mystery of yawning
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La parakinésie brachiale oscitante
Yawning: its cycle, its role
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Fetal yawning assessed by 3D and 4D sonography
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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
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18 septembre 2014
Med Hypotheses
2014;83(4):494-6
Yawning: Thompson Cortisol Hypothesis Discussed
Simon B.N. Thompson
 
Psychology Research Centre, Bournemouth University,
Talbot Campus, Poole. UK

Chat-logomini

Abstract
Yawning and its involvement in neurological disorders has become the new scientific conundrum. Cortisol levels are known to rise during stress and fatigue; yawning may occur when we are under stress or tired. However, the link between yawning, fatigue, and cortisol has not been fully understood. Expansion of the Thompson Cortisol Hypothesis proposes that the stress hormone, cortisol, is responsible for yawning and fatigue especially in people with incomplete innervation such as multiple sclerosis. This informs our understanding of the functional importance of the brain stem region of the brain in regulating stress and fatigue.
 
Thompson Cortisol Hypothesis : all the publications

Introduction
 
Hippocrates was one of the first early observers of human behaviour and physiology. Reporting in 400 BC, he noticed that yawning often preceded a high body temperature.[1] The hypothalamus was considered to be an important brain structure in regulating body temperature,[2] together with the pons, medulla and midbrain acting as relays and mediators.[3-5] Thermoregulatory theories are thought to be inadequate explanations of social and contagious yawning possibly because of the involvement of psychological mechanisms such as empathy,[6] and the desire towards group identity. For centuries, philosophers, scientists, and neurologists have proposed yawning to be a simple need to replace oxygen deficiency in the blood.[3] Evidence from clinical populations such as ischaemic stroke patients suggests that a basic and vital need to regulate other body chemicals may indicate the involvement of the insular and caudate in the production of the yawn.[7] Brain-stem lesions have often provided evidence of the link between yawning and release of paralysed neural pathways, particularly in the phenomenon parakinesia brachialis oscitans where the paralysed arm can rise involuntarily during a yawn.[8]
 
Oxytocin may also be associated with yawning,[9,10] especially because it is even seen in humans at pre-term.[11,12] Depressed mothers may be more prone to cease breastfeeding early. This may potentially lead to damage of the stress response within the infant as they become flooded with the cortisol stress-response hormone.[13] As the body's natural defence against the effects of stress,[14] cortisol is released by the pituitary gland to maintain the circadian rhythm in a role within the hypothalamus-pituitary-adrenal (HPA) axis.[15] It is not surprising that sleep deprivation and fatigue may be associated with lowered cortisol levels.[16] Hence, cortisol has a potentially significant role in the rejuvenation and well-being of the human body. When incomplete innervation occurs as in multiple sclerosis (MS), excessive yawning is frequently found with fatigue. The Thompson Cortisol Hypothesis[17] proposes that rises in cortisol levels are associated with yawning. An increase in electro-muscular activity around the jaw line occurs during yawning, seen as a 'yawning envelope' in the electromyogram,[18] and with elevated cortisol levels. Threshold level of cortisol may be required for yawning status. Functional interactivity was significantly reinforced during a phasic alertness task in a study at Amiens University Hospital and the University of Picardy Jules Verne.[19] Preferentially activity was seen in the dorsolateral prefrontal cortex (DLPFC) region of the brain, as compared to during intrinsic alertness. The DLPFC region may be involved in maintaining a state of alertness and in temporal preparation during alertness tasks. These teams are examining alertness and fatigue together with cortisol rises in healthy and MS patients both in France and in the UK (at Bournemouth University) in a collaborative study.
 
It is proposed that when the critical threshold level of cortisol is reached because of fatigue, yawning is elicited. This action gives rise to increased electro-myographical activity in the jaw muscles and regulates the production of adrenaline from the adrenal glands. Feedback further regulates cortisol and adrenaline production within the HPA axis.
 
Discussion
 
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 non-yawners (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 yawn-stimuli but for the yawners, cortisol levels reached the threshold necessary for the elicitation of a yawning response. 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 Hypothalamus-Pituitary-Adrenal 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.[2]
 
This may be the mechanism involved in the excessive yawning of people with multiple sclerosis via the hypothalamus as temperature regulator. Fatigue as a common symptom of multiple sclerosis seems also to be intimately linked with yawning and elevation in cortisol levels,[28] and it is proposed that the setting for the yawning response in social encounters may also involve the component of induced fatigue, as suggested by co-workers of the Anglo-French collaborative study into cortisol in MS.[19]
 
Conclusions
 
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; 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.
 
 
Oxytocin