- There are other apparent signs of sleepiness
that can be quite deceptive, even to the trained
observer, with the best example being
yawning. Despite it being a universal
human behaviour, no one really knows much about
it, other than that it usually has something to
do with boredom or sleepiness. Yawning
can be seen in many zoo mammals, as well as in
dogs, horses, and mice, for example, when it is
usually accompanied by stretching. The ostrich
also seems to do a lot of it, especially when
drowsily sitting on its eggs.
-
- Look up the word in a dictionary, and apart
from learning that it cornes from the old
English verb 'ganien' to gape, there usually
follbws only bland statements of the obvious.
Medical textbooks are little better, and often
the subject is conspicuous by its absence - t
should lie somewhere between 'yaba virus' and
'yaws'. Astute physians and scientists lost for
an explanation for a phenomenon willoften give
it an impressive new name, usually derived from
Latin. Thus the term once commonly adopted for
yawning was 'oscitation' from Oscitare'
(to open the mouth wide), and this can be found
in older medical texts. It implies that science
and medicine knew all about it, and one
ponderous explanation, providing an effective
screen to conceal ignorance is along the lines
of 'a deep inspircarried out with widely opened
glottis, typically with open mouth, and
frequently accompanied by movements of the arms,
etc. It is caused by certain psychic
influences.'
-
- Another account comes from a medical
textbook by Dr H. Russel,
from New York, dated 1891,
who proposed that yawning was produced by 'bad
air in the lungs designed by Nature as a
gymnastic to awaken the respiratory organs into
activity'.' Similar views prevail today that
somehow yawning 'aerates' the lungs and
increases the oxygen supply to the brain.
However, more enlightened research has clearly
shown that yawning has little to do with
'oxygenating the blood', because breathing
oxygen does not suppress the urge to yawn and,
conversely, raising carbon dioxide levels in the
blood does not increase yawning. If anything,
yawning leads not to a rise in blood oxygen
levels, but a fall, because breathing usually
ceases for a while after a yawn. It is also
caused by stress and fear, which may account for
its association with injury and severe bleeding.
In the First World War, yawning was commonly
seen among troops in the trenches waiting for
the whistle to blow, for going 'over the top'.
Heroin addicts withdrawing from the drug and
going 'cold turkey', which can be a frightening
experience, can yawn extensively-so can migraine
sufferers before an impending migraine, which
may or may not be linked to fear of the migraine
attack.
-
- The Victorians had other various theories
about yawning, many of which can best be
described as 'imaginative'. For example, yawning
stimulates arousal by boosting blood levels of
the hormone thyroxine (which raises metabolism).
The yawning of the lower jaw was supposed to
squeeze the thyroid gland, which is located in
the neck, to release more of this hormone into
the bloodstream. Certainly, yawning can cause a
momentary increase in heart rate, but this is a
reflex associated with any deep inspiration and
is followed by a slowing on expiration.
-
- The peak of research into yawning was in the
1920s. Notable was a Dr Carl Mayer who devoted
much time to precisely measuring yawning,
including taking radiographs of his wretched
subjects attempting to yawn, as well as having
their throats probed by laryngeal mirrors and
their necks palpated. He was at pains to note
that his measurements did not interfere with
yawning, and declared, 'the complete yawning
complex, unmodified by inhibition, was allowed
to
- develop'. He confidently claimed that
yawning could be divided into three precisely
timed and distinct phases: 'initial
inspiration', taking between 1.9 and 4.3
seconds, 'acme', lasting exactly 2.3 seconds,
and 'expiration' of 4.5-7.8 seconds' duration.
As to why we yawn, he dismissed it with two
words-'cerebral fatigue'.
-
- Despite common knowledge that yawning has
'something psychological about it', surprisingly
few psychologists have investigated it. Many
psychiatrists have taken a keen interest,
however, but often with some strange concepts.
For example, in patients with schizophrenia,
yawning has been taken as a sign of a good
prognosis, supposedly showing that the patient
wants to maintain contact with the real world.
Some antidepressant medicines can produce
frequent yawning, not because of increased
sleepiness, but through direct effects on
yawning control mechanisms in the brain.
-
- One of the most endearing accounts of
yawning was based on a series of experiments
performed in 1941, by Dr Joseph Moore
from the George Peabody College, in Tennessee.
His first study employed a stooge, who was able
to yawn at will and sat in a nearby public
library reading room, in full view of other
readers. He yawned obtrusively every ten minutes
while Moore sat unobtrusively in an overlooking
gallery, recording the events in his notebook.
Within a minute or so of each rendition almost
half of the unwitting audience would follow
suit. Another of Moore's studies was more
blatant, with a short movie of a girl yawning,
shown to an unsuspecting audience, which was
soon followed by a doubling of the incidence of
yawning among the onlookers. His last study was
more imaginative: can yawning be stimulated
simply by hearing it rather than by seeing the
yawner? Gramophone records of yawning were
played to college students, with little
response, but when played to blind students
yawning became most apparent. Indeed, yawning is
highly suggestible-try it now!
Mayer C Physiologisches und pathologisches
über das Gähnen Zeitschrift für
Biologie 1921;73:101-114
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