A thermal window for yawning in humans: Yawning as a brain cooling mechanism

•The thermoregulatory theory of yawning posits that yawns function in brain cooling.•Yawning is constrained to an optimal thermal zone of ambient temperature.•This theory explains basic features of both spontaneous and contagious yawning.•Applications include improved treatment of patients with thermoregulatory problems.

The thermoregulatory theory of yawning posits that yawns function to cool the brain in part due to counter-current heat exchange with the deep inhalation of ambient air. Consequently, yawning should be constrained to an optimal thermal zone or range of temperature, i.e., a thermal window, in which we should expect a lower frequency at extreme temperatures. Previous research shows that yawn frequency diminishes as ambient temperatures rise and approach body temperature, but a lower bound to the thermal window has not been demonstrated. To test this, a total of 120 pedestrians were sampled for susceptibly to self-reported yawn contagion during distinct temperature ranges and seasons (winter: 1.4 °C, n = 60; summer: 19.4 °C, n = 60). As predicted, the proportion of pedestrians reporting yawning was significantly lower during winter than in summer (18.3% vs. 41.7%), with temperature being the only significant predictor of these differences across seasons. The underlying mechanism for yawning in humans, both spontaneous and contagious, appears to be involved in brain thermoregulation.