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2014-08-12 08:28:33
David Robson
Yawning has puzzled scientists for more than two millennia. But could a new
theory settle the question once and for all? David Robson investigates.
Mid-conversation with Robert Provine, I have a compelling urge, rising from
deep inside my body. The more I try to quash it, the more it seems to spread,
until it consumes my whole being. Eventually, it is all I can think about but
how can I stop myself from yawning?
Provine tells me this often happens when people are talking to him; during
presentations, he sometimes finds the majority of his audience with their
mouths agape and tonsils swinging. Luckily, as a psychologist at the University
of Maryland, Baltimore County and author of Curious Behavior: Yawning,
Laughing, Hiccupping, and Beyond, he isn t offended. It makes a very effective
lecture, he says. You talk and then the audience starts yawning. And then you
can ask people to experiment on their yawns like closing the lips, or
inhaling through clenched teeth, or trying to yawn with the nose pinched
closed.
It is through experiments like these that Provine has tried to explore a
millennia-old mystery: why do we yawn? We all know that tiredness, boredom, or
the sight of someone else can all bring along the almost irrepressible urge
but what purpose does it serve the body? When he first started work on
so-called chasmology in the late 80s, Provine wrote that yawning may have
the dubious distinction of being the least understood, common human behaviour .
Nearly three decades later, we may be closer to an answer, but it s one that
has split the field.
Does infectious yawning ensure that we all go to bed at the same time? (Getty
Images)
Arguably the first studier of yawns was the Greek physician Hippocrates nearly
2,500 years ago. He believed that yawning helped to release noxious air,
particularly during a fever. Like the large quantities of steam that escape
from cauldrons when water boils, the accumulated air in the body is violently
expelled through the mouth when the body temperature rises, he wrote.
Different incarnations of the idea lingered until the 19th Century, when
scientists instead proposed that yawning aids respiration triggering a rush
of oxygen into the blood supply, while flushing out the carbon dioxide. If that
were true, you would expect people to yawn more or less frequently depending on
the oxygen and carbon dioxide concentrations in the air. Yet when Provine asked
volunteers to breathe various mixtures of gases, he found no such change.
Many theories have instead focussed on the strange, contagious nature of
yawning a fact that I know only too well from my conversation with Provine.
Around 50% of people who observe a yawn will yawn in response, he says. It is
so contagious that anything associated with it will trigger one seeing or
hearing another person, or even reading about yawning. For this reason, some
researchers have wondered if yawning might be a primitive form of communication
if so, what information is it transmitting? We often feel tired when we yawn,
so one idea is that it helps set everyone s biological clocks to the same
rhythm. In my view the most likely signalling role of yawning is to help to
synchronize the behaviour of a social group to make them go to sleep more or
less at the same time, says Christian Hess, at the University of Bern in
Switzerland. With the same routine, a group can then work together more
efficiently throughout the day.
Danario Alexander of the San Diego Chargers yawns before the start of a
American football match (Getty Images)
Yet we also yawn during times of stress: Olympic athletes often do it before a
race, while musicians sometimes succumb before a concert. So some researchers,
including Provine, believe that the strenuous movements might have a more
general role in rebooting the brain when you are sleepy they make you more
alert, or when you are distracted they make you more focussed. Spreading
through a group, contagious yawns could then help everyone reach the same level
of attention, making them more vigilant to a threat, for instance. The
mechanism is somewhat hazy though one French researcher, Olivier Walusinski,
proposes that yawning helps to pump cerebrospinal fluid around the brain, which
could trigger a shift in neural activity.
With so many competing and contradictory ideas, a grand unifying theory of
yawning may seem like a distant speck on the horizon. But over the last few
years, one underlying mechanism has emerged that could, potentially, appease
all these apparent paradoxes in one fell swoop. Andrew Gallup, now at the State
University of New York at Oneonta, was first inspired with the idea during his
undergraduate degree, when he realised that yawning might help to chill the
brain and stop it overheating. The violent movement of the jaws moves blood
flow around the skull, he argued, helping to carry away excess heat, while the
deep inhalation brings cool air into the sinus cavities and around the carotid
artery leading back into the brain. What s more, the strenuous movements could
also flex the membranes of sinuses fanning a soft breeze through the cavities
that should cause our mucus to evaporate, which should chill the head like air
conditioning.
The most obvious test was to see if people are more or less likely to yawn in
different temperatures. In normal conditions, Gallup found that around 48% felt
the urge to yawn, but when he asked them to hold a cold compress to their
foreheads, just 9% succumbed. Breathing through the nose, which could also cool
the brain, was even more effective, completely dampening his subjects urge to
yawn potentially suggesting a handy trick for anyone facing embarrassment
during a tedious conversation.
Can yawning give you a brain boost? (Thinkstock)
Perhaps the best evidence comes from two troubled women who approached Gallup
soon after he first published his results. Both were looking for relief from
pathological yawning attacks, sometimes lasting an hour at a time. It was
extremely debilitating and interferes with any basic activity, says Gallup.
They d have to walk away and go to a secluded area it affected their personal
and professional lives. Intriguingly, one of the women found the only way to
stop the yawning attack was to throw herself into cold water. Inspired, Gallup
asked them to place a thermometer in their mouths before and after the attacks.
Sure enough, he saw a slight rise in temperature just before the yawning bouts,
which continued until it dropped back to 37C.
Importantly, this brain chill might underlie the many, seemingly contradictory,
events that lead to yawning. Our body temperature naturally rises before and
after sleep, for instance. Cooling the brain slightly might also make us more
alert waking us up when we are bored and distracted. And by spreading from
person to person, contagious yawns could therefore help a whole group to focus.
Does this picutre make you yawn? (Thinkstock)
Gallup s unified theory has been somewhat contentious among yawning
researchers. Gallup s group has failed to present any convincing experimental
evidence to support his theory, says Hess. In particular, his critics point
out he hasn t made direct measurements of temperature changes in the human
brain, though Gallup says he has found the expected fluctuations in yawning
rats. Provine is more positive, however believing that it could be one way in
which yawning helps the brain change state, and focus.
Even if Gallup has managed to find that unified theory, many mysteries remain.
Why do foetuses yawn in the womb, for instance?
It could just be that they are practicing for life outside, or perhaps the yawn
plays a more active role in guiding the body s growth by helping to develop
articulation in the jaws joints, for instance, or by encouraging the growth of
the lungs, says Provine. If so, Provine suggests that yawning s functions in
the womb may be more important than our attacks as adults.
Provine also points out that yawning and perhaps other bodily functions, like
sneezing shares some strange parallels with sex. The facial expressions
involved are surprisingly similar, he says just take a look at this picture
and you can see where he s coming from.
(Thinkstock)
Like sex, yawns and sneezes involve a build-up that ends in a pleasant climax.
Once initiated, they go to completion you don t want a yawnus interruptus,
is how Provine puts it. For these reasons, he wonders if a shared neural
machinery underlying these different feelings. Mother Nature does not reinvent
the wheel, he says. As evidence, he points to the fact that certain
anti-depressants can lead some patients to orgasm during a yawn a rare side
effect that could quickly lose its appeal.
Eventually, the temptation to yawn just proved too irresistible during my
conversation with Provine. It was a warm summer day, so perhaps my yawns were
stopping my brain from over-heating during our stimulating conversation.
Whatever function it was serving, the relief was almost worth the agonising
wait.
I m willing to bet you ve been stifling a few yawns yourself by this point as
Provine points out, reading or even thinking about yawning can be enough to set
us off. So go ahead, let it out and do so in the knowledge that you are
enjoying one of life s most enduring mysteries.