Carotid Artery Temperature Modulates the Expression of Contagious Yawning

The existence of yawning across diverse species has led many researchers to postulate about its evolutionary significance. One hypothesis which has garnered recent support posits that yawns function to cool the brain by forcing hyperthermic blood away from the skull while simultaneously introducing cooler arterial supply. This study was designed to test whether alterations in brain/skull temperature modify yawning in humans. Participants were instructed to hold either a hot (40 ^o C), cold (4 ^o C) or room temperature (22 ^o C) pack firmly to their neck, just over one of their carotid arteries, prior to and during exposure to a contagious yawning stimulus. Immediately thereafter, participants self-reported on their behavior during testing. As predicted, results showed that contagious yawning varied significantly across conditions. Consistent with the brain cooling hypothesis, both the urge to yawn and overall contagious yawn frequency were highest in the hot condition and lowest in the cold condition.