Abstract
<p>Shared laughter, a salient social cue in peer interactions, promotes bonding, liking and prosociality. Recent theoretical accounts on the neural dynamics of social interaction propose that rhythmic communicative signals, such as laughter, may foster neural synchrony by aligning brain activities between interacting partners, facilitating mutual understanding and social bonding. Here, we test whether neural synchrony mediates the positive social effects of laughing together in child peer dyads. We used fNIRS hyperscanning to measure neural synchrony in 5-year-old dyads (n = 196; 98 pairs) randomly assigned to a laughter condition (funny animal videos) or a control condition (neutral videos). Inferior frontal gyrus (IFG) and temporoparietal junction (TPJ) activity was recorded both during the video manipulation and during a subsequent 5-minute free-play session, and quantified with Wavelet Transform Coherence. Laughter behavior was annotated, bonding indexed by body proximity, prosociality with a sticker sharing task, and liking with smiley scales. Hypotheses were tested with Bayesian models. Compared with controls, children in the laughter condition showed higher neural synchrony while co-watching the videos. During free play, after the manipulation, left-hemisphere synchrony was greater in the control group. Exploratory findings showed that more laughter was linked to stronger bonding and prosociality. We did not find support for a mediation between laughter, neural synchrony and social outcomes. In summary, we show that neural synchrony among children changes with shared laughter. By revealing condition-specific and region-specific effects across time, this study highlights the dynamic nature of neural synchrony processes in child peer interactions.</p>