06 March 2008

The Big Yawn: An Autopsy (reprise)

Have you ever wondered why we yawn? Yes, we yawn when we’re bored, sleepy or tired, but what purpose does a yawn serve? How are yawns triggered? And were you aware of the fact that in humans, there is a relationship between yawning and orgasm? Hey now!

Most of the higher vertebrate species yawn: mammals, reptiles, birds and even fish. It’s known that human fetuses yawn as early as the end of the first trimester of prenatal development. These facts make it clear that yawning must have evolved quite a long time ago, far back in the evolutionary line.

A yawn consists of a powerful movement of jaw-gaping along with deep inhalation and exhalation. But it involves much more than just that. While yawning, the head tilts slightly backwards, the eyes narrow, the facial muscles stretch. Inside the middle ear, the eustachian tubes open, while the tear glands and salivary glands have increased activity, not to mention a whole bunch of other brain areas, as well as hitherto unspecified cardiovascular and respiratory acts.

In terms of biochemistry, it is not known exactly what triggers this highly complex motor program. Although it’s known that boredom or sleepiness can cause yawning, it has also been documented that certain changing colour patterns can induce yawning. People have also been observed to yawn when they are tensed, like paratroopers before a jump or musicians before a concert. I personally know two people who have a habit of nervous yawning and they say dogs will sometimes yawn when they are nervous or anxious.

Research has demonstrated that the conventional belief that yawns are caused due to a high level of carbon dioxide or a shortage of oxygen in the blood or brain, is completely false. However, after comparing some of the similarities between the physiology of yawning and that of sex, it has been suggested that the two acts might have a common neurological background.

For instance, the facial expression during sexual climax (the "Oh" face) is remarkably similar to the expression during yawning. Furthermore, some of the neurotransmitters associated with sexual activity, such as oxytocin and androgens (HOLLA!), are also connected to yawning.

Chemical agents that induce yawning in lab rats have also been observed to induce penile erection. Hey now! Most fascinating of all, old school antidepressant drugs such as clomipramine and fluoxetine, in some people, have the side effect of inducing yawns that trigger orgasms. Which sounds pretty awesome but actually would totally suck.

One trait of yawning that has so far only been documented in humans, and our closest living relatives, the chimpanzees: contagious yawning. Though yawning itself is an ancient practice, contagious yawning must have evolved relatively recently. Humans are not susceptible to contagious yawning until they are several years old.

We’ve all noticed how contagious a yawn can be. Watching someone yawn can cause us to yawn too. In fact, just thinking about yawning is sufficient to induce a yawn. I’m willing to wager that by the time you finish reading this post, you will have yawned (if you haven’t already done so) or at the very least, felt like yawning.

This property of contagiousness has the potential to give us some insights into the neurological basis of imitation, face detection, and various other such social behaviours. Scientists have found that individuals with disorders like schizophrenia or autism (where the ability to infer the mental states of others is impaired), or even just schizotypal people, are markedly less prone to contagious yawning. It has even been suggested that increased rates of yawning might indicate that a person may recover from schizophrenia. Hmmmm.

Yet another fascinating aspect of yawning is the relationship between yawning and stretching, also called ‘pandiculation’. In humans as well as in animals, yawning is invariably accompanied by stretching upon waking up after sleeping, but almost never before falling asleep.

"Baby, I'm tired, do u mind if we just pandiculate tonight?"

"Sure, honey"
In many people who are paralyzed due to brain damage, pandiculation causes their otherwise immobile limbs to rise and flex automatically. This suggests that yawning activates undamaged, unconsciously controlled nerve connections between the brain and the cord motor system.

Hopefully, science may some day discover a therapeutic value of yawning for people with such conditions.

If you are interested in reading more about the research on yawns, you’ll surely find it very useful to read Robert Provine’s brilliant, jargon-free research paper "Yawning: The yawn is primal, unstoppable and contagious; revealing the evolutionary and neural basis of empathy and unconscious behavior" which you can get find here.

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