New theory injects a wake-up call into yawning

 

One of the primary characteristics of yawning is that it is contagious. When you see someone else yawning, you feel like yawning yourself. Thinking about yawning will also induce the act - so prepare to yawn a lot as you read this article.

What is a yawn? You can study this matter carefully by inducing yourself to yawn a few times in front of a mirror. A typical yawn involves throwing the head back a little, opening the mouth wide, jutting out the chin and clenching the jaw, raising and arching the tongue, taking a deep lungfull of air, holding it for several seconds, then expelling the air with a sigh of satisfaction, closing the mouth and resuming normal behaviour. Why do we yawn? The traditional explanation for the yawn is that it is a device to quickly augment the supply of oxygen to the brain. Presumably this explanation springs from the observation that we tend to yawn more when we are tired, and apparently, when we are bored. It is assumed that tiredness reflects an oxygen-deficient brain and, hence, the automatic reflexive response of the yawn. (I'll bet you're yawning now).

If the traditional explanation is correct, it would follow that frequency of yawning will increase in people breathing air that is somewhat deficient in oxygen. This prediction has been tested by Robert Provine, a psychologist at the University of Maryland, USA. He gathered a group of students and asked them to think about yawning while he had them inhale mixtures of air adjusted to be either higher in oxygen, lower in oxygen, or normal with respect to this gas. The various gas mixtures had no effect on the rate of yawning which remained steady at approximately 24 yawns per hour. These results seem to knock the brain/oxygen-deficiency hypothesis on the head.

Ronald Baenninger a psychologist at Temple University, Philadelphia, takes up the story here. He carried out a study in which he asked his subjects to wear wrist bands that sense motion and to press a button on the band every time they yawned. After a couple of weeks, Baenninger analysed his data and discovered that yawning preceded active periods. The subjects were physically active within 15 minutes of yawning.

It seems then that the purpose of yawning is to induce physiological arousal in preparation for activity. It has been generally observed over the years that athletes yawn a lot before competition, students before examinations, soldiers before parachute jumps, etc.

Why then do we yawn more when we are tired and before going to bed? This new theory would say that we yawn in these circumstances in order to help us to stay awake and alert. Yawning is refreshing and relaxing. When we yawn we send an extra spurt of blood to the brain which has the effect of picking us up. In harmony with this, it has been noted that people yawn more when they are having a haemorrhage or suffering from motion sickness. Both of these conditions tend to decrease the amount of blood going to the brain.

What prevents spontaneous yawning? Spontaneous yawning only occurs when we feel uninhibited. When you feel ill at ease and inhibited in someone's company you do not yawn. We associate yawning so closely with feeling at our ease that we all occasionally, when we find ourselves in awkward company, put on a fake yawn in order to signal that we are really at our ease. This is never a good idea. The fake yawn rarely rises above a pale imitation of the real thing and is readily spotted. The net effect of the fake yawn is usually to clearly signal the true state of your emotions, the exact opposite of what you intend.

Yawning is by no means exclusive to humans. Possibly the main activity of the day for animals in the zoo is feeding time. Primates, wolves and lions are inclined to bouts of yawning about an hour before feeding time. I have often seen dogs yawning. Various species of fish have also been observed to yawn between exertions, such as eating and courting.

Why is yawning contagious? The theory is that yawning is a device used to keep the mind focussed and ready for action. Perhaps its contagious properties were chosen by natural selection because they synchronise the activity of a group. As a chain reaction of yawning spreads through a group it will synchronise everybody to get ready for some activity.

Robert Provine has also carried out studies to determine what part of the yawn makes it so infectious. Video images of yawns with the mouth blocked out were found to be just as effective at inducing yawns in viewers as images of the whole yawn.

It is considered to be quite impolite to yawn during the course of a face to face meeting with someone. The other party interprets your yawn to mean that you do not find his/her company and conversation sufficiently stimulating to hold your attention. They might be a little less annoyed with you if they understood that, in yawning, you are trying to entice your brain into a more alert state in order to give them the benefit of your focussed attention.

Let me conclude by wishing you all a happy and a peaceful Christmas. I hope you have many long and pleasant yawns over the holiday period. (I am indebted to a piece by Amy Adams in the 19/26 December 1998 issue of New Scientist for some of the information I presented in this column).

William Reville is a senior lecturer in Biochemistry and director of Microscopy at UCC.