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Yawning as a Brain Cooling Mechanism: Nasal Breathing and Forehead Cooling Diminish the Incidence of Contagious Yawning

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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 (46°C) 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 (4°C) 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. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
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Evolutionary Psychology
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Original Article
Yawning as a Brain Cooling Mechanism: Nasal Breathing and Forehead
Cooling Diminish the Incidence of Contagious Yawning
Andrew C. Gallup, Department of Psychology, State University of New York at Albany, Albany, NY
12222, USA.
Gordon G. Gallup Jr., Department of Psychology, State University of New York at Albany. Email:
gallup@albany.edu (Corresponding author)
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 (46
0
C) 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 (4
0
C) 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.
Keywords: yawning, contagious yawning, nasal breathing, forehead cooling, brain
temperature, thermoregulation, information processing, group vigilance.
________________________________________________________________________
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
Yawning as a Brain Cooling Mechanism
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
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Yawning as a Brain Cooling Mechanism
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, ҳ
2
(3) = 20.45, p<.001. A comparison of the number of people
yawning in the oral and nasal breathing groups also differed significantly, ҳ
2
(1) = 6.00,
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Yawning as a Brain Cooling Mechanism
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).
Breathing Experiment
0
2
4
6
8
10
12
14
16
18
20
Oral Nose Plug Nasal Normal
Breathing Condition
Numbe
r
People who yawned
Total yawns
Figure 1: Number of people out of eleven in each group who yawned and total number
of yawns as a function of breathing condition.
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.
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Yawning as a Brain Cooling Mechanism
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
o
C) or cold water (4
o
C) 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, ҳ
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.
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Temperature Experiment
0
1
2
3
4
5
6
7
8
9
10
Warm Pack Cold Pack Room
Temperature
Temperature Condition
Numbe
r
People who yawned
Total yawns
Figure 2: Number of people who yawned and the total number of yawns as a function of
forehead temperature condition.
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 yawning (Provine,
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Yawning as a Brain Cooling Mechanism
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
any physiological consequences that are concordant with those
oregulation has been strongly linked to structures of the hypothalamus
has been shown to increase
athing antagonized yawning is consistent with the
rmo
Yawning has m
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 increased 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.
Therm
(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
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 bre
the regulatory 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).
Evolutionary Psychology – ISSN 1474-7049 – Volume 5(1). 2007.
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Yawning as a Brain Cooling Mechanism
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
redictions of the Model
is evidence we propose that yawning has a thermoregulatory
lt mental
wning should
cknowledgment: The authors thank Jessica Wess for help reviewing the literature.
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.
P
On the basis of th
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
o
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
o
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
o
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 difficu
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, ya
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.
A
Evolutionary Psychology – ISSN 1474-7049 – Volume 5(1). 2007.
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Yawning as a Brain Cooling Mechanism
Received 8 September 2006; Revision received 16 January 2007; Accepted 17 January
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... This view is supported by psychological research showing that the expression of contagious yawning can be effectively modulated by the same physiological variables known to modulate spontaneous yawning. These include circadian factors Giganti & Zilli, 2011), cooling and warming of the brain via temperature manipulations to the neck and skull (Gallup & Gallup, 2007;Ramirez et al., 2019), ambient temperature variation (e.g. Eldakar et al., 2015;Massen et al., 2014) and stressful situations (Eldakar et al., 2017). ...
... More recent research provides evidence for a thermoregulatory function to yawning in homeotherms (Gallup & Gallup, 2007. This hypothesis proposes that yawns function to cool the brain, which in turn could improve alertness and mental processing efficiency of the yawner. ...
... A separate, but not mutually exclusive, adaptive hypothesis for yawn contagion stems from the purported brain cooling function of yawning. In particular, Gallup and Gallup (2007) proposed that contagious yawns may have evolved to promote overall group vigilance. Accordingly, if yawns serve to counteract rising brain temperature and reduced alertness and mental processing, the transfer of this behaviour to nearby conspecifics could then increase their vigilance as well. ...
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Yawning is a stereotyped action pattern that is prevalent across vertebrates. While there is growing consensus on the physiological functions of spontaneous yawning in neurovascular circulation and brain cooling, far less is known about how the act of yawning alters the cognition and behaviour of observers. By bridging and synthesizing a wide range of literature, this review attempts to provide a unifying framework for understanding the evolution and elaboration of derived features of yawning in social vertebrates. Recent studies in animal behaviour, psychology and neuroscience now provide evidence that yawns serve as a cue that improves the vigilance of observers, and that contagious yawning functions to synchronize and/or coordinate group activity patterns. These social responses to yawning align with research on the physiological significance of this behaviour, as well as the ubiquitous temporal and contextual variation in yawn frequency across mammals and birds. In addition, these changes in mental processing and behaviour resulting from the detection of yawning in others are consistent with variability in the expression of yawn contagion based on affinity and social status in primates. Topics for further research in these areas are discussed.
... Yawning is a complex reflex that has been documented across all classes of vertebrates [1][2][3][4]. From an evolutionary perspective, this stereotyped motor action patten appears to be a neurological adaptation that stimulates changes in state [5] and arousal [6] through intracranial circulation and brain cooling [7][8][9][10]. While yawning occurs with greatest frequency around sleeping and waking transitions [11][12][13][14], this response is also considered a displacement behavior that can be indicative of stress or conflict [15,16]. ...
... Lastly, given that physiological variables known to alter spontaneous yawning also modulate yawn contagion [27], we also hypothesized that participant tiredness at the time of testing would predict interspecies contagious yawning. Relatedly, based on the association between yawning and sleep/wake cycles [7][8][9][10], we also took into account the duration of the sleep the night prior to testing. Lastly, participant age and gender were also collected since some studies have shown these variables can affect intraspecific yawn contagion [69][70][71]. ...
... However, as predicted, participants that were more tired at the time of testing reported both a higher incidence and a greater overall frequency of yawning (see Tables 2 and 3). The fact that tiredness was the best predictor of yawn contagion in this study replicates recent research on intraspecific contagious yawning in humans [27] and further supports previous studies showing that contagious yawns are modulated by physiological factors known to trigger spontaneous yawning [8,[80][81][82][83]. ...
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Contagious yawning, or the reflexive tendency to yawn following the detection of yawning in others, is well-documented among humans and a growing number of social vertebrates. While the most common form of yawn contagion occurs between conspecifics, some non-human animals in captivity have been reported to yawn in response to yawns from human handlers/caregivers. The current research sought to provide the first formal investigation of whether people yawn contagiously in response to yawns from non-human animals. In addition, this study aimed to test whether this response was modulated by phylogenetic relatedness and domestication/social closeness. A total of 296 participants from Amazon Mechanical Turk self-reported on their yawning behavior following exposure to a (1) control (non-yawning) condition or a compilation of yawning stimuli either from (2) fish, (3) amphibians, (4) reptiles, (5) birds, (6) non-primate mammals, (7) apes, or (8) domesticated cats and dogs. The results provide strong support for interspecific yawn contagion. However, neither the propensity to yawn (binary) nor total yawn frequency varied significantly across interspecific conditions. Overall, these findings suggest that the mechanisms governing yawn contagion can be activated by varied forms of yawning stimuli, including those from distantly related and unfamiliar species.
... Interestingly, both ASD and the prevalence of psychopathic traits are more common among males 46,47 . These populations are also of interest to study with regards to the hypothesized functional significance of yawn contagion in promoting collective vigilance and synchronized group behavior/ movement [48][49][50][51][52][53] . Impairments in imitation and joint attention among individuals with ASD diminish cooperation and coordinated actions 54 . ...
... Four distinct measures of psychopathy were included to assess the generalizability of this association, and given the importance of physiological variables in influencing yawn contagion (e.g. 15,48,[73][74][75][76][77][78] ), measures of sleep and fatigue were taken into consideration. Lastly, given recent debates on the importance of attention in contributing to yawn contagion 22,23,34,65 , both objective and subjective measures of attention to the contagious yawning video stimulus were included. ...
... Thus, the reduced tendency to yawn contagiously among individuals scoring high in psychopathic traits could reflect a generalized impairment in biobehavioral synchrony. Moreover, it has been theorized that contagious yawning evolved to enhance collective vigilance 48,49 and coordinate or synchronize group behavior [50][51][52][53] , and these functional accounts for yawn contagion can explain the negative association between contagious yawning and psychopathy in the absence of emotional contagion. For example, groups characterized by higher levels of psychopathy have previously been shown to have more dysfunctional interactions and lower levels of cohesion 60 . ...
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Considerable variation exists in the contagiousness of yawning, and numerous studies have been conducted to investigate the proximate mechanisms involved in this response. Yet, findings within the psychological literature are mixed, with many studies conducted on relatively small and homogeneous samples. Here, we aimed to replicate and extend upon research suggesting a negative relationship between psychopathic traits and yawn contagion in community samples. In the largest study of contagious yawning to date (N = 458), which included both university students and community members from across 50 nationalities, participants completed an online study in which they self-reported on their yawn contagion to a video stimulus and completed four measures of psychopathy: the primary and secondary psychopathy scales from the Levenson Self-Report Psychopathy Scale (LSRPS), the psychopathy construct from the Dirty Dozen, and the Psychopathic Personality Traits Scale (PPTS). Results support previous findings in that participants that yawned contagiously tended to score lower on the combined and primary measures of psychopathy. That said, tiredness was the strongest predictor across all models. These findings align with functional accounts of spontaneous and contagious yawning and a generalized impairment in overall patterns of behavioral contagion and biobehavioral synchrony among people high in psychopathic traits.
... Although not necessarily an emotional expression, yawning is highly contagious, also in orangutans . It has been proposed that it may synchronize vigilance levels between individuals (Gallup & Gallup, 2007;Miller et al., 2012); thus, its rapid detection may be beneficial in threatening situations. ...
... Yawning potentially facilitates thermoregulation of the brain (Massen et al., 2021), where cooling may promote vigilance. The contagiousness of yawning within a group may consequently synchronize vigilance (Bower et al., 2012;Gallup & Gallup, 2007) and thus may be beneficial to quickly attend to. Given that yawning is a dynamic facial expression, the still images of yawns in our study may lack crucial information for orangutans to elicit an attention bias. ...
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Attention may be swiftly and automatically tuned to emotional expressions in social primates, as has been demonstrated in humans, bonobos, and macaques, and with mixed evidence in chimpanzees, where rapid detection of emotional expressions is thought to aid in navigating their social environment. Compared to the other great apes, orangutans are considered semi-solitary, but still form temporary social parties in which sensitivity to others' emotional expressions may be beneficial. The current study investigated whether implicit emotion-biased attention is also present in orangutans (Pongo pygmaeus). We trained six orang-utans on the dot-probe paradigm: an established paradigm used in comparative studies which measures reaction time in response to a probe replacing emotional and neutral stimuli. Emotional stimuli consisted of scenes depicting conspecifics having sex, playing, grooming, yawning, or displaying aggression. These scenes were contrasted with neutral scenes showing conspecifics with a neutral face and body posture. Using Bayesian mixed modeling, we found no evidence for an overall emotion bias in this species. When looking at emotion categories separately, we also did not find substantial biases. We discuss the absence of an implicit attention bias for emotional expressions in orangutans in relation to the existing primate literature, and the methodolog-ical limitations of the task. Furthermore, we reconsider the emotional stimuli used in this study and their biological relevance.
... In amphibians, reptiles, and mammals, the firing rates of LC neurons increase in more acidic environments [100,105,[107][108][109]. In response, enhanced LC activity promotes respiration [105,110], which reduces the CO 2 concentration and increases the body temperature [111][112][113]. Unlike in the endotherms, the CO 2 /pH in ectotherms fluctuates with body temperature. ...
... In ectothermic non-mammals, the environmental temperature negatively regulates the basal firing rate of LC, but positively modulates the chemosensitivity of LC [100,101,105,107,120]. In mammals, body temperature change and LC activity reciprocally interact with each other [104,112,113,121,122]. Direct thermosensitivity of LC has been shown in non-mammals [100] but remains elusive in mammals. ...
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The locus coeruleus (LC) is a vertebrate-specific nucleus and the primary source of norepinephrine (NE) in the brain. This nucleus has conserved properties across species: highly homogeneous cell types, a small number of cells but extensive axonal projections, and potent influence on brain states. Comparative studies on LC benefit greatly from its homogeneity in cell types and modularity in projection patterns, and thoroughly understanding the LC-NE system could shed new light on the organization principles of other more complex modulatory systems. Although studies on LC are mainly focused on mammals, many of the fundamental properties and functions of LC are readily observable in other vertebrate models and could inform mammalian studies. Here, we summarize anatomical and functional studies of LC in non-mammalian vertebrate classes, fish, amphibians, reptiles, and birds, on topics including axonal projections, gene expressions, homeostatic control, and modulation of sensorimotor transformation. Thus, this review complements mammalian studies on the role of LC in the brain.
... In sum, Doelman and Rijken provide speculations to account for some of the intraspecific variation observed regarding yawning frequencies of a few selected studies, which, to this point, do not improve our understanding of yawning nor of its evolutionary function. Table 1 Other documented effects that cannot be explained by the airway hypothesis (1) The influence of nasal vs. oral breathing and carotid artery and forehead temperature on yawn frequency [23,24] (2) The link between yawn duration and brain size after accounting for body size [5] (3) How chewing on gum decreases, rather than increases, yawning [25,26] (4) The connection between abnormal yawning and thermoregulatory dysfunction in the absence of breathing problem [27] (5) Why there is a reduction in yawning frequency with senescence [28], as airway mechanics and lung function decline with age [29] (6) The fact that fish, which have a completely different oxygenation system, also yawn [30] ...
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Dear Editor, In a recent paper in Sleep and Breathing entitled “Yawning and airway physiology: a scoping review and novel hypothesis”, Doelman and Rijken [1] propose a novel hypothesis for the main function of yawning based on the physics involved in this stereotypical behaviour. In particular, they suggest that, by repositioning the muscles around the airway, yawning evolved to secure long-term oxygenation. Given the growing appreciation for the evolutionary significance of yawning [2], research uncovering new potential function(s) of this motor action pattern is of clear importance. Doelman and Rijken indeed provide a nice overview, including very detailed and useful visualizations, of the physics of a yawn, and as such their paper could function as a reference work. However, the exclusion criteria used for their scoping review are concerning, and the studies presented as evidence for their hypothesis either have important confounding variables, can be explained by other factors, or fail to even measure yawning. In addition, their paper neglects several phenomena related to yawning that their hypothesis cannot explain, as well as a myriad of studies that do account for these phenomena, yet that support an alternative hypothesis.
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Negli ultimi decenni si è assistito ad un crescente interesse verso un comportamento a lungo ignorato, lo sbadiglio. La ricerca ha messo in evidenza le condizioni a cui si associa una variazione della sua frequenza, i meccanismi neurofisiologici e patologici che lo regolano. A fronte di questi avanzamenti, la discussione sulle potenziali funzioni svolte dallo sbadiglio è ancora aperta e continuano ad emergere teorie alternative volte a spiegare la sua origine filogenetica. In particolare, sono state avanzate diverse ipotesi ciascuna delle quali attribuisce un ruolo primario ad una funzione fisiologica (respiratoria, legata alla regolazione dell’arousal, termoregolatoria e vincolata ai livelli di cortisolo ematico) o sociale-comunicativa attribuita allo sbadiglio. Questa rassegna offre una sintesi dei risultati sperimentali e delle formulazioni teoriche che si sono accumulate negli ultimi anni nello studio dello sbadiglio, mettendo in luce la difficoltà nel ricondurre la complessità manifestata da questo comportamento ad un’unica spiegazione funzionale.
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Yawning is a long neglected behavioral pattern, but it has recently gained an increasing interdisciplinary attention for its theoretical implications as well as for its potential use as a clinical marker, with particular regard to perinatal neurobehavioral assessment. The present study investigated the factors affecting yawning frequencies in hospitalized preterm neonates (N = 58), in order to distinguish the effects of hunger and sleep-related modulations and to examine the possible impact of demographic and clinical variables on yawning frequencies. Results showed that preterm neonates yawned more often before than after feeding, and this modulation was not explained by the amount of time spent in quiet sleep in the two conditions. Moreover, second born twins, known to be more prone to neonatal mortality and morbidity, showed increased yawning rates compared to first born twins. Overall, our results are consistent with the hypothesis that yawning frequencies in preterm neonates are modulated by separate mechanisms, related e.g. to hunger, vigilance and stress. These findings, although preliminary and based only on behavioral data, might indicate that several distinct neuropharmacological pathways that have been found to be involved in yawn modulation in adults are already observable in preterm neonates.
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Alexander Lowen emphasized the importance of changes in the body as a main goal of a body oriented psychotherapy. He focused especially on breathing and vibrating as involuntary movements and keys of changing and supporting a person’s grounding. Although yawning as another involuntary movement that shows a lot of changes on a body level, it is not in the center of Bioenergetic work yet. In my practice, yawning became an important and welcomed sign of therapeutic process and development which helps guide me through Bioenergetic sessions. The article will give some information about the current scientific findings and neurobiological aspects of yawning. A little study according to a simple yawning exercise gives data of self-experience of participants. Following phenomenological methods, new hypotheses of the reason and the purpose of yawning are presented. Some therapeutic implications, such as how the yawning of the client and of the therapist can be used in the process of a body-oriented psychotherapy, conclude the paper.
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The vascular theory of emotional efference (VTEE) states that facial action can alter the volume of air inhaled though the nose, which in turn influences brain temperature and affective states. Cooling enhances positive affect, whereas warming depresses it. Three studies assessed this hypothesised series of effects. Study 1 found that when subjects engaged facial muscles in a manner analogous to a negative emotional expression, the volume of ambient air inhaled through the nose decreased, forehead temperature (a measure of brain temperature) increased, and participants reported feeling more negative affect. Study 2 established that prevention of nasal breathing generated negative affect. Study 3 indicated that forehead temperature increased when nasal breathing was prevented, without forehead muscle movement. Further, facial movement and prevention of nasal inhalation had no effects on arm temperature, showing that facial movement has only locally specific temperature effects. The hypotheses generated from VTEE were thus generally supported, and suggest a means by which facial action can cause changes in affective state in the absence of cognitive appraisal.
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The hypothesis that Ss yawn more while observing uninteresting than while observing interesting stimuli was tested by comparing the yawns produced by 32 male and female college freshmen while they observed a 30-min rock video—a complex and interesting audiovisual stimulus—and a 30 min color-bar test pattern without an audio track, an unchanging and very uninteresting stimulus. Significantly more and longer yawns were produced during the uninteresting stimulus than during the interesting stimulus, and males had longer yawns than females. The folk belief that people yawn more during boring than interesting events was confirmed. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
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There have been relatively few empirical or theoretical investigations of the yawning response. Based on field and laboratory research with four vertebrate species, data are presented on yawning frequency. In general, human yawning occurred more frequently in the relative absence of social, cognitive, or physical stimulation; yawning by the other species was more frequent in the presence of such stimulation. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
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The “radiator” theory of brain evolution is proposed to account for “mosaic evolution” whereby brain size began to increase rapidly in the genus Homo well over a million years after bipedalism had been selected for in early hominids. Because hydrostatic pressures differ across columns of fluid depending on orientation (posture), vascular systems of early bipeds became reoriented so that cranial blood flowed preferentially to the vertebral plexus instead of the internal jugular vein in response to gravity. The Hadar early hominids and robust australopithecines partly achieved this reorientation with a dramatically enlarged occipital/marginal sinus system. On the other hand, hominids in the gracile australopithecine through Homo lineage delivered blood to the vertebral plexus via a widespread network of veins that became more elaborate through time. Mastoid and parietal emissary veins are representatives of this network, and increases in their frequencies during hominid evolution are indicative of its development. Brain size increased with increased frequencies of mastoid and parietal emissary veins in the lineage leading to and including Homo, but remained conservative in the robust australopithecine lineage that lacked the network of veins. The brain is an extremely heatsensitive organ and emissary veins in humans have been shown to cool the brain under conditions of hyperthermia. Thus, the network of veins in the lineage leading to Homo acted as a radiator that released a thermal constraint on brain size. The radiator theory is in keeping with the belief that basal gracile and basal robust australopithecines occupied distinct niches, with the former living in savanna mosaic habitats that were subject to hot temperatures and intense solar radiation during the day.
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Objective How risk factors for sudden infant death syndrome (SIDS) interrelate is not clear. Perhaps normal brain-cooling mechanisms are frustrated. Some mammals have selective brain cooling. Scrutiny of the relationship between body core and brain temperatures in mammals with cerebral vascular systems like man was planned. Design/sample Pilot studies were undertaken in five rabbits (Orytolagus cuniculus) and three monkeys (Macaca mulatta). The first showed that the parietal lobe of the brain was cooled relative to rectal temperature while the body was being heated which suggested that brain cooling might be mediated by cooled carotid arterial blood. Measurements In the monkeys (10.5–11.4 kg) direct temperature measurements (calibration against the internal carotid thermocouple to an accuracy of 0.2 °C for the right cerebral hemisphere and 0.15 °C for the left: r = 0.99, P < 0.001) were monitored in the internal carotid, the brain and the rectum, as well as room air. Monkeys were anaesthetized, not intubated and breathing spontaneously, heavily wrapped and laid on a heated pig farrowing pad. In one monkey the subsequent period of cooling was interrupted by causing the monkey to breathe warm air from a hair dryer. Results Internal carotid blood was found to be 1.5–2.0 °C cooler than body core, presumably because of its proximity to the respiratory airway. Brain temperature remained substantially hotter than carotid blood. Both rose as the body temperature increased to 39.5–40.8 °C, at which point brain temperature rise began to outstrip the rises in the body and carotid blood, presumably due to brain metabolism. When body heating was withdrawn, all temperatures fell, but on breathing warmed air, although rectal temperature continued to fall, carotid and brain temperature again rose. Conclusions and implications Carotid blood limits the rise of cerebral temperature caused by brain metabolism. The conditions under which this mechanism may fail include body core pyrexia and a rise in inspired air temperature. The phenomenon may explain the operation of risk factors for SIDS. Further implications suggest a related cooling mechanism for the brainstem and lead to questions about cooling of the uterus during pregnancy.1,2
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Yawning was induced by instructing subjects to “think about yawning.” Yawns were consistent in duration (X = 5.9 s), periodic (X interyawn interval = 68.3 s), and within-subject stability in yawn duration and frequency was maintained for at least several weeks. These and other characteristics qualified yawning as a stereotyped action pattern. Although visually observed yawns were potent yawn releasing stimuli, “thinking about” or reading about yawning also elicited yawning and were additional vectors for its “infectiousness.” The respiratory, stretching and “imitative” aspects of yawning were also evaluated.
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Yawning is a ubiquitous activity among humans, nonhuman primates, mammals, birds and other vertebrates. Comparative analysis suggests that yawning has two major features: (1) communication — whereby the behavior of other individuals is affected, and (2) direct physiological benefit — whereby the organism is receiving some direct physiological benefit from yawning. Various functional hypotheses used to explain yawning in an evolutionary context are reviewed. The contagious nature in humans and the manifest lack of contagion in other species suggests that yawning in humans has a different and as yet poorly understood evolutionary history.
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Using human college-age subjects, the present study tested the commonly cited but previously untested hypothesis that yawning is facilitated by higher than normal levels of CO2 or lower than normal levels of O2 in the blood by comparing the effect on yawning of breathing 100% O2 and gas mixtures with higher than normal levels of CO2 (3 or 5%) with compressed air, the control condition. If yawning is a response to heightened blood CO2, the CO2 mixtures should increase yawning rate and/or duration. If low blood O2 produced yawning, breathing 100% O2 should inhibit yawning. The CO2/O2 hypothesis was rejected because breathing neither pure O2 nor gases high in CO2 had a significant effect on yawning although both increased breathing rate. A second study found that exercise sufficient to double breathing rate had no effect on yawning. The two studies suggest that yawning does not serve a primary respiratory function and that yawning and breathing are triggered by different internal states and are controlled by separate mechanisms.
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Rates of wrist activity and yawning were recorded continuously for 7–15 days in adult human male and female subjects. In the 15 min following 747 yawns wrist motion increased reliably in all subject records. The data were consistent with an hypothesis that yawning is predictive of an increase in activity level. In a second study, data from daily logs kept by 45 subjects confirmed previous findings that yawning frequency is unrelated to prior amount of sleep, or to times of awaking or retiring. More yawning occurred during the week than during weekends.