of the same age, ethnic makeup, and socioeconomic background as the risk group. The controls were also matched for left- or right-handedness and IQ.

Using functional MRI, the researchers examined the brain activity of these children while they listened to genuine laughter, “fake” laughter, and crying sounds as distractors.

To assess their behavioral responses, the boys were asked to answer the questions, ”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?” using a scale from 0 to 7.

The former question was designed to measure subjective laughter contagion, and the latter measured the ability to emotionally discern authentic laughter from fake laughter.

It was found that children who exhibited both risk factors for psychopathy reported a much weaker desire to join in with the laughter compared with the control group, and with the boys who were disruptive but did not have the callous-unemotional trait.

Also, the boys who exhibited both risk factors for psychopathy showed decreased brain activity in two regions: the anterior insula and the supplementary motor area.

As the authors explain, previous neuroimaging studies have shown that hearing laughter tends to activate “motor and premotor areas,” as the brain prepares for vocalizations of laughter – namely, joining in.

These areas represent “a neural mechanism for experiencing these emotions vicariously and promoting social connectedness,” the authors write.

‘Social cues do not register in the same way’

Prof. Viding cautions that the study cannot establish causality. However, she does say that the findings should prompt further research into how children at risk of psychopathy and antisocial personality disorder display or relate to social affiliation.

The researchers are also interested in how caregiving relates to social connectedness in these children, suggesting that poor caregiving may lead to poor social affiliation. In this sense, the authors emphasize the need for longitudinal research that follows the development of these children over time.

They would also like to investigate how boys at risk of psychopathy respond to smiling faces or displays of affection.