Yawning is a complex stereotyped reflex, the
physiological function of which remains unknown.
Yawning can be drug-induced, and
antidepressants, in particular serotonin
reuptake inhibitors, are drugs that have been
implicated in excessive yawning [1].
However, the reason why drug-induced yawns occur
is a bit of a mystery. There is also very little
research, because for most people yawning is not
a problem. It would be therefore interesting to
explore whether excessive yawning among patients
is an unwanted, negative consequence associated
with the use of antidepressant medications or
has an important beneficial role in regulation
of brain homeostasis.
Recently, an interesting article in Medical
Hypotheses has identified that majority of
therapeutic strategies against mania are
hypothermic, while thermogenic strategies are
used to combat depressive disorders. Hence,
during treatment, brain temperature may rise in
patients with depression, and fall in patients
with mania [2]. Studies have revealed
that yawning has many physiological consequences
that are concordant with those needed for the
regulation of brain temperature [3]. I
therefore propose that the drug induced yawning
serves as a compensatory brain cooling mechanism
when regulatory mechanisms fail to operate
favourably. Another interesting aspect is the
inhibitory role of opioid system on yawning
[1], which could be possibly explained
on the basis of their hypothermic action
(antimanic property) [4].
In general, therefore, whenever there is an
increase in brain temperature, protective
mechanisms such as the one described here, are
triggered. Failure of the latter will lead to an
increase in the severity of adverse effects with
life-threatening consequences. I believe that
the human yawn reflex is a vital protective
reflex, and its integrity is important to keep
the brain in thermal homeostasis. I suggest that
excessive yawning should be viewed as an
important warning sign of CNS toxicity, but not
as the ''side-effect'' of drug usage. More
clinical and basic research in this area is
needed to advance our understanding of the
pathogenesis of drug-induced yawning.
Salerian AJ, Saleri NG, Salerian JA. Brain
temperature may influence mood: a hypothesis.
Med Hypotheses 2008; 70(3):497&endash;500.
Gallup AC,
Gallup Jr GG. Yawning as a brain cooling
mechanism: nasal breathing and forehead cooling
diminish the incidence of contagious yawning.
Evol Psychol 2007;5(1):92&endash;101.
Sandyk R. Antimanic effects of clonidine and
the endogenous opioid system. Am J Psychiatry
1985;142(8):992&endash;3.
mise à jour
du
25 mai
2008
Yawning..
and why yawns are
contagious:
a
theory on evolution and
atavism
Hari Prasad
I would like to congratulate Matikainen and
Elo on their unearthing of mechanism giving rise
to increased arousal, alertness and wakefulness,
while yawning [1]. Observational studies
on animal and human yawning yield important
clues for understanding primate evolution. In
response to this article, I would like to draw
your attention to our observation regarding
contagious yawn usage in humans, which I believe
may help enhance our knowledge of human and
primate evolution.
We have all noticed that when one person
yawns, it sets off a chain reaction of yawns
amongst others in the group. However, the reason
why yawns are contagious is a bit of a mystery.
There is also very little research done, because
for most people contagious yawning is not a
problem. It was previously thought that, while
yawning occurs in many animal species, only
humans yawned contagiously. It turns out, chimps
and stumptail macaques may yawn contagiously as
well [2,3]. Its universal and widespread
nature suggests that it must have either
functional or atavistic basis, if not so
[4].
In non-human animals, contagious yawning can
serve as a warning signal. For example, baboons
use yawn to threaten their enemies, possibly by
displaying large, canine teeth [5].
Although human beings no longer require the use
of displaying their unimpressive incisor teeth
to exhibit dominance or anger, It is possible
that a contagious yawn is a vestigial reflex,
similar to the formation of goose bumps in
humans under stress, because at one time in
evolutionary history, the yawn served to
coordinate the aggressive social behaviour of a
group of animals. I strongly believe that this
unconscious automatic action is a
non-anatomical, physiological atavistic trait
present in humans.
