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Why Do We Yawn?

Yawning is ubiquitous across the animal kingdom, but remains one of the few essential reflexes that scientists have still yet to understand. It is a known indicator of empathy, even across species: yawn enough and even your dog will follow. Even fetuses yawn from within the womb.

Yet despite its widespread commonality, there still lacks a scientific consensus on the purpose of yawning, aside from indicating sleepiness and fatigue. The only thing doctors know for certain is that a yawning child is indeed a sleepy one who should be getting the proper rest his or her body needs to grow.

Recent research, however, has provided compelling evidence for a surprising theory underlying why we yawn: it cools down the brain. Here is a look at the mechanism of yawning, and what our bodies are trying to tell us when we yawn.

Theories of Yawning

There are a number of theories floating around as to why we yawn as a species. The most prevalent, although not most scientifically compelling, is that we yawn to increase our oxygen intake into the bloodstream. Studies have shown that oxygen intake may actually be reduced while yawning, when compared to breathing normally.

The latest research suggests that yawning is a physiological mechanism for heat regulation, which aids in relaying cool air to the brain when it overheats. Our natural circadian rhythms indicate that our temperatures are at their highest right before falling asleep, and just after waking: both times when we are most likely to yawn. The brain performs at its best when it is cool. Researchers found that in lab tests involving rats, brain temperatures were at their highest immediately preceding a yawn, with a noticeable drop in temperature recorded as a result of yawning.

The physical mechanism of yawning involves two basic steps: the exaggerated stretching of the jaw, which improves blood flow to the head; and inhaling deeply, forcing the downward flow of blood and spinal fluid from the brain. The cool air inhaled in turn chills these fluids, resulting in a drop in temperature.

Lead researcher Dr. Andrew Gallup, of Princeton University, explains: “Together these processes may act like a radiator, removing [excessively hot] blood from the brain while introducing cooler blood from the lungs and extremities, thereby cooling [brain] surfaces.” To support his theory, Gallup found in repeated studies that participants yawn significantly more in cold weather versus hot weather, further suggesting that yawning is a mechanism to relay cool air to the brain when it is overheated.

In a study of two women suffering from chronic and debilitating fits of yawning, researchers found that both women suffered from a dysfunction in brain temperature regulation. Like the rats, both subjects recorded temperatures highest immediately preceding a yawn, with a measured decrease following thereafter. The patients responded well to brain-cooling methods, citing that the treatment significantly relieved or delayed their symptoms.

Why is Yawning Contagious?

It has been shown that yawning is linked to empathy: and that your likeliness to mimic the yawning of others is a direct indication of your personal ability to relate to others. Socially, scientists speculate that the evolutionary role yawning plays is to maintain the alertness level of the pack: that when one of us yawns, it is a reminder to others that we must remain alert in the case of predation. This social chain reaction ensures the awareness, and thus survival, of our pack.

Whatever the evolutionary reason, yawns act as a social cue to coax others to stay alert.

What Does it Mean?

In relation to the brain-cooling theory of yawning, excessive yawning can thus be used as a significant diagnostic symptom to indicate the presence of conditions where the brain is unable to regulate its internal temperature. Dr. Gallup explains, “Excessive yawning appears to be symptomatic of conditions that increase brain and/or core temperature, such as central nervous system damage and sleep deprivation.”

While this may also extend to the diagnosis of neurological conditions such as epilepsy, yawning is an established symptom of sleep debt and possibly even a sleep disorder. If your child is yawning excessively throughout the day, it is time to examine his/her sleep hygiene.

Schedule a Sleep Study with Dr. Shukla

If you find yourself or your child yawning excessively, it is a sign that you are not getting the sufficient quantity and quality of rest your body needs. Schedule a sleep study with esteemed pediatric sleep specialist Dr. Mayank Shukla today. With over 15 years of patient satisfaction, advanced technology, and the caring staff at the Asthma Allergy Sleep Center of New York, Dr. Shukla will have you feeling refreshed and re-energized in no time.

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