mise à jour du 6 juin 2002
 Trends Pharmacol Sci
1988; 9; 4; 119
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


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.


  1. Provine, R. R. (1986) Ethology, 72,109-122
  2. Provine, R. R., Tate, B. C. and Geldmacher, L. L. (1987) Behav. Neural Biol. 48, 382-393
  3. Barbizet, J. (1958) 1. Neurol. Neurosurg. Psychiatry 21, 203-209
  4. Montagu, A. (1962) 1. Amer. Med. Assoc 182,732