- mise à jour
du 6 juin 2002
- Trends
Pharmacol Sci
- 1988; 9; 4;
119
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- Now
you'll start yawning and you won't know
why
- Ivan Izquierdo
- Centro de Memoria,
Departmento de Bioquimica, lnstituto de
Biociencias, UFRGS, 90049 Porto Alegre, RS,
Brazil
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Because reading about yawning, watching
other people yawn, or even thinking about
yawning makes you yawn. Most species simply lack
this behaviour'; people who sit in too many
committees and are then forced to get to sleep
late in order to get some real work done, are,
on the other hand, great specialists.
In spite of the great sociobiological
importance and the extraordinari.y widespread
incidence of this stereotyped behaviour (which,
by the way, if practised in excess may even be
symptomatic of serious disease such as chorea,
brain tumours, or encephalitis) very few have
endeavoured to study the physiology or
pharmacology of yawning.
Robert Provine
and his colleagues have recently studied an
aspect of the ecotoxicology of yawning. For no
apparent reason, it was assumed for years that
hypoxia or high blood C02 levels trigger yawning
and that yawning may reverse those respiratory
changes. Provine et al. submitted 17- to
21-year-old healthy volunteers to normal room
air (21% 02, 0.03% C02, 79% N2), to atmospheres
containing 100% 02 or 3-5% C02, or to 10 min of
exercise (stepping up and clown a 10-inch step
once every 2 s). The environmental changes had
no effect on the rate of breathing or yawning or
on yawn duration. The exercise doubled the
respiratory rate, which went back to normal 3-4
min after the exercise was stopped; the rate of
yawning declined monotonically from the
beginning of exercise on, and went on declining
over the 10-min post-exercise rest period, i.e.
it bore no relation to respiratory rate
changes.
So, respiration, 02 and C02 seem to have
little to do with yawning. There must be some
other explanation for the remarkable
contagiousness of this behaviour and for its
tendency to occur when one gets bored or sleepy.
If readers of this article have been induced to
yawn a lot just because of reading it, I can
offer them just one consolation: I did too, when
writing it. And we don't really know why. To
parody Walt Whitman:
- 0 friend unseen, unborn,
unknown
- Student of our sweet English tongue
- Read out my words at night, alone...
- And for a reason still unsung
- Like me, my friend, you'Il yawn and
yawn.
References
- Provine, R.
R. (1986) Ethology, 72,109-122
- Provine, R. R.,
Tate, B. C. and Geldmacher, L. L. (1987)
Behav. Neural Biol. 48, 382-393
- Barbizet,
J. (1958) 1. Neurol. Neurosurg. Psychiatry
21, 203-209
- Montagu, A.
(1962) 1. Amer. Med. Assoc 182,732
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