The infamous Dr. Nanjo wrote:
> 1) What exactly is the role of yawning in the course of human physiological
> functioning? Is there any truth to that "yawning is contagious" business?
According to Baenninger (1997), yawning probably functions to increase arousal
in situations of low stimulation, especially when decreased arousal is costly.
He argued that, contrary to popular belief, yawning probably does not function
primarily to get oxygen to the brain: there is little evidence for this claim
and it seems that yawning delivers less oxygen to the brain than would simply
breathing faster or more deeply. In fact, one study had subjects breathe air
that was higher in carbon dioxide levels than normal air: these subjects
breathed more quickly but yawning was not affected. The same was true when
oxygen levels were increased.
Some have argued that there is a biological rhythm associated with yawning. For
example, college students seem to yawn most frequently during the hour after
waking and the hour before sleeping, as well as perhaps a smaller peak during
the early afternoon. Baenninger suggested that a more parsimonious explanation
was the following: "If yawning occurs in anticipation of regular daily events
that require increased arousal, we would expect yawning after sleeping, during
sedentary activities that require arousal or vigilance..., and as a way of
maintaining wakefulness in the late evening" (p. 199). It may be that yawning
helps to increase cerebral blood flow. For example, in thrombosis patients,
yawning seemed most likely to occur when cortical activity was low (as measured
by EEG) and when "partial pressure of oxygen in the carotid artery decreased"
(p. 203). Yawning may do the following:
"inhaling stretches bronchial muscles and stimulates vagus nerve terminals that
bring about dilation of arterioles via cholinergic pathways. This decreases
resistance to peripheral circulation and enhances blood flow. Gaping of the jaw
contracts the lateral pterygoid and soleus muscles, which empties rich venous
plexuses contained in them.... This action of the jaw muscles enhances venous
return, which promotes blood hyperoxygenation and thus stimulates cerebral
blood flow (including the ascending reticular activating system)." (p. 203)
But he also noted that, although plausible, there still was little evidence for
this theory.
Baenninger also examined cross-species evidence for his claim that yawning has
an arousal function. It was amazing to me the number and diversity of species
that show behavior that looks like yawning: it seems to occur in all classes of
vertebrates. One also can increase yawning through artificial selection. A
strain of rats has been bred that yawns, on average, about 25 times an hour. Of
course, yawning in other species may involve different functions than yawning
in humans; but Baenninger provided some evidence for the arousal hypothesis in
at least some species
My students can beat this strain of rates hands down. In fact, I often tell
them that I appreciate their yawns. If Baenninger's claim is correct, the fact
that they are yawning during class is a sign of their respect for me: they are
trying to remain vigilant and to increase their arousal levels. However, once
one person begins to yawn (or even when simply talking about it: I'll bet some
of you are yawning right now), others begin to yawn. Baenninger mentioned that
it is obvious that yawning is contagious (even blind people yawn when they hear
others yawning) but that this has been difficult to study in the lab because
subjects are reluctant to yawn in front of researchers (it is seen as
impolite).
Almost anything you might want to know about yawning is in this article. I
don't know if he has continued this research. Perhaps someone else knows about
more recent articles?
Jeff
Reference:
Baenninger, R. (1997). On yawning and its functions. Psychonomic Bulletin and
Review, 4, 198-207.
--
Jeffry P. Ricker, Ph.D. Office Phone: (480) 423-6213
9000 E. Chaparral Rd. FAX Number: (480) 423-6298
Psychology Department [EMAIL PROTECTED]
Scottsdale Community College
Scottsdale, AZ 85256-2626
"The truth is rare and never simple."
Oscar Wilde
"Science must begin with myths and with the criticism of myths"
Karl Popper
Listowner: Psychologists Educating Students to Think Skeptically (PESTS)
http://www.sc.maricopa.edu/sbscience/pests/index.html
