- Yawning has become an interesting and
curious scientific conundrum. Links between
several neurological disorders can be found
through the commonality of yawning episodes and
contagious yawning. However, the reasons why we
yawn are uncertain. Cortisol levels are known to
rise during stress and fatigue; yawning may
occur when we are under stress or tired. We do
not know whether cortisol levels fluctuate
during yawning. Potentially, yawning and
cortisol levels may provide a valuable
diagnostic tool and warning of untoward
underlying neurological problems. A new
hypothesis is proposed that links cortisol
levels with yawning episodes.
Cortisol Hypothesis : all the
- Yawning has received considerable interest
in recent years with new theories being proposed
concerning the mechanisms involved, including
stereotyped action , mental
attribution theory , mirror neuron
system , and thermo-irregulation
 and . However, there is
still a striving towards a common theory that
can explain the incidences of yawning and
contagious yawning in normal humans as well as
in those with underlying neurological
- Indeed, it has been proposed that yawning
may serve as a warning for untoward disorders
. It is known that yawning occurs in
every human even at pre-term  and
also in a variety of non-humans such as
vertebrates . It is proposed that an
explanation may lie in blood cortisol levels and
the author hypothesises that the known
co-existence of fatigue and cortisol levels due
to the protective qualities of cortisol, such as
in protection against cold (particularly when
exposed to very cold temperatures) ,
and against stress , makes this a
- The fact that yawning may follow a circadian
pattern has been suggested previously
, and tends to occur more often
before sleep. Yawning is known to be linked with
fatigue. Curiously, yawning is also linked with
levels of serotonin, considered important in the
feeling of well-being and pleasure, and with
amygdalar activation , and also
perhaps with mood changes .
Compelling evidence remains that implicates the
brain stem  and .
- Linking neurological
- Several neurological disorders have been
studied to date in order to discern commonality
in mechanisms and neurological pathways. In
particular, symptoms have commonality between
some disorders which may arise because they
share dysfunction in neurological pathways or in
the regulation of neurotransmitters between
synaptic junctions. For example, serotonin is
implicated in both depressive disorders as well
as in Parkinson's disease and Alzheimer's
disease , and the symptoms of mood
change are often exhibited.
- Similarly, yawning may be a symptom of more
than one disorder, such as in specific instances
found in multiple sclerosis and in stroke.
Fatigue is often present after onset of these
disorders and may give rise to yawning episodes.
The link between fatigue and yawning is known;
the link between thermoregulation and yawning
has been proposed; and instances of involuntary
arm-raising in the parakinesia brachialis
oscitans of stroke patients has also been
evidenced . There is also the known
link between elevated blood cortisol levels and
fatigue, and also between cortisol levels and
stress. It is proposed that cortisol levels may
be elevated during yawning because excessive
yawning is suspected as being implicated in a
number of untoward neurological disorders. Thus,
yawning, as a warning of an underlying
neurological disorder, may also give rise to
elevated cortisol levels.
- Cortisol and stress
- Cortisol is known to be present and elevated
during stressful situations. Blood cortisol
levels are directly related to salivary cortisol
levels  and is documented in a
number of different paradigms. The cortisol
level and stress correlation is curvilinear.
However, in pre-term infants cortisol levels may
be lower during heel-stick pain procedure
, and also in girls whose parents
had depressive problems, cortisol levels were
blunted . In animal models, the
cortisol level profile is also similar to humans
during stressful situations .
Cortisol levels appear higher after subjected
stress including work-related stress
- Cortisol and exposure to cold
- During exposure to cold, the cortisol level
in humans rises dramatically, except when
exposed quickly (as in the Cold-Face Test) when
there are reduced cortisol rises, perhaps due to
vagal inhibition . It is suspected
that exposure to extreme cold temperature gives
rise to a similar "stress-like" response with
respect to cortisol levels in humans.
- Cortisol and fatigue
- The link between fatigue and hormonal
changes is well-documented. A greater level of
neuromuscular fatigue and larger responses in
serum hormone concentrations has been evidenced
after hypertrophic variable resistance loadings
. This has led to identifying
markers of fatigue , particularly
following post-match professional rugby
, and in young athletes
. Findings have enabled scientists
to document damaged muscle recovery periods.
Elevated salivary cortisol levels have also been
seen in elite tennis players . Sleep
deprivation and fatigue have been linked with
salivary cortisol levels; in this instance,
cortisol levels are lowered .
- Fatigue and yawning
- Tiredness due to physical exercise or mental
concentration on tasks is often referred to as
'fatigue'. Yawning is seen when humans (and
animals) become fatigued, though the reasons for
this behaviour remain inconsistently supported.
For example, a lack of oxygen, stretching the
chest muscles (and increasing the lungs
capacity), increasing alertness, are all reasons
that have been proposed . What is
unknown is the cortisol level during yawning.
For instance, is the cortisol level higher when
yawning occurs after exposure to cold as
compared to exposure to a stressful situation?
Also, is there an elevation in cortisol levels
when neurologically-impaired patients yawn? The
answers to these questions may provide a
cortisol marker or warning of such
- Hence, it is proposed that cortisol levels
rise during yawning and that they are correlated
with yawning episodes. The level of cortisol may
also be related to a particular neurological
- These are important considerations not only
because they may potentially provide the answer
to why we yawn but also because there may be a
potential diagnostic test arising from cortisol
activity. The research team led by the author at
Bournemouth University are investigating these
propositions and intend to measure nerve
electrical activity, cortisol levels and fatigue
across different populations. It will be
interesting to determine whether or not we are
truly "born to yawn" as a protective indicator
of untoward neurological dysfunction &endash;
yawning is perhaps a warning for us,
-  R.R.
Provine, Yawning as a stereotyped action
pattern and releasing stimulus. Ethol, 72
(1986), pp. 109&endash;122.
-  S.M.
Platek, S.R. Critton, T.E. Myers and G.G.
Gallup, Contagious yawning: the role of
self-awareness and mental state attribution. Cog
Brain Res, 17 2 (2003), pp. 223&endash;227.
N.R. Cooper, I. Puzzo and A.D. Pawley,
Contagious yawning: the mirror neuron system may
be a candidate physiological mechanism. Med
Hypotheses, 71 (2008), pp. 975&endash;987.
-  D.G. Baker, Multiple sclerosis
and thermoregulatory dysfunction. J App Phys, 92
(2002), pp. 1779&endash;1780.
-  G.G. Gallup and A.C. Gallup,
Excessive yawning and thermoregulation: Two case
histories of chronic, debilitating bouts of
yawning. Sleep Breathing 2010;14(2):157-159
-  S.B.N.
Thompson, The dawn of the yawn: is yawning a
warning? Linking neurological disorders. Med
Hypotheses, 75 (2010), pp. 630&endash;633.
-  F.
Giganti, M.J. Hayes, G. Cioni and P.
Salzarulo, Yawning frequency and
distribution in preterm and near term infants
assessed throughout 24 h recordings. Inf Beh
Dev, 30 (2007), pp. 641&endash;647.
-  M.W. Campbell and F.B. de Waal,
Ingroup&endash;outgroup bias in contagious
yawning by chimpanzees supports link to empathy.
Plos One, 6 4 (2011), pp. 1&endash;4.
-  R.L. Marca, P. Waldvogel, H.
Thon, M. Tripod, P.H. Wirtz and J.C. Pruessner,
et al. Association between Cold Face
Test-induced vagal inhibition and cortisol
response to acute stress. Psychophysiology, 48 3
(2011), pp. 420&endash;429.
-  B. Karlson, F. Eek, A.M.
Hansen, A.H. Garde and P. Ørbæk,
Cortisol variability and self-reports in the
measurement of work-related stress. Stress
Health, 26 2 (2011), pp. e11&endash;e24.
-  R.R.
Provine, H.B. Hamernick and B.B. Curchack,
Yawning: relation to sleeping and stretching in
humans. Ethol, 76 (1987), pp.
-  A.J. Salerian, N.G. Saleri and
J.A. Salerian, Brain temperature may influence
mood: a hypothesis. Med Hypotheses, 70 3 (2008),
-  O.
Walusinski, J.-P. Neau and J. Bogousslavsky,
Hand up! Yawn and raise your arm. Int J Stroke,
5 (2010), pp. 21&endash;27.
-  R.P.
Munhoz and H.A. Teive, Parakinesia
brachialis oscitans due to brain stem stroke.
Report of two cases. Parkinson Rel Dis, 15
Suppl. 2 (2009), p. S154.
-  S.B.N. Thompson, Dementia and
memory: a handbook for professionals and
students, Ashgate, Aldershot (2006).
-  E. Aardal-Eriksson, B.E.
Karlberg and A. Holm, Salivary cortisol &endash;
an alternative to serum cortisol determinations
in dynamic function tests. Clin Chem Lab Med, 36
(2005), pp. 215&endash;222.
-  R.E. Grunau, L. Holsti and D.W.
Haley, Neonatal procedural pain exposure
predicts lower cortisol and behavioural
reactivity in preterm infants in the NICU. Pain,
113 3 (2005), pp. 293&endash;300.
-  E.M.C. Bouma, H. Riese, J.
Ormel, F.C. Verhulst and A.J. Oldehinkel,
Self-assessed parental depressive problems are
associated with blunted cortisol responses to a
social stress test in daughters.
Psychoneuroendocrinology, 36 6 (2011), pp.
-  B. Beerda, M.B.H. Schilder,
J.A.R.A.M. Van Hooff, H.W. De Vries and J.A.
Mol, Behavioural and hormonal indicators of
enduring environmental stress in dogs. Animal
Welfare, 9 1 (2000), pp. 49&endash;62.
-  S. Walker, R.S. Taipale, K.
Nyman, W.J. Kraemer and K. Häkkinen,
Neuromuscular and hormonal responses to constant
and variable resistance loadings. Med Sci Sports
Exer, 43 1 (2011), pp. 26&endash;33.
-  G. Bresciani, M.J. Cuevas, O.
Molinero, M. Almar, F. Suay and A. Salvador, et
al. Signs of overload after an intensified
training. Int J Sports Med, 32 5 (2011), pp.
-  C.P. McLellan, D.I. Lovell and
G.C. Gass, Markers of postmatch fatigue in
professional rugby league players. J Strength
Condit Res, 25 4 (2011), pp.
-  S. Locke, M. Osborne and P.
O'Rourke, Persistent fatigue in young athletes:
measuring the clinical recovery and identifying
variables affecting clinical recovery. Scand J
Med Sci Sports, 21 1 (2011), pp.
-  R.V. Gomes, A.J. Coutts, L.
Viveiros and M.S. Aoki, Physiological demands of
match-play in elite tennis: a case study. Eur J
Sport Sci, 11 2 (2011), pp. 105&endash;109.
-  M. Carev, N. Karanovic´,
J. Bagatin, N.B. Matulic´, R. Pecotic´
and M. Valic´, et al. Blood pressure
dipping and salivary cortisol as markers of
fatigue and sleep deprivation in staff
anesthesiologists. [Noc´no sniz˙enje
arterijskog krvnog tlaka i kortizol u slini kao
moguc´i pokazatelji umora i nedostatka
spavanja u anesteziologa]. Coll Antropol, 35
Suppl. 1 (2011), pp. 133&endash;138.