Expressing appreciation is linked to interpersonal closeness and inter-brain coherence, both in person and over Zoom.

Expressing appreciation is essential for establishing interpersonal closeness, but virtual interactions are increasingly common and create social distance. Little is known about the neural and inter-brain correlates of expressing appreciation and the potential effects of virtual videoconferencing on this kind of interaction. Here, we assess inter-brain coherence with functional near-infrared spectroscopy while dyads expressed appreciation to one another. We scanned 36 dyads (72 participants) who interacted in either an in-person or virtual (Zoom®) condition. Participants reported on their subjective experience of interpersonal closeness. As predicted, expressing appreciation increased interpersonal closeness between dyad partners. Relative to 3 other cooperation tasks (i.e. problem-solving task, creative-innovation task, socio-emotional task), we observed increased inter-brain coherence in socio-cognitive areas of the cortex (anterior frontopolar area, inferior frontal gyrus, premotor cortex, middle temporal gyrus, supramarginal gyrus, and visual association cortex) during the appreciation task. Increased inter-brain coherence in socio-cognitive areas during the appreciation task was associated with increased interpersonal closeness. These findings support the perspective that expressing appreciation, both in-person and virtually, increases subjective and neural metrics of interpersonal closeness.