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73
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- Andrew
C. Gallup. Yawning and the thermoregulatory
hypothesis
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- Abstract: We conducted two
experiments that implicate yawning as a
thermoregulatory mechanism. The first experiment
demonstrates that different patterns of
breathing influence susceptibility to contagious
yawning. When participants were not directed how
to breathe or were instructed to breathe orally
(inhaling and exhaling through their mouth), the
incidence of contagious yawning in response to
seeing videotapes of people yawning was about
48%. When instructed to breathe nasally
(inhaling and exhaling through their nose), no
participants exhibited contagious yawning. In a
second experiment, applying temperature packs to
the forehead also influenced the incidence of
contagious yawning. When participants held a
warm pack (460C) or a pack at room temperature
to their forehead while watching people yawn,
contagious yawning occurred 41% of the time.
When participants held a cold pack (40C) to
their forehead, contagious yawning dropped to
9%. These findings suggest that yawning has an
adaptive/functional component that it is not
merely the derivative of selection for other
forms of behavior.
-
- Introduction
- Yawning is characterized by gaping of the
mouth accompanied by a long inspiration followed
by a shorter expiration. In humans, yawning
begins in utero by 20 weeks gestation (Sherer,
Smith, and Abramowicz, 1991) and continues
throughout life. People typically close their
eyes at the peak of a yawn, and a single yawn
can last for as long as 10 seconds (Daquin,
Micallef, and Blin, 2001). Yawning is commonly
accompanied by stretching and occurs most
frequently before sleep and after waking
(Provine, Hamernik, and Curchack, 1987). Yawning
has long been associated with boredom and sleep.
Under laboratory conditions subjects yawn more
frequently after watching uninteresting color
patterns than music videos (Provine and
Hamernik, 1986). Yawning is widespread and has
been recorded in many vertebrates (Baenninger,
1987). In some primates there is a special
category of yawning that functions as a threat
display (Hinde and Tinbergen, 1958; Tinbergen,
1952). Display yawns expose canine teeth, and
unlike normal yawns the yawner keeps their eyes
open during the yawning episode to monitor the
effect of the yawn on the target subject.
-
- Yawning is under the central control of
several neurotransmitters and neuropeptides
including dopamine, excitatory amino acids,
acetylcholine, serotonin, nitric oxide,
adrenocorticotropic hormone-related peptides and
oxytocin (Argiolas and Melis, 1998). Yawning can
be drug-induced, and drugs are especially
effective when injections are made into the
hypothalamus (Dourish and Cooper, 1990).
Apomorphine injections have been reported to
produce drug-induced yawning along with penile
erection in male mice (Melis, Argiolas, and
Gessa, 1987). There have been many attempts to
identify the function(s) of yawning in humans
(Smith, 1999). However, the
adaptive/functional/biological significance of
yawning has yet to be established (Provine,
2005). It has long been thought (and is still
commonly misconstrued) that the function of a
yawn is to increase O2 levels in the blood.
However, breathing increased levels of oxygen or
carbon dioxide do not affect yawning (Provine,
Tate, and Geldmacher, 1987). Yawning is
contagious. Seeing, hearing, thinking or reading
about yawning can trigger yawns, and attempts to
shield a yawn do not stop its contagion
(Provine, 2005). Under laboratory conditions,
slightly less than half of college students yawn
contagiously, and individual differences in
susceptibility to contagious yawning have been
shown to be related to differences in processing
information about oneself (Platek, Critton,
Myers, and Gallup, 2003). Witnessing people yawn
activates parts of the brain also associated
with self-processing (Platek, Mohamed, and
Gallup, 2005).
-
- Here we investigate the physiological
significance of yawning in humans, specifically
whether yawning may function as a
thermoregulatory mechanism. We propose that
yawning serves to keep the brain in thermal
homeostasis, and that yawning serves to maintain
optimal mental efficiency. We believe that
yawning serves as a compensatory cooling
mechanism when regulatory mechanisms fail to
operate favorably. In order to test this
hypothesis, we conducted two separate
experiments designed to indirectly manipulate
brain temperature. Based on evidence supporting
the selective brain cooling model (du Boulay,
Lawton, and Wallis, 2000; Mariak, White, Lewko,
Lyson, and Piekarski, 1999; Zenker and Kubik,
1996; Falk, 1990; Cabanac, 1986; Cabanac and
Caputa, 1979), we choose to manipulate breathing
conditions and forehead temperature by
noninvasive means. Nasal breathing (du Boulay,
Lawton, and Wallis, 2000; Mariak et al., 1999)
and forehead cooling (Zenker and Kubik, 1996;
Cabanac, 1986) have been shown to be involved in
the thermoregulation (cooling) of the brain.
Contagious yawning was used as a proxy for
yawning in both these experiments for two
reasons. Contagious yawning is indistinguishable
from spontaneous yawning aside from the fact
that the triggers differ, and contagious yawning
can be manipulated under laboratory conditions
(e.g., Platek et al., 2003).
-
- Experiment 1: Breathing
Manipulation
- The first experiment investigated whether
different methods of breathing would affect the
occurrence of contagious yawning, and was
approved by the local Institutional Review
Board. Breathing was the focus of this
experiment because of its influence on brain
temperature (du Boulay, Lawton and Wallis, 2000;
Mariak et al, 1999).
-
- Methods
- Participants Participants were 44
undergraduate students at the University of
Albany. Twenty-seven participants were male and
17 were female, and all were eighteen to
twenty-five years of age.
-
- Procedure Each participant signed a consent
form, and was asked to step into a room and sit
by themselves in front of a computer screen.
Each participant was then instructed to either
inhale and exhale strictly orally, strictly
nasally, strictly orally while wearing a nose
plug, or allowed to breathe normally (i.e., not
instructed how to breathe) during the
experiment. Eleven participants were randomly
assigned to each of the four breathing
conditions. Participants were told to breathe in
the manner instructed for a period of two
minutes prior to and while watching a brief
video tape lasting two minutes and fifty
seconds. This same video was used in a previous
contagious yawning study by Platek et al.
(2003).
-
- The video consisted of 24 7-s digital videos
of eight volunteers (four male, four female),
each depicting three separate conditions
(neutral, laughing or yawning). These videos
were presented in random order on the computer
screen to each participant using Microsoft Media
Player. Each participant was observed through a
one-way mirror by a researcher who recorded
their yawns. At the conclusion of the video
presentation, participants were asked whether
they had yawned during the experiment. Two of
the participants (one in the oral group and one
in the normal breathing group) who did not show
detectable signs of a yawn, each reported
yawning once. These self-reported instances of
yawning were included in the data set.
-
- Results
- Figure 1 shows the distribution of yawning
across all four groups. There were no yawns in
the nasal breathing group. In all other groups,
at least 45% of viewers yawned at least once. In
the strictly oral breathing group (not the nose
plug condition), 54% of viewers yawned at least
once. There were no significant effects of
gender on yawning. Of the 16 yawners (9 male,
seven female), six yawned several times (two
male, four female). Multiple yawning occurred
most frequently in the two oral breathing
conditions. The average number of yawns per
group ranged from three yawns per person in the
oral group to 1.2 yawns per person in the normal
breathing group. Frequency of yawns between
groups was significantly different, •2(3) =
20.45, p<.001. A comparison of the number of
people yawning in the oral and nasal breathing
groups also differed significantly, •2(1) =
6.00,p<.02. Using a binomial test based on
the frequency of contagious yawning (41.5%)
reported by Platek et al. (2003), the absence of
yawning in the nasal breathing group was
significant (p = .0027).
-
-
- Experiment 2: Forehead Temperature
Manipulation
- The second experiment investigated whether
forehead cooling had an impact on the occurrence
of contagious yawning. Forehead temperature was
the focus of this experiment because of its
influence on brain temperature (Zenker and
Kubik, 1996).
-
- Participants
- Participants consisted of an additional
sample of 33 undergraduate students at the
University of Albany. Twenty participants were
female and 13 were male, and all were eighteen
to twenty-five years of age.
-
- Procedure
- After each participant signed a consent
form, they were asked to step into the same room
used in the previous experiment and were seated
in front of the same computer screen. Each
participant was then either instructed to hold a
warm pack, a cold pack, or a pack at room
temperature to their forehead during this
experiment, which lasted for the same length of
time as the previous experiment (4 min, 50sec).
Eleven participants were randomly assigned to
each condition.
- Each pack consisted of a hand towel folded
over a few times and placed into a Ziploc
plastic bag. To influence the temperature of the
hot and cold packs, the hand towel was soaked in
either warm water (46 oC) or cold water (4 oC)
before being placed into the plastic bag.
Temperature of the water and packs was monitored
using a digital thermometer.
-
- The hot and cold packs were all within one
degree Celsius of the intended temperature for
every participant at the beginning of the
testing procedure. The room temperature
condition was achieved by placing a separate,
dry towel into the plastic bag.
- Participants were instructed to hold the
pack to their forehead for a period of two
minutes prior to the video, and to continue
holding the pack to their forehead for the
duration of the video. The same video from the
first study was shown to the participants on a
computer screen using Windows Media Player. Each
participant was observed through a one-way
mirror by a researcher who recorded the
incidence of yawning. Two of the participants
(one in the cold pack group and one in the hot
pack group) who did not show detectable signs of
a yawn, each reported yawning once. These
self-reported instances of yawning were included
in subsequent analyses.
-
- Results
- Only one participant yawned in the cold pack
group (see Figure 2), which was a self-reported
but not independently verified instance. In the
other two groups 41% of the participants yawned
at least once. In the hot pack group, 36% of the
participants yawned, while in the room
temperature condition, 45% of the participants
yawned. Eighteen yawns were recorded in the hot
and room temperature groups while only one
self-reported yawn was recorded in the cold
condition. There were no significant effects of
gender on yawning. Of the 10 people who yawned,
three yawned more than once (two male, one
female). Figure 2 shows the distribution of
yawning across all three groups. Of the people
who yawned, the average number of yawns ranged
from 2.25 per person in the warm pack group to
one yawn per person in the cold pack group. The
difference in number of yawns between groups was
significant, •2(2) = 6.87, p<.05. Again,
using the data from Platek et al. (2003) on the
occurrence of contagious yawning, a binomial
test applied to the number of people yawning in
the cold pack group was also significant, p =
.0199.
-
- General Discussion
- Different methods of breathing had a
significant effect on the incidence of
contagious yawning. Nasal breathing antagonized
contagious yawning, while participants in the
other breathing conditions yawned around 48% of
the time. Manipulating forehead temperature also
had a significant effect on the occurrence of
contagious yawning. A cold pack held to the
forehead greatly reduced contagious yawning,
while warm and room temperature packs had no
effect. The two conditions thought to promote
brain cooling (nasal breathing and forehead
cooling), practically eliminated contagious
yawning. Only one out of a total of 22 combined
participants in the nasal breathing and forehead
cooling conditions yawned, and that participant
showed only one self-reported, but not
independent verified instance of yawning. In the
other conditions, 25 out of 55 participants
yawned for a total of 51 yawns.
-
- The manipulations involved in the breathing
experiment are related to those done in a study
by Provine (1986), where participants were
instructed to think about yawning while
clenching their teeth. Clenched teeth yawns were
rated as abnormal and less satisfying, however
clenching the teeth did not block yawns. Yawning
still occurred as often as in baseline
conditions and the duration of these yawns was
not significantly different. This suggests that
it was not simply the immobilization of the jaw
in the nasal breathing group that eliminated
yawning (even though the participants were not
instructed to close their mouths, they were
instructed to inhale and exhale nasally).
-
- Based on evidence that clenching the teeth
does not block yaning (Provine, 1986) we submit
that it is the breathing manipulation (and the
corresponding thermoregulation effects: see
below) that alter the incidence in contagious
yawning and not the difference between an opened
or closed jaw.
-
- Brain cooling model
- Yawning has many physiological consequences
that are concordant with those needed for the
regulation of brain temperature. The
constriction and relaxation of facial muscles
during yawning increases facial blood flow and
these changes alter cerebral blood flow (Zajonc,
1985). Yawning causes an overall increase in
blood pressure (Arkenasy, 1996), arousal as
measured by skin conductance (Greco and
Baenninger, 1991), and heart rate (Heusner,
1946); all of which promote inc?eased blood flow
during the period immediately prior to yawning.
Research by Cabanac and Brinnel (1985) shows
that during hyperthermia (exercise-induced heat
stress), blood flow is increased from the skin
of the head into the cranial cavity, and this
increase is essential for proper cooling of the
brain. Similar physiological consequences occur
during powerful stretching, and yawning is
accompanied by stretching almost half the time
(Provine, Hamernik, and Curchack, 1987). This
increase in blood flow and cerebral blood flow
(as a result of yawning) function like a
radiator to produce alteration of temperature in
the brain. Likewise, the gaping of the mouth and
deep inhalation of cool air taken into the lungs
during a yawn can alter the temperature of the
blood in the brain through convection.
-
- Thermoregulation has been strongly linked to
structures of the hypothalamus (Cooper, 2002).
Some recent research using tissue slices
pinpoints the complex circuits within the
hypothalamus serving thermoregulation (Boulant,
'1996). Interestingly, yawning also appears to
be regulated by the hypothalamus. Yawning is
under the control of many neurotransmitter and
neuropeptides, and the interaction of these
substances in the nucleus of the hypothalamus
can facilitate or inhibit yawning respectively
(Argiolas and Melis, 1998). Dopamine is a common
neurotransmitter that is released by the
hypothalamus. When injected into the brain,
dopamine agonists (compounds that activate
dopamine receptors) not only produce yawning
(Collins, Witkin, Newman, Svensson, Cao, Grundt,
and Woods, 2005), but have also been shown to
increase heat production (Yamawaki, Lai, and
Horita, 1983; Lin, 1979).
-
- Acute dopamine/norepinephrine reuptake
inhibition has been shown to increase both brain
and core temperature in rats (Hasegawa, Meeusen,
Sarre, Diltoer, Piacentini, and Michotte, 2005).
Prolonged sleep deprivation in rats also
produces increases in brain temperature (Everson
Smith, and Sokoloff, 1994). Interestingly,
yawning is ordinarily 'associated with being
sleepy or tired, and a common symptom on many
sleep deprivation checklists is excessive
yawning.
-
- The fact that nasal breathing antagonized
yawning is consistent with the thermoregulatory
hypothesis. Nasal breathing has been identified
as one of the three putative mechanisms involved
in cooling the brain. The vertebral venous
plexus, which is located in the brainstem, is
cooled by the vertebral artery as a result of
nasal breathing (du Boulay, Lawton, and Wallis,
2000). Nasal breathing also cools other parts of
the brain, including the frontal cortex (Mariak
et al., 1999). Nasal mucosal blood flow
decreases in response to skin cooling, increases
in response to skin warming, and it rises in
response to increases in core temperature
(McIntosh, Zajonc, Vig, and Emerick, 1997).
-
- We suggest that the cerebral cooling
stimulated by nasal breathing was strong enough
to inhibit mechanisms that would normally
trigger yawning.
-
- Cooling the forehead simulates a combination
of the other two mechanisms thought to cool the
brain, one being cooling of venous blood by the
skin which in turn cools the arterial (carotid)
blood supply to the brain. The other major brain
cooling mechanism is the dissipation of heat
through facial emissary veins (Zenker and Kubik,
1996; Cabanac, 1986; Cabanac and Brinnel, 1985),
or heat loss through the skull. The density of
sweat glands on the forehead is three times that
of the rest of the body (Cabanac, 1986) and
under normal conditions, blood from the face and
forehead would be cooled by evaporation of sweat
from the face and scalp.
-
- Predictions of the Model
- On the basis of this evidence we propose
that yawning has a thermoregulatory function,
and that yawning evolved to promote/maintain
mental efficiency by keeping brain temperature
in homeostasis. There are several other ways to
test this model. For instance, we predict that
yawning should be influenced by variation in
ambient temperature. We predict that as ambient
temperatures approach body temperature, yawning
should diminish, and once temperature exceeds
body temperature yawning should stop. If yawning
functions to regulate brain temperature, yawning
above 37°C would warm the brain and would
be counterproductive unless the individual is in
a hypothermic state. Conversely, when ambient
temperature drops below a certain point, perhaps
-10'C, yawning could produce a thermal shock by
sending a wave of unusually cold blood to the
brain. It follows that when people develop a
fever, yawning should stop. That is, when body
temperatures exceed normal values, it may
simulate conditions ordinarily associated with
an increase in ambient temperature above
37°C and activate mechanisms that inhibit
yawning. This may be the reason the application
of the warm pack to the forehead in Experiment 2
failed to stimulate an increase in yawning.
-
- We also predict yawning to increase when
people are engaged in difficult mental tasks.
Increased cortical metabolic activity associated
with higher information processing loads would
increase brain temperature and trigger
compensatory yawning. It has been noted that
yawning occurs frequently in transition periods
from inactivity to activity and vice versa
(Baenninger, Binkley, and Baenninger, 1996;
Provine, Hamernik, and Curchack, 1987), which is
consistent with the idea that yawning plays a
role in mental efficiency. It has also been
argued that the contraction of facial muscles
during a yawn forces blood through cerebral
blood vessels to the brain, which may function
to increase alertness (Barbizet, 1958; Heusner,
1946).
-
- According to our, hypothesis, rather than
promoting sleep, yawning should antagonize
sleep. It has been widely believed that yawning
in the presence of others is disrespectful and a
sign of boredom (e.g., witness the fact that
many people cover their mouths when they yawn).
However, according to our account yawning more
accurately reflects a mechanism that maintains
attention. Likewise, when someone yawns in a
group setting as evidence for diminished mental
processing efficiency, contagious yawning may
have evolved to promote the maintenance of
vigilance.
-
- -Gallup
AC, Miller ML, Clark AB Yawning and
thermoregulation in budgerigars Melopsittacus
undulatus Animal Behav 2009;77(1):109-113
- -Gallup AC,
Gallup G. Yawning as a brain cooling
mechanism: nasal breathing and forehead cooling
diminish the incidence of contagious yawning.
Evolutionary Psychology www.epjournal.net;
2007;5(1): 92-101
- -Gallup
AC, Gallup GG Jr. Yawning and
thermoregulation. Physiol Behav.
2008;95(1-2):10-16
- -Gallup
AC, Miller ML, Clark AB Yawning and
thermoregulation in budgerigars Melopsittacus
undulatus Animal Behav 2009;77(1):109-113
- -Gallup
AC, Gallup Jr GG Venlafaxine-induced
excessive yawning: a thermoregulatory connection
Prog Neuro Psychopharmacol Biol Pyschiatry
2009;33(4):747
- -Gallup AC, Gallup
GG Jr, Feo C. Yawning, sleep, and symptom
relief in patients with multiple sclerosis.
Sleep Med. 2010
- -Platek
SM, SR Critton, et al Contagious yawning:
the role of self-awareness and mental state
attribution Cogn Brain Res 2003; 17; 2;
223-7
- -Platek
S, Mohamed F, Gallup G Contagious yawning
and the brain Cognitive Brain Research,
2005;23:448-452
-
Deklunder G, Dauzat M, Lecroart JL, Hauser JJ,
Houdas Y.
- Influence of ventilation of the face on
thermoregulation in man during hyper- and
hypothermia.
- Eur J Appl Physiol Occup Physiol.
1991;62(5):342-348.
-
- It has been suggested that a thermal
countercurrent exchange may occur in the
cerebral vascular bed of humans, thereby
creating for the brain a state of relative
thermal independence with regard to the rest of
the body. However, worrying questions have
arisen concerning this suggestion. Experiments
were carried out on seven young male volunteers.
Hyper- and hypothermic conditions were produced
by immersion in water at 38.5 degrees C and 25
degrees C, respectively. During the last few
minutes of immersion, the face was cooled or
warmed by ventilation with a 200 l.min-1 air
flow at 5 degrees C or 40 degrees C,
respectively. Internal and peripheral
temperatures were recorded. Blood flow in the
anastomotic vessels between face and brain was
measured by Doppler techniques associated with
computerized frequency analysis. The general
responses were as classically described, i.e. an
increase in peripheral and central temperatures
during immersion in the warm bath and a decrease
in these variables in the cold bath. The
reactions produced by cooling or warming the
face were small and easily explained by the
direct changes of the heat load they induced.
Whatever the thermal conditions, the blood flow
in the anastomotic vessels between the vascular
bed of the face and that of the brain was never
reversed. It was concluded that there was no
experimental evidence for an efficient thermal
counter-current exchange in the vascular bed of
the human head
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are discussed. To assess possible changes
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different between Australopithecus
africanus and Australopithecus
(Paranthropus) robustus. Moreover,
providing further data about the small
sample of South African Plio-Pleistocene
hominids, we also attempt to re-analyse
the incidence of divided hypoglossal
canals and four emissary foramina in a
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representing all ages, species and
subspecies, in A. africanus and in "robust
australopithecines". Up to now, only very
poor data on extracranial dimensions of
venous foramina were available for fossil
hominids. However, this topic provides
interesting information about the
modifications of volume flow during human
evolution. Assuming that in fossil
hominids, as in humans, dimensions of
condylar and mastoid foramina, as well as
those of jugular foramina, depended on
volume flow through them, we conclude,
first, that volume flow through internal
jugular veins was comparable in South
African australopithecines, extant
chimpanzees and humans, and second, that,
in comparison with the extant
less-encephalized chimpanzees (presumably
reflecting the ancestral condition),
volume flow was higher through condylar
veins in A. (P.) robustus. This increase
was responsible for a significantly
greater amount of blood drainage from the
brain (and consequently an increased
arterial blood supply). We support the
view that encephalization was the
prevailing functional explanation for
volume flow increase through condylar
veins in A. (P.) robustus, in comparison
with its ancestor with its presumably more
ape-like degree of encephalization.
Considering the incidence of emissary
canals and foramina, significant
differences between A. africanus, "robust
australopithecines" and all the extant
African ape species, were tested
statistically. Concerning the condylar
canal, we did not find differences between
"robust australopithecines" and extant
African apes. Concerning the incidence of
divided hypoglossal canals, mastoid
canals, parietal and occipital foramina,
no difference was found between extant
African apes, A. africanus and "robust
australopithecines". High frequencies of
either condylar or mastoid canals cannot
be regarded as a "pongid condition".
Moreover, we did not find convincing data
to support the hypothesis that mastoid
emissary veins (partly representing a
putative "radiator" for cooling the brain)
were selected in A. africanus, in
comparison with "robust
australopithecines".
-
- Greco,
M., and Baenninger, R. (1991). Effects of
yawning and related activities on skin
conductance and heart rate. Physiology and
Behavior, 50, 1067- 1069.
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- Hasegawa,
H., Meeusen, R., Sarre, S., Diltoer, M.,
Piacentini, M.F., and Michotte, Y. (2005).
Acute dopamine/norepinephrine reuptake
inhibition increases brain and core temperature
in rats. Journal of Applied Physiology, 99,
1397-1401.
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- Heusner, A.P.
1946. Yawning and associated phenomena.
Physiological Review, 25, 156168.
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- Hinde, R.A., and Tinbergen, N. (1958). The
comparative study of species specific behavior.
In A. Roe and G. C. Simpson (Eds.), Behavior and
Evolution, 251-268. New Haven, CT: Yale
University Press.
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- Lin,
M.T. (1979). Effects of dopaminergic
antagonist and agonist on thermoregulation in
rabbits. Journal of Physiology, 293,
217-228.
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- Mariak,
Z., White, M.D., Lewko, J., Lyson, T., and
Piekarski, P. (1999). Direct cooling of the
human brain by heat loss from the upper
respiratory tract. Journal of Applied
Physiology, 87,1609-1613.
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- McIntosh, D.N., Zajonc, R.B., Vig, P.S., and
Emerick, S.W. (1997). Facial movement,
breathing, temperature, and affect: Implications
of the vascular theory of emotional efference.
Cognition and Emotion, 11, 171-195.
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- Melis,
M.R., Argiolas, A., and Gessa, G.L. (1987)
Apomorphine-induced penile erection and yawning:
Site of action in the brain. Brain Research,
415, 98-104.
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- Platek,
S.M., Critton, S.R., Myers T E, and Gallup, Jr.
G.G. (2003). Contagious yawning: the role of
self-awareness and mental state attribution.
Cognitive Brain Research, 17, 223-227.
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- Platek,
S.M., Mohamed, F.B., and Gallup, Jr., G.G.
(2005). Contagious yawning and the brain.
Cognitive Brain Research, 23, 448-452.
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- Provine,
R.R. (1986). Yawning as a stereotyped action
pattern and releasing stimulus. Ethology, 72,
109-122.
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- Provine,
R.R. (2005). Yawning. American Scientist,
93, 532-539.
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- Provine,
R.R., and Hamernik, H. B. (1986). Yawning:
Effects of stimulus interest. Bulletin of the
Psychonomic Society, 24, 437-438.
-
- Provine,
R.R., Hamernik, H.B., and Curchack, B.B.
(1987). Yawning: Relation to sleeping and
stretching in humans. Ethology, 76,
152-160.
-
- Provine,
R.R., Tate, B.C., and Geldmacher, L.L.
(1987). Yawning: No effect of 3-5% C02, 100% 02,
and exercise. Behavioral Neural Biology, 48,
382-393.
-
- Sherer, D.M.,
Smith, S.A., and Abramowicz, J.S. (1991).
Fetal yawning in utero at 20 weeks gestation.
Journal of Ultrasound Medicine, 10, 68.
-
- Smith, E.0.
(1999). Yawning: An evolutionary perspective.
Human Evolution, 14, 191-98.
-
- Tinbergen N (1952) Derived activities Their
causation, biological significance, origin, and
emancipation during evolution. Quarterly Review
of Biology, 27, 1-32.
-
- Yamawaki,
S., Lai, H., and Horita, A. (1983).
Dopaminergic and serotonergic mechanisms of
thermoregulation: Mediation of thermal effects
of apomorphine and dopamine. Journal of
Pharmacology and Experimental Therapeutics, 227,
383-388.
-
- Zajonc, R.B. (1985). Emotion and Facial
Efference: A Theory Reclaimed. Science, 288,
15-21.
-
- Zenker, W., and Kubik, S..(1996). Brain
cooling in humans - anatomical considerations.
Anatomy & Embryology (Berl), 193, 1-13.
- Vascular arrangements allowing a bulky
transfer of venous blood from the skin of
the head and from nasal and paranasal
mucous membranes to the dura matter
provide an excellent anatomical basis for
the convection process of cooling, caused
by evaporation of sweat or mucus. The dura
mater, with its extraordinarily high
vascularization controlled by a potent
vasomotor apparatus, may transmit
temperature changes to the cerebrospinal
fluid (CSF) compartment. Temperature
gradients of the CSF may in turn influence
the temperature of brain parenchyma (1)
directly, along the extensive contact area
between the cerebrocortical surface and
the CSF-compartment, or (2) indirectly,
via brain arteries that extend over long
distances and arborize within the
subarachnoid space before entering the
pial vascular network and brain
parenchyma. Numerous subarachnoid and pial
arterial branches exposed to the CSF have
diameters in the range of the vessels of
the retia mirabilia of animals in which
selective brain cooling has been clearly
established experimentally. It is also
shown that the arrangements of venous
plexuses within the vertebral canal
provide anatomical preconditions for a
cooling of the spinal cord via the CSF.
The possibility of spinal cord and spinal
ganglia cooling by temperature convection
via venous blood--cooled in the venous
networks of the skin of the back--flowing
through numerous anastomoses to the
external and internal vertebral plexuses
and, finally, into the vascular bed of the
spinal dura is discussed on the basis of
anatomical facts.
-
Who
knows whether there is really a need for cooling
the brain?
-
- Gallup
& Gallup conducted two experiments that
implicate yawning as a thermoregulatory
mechanism.
-
- Gallup and Gallup propose to renew the
theory of the yawn's finality. In order to
observe yawns among the participants with the
experiments, they projected a film showing the
successive yawns of eight people (man and woman)
randomly stopped by scenes of laughter or
neutral facial expressions. Then, they counted
up the yawns induced by "contagion"
(echokinesia). In general, the unavoidable
interaction between voluntary and automatic
control affects the outcome of many experiments
in humans. Moreover, contagious yawning is not
identical to spontaneous yawning.
-
- First
experiment :
- They show that the yawns occur normally and
that 45% of the particpants yawn when they can
open the mouth but that no yawn takes place if
the instruction is given to hold the mouth
completely closed. This fact is established for
a long time: for example, the Equidae, which
breathes only by the nostril, yawns opening
widely the mouth like all the other
vertebrates.
-
- "The first experiment demonstrates that
different patterns of breathing influence
susceptibility to contagious yawning. When
participants were not directed how to breathe or
were instructed to breathe orally (inhaling and
exhaling through their mouth), the incidence of
contagious yawning in response to seeing
videotapes of people yawning was about 48%. When
instructed to breathe nasally (inhaling and
exhaling through their nose), no participants
exhibited contagious yawning."
-
- Second
experiment:
- "In a second experiment, applying
temperature packs to the forehead also
influenced the incidence of contagious yawning.
When participants held a warm pack (460C) or a
pack at room temperature to their forehead while
watching people yawn, contagious yawning
occurred 41% of the time. When participants held
a cold pack (40C) to their forehead, contagious
yawning dropped to 9%. These findings suggest
that yawning has an adaptive/functional
component that it is not merely the derivative
of selection for other forms of
behavior."
-
- The only fact of laying a cold stimulus on
the forhead is enough to stimulate the awakening
and inhibits the yawn. In the same way, a
constant attention does not make receptive to
the echokinesia of yawning. Inversely, heat does
not have this waking up effect. The increase in
the ambient temperature facilitates sleepiness
and thus yawning.
-
- Room temperature is not considered. However,
a quantitative analysis of the effects of
different temperatures of the air inhaled via
nose or mouth would be interesting.
-
- Forehead cooling is not affecting directly
and only the brain. It is a peripheral thermal
input favoring inhibition and reinforcement of
oral and nasal respiration, respectively, to
warm the inhaled air. Oral ventilation in this
condition would be necessary only to comply with
the oxygen demand during exercise
-
- The researchs of Cabanac and Brinnel as
reported by G & G relate to the control of
the cerebral temperature during the fever.
There is no work (to my knowledge) indicating
that the cerebral activity modifies the internal
temperature of the brain in a variable way
according to the level of attention.
Functional MRI studies in humans have shown that
even when the brain is not engaged in any
specific tasks, spontaneous fluctuations occur
in the blood-oxygen-level dependent (Bold)
signal (which is thought to reflect neural
activity). These resting state fluctuations are
not chaotic but are in fact anatomically and
temparally consistent. The significance of this
resting state activity is unclear but,
intriguingly, it even occurs when humans or
animals are unconscious. Thus, spontaneous
fluctuations in brain activity maintain the
brain in constant temperature somehow the step
of neuronal activities (Vincent
JL. et al.).
-
- Sleep onset is likeliest to occur on the
falling limb of the temperature cycle. The
offset of sleep occurs most often on the rising
limb of the circadian body temperature curve. In
human, the most pronounced occurrences of
yawning stays at awakening in the morning, in
association with the stretching of muscles
(pandiculation), and as sleep is about to occur,
without stretching, as well as in any condition
of lessened vigilance (Baenninger 1996, Greco
1993). Repetitive and monotonous activities
trigger repeated yawns as have shown studies of
individuals at their work stations. In not a
single circumstance, the yawns appear with the
acme of the circadian rhythm of the
temperature.
-
- The old authors often spoke about the yawns
during the fever but have given to them the
significance of a clinical sign fortelling the
onset of vigilance's disorders. The assertion
"deep inhalation of cool air taken into the
lungs during a yawn can later the temperature
the temperature of the blood in the brain
through convection" appears largely conjectural.
The air in the lung attains 37° so far its
inhalation and prevents to harm the lungs. Ford
GP, Reardon DC. report that intubated delivery
of air into the lungs at a temperature
significantly below body temperature, especially
over a prolonged period, is likely to inhibit
recovery from brain injuries.
-
- Many authors (Parmeggiani
2007) have reported changes in brain
temperature during the ultradian sleep cycle in
several mammalian species. The temperature
decrease in NREM sleep appears as a normal
effect of thermoregulation operating at a lower
set point temperature than in wakefulness. In
contrast, the increase in brain temperature
related to REM sleep appears paradoxical from
the viewpoint of normal thermoregulation. The
problem of the physiologic mechanisms underlying
this temperature change remains unresolved.
-
- Changes in brain temperature are in general
relevant to both the energy metabolism of the
brain and the function of the
preoptic-hypothalamic thermostat. Heat is
produced by cellular energy metabolism and is
transferred to the arterial blood in inverse
relation to its temperature, which is lower than
that of the brain in normal conditions. It is
obvious that brain homeothermy is altered
essentially by quantitative imbalances between
metabolic heat production and heat loss.
-
- There are different mechanisms for cooling
the brain in mammals and more than a single
mechanism may be operative. In general, the cool
venous blood flowing from the systemic heat
exchangers of the body (upper airway mucosa, ear
pinna, horn, tail, skin, according to species)
to the heart mixes with the warm venous blood
returning to the heart from heat-producing body
tissues.
-
- This systemic mechanism cools the arterial
blood including that flowing to the brain
(systemic brain cooling). In addition to
systemic brain cooling, there is also a
mechanism for selective brain cooling. In
species like the cat, dog, sheep and goat, the
carotid blood supply to the brain is again
thermally conditioned prior to entering into the
circle of Willis by countercurrent heat exchange
between carotid rete and venous sinuses (e.g.,
sinus cavernosus). The carotid rete is a network
of fine vessels (rudimental in the dog), derived
from the external branch of the common carotid
artery. The arterial blood flowing to the brain
in the carotid rete is surrounded by sinus
venous blood cooled in the upper airway mucosa
and flowing in an opposite direction to the
heart. The carotid rete is connected to the
circle of Willis through a short artery
(homologous to the distal part of the internal
carotid artery of species lacking the carotid
rete). As a result of the countercurrent heat
exchange, the temperature of the carotid blood
reaching the circle of Willis is further
decreased with respect to that of the aortic
arch blood. Vertebral artery blood is not
thermally conditioned by a countercurrent heat
exchange mechanism and enters into the circle of
Willis at the temperature of the blood in the
aortic arch.
-
- In conclusion, the difference between the
temperatures of vertebral artery blood (systemic
cooling only) and carotid artery blood (both
systemic and selective cooling) flowing into the
circle of Willis depends on the heat loss from
the carotid rete. Eventually, the average brain
temperature is determined by the relative
amounts of carotid and vertebral artery blood
contributing to the total blood flow of the
brain.
-
- Another mechanism for selective brain
cooling is typical of species lacking the
carotid rete (e.g., rabbit and rat). It is
provided by conductive heat exchange between the
basal portion of the brain, including the circle
of Willis, and the basal venous sinuses that
drain cool venous blood from the upper airway
mucosa.
-
- The effects of systemic and selective brain
cooling appear in the temperatures of the
hindbrain and forebrain, respectively. This is
shown by the positive difference between pontine
and preoptic-hypothalamic temperatures in cats,
rabbits and rats.
-
- Heat loss from systemic heat exchangers,
affecting carotid blood temperature through the
systemic venous return to the heart (systemic
brain cooling), is the most important
determinant of brain temperature in primates.
Concerning humans, in particular, there is no
consensus as to whether a mechanism for
selective brain cooling plays a significant
role.
-
- Skin or hypothalamus cooling: a
behavioral choice by rat
- Dib B, Cabanac M.
- Brain Res.
1984;302(1):1-7
- Rats were chronically
implanted with a hypothalamic thermode. After
recovery the thermode was heated and the rats
were exposed to 4 ambient temperatures (Ta) 20,
30, 35 and 40 degrees C. For each Ta they were
subjected to 3 conditions: (1) they could press
a bar which provided them with a cool wind; (2)
they could press a bar which cooled the
hypothalamic thermode; and (3) both bars were
active and the rat could press either one. Skin,
hypothalamic, and rectal temperatures were
recorded at the same time. The results indicate
that when rats had either only or by choice
access to the lever that cooled their
hypothalamus, they used it in such a way as to
prevent their hypothalamus from overheating. A
lower priority was given to the maintenance of
skin temperature.
-
-
- REM
sleep related increase in brain temperature: a
physiologic problem.
- Parmeggiani PL. Arch Ital
Biol. 2007;145(1):13-21.
-
- Prolonged unintended brain cooling may
inhibit recovery from brain injuries: case study
and literature review
- Ford GP, Reardon DC Med Sci
Monit
2006;12(8):CS74-77
-
Andrew
C. Gallup. Yawning and the thermoregulatory
hypothesis
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