Lack of behavioral imitation in human interactions enhances salivary cortisol levels

As inherently social animals, humans are very sensitive to behavioral signals from other members of their group. Nonconscious imitation of conspecifics' behavior (also called social mirroring) is a common manner in which people express their sense of similarity and affiliation with others. This evolutionary important behavioral repertoire has been referred to as 'social glue' as it cultivates pro-social behaviors that foster one's acceptance by the group as well as sustain societal unity. Lack of behavior imitation therefore serves a subtle cue signaling rejection by others. Because being rejected is a stressful experience that is known to raise cortisol levels in humans and other primates such as baboons, we reasoned that not being imitated by another person during an interpersonal interaction may enhance cortisol levels as an acute physiological stress reaction to the behavioral rejection signal by their conspecifics. In the present study, female participants were unobtrusively imitated or not imitated by another person. None of the participants indicated awareness of (not) being imitated. The salivary cortisol concentrations of not imitated participants did not differ from those of the imitated participants on a baseline measurement, but they increased considerably after the interaction, whereas the cortisol level of imitated participants remained stationary. This stressful consequence of a lack of behavioral imitation was mediated by self-reported need to belong. These findings provide new insights into the impact of a lack of behavioral imitation on the receiver's hormonal secretion and its functionality in social interactions.