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Yawning
Yawning is a strange but surprisingly pleasant process. You open your jaws wide, slightly close your eyes, inhale deeply... It's also highly contagious. If we see someone yawn, we want to join in. We don't even need to see it, it's often enough just to read about it. It's as if just the thought of yawning sets off the action. You're probably feeling the need to yawn right now.But why? What's the point?
Why Do We Yawn?
As with so much related to the world of sleep, the answer is that no-one really knows for sure what causes yawns. There are a variety of theories and hypotheses.The most well-established explanation for yawning is to increase blood oxygen. According to this theory, when we are feling tired or even just bored our brains cause us to yawn spontaneously in order to get a "hit" of oxygen. Yawning is thus triggered by a build-up of carbon dioxide (CO2) in the blood.
It's a nice theory, unfortunately some of the research that has been done that shows little relationship between CO2 levels and yawn frequency.
Another theory is that yawning isn't a "deliberate" act by the brain at all. This theory suggests that yawns are an accidental side-effect of the changing levels of certain brain chemicals such as serotonin. When we're bored or weary, this affects the level of these chemicals and hence results in a yawn. Research has indeed shown that certain chemicals can increase yawn frequency in animals, however as far as I know the hypothesis is still considered unproven.
Why is Yawning Contagious?
If we see people yawning, we need to yawn - a classic case of "monkey see, monkey do". In fact that comparison is very accurate since researchers have shown that yawning is contagious in chimpanzees! (OK, a chimp is actually an ape not a monkey, but you get the point).One possible explanation of the contagious nature of yawning is that it is a form of herd instinct. In pre-verbal days actions such as yawning might have been used to co-ordinate a pack. This might include passing on a warning message, co-ordinating sleep patterns or simply baring the teeth: the whole pack "bigging itself up" in unison!
Scientific research has shown a neurological element to the excessive contagiousness of yawns. Apparently, when you feel the need to copy a yawn there is a measurable deactivation of the brain's left periamygdalar region. Unfortunately not even the scientists who carried out the research really know what that means.
References:
Yawning: no effect of 3-5% CO2, 100% O2, and exercise