C. Gallup. Yawning and the thermoregulatory
- The thermoregulatory theory of yawning
posits that yawns function to cool the brain in
part due to counter-current heat exchange with
the deep inhalation of ambient air.
Consequently, yawning should be constrained to
an optimal thermal zone or range of temperature,
i.e., a thermal window, in which we should
expect a lower frequency at extreme
temperatures. Previous research shows that yawn
frequency diminishes as ambient temperatures
rise and approach body temperature, but a lower
bound to the thermal window has not been
demonstrated. To test this, a total of 120
pedestrians were sampled for susceptibly to
self-reported yawn contagion during distinct
temperature ranges and seasons (winter: 1.4oC, n
= 60; summer: 19.4oC, n = 60). As predicted, the
proportion of pedestrians reporting yawning was
significantly lower during winter than in summer
(18.3% vs. 41.7%), with temperature being the
only significant predictor of these differences
across seasons. The underlying mechanism for
yawning in humans, both spontaneous and
contagious, appears to be involved in brain
- 1. Introduction
- Yawning occurs with an average duration of 4
to 7 sec, and consists of three distinct phases:
an active gaping of the jaw with inspiration, a
brief period of acme corresponding with apnea
and peak muscle contraction, and a passive
closure of the jaw with shorter expiration
. In humans , as well as a
handful of other social vertebrates
[3-7], yawning can be categorized into
two basic forms: spontaneous and contagious.
Both forms include similar motor action
patterns, but spontaneous yawns seem to be
triggered by physiological mechanisms of
homeostasis and arousal since they reliably
occur during distinct behavioral contexts
[8, 9] and follow a consistent circadian
pattern . In contrast, contagious
yawns are elicited simply by sensing or even
thinking about the action in others
. Unlike its spontaneous form, which
appears evolutionarily older by its observed
presence in all classes of vertebrates
 and early onset in uterine
development , contagious yawning
appears to be a more recently derived behavior
as evidenced by its presence in relatively few
highly social species [2-7] and delayed
ontogeny [14-18]. Research investigating
contagious yawning has emphasized the influence
of interpersonal and emotional-cognitive
variables on its expression [4, 5,
19-28], but there have been few attempts to
combine theoretical frameworks when explaining
both contagious and spontaneous effects. Due to
the potential multifunctionality of yawning
across species [12,29], however, recent
reports on social primates have highlighted
potentially important differences in yawn
morphology or intensity [5, 30, 31]
Although it is commonly believed that yawns
serve a respiratory function, experimental
procedures have shown yawn frequency is
independent of brain/blood levels of O2 and CO2
. A more recent theory, which posits
that the motor action of yawning functions as a
brain cooling mechanism [33, 34], has
received growing empirical support [reviewed
by 35]. For example, research on both rats
and humans shows that yawning is preceded by
intermittent rises in brain temperature and
localized mild hyperthermia and then followed by
equivalent decreases in temperature immediately
thereafter [36, 37]. While various
critiques have been proposed regarding the
thermoregulatory theory [38-42], no
study has found evidence contrary to its main
predictions and all current arguments remain
untenable [35, 43].
- According to the thermoregulatory theory,
the cooling effects of yawns occur through
thermoregulatory mechanisms of counter-current
heat exchange, evaporative cooling and enhanced
cerebral blood flow . Consequently,
the effectiveness of yawning is dependent on the
ambient air temperature, and the expression of
this behavior should be constrained to an
optimal thermal zone or range of temperature,
i.e., a thermal window. In particular, this
theory posits that yawns should (1) increase in
frequency with initial rises in ambient
temperature, as this stimulates thermoregulatory
mechanisms to control temperatures within a
normal range, (2) decrease as ambient
temperatures draw near or exceed body
temperature, since taking a deep inhalation of
air above one's body temperature would be
counter productive, and likewise (3) should
diminish when temperatures fall below a certain
point, because thermoregulatory cooling
responses are no longer necessary and
countercurrent heat exchange could result in
deviations below optimal thermal homeostasis.
Since both spontaneous and contagious yawns are
indistinguishable, aside from different
triggers, the predictions of the thermal window
hypothesis should apply to both forms.
Experimental and observational research reports
of spontaneous yawning in non-human primates
[10, 5], birds [46, 47], and
rats  have confirmed the first two
predictions of this model. Additionally, it was
recently discovered that self-reported
contagious yawning frequency in humans varies
with seasonal climate variation
- In particular, two independent groups of
pedestrians were sampled in an arid desert
climate (Tucson, AZ, USA): the first in summer
(37°C) and the other during 'winter'
(22°C). Contagious yawning frequency was
significantly lower during the hot summer
climate (24% vs 45%), with temperature being the
only significant factor contributing to this
response after controlling for other variables,
such as humidity, sleep and time spent outside.
Here we tested the lower bound of the thermal
window hypothesis by investigating the frequency
of self-reported contagious yawning in a climate
with a colder winter season (Vienna, Austria).
In this case the summer condition provided
temperatures equivalent to those in winter
months of Tucson, while the winter condition
included temperatures at and slightly below
- 4. Discussion
- Overall, these results show that
significantly fewer pedestrians reported
contagious yawning during the cold winter (-4 to
7oC), and that, similar to effects observed in
an arid desert climate , temperature
was the only significant predictor of this
response when controlling for other variables.
As predicted by the thermal window hypothesis,
reports of yawning were constrained to an
optimal thermal zone or range of ambient
temperature (figure 1). Importantly, changes in
daylight across the seasons cannot account for
these results. First, a particular time frame
was chosen for both studies (between 1 and 3 pm)
whereby contagious yawning frequencies remain
unchanged . Second, the proportion
of people that reported yawning in the summer in
Vienna, Austria (current study) was comparable
to that of the winter in Tucson, Arizona USA
, whereas there is a large
difference in daylight hours between these
samples (Summer in Vienna: ± 16h vs. Winter
in Tucson: ± 10h). Lastly, an inverse
seasonal pattern emerged between the two study
locations; i.e., whereas in Tucson there was a
high frequency of reported yawning in winter,
and a low frequency of reported yawning in
summer, in Vienna there was a high frequency of
reported yawning in summer, and a low frequency
of reported yawning in winter. Thus, it cannot
be generalized that people yawn more or less in
winter vs. summer, nor with greater or fewer
hours of daylight. Instead, the ambient air
temperature accompanying the season appears to
determine reported yawn frequency. This report
adds to accumulating research suggesting that
the underlying mechanism for yawning, both
spontaneous and contagious, is involved in brain
thermoregulation. The thermoregulatory theory
provides clear predictions for both the
primitive and derived features of this behavior.
That is, the thermoregulatory benefits resulting
from yawning provide the mechanism by which
arousal or state change can be achieved [8,
10], while the spreading of this behavior,
i.e., yawn contagion, would therefore coordinate
arousal in a group and enhance overall group
vigilance . In addition to enhancing
the basic understanding of why we yawn,
applications from this research include improved
treatment and diagnosis of patients with
thermoregulatory problems [34, 37, 54,
- 1. Barbizet J. Yawning. J Neurol Neurosurg
- 2. Provine RR, Yawning as a stereotyped
action pattern and releasing stimulus.
- 3. Anderson JR, Myowa-Yamakoshi M, Matsuzawa
T. Contagious yawning in chimpanzees. Proc R Soc
- 4. Demuru E, Palagi E. In Bonobos Yawn
Contagion Is Higher among Kin and Friends. PLoS
- 5. Palagi E, Leone A, Mancini G, Ferrari PF.
Contagious yawning in gelada baboons as a
possible expression of empathy. PNAS
- 6. Miller ML, Gallup AC, Vogel AR, Vicario
SM, Clark AB. Evidence for contagious behaviors
in budgerigars (Melopsittacus undulatus): An
observational study of yawning and strecthing.
Behav Process 2012;89:264-270.
- 7. Joly-Mascheroni RM, Senju A, Shepherd AJ.
Dogs catch human yawns. Biol Lett
- 8. Baenninger R. On yawning and its
functions. Psychon Bull Rev 1997;4:198-207.
- 9. Deputte BL. Ethological study of yawning
in primates. I. Quantitative analysis and study
ofcausation in two species of old world monkeys
(Cercocebus albigena and Macaca fascicularis).
- 10. Provine, RR, Hamernik, HB, Curchack, BC.
Yawning: relation to sleeping and stretching in
humans. Ethology 1987;76:152-160.
- 11. Provine RR. Yawning: the yawn is primal,
unstoppable and contagious, revealing the
evolutionary and neural basis of empathy and
unconscious behavior. Am Sci
- 12. Baenninger R. Some comparative aspects
of yawning in Betta splendens, Homo sapiens,
Panthera leo, and Papio sphinx. J Comp Psychol
- 13. de Vries JIP, Visser GHA, Prechtl HF.
The emergence of fetal behaviour. I. Qualitative
aspects. Early Hum Develop 1982;7:301-322.
- 14. Anderson JR, Meno P. Psychological
influences on yawning in children. Curr Psychol
Lett Behav Brain Cog 2003:11;2-7
- 15. Millen A, Anderson JR. Neither infants
nor toddlers catch yawns from their mothers.
Biol Lett 2010;7: 440-442.
- 16. Hoogenhout M, van der Straaten K,
Pileggi L-A, Malcolm-Smith S. Young children
display contagious yawning when looking at the
eyes. J Child Adolesc Behav 2013;1:1.
- 17. Madsen EA, Persson T. Contagious yawning
in domestic dog puppies (Canis lupis
familiaris): the effect of ontogeny and
emotional closeness on low-level imitation in
dogs. Anim Cogn 2012;16: 233&endash;240.
- 18. Madsen, EA, Persson, T, Sayehli, S,
Lenninger, S, Sonesson, G. Chimpanzees show
adevelopmental increase in susceptibility to
contagious yawning: A test of the effect of
ontogeny and emotional closeness on yawn
contagion. PLoS ONE 2013;8:e76266.
- 19. Campbell MW, de Waal FBM.
Ingroup-Outgroup Bias in Contagious Yawning by
Chimpanzees Supports Link to Empathy. PLoS ONE
- 20. Norscia I, Palagi E. Yawn contagion and
empathy in Homo sapiens. PLoS ONE 2011;6:
- 21. de Waal FBM. Empathy in primates and
other mammals. In: Decety J, editor. Empathyfrom
bench to bedside, Cambridge: MIT Press; 2012, p.
- 22. Platek SM, Critton SR, Myers TE, Gallup
GG. Contagious yawning: the role of
selfawareness and mental state attribution. Cogn
Brain Res 2003;17:223-227.
- 23. Platek SM, Mohamed FB, Gallup GG Jr.
Contagious yawning and the brain. Cognit
- 24. Arnott SR, Singhal A, Goodale MA. An
investigation of auditory contagious yawning.
CognAffect Behav Neurosci
- 25. Nahab FB, Hattori N, Saad ZS, Hallett M.
Contagious yawning and the frontal lobe: AnfMRI
study. Hum Brain Mapp
- 26. Haker H, Kawohl W, Herwig U, Rossler W.
Mirror neuron activity during contagiousyawning
&endash; an fMRI study. Brain Imaging Behav
- 27. Cooper NR, Puzzo I, Pawley AD,
Bowes-Mulligan RA, Kirkpatrick EV, Antoniou
PA,Kennett S. Bridging a yawning chasm: EEG
investigations into the debate concerning the
role of the human mirror neuron system in
contagious yawning. Cogn Affect Behav Neurosci
- 28. Massen JJM, Vermunt DA, Sterck EHM. Male
yawning is more contagious than femaleyawning
among chimpanzees (Pan troglodytes). PLoS ONE
2012;7:e40697.29. Gallup AC. Why do we yawn?
Primitive versus derived features. Neurosci
Biobehav Rev 2011;35:765-769.
- 30. Leone, A, Ferrari, PF, Palagi, E.
Different yawns, different functions? Testing
social hypotheses on spontaneous yawning in
Theropithecus gelada. Sci Reports 2014;4.
- 31. Vick, SJ, Paukner, A. Variation and
context of yawns in captive chimpanzees (Pan
troglodytes). Am J Primatol
- 32. Provine, RR, Tate, BC, Geldmacher, LL.
Yawning: No effect of 3&endash;5% CO2, 100% O2,
andexercise. Behav Neur Biol
- 33. Gallup AC, Gallup Jr GG. Yawning as a
brain cooling mechanism: Nasal breathing
andforehead cooling diminish the incidence of
contagious yawning. Evol Psychol
- 34. Gallup AC, Gallup Jr GG. Yawning and
thermoregulation. Physiol Behav
- 35. Gallup AC, Eldakar OT. The
thermoregulatory theory of yawning: what we know
from fiveyears of research. Front Neurosci
- 36. Shoup-Knox ML, Gallup AC, Gallup Jr GG,
McNay EC. Yawning and stretching predictbrain
temperature changes in rats: support for the
thermoregulatory hypothesis. Front Evol Neurosci
- 37. Gallup GG Jr, Gallup AC. Excessive
yawning and thermoregulation: two case studies
of chronic, debilitating bouts of yawning. Sleep
- 38. Walusinski O. Why do we yawn? Past and
current hypotheses. In: Shoja MM, Agutter PS,
Tubbs RS, Ghanei M, Ghabili K, Harris A, Loukas
M, editors. Hypotheses in Clinical Medicine,
Hauppauge, NY;Nova Science Publishers: 2013, p.
- 39. Elo H. Yawning and thermoregulation.
Sleep Breath 2010;14:391-392.
- 40. Elo H. Yawning cannot cause significant
temperature decreases in humans. Sleep Med.
- 41. Guggisberg AG, Mathis J, Schnider A,
Hess CW. Why do we yawn? Neurosci Biobehav Rev
- 42. Guggisberg AG, Mathis J, Schnider A,
Hess C W. Why do we yawn? The importance of
evidence for specific yawn-induced effects.
Neurosci Biobehav Rev 2011;35:1302-1304.
- 43. Gallup AC. The thermoregulatory
hypothesis of yawning: time to reconsider terms
such as "impossible" and "cannot" and evaluate
theories based on evidence. Sleep Med
- 44. Gallup AC, Hack GD. Human paranasal
sinuses and selective brain cooling: A
ventilation system activated by yawning? Med
- 45. Campos FA, Fedigan LM. Behavioural
adaptations to heat stress and water scarcity in
white-faced capuchins (Cebus capucinus) in Santa
Rosa National Park, Costa Rica. Am J Phys
- 46. Gallup AC, Miller ML, Clark AB. Yawning
and thermoregulation in
budgerigars(Melopsittacus undulatus). Anim Behav
- 47. Gallup AC, Miller ML, Clark AB. The
direction and range of ambient temperature
influencesyawning in budgerigars (Melopsittacus
undulatus). J Comp Psychol
- 48. Gallup AC, Miller RR, Clark AB. Changes
in ambient temperature trigger yawning but
notstretching in rats. Ethology
- 49. Gallup AC, Eldakar OT. Contagious
yawning and seasonal climate variation. Front
Evol Neurosci 2011;3(3):1-5.
- 50. Greco M, Baenninger R. Self-report as a
valid measure of yawning in the laboratory. Bull
Psychonomic Soc 1989;27:75-76.
- 51. Giganti F, Toselli M, Ramat S.
Developmental trends in a social behaviour:
contagiousyawning in the elderly. Eta Evolutiva
- 52. Baenninger R, Greco M. Some Antecedents
and Consequences of Yawning. Psychol
- 53. Giganti F, Zilli I. The daily time
course of contagious and spontaneous yawning
among humans. J Ethol 2011;29:215-219.
- 54. Gallup AC, Gallup GG Jr, Feo C. Yawning,
sleep, and symptom relief in patients
withmultiple sclerosis. Sleep Med
- 55. Gallup AC, Gallup JA. Frequent yawning
as an initial signal of fever relief. Med