Researches from the New York Polytechnic Institute tested a hypothesis about the role of brain thermoregulation in the origin of yawning
Everyone knows that yawning is contagious. When one yawns, it is hard for another one to resist yawning in response. Trying to deliberately suppress yawning rarely works – it’s like forbidding yourself to sneeze if the process has already begun. Andrew Gallup, a psychologist from New York Polytechnic Institute, and his colleagues based their research on a new theory of the yawning function.
It used to be a popular belief that a person yawns to oxygenate the blood. Yet in 2010, scientists challenged this hypothesis and presented a new one: they inserted temperature sensors into rats’ brains and found that an increase in brain temperature by only 0.1 °C instantly provoked attacks of yawning in the rodents, followed by a decrease in brain temperature by 0.5 °C. That is, yawning performs the function of thermoregulating the brain. It turns out that when a person yawns, the position of the muscles of the head and neck change. This opens the way for cool air to enter, and consequently the temperature of the brain decreases slightly.
Andrew Gallup and his colleagues wondered that if yawning is just a way to cool your brain, why is it contagious? After all, when you see another person yawning, your brain does not heat up. To study the connection between body thermoregulation and the contagiousness of yawning, the researchers conducted an experiment. Participants in the experiment applied various compresses to the neck in the region of the carotid arteries: cold (4 °C), warming (46 °C) and those of standard room temperature (22 °C). The carotid arteries are large paired vessels located in the neck that provide blood flow to the brain. During the temperature exposure, participants watched videos of people yawning. This stimulus elicited a “contagious yawning” response.
Thermographic data showed actual brain cooling with compresses.
When watching videos of people yawning, 48.5% of participants with cooling compresses on their necks and 84.8% with warmers yawned in response. It turns out that the “contagiousness” of yawning depends not only on external stimuli, but it is also influenced by the temperature of the brain.
Not only humans but also many species of animals cool their brains through yawning. Neurophysiologists argue that yawning is neurologically important because it serves as a compensatory mechanism for cooling the brain. It is also known that the temperature of the brain is 1 °C lower than the body temperature, and this provides it with protection from the attacks of the immune system.