Mapping the differential impact of spontaneous and conversational laughter on brain and mind: A fMRI study in autism

Abstract

Abstract Background While most research on the non-verbal communication challenges encountered by autistic people centres on visual stimuli, non-verbal vocalizations remains overlooked. Laughter serves as a socio-emotional signal for affiliative bonding in interactions. Autistic people seem to experience and produce laughter differently to non-autistic people and are known to have mentalizing difficulties. Neuroimaging evidence suggests that non-autistic people engage in mentalizing to understand the meaning behind conversational laughter. Here, we propose that autistic people’s difficulties lie not in processing all types of laughter, but only in processing conversational laughter. Methods We used fMRI to explore the neural mechanisms underlying implicit processing of different types of laughter in autistic and non-autistic adults. 23 autistic and 23 non-autistic adults matched for age, gender, and IQ were scanned whilst passively listening to funny words followed by spontaneous laughter, conversational laughter, or noise-vocoded vocalizations. Post-scan, they listened to the word plus laughter pairs again and rated the funniness of each word. Results Behaviourally, words plus spontaneous laughter were rated as funnier than words plus conversational laughter, and the groups did not differ. However, neuroimaging results showed increased activation in the medial prefrontal cortex only for non-autistic adults during implicit processing of words plus conversational laughter. Additionally, autistic adults showed greater activation in the supplementary motor area, a part of the sensorimotor network, when listening to words plus either type of laughter. Limitations Our current design does not disentangle the processing of humour and laughter, with insufficient temporal resolution for their neural distinction, suggesting a need for future research with more temporally-precise techniques. Conclusions While both non-autistic and autistic adults find laughter makes funny words funnier, there are differences in autism in the neural mechanisms that support mentalizing and contagion during implicit laughter processing. This study reinforces the idea that the essence of laughter serves both as an emotional expression and a sophisticated social signal during communication. It also highlights the challenges that autistic people face in understanding the meaning behind the conversational laughter we consistently encounter in everyday life, which may lead them to social vulnerability. Altogether, we advocate for clearer communication with autistic people.