Wednesday, February 24, 2010

Apollo Yawn-O

An interesting bit of news making the rounds on the "internets" right now is this story about how Olympic short track skater Apollo Ohno likes to yawn before he competes.  When asked about this purportedly peculiar tradition, Ohno replied: "It makes me feel better... It gets the oxygen in and the nerves out."
I find this little story interesting for a couple of reasons.  First, yawning in anticipation of a competitive event is not that unusual.  According to Robert Provine, professor of psychology at the University of Maryland Baltimore County, "at track and field events, sometimes you'll find participants in the race of their life will be standing around on the sidelines or in the starting block and they may be yawning. Or before a concert, a musician may yawn to prepare for an increasingly energized state".  And this trait is not only obvious in humans.  Ronald Baenninger from Temple University reports that "lions, mandrills, and fighting fish all yawn in anticipation of metabolically expensive events such as feeding or fighting."  So, Ohno's pre-skating tradition may not be so unusual.  
But since the subject has been broached, I'm curious... In seeing that picture or in reading this post on yawning, have you felt the urge to yawn?  Maybe let one or two slip by?  Sadly, I've already yawned several times just in writing this.  So, what causes Apollo Ohno, or more generally, the rest of us to yawn?  And why are yawns contagious?

The truth is no one really knows.  Several hypotheses have been put forward over the years, with the most popular going something like this: yawning is caused by either excessive carbon dioxide or a lack of oxygen either in the lungs or in the circulation.  This idea is so prevalent, it can still be found in some medical texts.  However, in a study conducted in the 1980s by the same Robert Provine quoted above, subjects were exposed to environments that were either high in carbon dioxide or high in oxygen with neither having an effect on yawning.  So, neither low oxygen, nor high carbon dioxide are to blame for our yawns, but how about heat, or, rather, overheating?  The latest hypothesis to be put forward is that yawning may act to cool our overheated brains, kind of like the radiator in your car.  The more the engine works, the hotter it gets, the radiator takes the ambient air, which is cooler and uses it to bring down the temperature of the engine.  In a similar way, our brains actually increase in temperature as a result of use and fatigue, and yawning takes in cooler, ambient air, and increases blood flow in the face and head, thus carrying cooler blood past the brain.  The evidence for this hypothesis comes mainly from a single study that showed that contagious yawning could be decreased by holding a cold pack up against one's head (or by making a conscious effort to breathe through the nose, which also cools the brain).  Of course, more study will be needed to say whether or not yawning is meant to cool our brains, but it is interesting that certain diseases, like multiple sclerosis, which have a component of thermodisregulation (inability to regulate temperature) are also characterized by excessive yawning.
Regardless of whether or not cooling the brain is the end goal, it appears that the overall purpose of yawning is to help us stay awake and alert, which is why being tired or bored are the most common triggers, and why athletes will yawn before a big event as they try to get focused.
But what of the contagiousness of yawns?  Aside from the fact that a person with a cool brain seems to be less susceptible to catching your yawn, what else do we know?
Much like the function of yawning, several attempts have been made to try and explain the contagiousness of yawning. When the oxygen and carbon dioxide hypothesis was still considered valid, it was proposed that the yawns of people around you expelled excess carbon dioxide into the air you breathe, causing you to take in excessive carbon dioxide, and thus you yawn.
Obviously, there are a couple problems with this... first, yawning is not caused by changes in carbon dioxide (or oxygen) as we saw above.  Second, even if carbon dioxide levels were to blame, it has been shown that just watching video of people yawning, or hearing someone yawn, or reading about yawning can all cause people to yawn more (and since the stimulus yawn isn't even happening in the same room or at the same time, there is no change in CO2 or oxygen levels).
Okay, so what else?  Well, another hypothesis that came into vogue after it was discovered that carbon dioxide was not to blame was that yawning somehow activated the mirror neuron system.  The mirror neuron system is made up of neurons that fire not only when we perform a certain action, but when we see the same action being performed by someone else.  Many neuroscientists speculate that these mirror neurons are important for our ability to imitate others (which is how we learn to do many things like talk, write, play sports, learn a trade or craft, etc.)  However, studies published in 2005, and in 2009 that used fMRI imaging to examine the brains of people who were "catching" a yawn suggests that the parts of the brain where the mirror neurons reside don't seem to be activated in this process.
So, the latest hypothesis gets back to the now more accepted idea that yawns are meant to stave off exhaustion and increase alertness.  Examples of contagious yawning in other social animals (like baboons) suggests that there may be an evolutionary benefit to catching a yawn.  While some suggest that the contagiousness of yawns in social animals reflects empathy and a means to strengthen social bonds by synchronizing behaviors (like when to go to sleep), others have suggested that the raised awareness brought on by a yawn provides enough of an evolutionary incentive for it to "catch" on.  For example, many species of birds feed in large groups because feeding is a dangerous activity for them, one that usually involves lowering their head and eyes to the ground to pick up food.  A single bird by itself could get caught unaware by a predator whenever its head is down, but in a large group of birds, it is much more likely that when one bird has its head down, several others have their heads up, and are looking around.  Thus, each bird can feel safe pecking at the ground, confident that one of his neighbors will sound the alarm if a predator approaches.  When you have animals that live together in groups, and are likely on synchronized sleep/wake cycles (like baboons and early humans), then yawning may act as another sort of alarm.  When one in the group yawns, he or she is signifying fatigue, or a need to stay alert.  Others that follow this lead will likely reap the same arousing effect and be more likely to have the alertness and focus needed to successfully elude an approaching predator, or to have a successful hunt.  Thus contagious yawning may have evolved in our primate ancestors as a means for increasing alertness when it was needed, and yawning athletes appear to be a manifestation of this held-over trait, giving them added alertness before they enter the "hunt" for gold.

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