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

mystery of yawning 





mise à jour du
15 mai 2016
Journal of Neurology and Neuroscience
Yawning As a New Potential Diagnostic Marker
for Neurological Diseases
Simon B N Thompson and Mia Simonsen
Psychology Research Centre, Bournemouth University, UK


Yawning apparatus and exact location of the yawn reflex remains controversial. Yet yawning is a significant behavioural response and potentially a new diagnostic marker of neurological disease. Association between cortisol, electromyography (EMG) and yawning was found in humans supporting Thompson Cortisol Hypothesis (TCH) which complements thermoregulation hypotheses indicating brain cooling occurs when yawning. 28 male, 54 female volunteers, 18-69 years, randomly allocated to experimentally controlled conditions of provoked yawning. Saliva samples were collected at start and after yawning, or after stimuli presentation, in absence of yawning. EMG data was collected from jaw muscles at rest and after yawning. Specially designed yawning susceptibility scale, Hospital Anxiety and Depression Scale, General Health Questionnaire, demographic, health details were collected. Between- and within-subjects comparisons of yawners and non-yawners was conducted. Exclusion criteria: chronic fatigue, diabetes, fibromyalgia, heart condition, high blood pressure, hormone replacement therapy, multiples sclerosis, stroke. Yawning group: significant difference between saliva cortisol samples, rest and yawning t (37)=2.842, p=0.007, compared with non-yawners, rest and post-stimuli, which was non-significant. Yawners, rest EMG: -100 to 200 millionth of a volt (mean=182.2) and -60 000 to 18 000 (mean=3 897.4) after yawning. Non-yawners, rest EMG: -80 to 120 (mean=37.2) and -400 to 800 (mean=57.5) after stimuli presentation. Yawners showed larger peak following yawn compared with post-stimuli for non-yawners. Significant supporting evidence for TCH suggests cortisol levels are elevated during yawning. Changes in cortisol levels may become a new diagnostic tool in early diagnosis of neurological symptoms.
Les mécanismes intimes du bâillement et la localisation cérébrale exacte de son origine restent controversés. Pourtant, le bâillement est une réponse comportementale importante et potentiellement un nouveau marqueur diagnostique de maladies neurologiques.
Cette étude, associant celle des niveaux du cortisol et l'électromyographie (EMG), a montré son intérêt chez l'homme pour valider la théorie cortisolique du bâillement (Thompson Cortisol Hypothesis - TCH). Celle-ci complète les hypothèses de thermorégulation retrouvant un refroidissement du cerveau lors du bâillement.
28 hommes et 54 femmes volontaires, de 18 à 69 ans, répartis de façon aléatoire, ont participé à une étude contrôlée de bâillements provoqués. Des échantillons de salive ont été prélevés au début et après le bâillement, ou après la présentation de stimuli, en l'absence de bâillement. Les données EMG ont été recueillies au niveau des muscles de la mâchoire au repos et après le bâillement.
Une échelle de susceptibilité aux bâillements a été spécialement conçue, l'anxiété a été appréciée à l'aide de l'échelle 'Hospital and Depression Scale', un questionnaire général sur la santé rempli, ainsi que des renseignements d'identification.
L'étude a comporté des comparaisons entre bâilleurs et non bâilleurs. Les critères d'exclusion étaient la fatigue chronique, le diabète, la fibromyalgie, les maladies cardiaques, l'hypertension artérielle, le traitement substitutif hormonal, la sclérose en plaques, les antécédents d'accidents vasculaires cérébraux.
Des différences significatives ont été retrouvées entre bâilleurs et non bâilleurs. Les bâilleurs ont présenté un pic du niveau de cortisol plus important que les non bâilleurs ce qui confirme l'hypothèse d'une élévation du cortisol lors du bâillement. Les changements dans les niveaux de cortisol pourraient devenir un nouvel outil de diagnostic précoce lors de certains symptômes neurologiques.
Thompson Cortisol Hypothesis : all the publications
The first yawn of the day is usually when we awake to stretch our intercostal muscles surrounding our lungs to bring in more oxygen. Many of us recognise yawning as a sign of tiredness or boredom yet we also yawn before that important job interview. We contagiously yawn when our pets yawn and because we are empathe c towards another yawning human being and therefore, most of us can relate to yawning.
Yet the physiological apparatus and exact loca on of our yawning response is uncertain. So much so, that yawning has been the debate of neuroscien sts and philosophers since 400 BC when Hippocrates wrote about yawning in De Flatibus Liber (A Trea se on Wind), "because the large quan ty of air ascends all at once, li ing with the ac on of a lever and opening the mouth, the accumulated air in the body, like steam escaping from hot cauldrons, is violently expelled when the body temperature rises" [1].
Hippocrates' theory was not so far from reality but the focus of the study of yawning on is on our body temperature which is lowered when we yawn and thus protec ng us from cri cal brain temperature rises especially when we become very fa gued. A common symptom of mul ple sclerosis (MS) is fa gue [2] which is also associated with excessive yawning and a rise in brain temperature, governed by a small structure in the top of the brain, the hypothalamus [3,4]
Temperature regulation and circadian rhythm is the responsibility of the hypothalamus which is in mately linked to two other body structures, the pituitary gland, also situated in the brain, and the adrenal glands which secrete adrenaline. The hypothalamus- pituitary-adrenal (HPA) axis helps us produce enough hormones to protect against stress and provides us with readiness for physical activity.
Yawning is exhibited in many different situations and it is because of this that it has made yawning so difficult to research resulting in its origin being so allusive. Anecdotally, yawning has been seen in response to migraine headaches; following excessive fatigue or sleepiness [5]; after ingesting "magic mushrooms" whose active ingredient is psilocybin; following taking the antidepressant Prozac; after an anxiety or panic attack; after seeing images of animals and humans yawning; after reading an article about yawning !
The link between excessive yawning and neurological disease has been noted elsewhere. For example, Lana-Peixoto, et al. [6] found that excessive yawning was the presenting symptom of five patients with neuromyelitis optica spectrum disorders (NMOSD). Brain MRI was abnormal and most frequently showed brainstem and hypothalamic lesions. The authors conclude that pathological yawning may be a neglected although not a rare symptom in NMOSD.
Excessive yawning is also noted in adrenal insufficiency [7]; this is thought to occur because of an irregulation of adrenaline and cortisol, both actively involved in the HPA-axis. It is probable that other neurological diseases such as Parkinson's disease and Motor Neurone Disease may also be implicated in the HPA feedback loop.
The Thompson Cortisol Hypothesis [8] is the first evidence-based report that links the naturally produced protective "stress" hormone, cortisol, with yawning, and demonstrates that cortisol rises when we yawn.
Produced by the zona fasciculate of the adrenal cortex within the adrenal gland [7], it is suggested that the rise in cortisol level triggers our yawning response. Implications of this research are that yawning is an important mechanism for controlling hormone regulation and hypothalamus temperature regulation.
Physicians working in the rehabilitation of stroke patients have reported on significant findings from yawning stroke patients [9]. Sir Francis Walshe, a British neurologist, first reported on patients with lesions in the braintistem region who could raise their paralyzed arm when spontaneously yawning [10]. This has been evidenced since and consistently, by others [11-13] and particularly, in patients with left hemiplegia, the yawning response has been attributed to pseudobulbar syndrome [14]. Swallow reflex and yawning have been postulated to be temporally related in a study that considered gape, smile and yawning responses [15]. Participants were observed to swallow directly after yawning; again suggesting that the brain stem region might be the commonality between both reflexes. Findings supporting the presence of common neuroanatomico-physiological pathways for spontaneous swallows and yawning have also been reported [16].
Mental Attribution Theory [17,18] has been presented as the reason for us contagiously yawning as we seem to be empathic to others who yawn, especially when we perceive our belonging to a particular social grouping and yet it seems that yawning is so important to our maintenance and regulation that it does not wait un l we are born. In fact, it happens in the womb [19].
Consistent reports have shown photographic evidence of yawning in the foetus, reinforcing the fact that it is one of the first crucial developments we make. New-born babies yawn more frequently than toddlers do, since sleep deprivation increases the chances of us yawning and makes us more susceptible to the effects of stress and fatigue [20].
Yawning is not confined to humans either, with most vertebrates experiencing yawning perhaps because of the need to raise arousal and the level of alertness. Universal yawning seems to be found in vertebrates in association with arousal but also with sleep, hunger and satiety [21]. 'Emotional yawning' has been reported in animals visiting the veterinary surgeon, in elite athletes and actors before performing, and in parachutists about to jump [22].
From fMRI studies, communicative yawning, such as in contagion, appears to involve the frontal and parietal lobes, insula and amygdala [23-25], and has been postulated to be related to the mirror-neuron system [26]. Interestingly, temperature contagion has been evidenced in participants observing and ra ng others whose hands were immersed in ice cold water [27]. Hence, it is possible that yawning and temperature, seen to be linked in conditions such as MS, may also be subject to contagion and empathy.
Regardless of the function of the yawn, it is probable that the critical threshold level of cortisol is reached because of fatigue, empathy, or sleep deprivation, to elicit the yawning response. Electromyography (EMG) activity in the jaw muscles is increased which in turn regulates the further production of cortisol and also of adrenaline from the adrenal glands [28]. Feedback via the HPA-axis continues to regulate cortisol and adrenaline production within the closed loop.
There are several interesting findings of this study, which are consistent with the Thompson Cortisol Hypothesis. Significant difference in saliva cortisol levels for those who yawned, between sample one and sample two, were found, which lends support for the hypothesis. No significant difference was found for the non-yawners between saliva cortisol sample 1 and sample 2. EMG activity also increased with elevated cortisol levels and when yawning.
Small (non-significant) rises in saliva cortisol levels in the nonyawners (between rest and post-stimuli) may be explained in terms of the experimental procedure. Since two time points of saliva cortisol sampling were taken for both groups, it is possible that cortisol levels rose for both groups in the presence of yawnstimuli but for the yawners, cortisol levels reached the threshold necessary for the elicitation of a yawning response.
Previous studies have not consistently focused on repeat sampling which provides the advantage of indicating change in cortisol levels.
Neurological diseases are complicated because they present with different ranges of symptoms and severity. However, it is intriguing that diseases are often exacerbated by stress and thus by fluctuation in cortisol and adrenaline levels. Since both naturally occurring hormones are involved intimately in the body's HPA-axis, it is probable that they also play a part in regulating the effects of neurological disease. Other researchers have alluded to the fact that a common symptom in several neurological conditions and diseases is excessive yawning.
For example, in multiple sclerosis, fatigue often gives rise to excessive yawning together with brain temperature rise3. In brain-stem ischaemic stroke, patients who excessive yawn are seen to execute an involuntary rise of their affected "paralyszed" arm [11,13]. In Parkinson's disease, it is has been long considered to be effective to regulate serotonin as well as dopamine levels, and it is possible that cortisol levels may also have an interaction with the overall homeostasis of hormones [4,7,8]. The Thompson Cortisol Hypothesis provides an explanation for excessive yawning, and links cortisol with this reflex behaviour. The extent to which they are involved in each neurological disease and condition is yet to be investigated.
It is understood that cortisol acts to protect our body against stress and plays a role in the regulation and balance of hormones released within the HPA-axis. The yawn response may give rise to an increase in cortisol levels to provide symptom relief such as in lowering brain temperature as proposed by Gallup [3]. This may be the mechanism involved in the excessive yawning of people with multiple sclerosis via the hypothalamus as temperature regulator.
To understand the extent to which brain temperature may be regulated by the hypothalamus would require temperature monitoring around the surface of the skull together with induced fa gue paradigms to discern threshold levels of cortisol release. The author is leading a team in the UK and in France (Université Paris X Ouest Nanterre La Défense; Hôpital Universitaire Amiens; and Jules Verne Université de Picardie) to conduct a series of fMRI studies involving people with multiple sclerosis to analyse fatigue, temperature moderation and yawning-cortisol response. It is hoped that this with further our limited knowledge of the complex yet intriguing mechanism that we see as simply yawning.
Yawning and cortisol is of interest to clinical scientists, practitioners, neurologists and neuroscientists. Whilst still presenting a scientific conundrum, it has presented as a fascination for centuries but is now emerging with potential clinical and neuro-scientific importance, especially in the domain of diagnostic biomarkers. Clearly, further research is indicated; particularly, mapping the frequency and variance in cortisol levels in different neurological diseases. However, it is fitting that this ancient mechanism, common to most of us that has been reported for many centuries, is perhaps a breakthrough for modern neuroscience and rehabilitation.
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