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
26 février 2015
Physiology & Behavior
Yawning, acute stressors, and arousal reduction in Nazca booby adults and nestlings
Amy C. Liang, Jacquelyn K. Grace,
Emily M. Tompkins, David J. Anderson
Department of Biology, Wake Forest University, Winston-Salem USA


Yawning is a familiar and phylogenetically widespread phenomenon, but no consensus exists regarding its functional significance.
The authors tested the hypothesis that yawning communicates to others a transition from a state of physiological and/or psychological arousal (for example, due to action of a stressor) to a more relaxed state. This arousal reduction hypothesis predicts little yawning during arousal and more yawning (above baseline) during and after down-regulation of arousal.
Experimental capture-restraint tests with wild adult Nazca boobies (Sula granti), a seabird, increased yawning frequency after release from restraint, but yawning was almost absent during tests. Natural maltreatment by non-parental adults also increased yawning by nestlings, but only after the maltreatment ended and the adult left.
CORT (corticosterone) was a logical a priori element of the stress response affecting the stressor&endash;yawning relationship under the arousal reduction hypothesis, and cannot be excluded as such for adults in capture-restraint tests but is apparently unimportant for nestlings being maltreated by adults.
The arousal reduction hypothesis unites formerly disparate results on yawning: its socially contagious nature in some taxa, its clear pharmacological connection to the stress response, and its temporal linkage to transitions in arousal between consciousness and sleep.
Gallup AC, Clark AB Commentary: yawning, acute stressors, and arousal reduction in Nazca booby adults and nestlings. Fontiers in Psychology 29 october 2015
Les auteurs ont testé l'hypothèse que le bâillement communique aux autres une transition d'un état d'excitation physiologique et / ou psychologique (par exemple, grâce à l'action d'un facteur de stress) à un état plus détendu. Cette hypothèse de réduction de l'excitation prédit peu bâillements pendant l'éveil et plus bâillements pendant et après la régulation de l'excitation.
Les expériences ont été menées avec des oiseaux de mer adultes sauvages "les fous de Nazca (Sula de granti)". D'abord saisis, puis maintenus en cage, c'est après leur libération que l'augmentation de la fréquence des bâillements a été mesurée. Lors des test initiaux, les bâillements étaient presque inexistants.
Après avoir constaté que dans la nature, des oisillons subissent de mauvais traitements de la part d'adultes autres que leurs parents, les bâillements des oisillons ont été comptabilisés dans ces circonstances. L'augmentation du nombre de bâillements intervient après la fin de la maltraitance quand l'adulte responsable est parti.
La corticostérone, un des facteurs de la réponse au stress, affecte a priori la relation stress - bâillements dans l'hypothèse de l'effet apaisant post-stress du bâillement. Ceci est apparu probable chez les adultes après capture mais n'a pas été confirmé pour les oissilons victimes de maltraitance.
L'hypothèse de réduction de l'état de stress permet de rassembler des résultats autrefois disparates concernant le bâillement: sa nature socialement contagieuse dans certains taxons, son lien pharmacologiquement avéré avec la réponse au stress, et son lien temporel des états transitionnels entre l'éveil et le sommeil.

1. Introduction
Although yawning is ubiquitous in humans and phylogenetically widespread, studies targeting functional significance have produced little consensus. The wide variety of functional explanations includes increasing alertness, renewing surfactant in the lungs, and evacuating infectious substances fromthe tonsils. The popular viewthat yawning adjusts oxygen and carbon dioxide levels in the blood persists, despite the demonstration by Provine et al. that human subjects breathing an elevated level of oxygen did not yawn more or less than did subjects breathing air with elevated carbon dioxide. Our goal in this paper is not to review this extensive and diverse literature; instead,we focus on one idea, that yawning and recent exposure to a stressor are linked (by "stressor" we mean an extrinsic factor, real or perceived, that threatens homeostasis). A variety of evidence connects yawning, or at least behavior that resembles yawning, to stressors, both physiological and social.
The HPA (Hypothalamus&endash;Pituitary&endash;Adrenal) axis response via glucocorticoids, a widely investigated aspect of the stress response, is of special interest. Adrenalectomy stops production of glucocorticoids and virtually abolishes yawning in rats; administration of the synthetic glucocorticoid dexamethasone to these same rats restores yawning. The hormones dopamine and oxytocin are both products and regulators of the HPA axis; exogenous administration of these hormones or their agonists induces yawning. Circulating levels of corticosterone (CORT), the primary glucocorticoid in birds, and cortisol (the mammalian homologue of CORT) are also correlated with alertness, vigilance, and arousal, rising in the hours before awakening, rising faster just after awakening, and promoting arousal and memory consolidation.
Dourish and Cooper linked yawning and both of these actions of the HPA axis, suggesting that yawning "may signal the termination of stressful experience or of sustained concentration", an idea that we call the "arousal reduction hypothesis" to distinguish it from Baenninger's suggestion that yawning increases arousal. Under this hypothesis, adaptive down-regulation of arousal also causes yawning and occurs when an animal perceives that a stressor has passed and that arousal in response to the stressor is no longer required. Here we test the arousal reduction hypothesis, measuring yawning in response to temporary stressors in a wild bird, the Nazca booby (Sula granti), using both experimental and natural acute stressors. Wild Nazca boobies tolerate close human presence and handling well, facilitating behavioral observation even after experimental administration of stressors.
In adults, a standardized capture-restraint stress test induced an HPA axis response, raising the circulating concentration of CORT .We monitored the birds' behavior, including yawning, during the test and after release from restraint and compared the yawning rate to that of undisturbed adults. In nestlings, we exploited the natural phenomenon of episodes of nestling maltreatment by Non-parental Adult Visitors (NAVs). NAVs exhibit an intense social attraction to nonfamilial conspecific nestlings, which frequently manifests as aggressive interactions with nestlings, with a gradation in severity.
We compared the yawning of nestlings that experienced a low severity aggressive NAV interaction, which induces thermoregulatory stress, to that of time- and age-matched undisturbed nestlings. We predicted low rates of yawning during and shortly after the period of stress and a higher rate after a period of surveillance following removal of the stressor. If CORT is the target of the down-regulation under this hypothesis, then we predicted that only a stressor that induced elevated [CORT]would induce subsequent yawning and that [CORT] during the period of stress would predict the subsequent yawning.
4. Discussion
This study is the first to evaluate known stressors as triggers of yawning in a wild, free-living animal; the results are consistent with the arousal reduction hypothesis, while indicating that the target(s) of arousal down-regulation could include circulating CORT but does not in at least some contexts. Adult Nazca boobies had higher circulating [CORT] during nocturnal capture-restraint tests, demonstrating activation of the HPA axis.
Our Control adults showed that yawning is rare at night and during capture-restraint tests, but these adults all yawned at least once in the 60 min following the capture-restraint stressor, while time-matched controls did not. Nestlings were prevented from thermoregulating in this tropical environment during diurnal visits from NAVs, at a time of day when solar insolation induced all time-matched, unvisited nestlings to dump heat continuously by gular flutter. The social and thermal stressors of these low-severity NAV events did not induce a detectable [CORT] response in nestlings (in contrast to high-severity NAV events), but did induce yawning (and thermoregulation by gular flutter) in all Post-NAV nestlings within 15 min of the NAV's departure . Thus, two types of stressor reliably triggered yawning, in the temporal sequence predicted by the arousal reduction hypothesis, and a detectable CORT response was not required in one of the stressor&endash;yawning relationships.
Our results provide insight into the cause-and-effect relationship of stressors and yawning. If [CORT] caused the yawning response in adults then the large variation in CORT response during the test might predict the latency to yawn, but no predictive ability was detected. Instead, the latency to yawn after the test showed little variation, consistent with a yes/no trigger by the stressor (which could be CORT, if its effect is qualitative). The thermal stressor affecting nestlings also showed apparent quantitative variation: some nestlings abandoned the pelican posture and stood upright immediately after their NAV's departure, while others waited up to 7 min to stand (Fig. 4), probably reflecting variation in perception of the end of the risk from the NAV. All control nestlings dumped heat via gular flutter for 100% of the observation period, and all victim nestlings resumed gular flutter within minutes of standing, so the variation in latency to stand probably does not reflect meaningful variation in thermal load incurred before the NAV visit, and the added load in pelican posture during the visit was presumably similar for all victims. Instead, latency to stand should serve as a proxy for cumulative thermal load (longer latency extends the period without gular flutter), and the latency to the first yawn after standing showed a significant positive relationship with the latency to stand. Thus, the yawning response to a stressor can be qualitative or quantitative, depending on context.
Several hypotheses have been proposed to explain the causation of yawning. Under the thermoregulation hypothesis, yawning is triggered by brain hyperthermia and cools at least part of the brain via targeted ventilation.Our results from adults are silent on this issue because we have no data on the adults' temperatures. For nestlings, this hypothesis predicts a negative relationship between latency to stand (a proxy for hyperthermia) and latency to yawn after standing, but we observed a significant positive relationship.
The arousal promotion hypothesis casts yawning as a means of regulating arousal, increasing attention to surroundings "when environments provide relatively little stimulation"; humans use yawning to counter boredom under this hypothesis. [CORT] exhibits correlation with the sleep&endash;wake cycle (for Nazca boobies,) consistent with a primary role in arousal/attention. Nazca booby adults exhibited variation in [CORT] at the end of their restraint, so this hypothesis predicts a quantitative, negative relationship between [CORT] and latency to yawn, which was not observed. Noting that Post-Test adults and Victim nestlings in this study experienced significant stimulation only minutes before their first yawn, and gave no indications of drowsiness, the essential assumption of the arousal promotion hypothesis seems to be largely invalid in our study.
Dourish and Cooper's arousal reduction hypothesis is the reverse of the arousal promotion idea. The results of several studies support this hypothesis. In these studies the animal was released from a stressor, had time for surveillance of the stressor and a decision that the stressor had passed, and then showed enhanced yawning. For Nazca booby adults, yawning was essentially absent during the recapturerestraint test and for 30 min after release, and then potentiated in the next 30 min. Nestlings also showed an inhibition/potentiation cycle: despite probable hyperthermia, 18 of 27 (0.67) nestlings visited by NAVs showed a latency to yawn of at least 1 min after assuming a normal posture that would permit gular flutter. In a study with a similar design, budgerigars (Melopsittacus undulatus) given a capturerestraint test suppressed yawning during the first 20 min after release, then increased yawning in the next 20 min, and finally returned to a control level 40&endash;60 min after release. Noting a correlation between yawning and body temperature in their experiment,Miller et al. suggested that yawning has a thermoregulatory function.
The arousal reduction hypothesis offers an alternate interpretation: after a period of alert surveillance, the stress response was down-regulated adaptively and signaled by yawning when the bird perceived that the stressor is gone. Finally, rats (Rattus rattus) experiencing shocks at predictable intervals (during which down-regulation of the stress response can be advantageous) yawned more frequently between shocks than did rats experiencing shocks at random intervals (during which down-regulation is not advantageous), suggesting an association between yawning and down-regulation of stress. Moyaho and Valencia concluded that yawning diminished arousal, exerting a calming effect, but the reversed arrow of causation posited by the arousal reduction hypothesis, that diminishing arousal causes yawning, is equally consistent with their results.
The arousal reduction hypothesis attributes communication value to the signal of a subjective perception that a stressor has passed: the animal is sending a message actively about its perception. This position connects logically to the well-known contagion of yawning in both non-humans and humans, and to the connection of susceptibility to contagious yawning and empathy for the emotion and motivation of others. As such, the arousal reduction hypothesis can be considered an element of the social/communication model for yawning combined into a single model of adaptive information-sharing of perceptions of threat status. Any animal that benefits from coordination of group members' attention to surroundings (c.f., even ephemeral groups like sexual pairs) can be expected to attend to a signal like yawning and to benefit from sending the signal in some situations. The more important such coordination is, the more likely propagation of the signal (contagion) should be. The fact that animals yawn when alone is not a difficulty of this model, possibly indicating that the generator of yawns lacks a negative feedback mechanism that checks for the presence of receivers of the signal.
We suggest a change in the sense of the hypothesis. Rather than signaling the "termination of stressful experience or of sustained concentration", the hypothesis should focus explicitly on the internal state of the animal: simply, yawning signals an attempt to down-regulate arousal. This focus on internal state, rather than extrinsic factors, admits the possibilities of adaptive down-regulation of arousal 1) even when the arousing stimulus still exists or
2) when no stressor is involved (for example, at the end of the normal awake period). A variety of phenomena are apparently consistent with this hypothesis. Common experience makes us associate impending sleep with yawning; downregulating arousal should facilitate the transition to sleep. Many athletes yawn immediately before a competition (speed-skater Apolo Anton Ohno is a notorious example), perhaps actively calming themselves at a time of on-going high tension and producing yawns as an epiphenomenon.
Captive budgerigars yawn more under ambient temperatures increasing from 27&endash;33 °C than from 23&endash;27 °C or decreasing from 34&endash;28 °C or decreasing from 28&endash;24 °C, perhaps indicating an attempt to suppress agitation in a situation with almost no options to dump heat. Yawning contagion propagates differentially from social leaders to others in highly social species like bonobos (Pan paniscus), chimpanzees (P. troglodytes), and ostriches (Struthio camelus) and is connected to stimulation of brain areas associated with empathy and social interpretation in "infected" individuals, suggesting systematic top-down signaling as part of yawning's communicative value. In humans, "evening types" display a relatively nocturnal circadian cycle and claim difficulty in the process of awakening and beginning the day, the opposite of "morning types"; the awakening stressor for evening types is associated with a yawning frequency at awakening that is several times that of "morning types", for whom awakening is apparently not a stressor, consistent with the arousal reduction hypothesis. In conclusion, acute stressors initially suppressed and later potentiated yawning in Nazca boobies in a temporal sequence consistent with elevated arousal followed by active down-regulation of arousal. CORT was a logical a priori factor affecting the stressor&endash;yawning relationship under the arousal reduction hypothesis, and cannot be excluded as such for adults in capture-restraint tests but is apparently unimportant for nestlings being maltreated by adults. Little information exists for any species to enable rigorous tests of the arousal reduction hypothesis, and we suggest experimental manipulation of arousal, especially in highly social species in which coordination of arousal will be favored by natural selection, and more careful monitoring of arousal state than was possible in our study.