Yawning study a bit of a mystery

Why do we do it and why is it contagious? Mark Schier and Yossi Rathner have some answers

CONSIDER the scenario. You’re driving on a long, straight stretch of country road at 2pm on a sunny afternoon, and you’re desperately keen to reach your destination. You’re trying to stay alert and attentive, but the urge to sleep is building.

In response you yawn, sit up straighter in your seat, possibly fidget around a little and engage in other mannerisms that may increase your level of arousal.

Is this the purpose of yawning? Yawning is generally triggered by several things, including tiredness, fever, stress, drugs, social and other psychological cues. These are generally well documented and vary between individuals.

The question of why we yawn evokes a surprising amount of controversy for what is a relatively minor field of study. We don’t have evidence that can point us to the exact purpose of yawning.

But there are several theories about the purpose of yawning. These include increasing alertness, cooling the brain, and the evolutionary theory of alerting others in your group that you’re too tired to keep watch, and someone else should take over.

Yawning is known to increase with drowsiness. This has led to the arousal hypothesis of yawning. Associated with the yawning are increased movement and stretching behaviour. The increased fidgeting behaviour may help maintain vigilance as the urge to sleep builds.

Also, specific muscles in the ear (the tensor tympani muscles) are activated during yawning.

This leads to a resetting of the range of movement and sensitivity of the eardrum and hearing, which increases our ability to monitor the world around us after we may have tuned out before the yawn.

Additionally, the opening and flushing of the eyes will probably lead to an increase in visual alertness.

Another theory for why we yawn is the thermoregulatory hypothesis. This suggests that yawning cools the brain. Yawning causes a deep inhalation that draws cool air into the mouth, which then cools the blood going to the brain.

Proponents of this theory claim a rise in brain temperature is observed before yawning, with a decrease in temperature seen after the yawn.

But the research report that gave rise to this theory only shows that excessive yawning may occur during an increase in brain and body temperature. It doesn’t suggest this has a cooling purpose.

Increased yawning rates are seen when fevers have been induced, which does suggest a correlation between body warming and yawning. But there is no clear evidence it leads to body cooling – just that body warming seems to be a trigger for yawning. (associated with stress and emotions). Blocking the oxytocin receptors here prevents that effect.

Patients with Parkinson’s disease don’t yawn as frequently as others, which may be related to low dopamine levels. Dopamine replacement has been documented to increase yawning.

Similarly, cortisol, the hormone that increases with stress, is known to trigger yawning, while removal of the adrenal gland (which releases cortisol) prevents yawing behaviour. This suggests that stress might play a role in triggering yawning, which could be why your dog may yawn so much on long car trips.

So, it seems yawning is somehow related to empathy, stress and dopamine release.