Yawning is a common behavioral act in a
wide variety of vertebrate species but its
functions are not well understood. Despite the
widely held beliefs that it serves as a signal
of boredom, results from a lack of oxygen, and
that it is a socially
contagious act we lack a comprehensive,
satisfactory explanation of its mechanisms and
functions. Yawning may serve different functions
in the variety
of species in which it has been observed
(2).
In some mammalian species yawning appears to
be associated with transitions between periods
of high and low activity or arousal (15).
Relatively sedentary species that sleep very
little, such as many herbivores, apparently yawn
infrequently if at all (4); species that sleep 8
or 10 h daily and that altemate between active
and inactive periods (e.g., predatory carnivores
and primates) yawn much more frequently (2).
Arousal of a sexual nature is associated with
yawning in several species of nonhuman
primates and rodents; a syndrome of yawning
and penile erection has been examined in detail
(12). The syndrome is released by several
steroid hormones, including testosterone,
although little bas been discovered about
possible reasons for such an association.
A circadian pattern has been found in
spontaneous yawning
by rats (1), with the highest frequency
being evident during daily transitions between
light and dark-. In normal, unstressed humans
daily peaks of yawning are also associated with
transitions from sleeping to waking and from
waking to sleeping (9,13).
Although clear differences exist between
individual humans, their daily
rhythms of activity are remarkably
consistent across long time periods when
measured with monitors on the wrist if regular
circadian patterns of yawning exist in
individuals reasoned that such patterns might be
related to such circadian patterns of overall
activity. We undertook the first of these
studies to examine both activity and yawning
patterns in the daily activities of busy adult
professionals, and to determine whether any
relationships between those patterns could be
found in general, or in individuals. For several
scientific reasons it was necessary to study
subjects outside the laboratory. First, yawning
is a low-frequency act, and human subjects
cannot be held captive until they yawn often
enoug-h to allow statistical analysis. Second,
human subjects actively inhibit their yawns when
under observation in the laboratory (3,7) so
that the apparent objectivity of the laboratory
context may result in inaccurate data. Third,
our interest was in the natural yawning and
activity patterns of people in their daily
lives. Previous research has established that
self-reports of yawing are valid measures (7)
and that interested volunteer subjects can
reliably report on their own yawning by keeping
loggs (9, 13)
Our working hypothesis has been that yawning
is associated with activity (and perhaps
arousal) levels in humans and other species (2,
8, 9). According to this hypothesis, we would
expect yawning frequency to increase when an
individual's activity or arousal level is low
and when the environment has not been
particularly stimulating, but where vigilance or
alertress is necessary. Under these
circumstances we would expect increased yawning
if our hypothesis is correct; in our view
yawning is one means of changing arousal level,
and a sign or marker that such a change is
occurring. Wrist activity has been used to
measure circadian activity rhythms in
free-living human subjects. [...]
General discussion : While the small
number of subjects in the first study may limit
the generality of our findings, both the yawning
frequency and activity rythms of individual
subjects were clear and quite consistent, and
yawn frequencies were similar to those in the
second study.
There did appear to be a simple relationship
between yawning and activity of individuals as
measured by wrist monitors. The increased
occurrence of yawning reliably predicted periods
of elevated activity in all of the eight
records. This close temporal relationship
between increased yawning and increased activity
held true even in the most active subject, even
though this active individual also yawned the
least. That the most active subject yawned least
is not damaging to our arousal hypothesis
because her low frequency of yawning may have
been a result of her already having a high level
of arousal. While yawning is reliably followed
by elevated activity, it does not follow (and
our hypothesis does not require) that elevated
activity is always preceded by yawning. Yawning
is surely only one means of regulating arousal
and activity; it may well be a marker of changed
arousal level rather than a cause.
Our preliminary findings presented here
support previous findings which suggest that
yawning is associated with changes in an
individual's activity or arousal level. In
nonhuman primates yawning (and penile erection)
appears in sexual and agonistic contexts
(10,15). Yawning may be associated with conflict
and stress (11) and is likely when transitions
occur between activity or excitation levels
(15). Perhaps the common element in these
apparently disparate stimulus situations is that
yawning is associated with increases in the
arousal, vigilance or attentiveness that his
important in such situations.
In the second experiment daily rhythm
parameters (e.g., wake-up time, to-sleep time)
were similar te, those previously reported for
university students (5). In this study, as in
the firstthe mean daily frequency of yawning was
between 7 and 8, but with a range from 0 to 28.
'Mese data are also comparable to those found in
earlier studies (9,13). We also confirmed the
result (14) that no sex difference in yawning
exists in humans. Among nonhuman primates males
typically yawn more frequently than females,
perhaps as a consequence of more frequent
aggonistic activity (12).
Daily frequency of yawning by the
undergraduates was not related to times of
either waking up or going to sleep. This finding
confirms the result (3) that there was no
correlation between number of yawns emitted and
the duration of sleep the previous night. In the
present study more time was spent sleepine on
weekends than during the week, while yawning was
more frequent during the week than on
weekends.
We can only speculate about how our subjects
spent their days since we did not ask them to
keep legs of their precise activities, nor what
they were doing each time they yawned. The fact
that more yawning occurred during the week than
on weekends is what our arousal hypothesis would
predict if subjects engaged in tasks that varied
in their arousal requirements during the week,
while spending time on week-ends at a lower,
more constant level of arousal. There is also
another hypothesis that accounts for the
difference: Undergraduate activity logs in an
earlier study (9) indicated that students yawned
most frequently while sitting in class (21% of
yawns), an activity that did not occur on
weekends.
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