Cool Your Brain with a Yawn

Research indicates that yawning helps to cool down your brain. (Photo credit: Will & Deni McIntyre/Photo Researchers, Inc.)

A yawn is the hallmark of boredom or sleepiness, right? According to recent research, that connection may not be correct. Instead, researchers contend that yawning has less to do with how much sleep you got last night or how bored you are in your third period math class. Instead, research results indicate that yawning is the body’s way of cooling down your brain.

These results support the thermoregulatory theory of yawning, which suggests that yawning is caused by brain temperature increases. The act of yawning is therefore used to cool the brain down. Scientists think that this cooling effect occurs due to an increase in blood flow to the brain caused by the stretching of the jaw as well as the countercurrent heat exchange that is associated with the deep inhalation of a yawn.

Andrew Gallup, a post-doctoral research associate at Princeton University, collaborated with Omar Eldakar, a post-doctoral fellow at the University of Arizona, on this research study, which was published in the September 2011 issue of the online journal Frontiers in Evolutionary Neuroscience. Their field-observational experiment involved measuring the incidence of yawning among a group of 160 randomly-chosen young adults in Arizona. Eighty of the participants were tested during the summer months and the remaining 80 participants were tested in the winter months. In their study, the scientists showed each participant an image of someone yawning (since yawning is contagious perhaps looking at the photo that accompanies this article made you yawn?) and measured the number of times each participant yawned.

Results from their research show that there is a higher incidence of yawning when ambient air temperatures were lower than human body temperature. They found that study participants yawned less frequently (around 25 percent of the time) during the summer months, when air temperatures often exceeded human body temperature and humidity was lower. During the winter months, when air temperature was mild (around 71 degrees Fahrenheit) and humidity was slightly higher, participants yawned more frequently (nearly 50 percent of the time). Their results also indicate that yawning is related to the amount of time a person spends outside exposed to the elements. The scientists found that though nearly 40 percent of the participants yawned within the first five minutes of being outside, in the summer months, this number drastically reduced as time outside increased. During the winter months, yawning occurred at a slightly higher frequency after more than five minutes outdoors had passed.

The results of this research support previous non-human animal studies. For example, a study involving rats found that the rats’ brain temperatures decreased immediately after a yawn. A second study using rats found that the incidence of yawning increased as air temperature increased. However, when the air temperature became too warm, the frequency of yawning decreased. Similar results occurred in a study involving parakeets. In one such study, parakeets were exposed to three different conditions: moderate air temperature, high air temperature, and increasing air temperature. Though yawning did not increase in the first two situations, the birds yawned at a significantly greater frequency when the air temperature increased over time.

So why do you yawn you are tired? Research indicates that both exhaustion and sleep deprivation are both associated with higher brain temperatures. These increased brain temperatures in turn trigger yawning to help the brain to cool down. Additionally, brain research also shows that yawning helps with the transition from sleeping to waking states, and vice versa.

The results from these studies have many practical implications. For example, studying the mechanism behind yawning could help researchers improve their knowledge about neurological diseases such as multiple sclerosis and epilepsy, both of which are associated with frequent yawning. The occurrence of excessive yawning could also be used as a diagnostic tool for thermoregulatory impairments.

More to Explore