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
Evolutionary Neuroscience
2011 september

Contagious yawning and seasonal climate variation
Andrew C. Gallup and OmarTonsi Eldakar
Department of Biological Sciences, Binghamton University, Binghamton, NY
Center for insect Science, University of Arizona, Tucson, AZ, USA


Andrew C. Gallup. Yawning and the thermoregulatory hypothesis
Recent evidence suggests that yawning is a thermoregulatory behavior. To explore this possibility further, the frequency of contagious yawning in humans was measured while outdoors in a desert climate in the United States during two distinct temperature ranges and seasons (winter: 22t; early summer: 3TC). As predicted, the proportion of pedestrians who yawned in response to seeing pictures of people yawning differed significantly between the two conditions (winter: 45%; summer: 24%). Across conditions yawning occurred at lower ambient temperatures, and the tendency to yawn during each season was associated with the length of time spent outside prior to being tested. Participants were more likely to yawn in the milder climate after spending long periods of time outside, while prolonged exposure to ambient temperatures at or above body temperature was associated with reduced yawning. This is the first report to show that the incidence of yawning in humans is associated with seasonal climate variation, further demonstrating that yawn-induced contagion effects can be mediated by factors unrelated to individual social characteristics or cognitive development.
Numerous hypotheses have been proposed to explain why vertebrates yawn, and the two prevailing hypotheses favor either physiological or social function (Guggisberg et al., 2010). Physiological hypotheses predict that yawning acts to aid in the regulation of a given body state (e.g., brain temperature or arousal), while the social hypothesis predicts that yawning functions to synchronize group behavior by communicating unpleasant mental and physical states. While experimental and observational evidence of contagious yawning in humans (e.g., Provine, 1986; Platek et al., 2003), a few select non-human primate species (chimpanzees, Pan troglodytes; stumptail macaques, Macaca arctoides; gelada baboons, Theropithecusgelada; Anderson et al., 2004; Paukner and Anderson, 2006; Campbell et al., 2009; Palagi et al., 2009), and dogs (Joly-Mascheroni et al., 2008; but see Harr et al., 2009 and O'Hara and Reeve, 2011) provides support that yawning may have a social role, tests of the specific predictions of the social model are lacking and it is unknown how yawning could reliably transmit specific information during varying contexts (Gallup, 2011). Furthermore, the ubiquity of non-social yawning across vertebrate classes (e.g., Baenninger, 1987) suggests that it has an underlying physiological significance, and thus may have multiple functional outcomes across species.
Although it is still commonly believed that yawning functions to equilibrate 02 and CO2 levels in the blood, there is no support for this hypothesis and it has been concluded that yawning and breathing operate by different mechanisms (Provine et al., 1987). On the other hand, one of the physiological hypotheses receiving growing support proposes a role of yawning in brain thermoregulation (Gallup and Gallup, 2007, 2008). Recent evidence for this model comes from prelimbic brain temperature recordings in rats (Rattus norvegicus), showing that yawning
is preceded by rapid increases in brain temperature and followed by corresponding decreases in brain temperature (ShoupKnox et al., 2010). According to this model, cooling is primarily the result of enhanced cerebral blood flow and countercurrent heat exchange with ambient air. Accordingly, the temperature of the ambient air is what gives a yawn its utility. Thus yawning should be counterproductive - and therefore suppressed in ambient temperatures at or exceeding body temperature, as taking a deep inhalation of air would no longer promote cooling. In other words, there should be a "thermal window" or a relatively narrow range of ambient temperatures in which to expect highest rates of yawning (Gallup and Gallup, 2007). Experimental studies on birds (Melopsittacus undulatus) and rats (Rattus norvegicus) support this view, showing that changes solely in ambient temperature are sufficient to influence yawning frequency (Gallup et al., 2009, 2010, 2011). In particular, yawns become more frequent during initial increases in ambient temperature, but then decrease as temperatures approach body temperature.
The current study explored this relationship in humans by measuring the incidence of contagious yawning while outdoors during two distinct periods of temperature and season (winter and early summer) in Arizona, USA. The summer condition provided temperatures that matched or slightly exceeded body temperature with relatively low humidity, while the corresponding winter condition included milder temperatures and slightly higher humidity. It was predicted that yawning would be less frequent in summer trials, but that it may be common just after entering the outside conditions since adaptive thermoregulatory responses take time to occur after encountering sudden climate changes. However, the rate of yawning should diminish sharply as the amount of time spent outside increases, since it would no longer result in a cooling response. Contagious yawning was used as a proxy for yawning in both conditions because it is indistinguishable from spontaneous yawning (aside from the fact that the triggers differ), and it can be manipulated using visual stimuli (e.g., Platek et al., 2003). In other words, a stretching of the jaw and a deep inhalation of air accompany both responses, and thus the physiological consequences should be similar. Furthermore, the study of contagious yawning provides the opportunity to determine whether underlying features related to thermal homeostasis mediate socially derived aspects of this behavior.
As predicted from the thermal window hypothesis of thermoregulatory model, the incidence of contagious yawning in humans was influenced by seasonal variation in climate conditions. According to this hypothesis, it is the temperature of the ambient air that gives a yawn its cooling utility and thus it was expected that yawning should be diminished when outdoor temperatures reach or exceed body temperature. Across seasonal trials yawning was associated with lower ambient temperatures, and in particular, yawning was less frequent in the summer condition when temperatures were higher and humidity was lower. Furthermore, the proportion of individuals yawning in the summer dropped greatly as the length of time spent outside increased, suggesting that the expression of social yawning may reflect a compromise with thermal effects. On the other hand, there was a positive relationship between time spent outdoors prior to testing and yawning in the winter condition. Since all trials were conducted in direct sunlight (where temperature exceeded that recorded in the shade), it seems likely that thermoregulatory responses will increase over time under these conditions, thus explaining this relationship.
The findings of this report are consistent with previous research suggesting that the triggers for spontaneous yawning are sensitive to ambient air temperature and mechanisms of brain thermoregulation. Recent experimental and observational research has shown a connection between yawning and ambient temperature manipulation/variation in other animals (Deputte, 1994; Campos and Fedigan, 2009; Gallup et al., 2009, 2010, 2011). Due to inherent limitations of field research, future studies should experimentally investigate the association between human yawning and more refined ambient temperature ranges in the laboratory. In addition, research should investigate the
frequency of yawning in extreme cold climates since yawning in severe cold temperatures would be expected to have adverse effects on brain thermoregulation, and thus should be inhibited. Moreover, considering yawning or yawn-like behaviors are ubiquitous across vertebrate classes, research should explore the relationship between yawning and seasonal climate variation in poikilotherms.
This study is the first to show that the expression of yawning in response to contagious stimuli can be altered by variation in seasonal climatic conditions. Furthermore, while previous research has shown that specific individual social characteristics and cognitive developmental factors are involved with the susceptibility to yawning contagiously in humans (e.g., Anderson and Meno, 2003; Platek et al., 2003; Senju et al., 2007; Millen and Anderson, 2010), this study further indicates that yawn-induced contagion effects can also be mediated by non-social factors (e.g., ambient temperature). These findings extend the logic of the thermal window hypothesis to humans, demonstrating a highly conserved, comparative aspect to the expression of this behavior. Consistent with the thermoregulatory model, these results dovetail with recent research showing that methods of behavioral brain cooling (nasal breathing and forehead cooling) inhibit contagious yawning in humans (Gallup and Gallup, 2007). Taken together, future studies of contagious yawning should be assessed under conditions where thermal effects are essentially neutral, or at least consistent, across conditions.
In summary, while the utility of yawning as a contagious behavior is still under debate, the current findings suggest the underlying mechanism for this response may be involved with thermoregulatory physiology, further challenging the view that the origin of yawning is social (Guggisberg et al., 2010).
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