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
http://www.baillement.com

mystery of yawning 

 

 

 

 

mise à jour du
19 juin 2018
Mult Scler Relat Disord. 2018;23:51-55
Yawning and cortisol levels in multiple sclerosis: Potential new diagnostic tool
Thompson SBN, Coleman A, Williams N.
Faculty of Science & Technology, Bournemouth University

Chat-logomini

Abstract
Yawning is a significant behavioural response and, together with cortisol, is potentially a new diagnostic marker of neurological diseases. Evidence of an association between yawning and cortisol was found which supports the Thompson Cortisol Hypothesis and thermoregulation hypotheses, indication that brain cooling occurs when yawning.
 
117 volunteers aged 18-69 years were randomly allocated to experimentally controlled conditions to provoke yawning. Thirty-three had been diagnosed with multiple sclerosis. Saliva cortisol samples were collected before and after yawning or after stimuli presentation in the absence of yawning. Hospital Anxiety and Depression Scale, General Health Questionnaire, demographic and health details were collected. Comparisons were made of yawners and non-yawners, healthy volunteers and MS participants.
 
Résumé
Le bâillement est une réponse comportementale significative et, avec le cortisol, est potentiellement un nouveau marqueur diagnostique des maladies neurologiques. Des preuves d'une association entre le bâillement et le cortisol ont été trouvées, ce qui confirme les hypothèses de Thompson sur le cortisol au cours du bâillement et de la thermorégulation, indiquant que le cerveau se refroidit lors d'un bâillement.
 
117 volontaires âgés de 18 à 69 ans ont été répartis au hasard dans des conditions contrôlées expérimentalement pour provoquer le bâillement. Trente-trois avaient reçu un diagnostic de sclérose en plaques. Des échantillons de cortisol de salive ont été recueillis avant et après le bâillement ou après la présentation des stimuli en l'absence de bâillements. Échelle d'anxiété et de dépression, questionnaire général sur la santé, données démographiques et sur la santé ont été recueillies. Des comparaisons ont été faites entre les bâillements et les non-bâillements, les volontaires sains et les participants affectés de SEP.

Thompson Cortisol Hypothesis : all the publications
1. Introduction
 
The first evidence-based report of cortisol level rises in multiple sclerosis (MS) together with observed yawning is presented as a potential new diagnostic indicator of signs associated with the onset of MS.
 
MS is a chronic debilitating condition that is progressive and affects the fatty tissue sheath surrounding nerves. Incomplete innervation due to loss of the myelin sheath is considered to be responsible for uncoordinated movements (Thompson, 2017). Brain temperature fluctuations are seen in people with MS together with symptoms of fatigue and especially when carrying out mentally or physically demanding tasks. These are also associated with excessive yawning (Gallup and Gallup, 2008; Gallup and Eldakar, 2013). Yet the cause of fatigue in MS is not fully understood.
 
Attempts to clarify brain recruitment during fatigue in MS has revealed involvement of the dorsolateral prefrontal cortex, inferior parietal cortex, anterior cingulate cortex and the thalamus (Périn et al., 2010).
 
Fatigue in MS has been investigated using variations in inducing fatigue together with MRI scans to determine functional areas of brain activation. For example, Thompson et al. (2016) discovered that cortisol levels were found to be higher during mental versus motor (physical) tasks. Recruitment of brainstem and hypothalamus regions, important in cortisol activity, was affected differently (Fig 1). At low cortisol levels, mental task participants had less activity in the hypothalamus than their physical task counterparts (Fig 2). When cortisol levels were higher, wider spread recruitment of both the hypothalamus and brainstem was observed in the mental task participants, and for the physical task participants, the spread was at comparative low levels of cortisol.
 
The authors concluded that cortisol is implicated in these brain regions and that brain region recruitment is likely to be dependent upon factors such as perception of stress in the task. It is likely that the mental tasks were perceived more stressful than the physical tasks and therefore required higher cortisol levels to promote wider spread brain region activity.
 
The hormone cortisol has been associated with yawning and fatigue and described in the Thompson Cortisol Hypothesis (Thompson, 2014). Threshold level rises of cortisol appear to trigger the yawn which is proposed to be part of a complex mechanism for lowering brain temperature (Thompson and Richer, 2015). Brain temperature rises dramatically in people with MS (Gallup and Gallup, 2010) and it has been proposed that cortisol is able to regulate brain temperature because of its role within the hypothalamus-pituitary-adrenal (HPA-axis) (Thompson et al., 2014), even in the foetus and in young babies (Giganti et al., 2007).
 
Secretion of cortisol is controlled by three inter-communicating regions of the brain: hypothalamus, pituitary and adrenal glands. During low levels of cortisol in the blood, the hypothalamus releases corticotrophin-releasing hormone causing the pituitary gland to secrete adrenocorticotropic hormone into the bloodstream. High levels of adrenocorticotropic hormone are detected in the adrenal glands which stimulate the secretion of cortisol, causing blood levels of cortisol to rise. As the cortisol levels rise, they start to block the release of corticotrophin- releasing hormone from the hypothalamus and adrenocorticotropic hormone from the pituitary (Thompson and Richer, 2015). As a result, the adrenocorticotropic hormone levels start to fall resulting in a fall in cortisol levels. This mechanism is known as a negative feedback loop.
 
Cortisol has been noted during exposure to stressful events and may even be modulated by contagious yawning (Eldakar et al., 2017). Yawning has also been observed to reduce facial temperature in rats (Eguibar et al., 2017) but substantive evidence of brain cooling in humans has been elusive to date.
 
Thompson (Thompson, 2010, 2011) presented the Thompson Cortisol Hypothesis which is the first evidence-based report linking cortisol with yawning in healthy participants and demonstrates that cortisol rises when we yawn. Other researchers have postulated that yawning may promote increased clearing of central nervous system-derived fluid into the central venous structures (Dolkart, 2017; Walusinki, 2014). Produced by the zona fasciculate of the adrenal cortex within the adrenal gland (Schillings, 2008), it is suggested that the rise in cortisol level triggers the yawning response in healthy people. When we become fatigued either mentally or physically, and in particular in MS, yawning becomes important for regulating cortisol. We believe that cortisol also affects the hypothalamus temperature regulation within the HPA-axis and may signal brain cooling particularly when elevation in brain temperature is common such as in MS.
 
In addition to the hypothalamus, evidence of the effects of cortisol has been found in the brainstem and motor cortex (Sale et al., 2008). Hasan et al. (2013) found sophisticated motor receptors in mice. The efficiency of cortisol-specific receptors and the communication between sensory and primary motor neurons is enhanced during motor learning. It is postulated that the link between the established sites within the HPA-axis and those of the motor cortex and brainstem may be less intimately linked by neural networks but instead by hormone system. This would help in our understanding of why brainstem lesion stroke patients may raise their affected arm during yawning where the yawning response is possibly triggered by threshold levels of cortisol. Cortisol-specific receptors on the motor end plates would give rise to muscle movements in the arm.
 
In stroke patients, cortisol levels may be inadequately detected and due to incomplete innervation, the brainstem may fail to act on changes in cortisol levels to prevent arm movement resulting in the observed parakinesia brachialis oscitans seen in brainstem ischaemic patients (Wimalaratna and Capildeo, 1988; Walusinski et al., 2010). Whilst it is accepted that hormones work within a system that comprises other hormones and complex neural circuitry, it is often through direct observation that pathways can be understood. It is hoped that such observation of people with MS (and yawning and cortisol) might provide us with an increased understanding of why brain temperature fluctuates with fatigue. This might have greater implications for people with a wide range of neurological disorders and cortisol-insufficiency syndromes such as Cushing's disease (AAES - American Association of Endocrine Surgeons, 2013). It may also be a potential diagnostic tool for detecting the signs of MS in the future.
 
4. Discussion
 
There are several interesting findings of this study. Of those participants who did not yawn, the cortisol samples at rest and then at the end of stimuli presentations was not significantly different within each group of participants. This is perhaps not surprising since it is known that cortisol levels rise during episodes of stress, whether perceived to be mentally fatiguing or if they are physically demanding. It may be that for those who did not yawn, the tasks were not demanding in mental or physical terms.
 
It is interesting that those participants with MS who did not yawn also had no significant difference in their cortisol levels which tends to suggest that, in the absence of yawning, cortisol levels in these participants did not significantly change by the end of the testing session. Perhaps of more scientific interest is the finding that participants who yawned had elevated cortisol levels. Previous studies by the research team have found that in healthy participants who yawn their cortisol levels rise significantly (Giganti et al., 2007; Thompson and Simonsen, 2015). People who have MS often become fatigued and yawning are often observed as a common symptom of MS (Gallup and Gallup, 2010). Therefore, it is of note that in those MS participants who did yawn during the stimuli presentations, their cortisol levels significantly raised in levels greater than their resting levels. It is also of note that not all of the participants yawned; this may be because their symptoms of MS were not identical to those who did yawn. Alternatively, it may be due to threshold levels of cortisol not being reached, as compared with healthy participants who did not yawn.
 
It is proposed that people with threshold levels of cortisol yawn, whether they have MS or not; however, changes in cortisol levels after yawning were not significantly different between the healthy and MS participants although there was a significant difference between the groups in their second saliva sample for the non-yawners. This is interesting because significant difference in levels between healthy participants and those with MS might suggest that cortisol levels are important in MS; and when associated with excessive yawning, these levels may signal MS symptoms. It will be interesting to see if the effects of these cortisol levels are directly correlated to lowering brain temperature since yawning seems to lower temperature.
 
These findings tend to support the Thompson Cortisol Hypothesis (Thompson, 2017, 2014) that proposes yawning occurs when threshold levels of cortisol are reached in order to reduce brain temperature. This is shown in both the healthy and MS participants. Communication with the motor cortex via cortisol-specific receptors may also explain how involuntary movement of the arm in brainstem ischaemic patients can occur partly due to incomplete innervation and irregulation of cortisol within the HPA-axis which has been extensively discussed elsewhere (Thompson, 2017; Wimalaratna and Capildeo, 1988; Walusinski et al., 2010; Walusinski, 2007).
 
The picture in neurological and biological diseases is complex because they present with a range of symptoms and severity. However, cortisol features in many disorders as well as the body's natural stress hormone. Hence it is suggested that it may provide an important key to our understanding of the way many neurological disorders are linked. It may also provide scientists and practitioners in the near future with a potential identifier or even diagnostic indicator of underlying and untoward neurological disease systems including MS.