Acute Physical Stress Modulates the Temporal Expression of Self-Reported Contagious Yawning in Humans

A growing number of studies on non-human animals have documented that stressors modulate the expression of yawning. In particular, recent experimental research shows that yawns are initially inhibited following physical stress, but then become potentiated thereafter. However, stress-induced yawning in humans has yet to be demonstrated experimentally. Here, we investigated the temporal relationship between self-reported contagious yawning and an acute physical stressor in 141 human subjects in the laboratory. Using a 2 × 2 between-subjects design, participants either underwent the cold pressor test (CPT) or a matched control condition prior to viewing a contagious yawning stimulus that was either displayed immediately thereafter or following a 20-min delay. Consistent with the comparative literature, we show an interaction between stress and time conditions, whereby both the incidence and frequency of yawning are lowest in the immediate-CPT trials and highest in the delayed-CPT trials. These findings support a homologous effect of acute physical stress on yawning across birds and mammals that may be related to an adaptive thermoregulatory and arousal function.