mystery of yawning
Le bâillement, du réflexe à la pathologie
Le bâillement : de l'éthologie à la médecine clinique
Le bâillement : phylogenèse, éthologie, nosogénie
 Le bâillement : un comportement universel
La parakinésie brachiale oscitante
Yawning: its cycle, its role
Warum gähnen wir ?
Fetal yawning assessed by 3D and 4D sonography
Le bâillement foetal
Le bâillement, du réflexe à la pathologie
Le bâillement : de l'éthologie à la médecine clinique
Le bâillement : phylogenèse, éthologie, nosogénie
 Le bâillement : un comportement universel
La parakinésie brachiale oscitante
Yawning: its cycle, its role
Warum gähnen wir ?
Fetal yawning assessed by 3D and 4D sonography
Le bâillement foetal

mise à jour du
27 septembre 2011
Medical Hypotheses


Born to yawn? Cortisol linked to yawning:
A new hypothesis
Simon B.N. Thompson
Clinical Psychology & Neuropsychology, Psychology Research Centre, Bournemouth University, United Kingdom


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.
-Thompson SB The dawn of the yawn: is yawning a warning? linking neurological disorders. Medical Hypotheses 2010;75(6):630-633
-Thompson SB Born to yawn? Cortisol linked to yawning: A new hypothesis. Medical Hypotheses 2011;77(5):861-862
-Thompson SB, Zisa L Yawning: Thompson Cortisol Hypothesis Discussed. 12-2011.
-Thompson SB Is Yawning A Warning, Neurologically? 12-2011.
-Thompson SB.Yawning, fatigue, and cortisol: Expanding the Thompson Cortisol Hypothesis. Med Hypotheses.Med Hypotheses. 2014 Oct;83(4):494-6.
-Thompson SB. Pathways to yawning: making sense of the Thompson Cortisol Hypothesis. Medical Research Archives 2015(3)
 -Thompson SB, Simonsen M. Yawning As a New Potential Diagnostic Marker for Neurological Diseases. Journal of Neurology and Neuroscience. 2015;6(3):22
Yawning has received considerable interest in recent years with new theories being proposed concerning the mechanisms involved, including stereotyped action [1], mental attribution theory [2], mirror neuron system [3], and thermo-irregulation [4] and [5]. 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 disorders.
Indeed, it has been proposed that yawning may serve as a warning for untoward disorders [6]. It is known that yawning occurs in every human even at pre-term [7] and also in a variety of non-humans such as vertebrates [8]. 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) [9], and against stress [10], makes this a viable proposition.
The fact that yawning may follow a circadian pattern has been suggested previously [11], 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 [6], and also perhaps with mood changes [12]. Compelling evidence remains that implicates the brain stem [13] and [14].
Linking neurological disorders
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 [15], 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 [13]. 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 [16] 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 [17], and also in girls whose parents had depressive problems, cortisol levels were blunted [18]. In animal models, the cortisol level profile is also similar to humans during stressful situations [19]. Cortisol levels appear higher after subjected stress including work-related stress [10].
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 [9]. 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 [20]. This has led to identifying markers of fatigue [21], particularly following post-match professional rugby [22], and in young athletes [23]. Findings have enabled scientists to document damaged muscle recovery periods. Elevated salivary cortisol levels have also been seen in elite tennis players [24]. Sleep deprivation and fatigue have been linked with salivary cortisol levels; in this instance, cortisol levels are lowered [25].
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 [6]. 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 conditions.
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 dysfunction.
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, neurologically speaking.
[1] R.R. Provine, Yawning as a stereotyped action pattern and releasing stimulus. Ethol, 72 (1986), pp. 109&endash;122.
[2] 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.
[3] 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.
[4] D.G. Baker, Multiple sclerosis and thermoregulatory dysfunction. J App Phys, 92 (2002), pp. 1779&endash;1780.
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[6] S.B.N. Thompson, The dawn of the yawn: is yawning a warning? Linking neurological disorders. Med Hypotheses, 75 (2010), pp. 630&endash;633.
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[11] R.R. Provine, H.B. Hamernick and B.B. Curchack, Yawning: relation to sleeping and stretching in humans. Ethol, 76 (1987), pp. 152&endash;160.
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[13] O. Walusinski, J.-P. Neau and J. Bogousslavsky, Hand up! Yawn and raise your arm. Int J Stroke, 5 (2010), pp. 21&endash;27.
[14] 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.
[15] S.B.N. Thompson, Dementia and memory: a handbook for professionals and students, Ashgate, Aldershot (2006).
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[17] 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.
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[19] 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.
[20] 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.
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[22] 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. 1030&endash;1039.
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