Yawn, yawn

The yawn is a reflex that consists of a deep inhalation followed by an "equally generous exhalation. Although it is a particularly common gesture not only among humans, but also among many animals, we still know little about the physiological mechanisms from which it originates.

Among mammals the act of yawning is found in different situations, in each of which it assumes a different meaning. We yawn, for example, in the moments preceding the rest dictated by circadian rhythms, during and after a meal, but also in situations that they have a certain social and sexual significance. It is not uncommon to see a cheetah yawn before leaving to attack the prey, as if it were a way to collect the oxygen necessary for the imminent and violent physical effort; the hippopotamus performs this gesture as a sign of threat, as if he wanted to intimidate the opponent by showing his powerful teeth; for men, yawning is a particularly contagious act.

But what are the physiological reasons for yawning? Numerous hypotheses have been advanced in this regard and it is very likely that this reflex derives from the integration of different stimuli. One of the first theories, which remained in vogue for several years and supplanted by the latest research, suggested that the onset of yawning was a way to increase the amount of oxygen in the body, in response to an excess of carbon dioxide in the blood. The hypothesis that yawning is a way to improve physical efficiency continues to be supported by several studies. One of these, wearing headgear warming or cooling on the heads of subjects intent on watching yawning videos, he concluded that yawning is a way to keep the brain temperature constant, preventing it from rising excessively. A similar conclusion has also been advanced by other authors, who argue that yawning is a way to regulate the temperature of the whole organism. Other theories concern the possibility that yawning is a reflex triggered by the same neurotransmitters (primarily serotonin) which, acting in the brain, affect emotions, mood, appetite and other aspects of our life. There are also those who argue that yawning is a way to communicate apathy (hence the contagiousness of the gesture), sharing the behavior and physiological state of those around us. Others believe that it could be an unconscious reflex of imitation, which it is the basis of human learning (as happens in the acquisition of language), or of a non-verbal communication tool to signal to the group members their state of fatigue, synchronizing the sleep-wake rhythms.

These and other theories, reported with their bibliographical references in the article yawning (English wikipedia), are a clear example of how complex are the physiological mechanisms that regulate the various bodily functions; for this reason, if you have not already done so during reading the article, the next time you miss a yawn you will most likely no longer dismiss it as a simple sign of fatigue.