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
21 novembre 2017
Temperature
2017;4(4):xxxxx
Thermal imaging reveals sizable shifts
in facial temperature surrounding yawning
in budgerigars (Melopsittacus undulatus)
 
Andrew C. Gallup, Elaine Herron, Janine Militello,
Lexington Swartwood, Carmen Cortes, Jose R. Eguibar

Chat-logomini

Andrew C. Gallup. Yawning and the thermoregulatory hypothesis
 
 
Abstract
Accumulating comparative and interdisciplinary research supports a brain cooling function to yawning. In particular, previous research has shown significant decreases in both brain and skull temperature following yawning in mammals. In a recent study using a thermal imaging camera, significant reductions in both the cornea and concha temperature were observed following yawns in the high-yawning subline of Sprague-Dawley rats. Here, we performed a similar experiment to investigate shifts in facial temperature surrounding yawning in an avian species with more typical yawning patterns: budgerigars (Melopsittacus undulatus). In particular, we took maximal surface temperature recordings from the face (cere or eye) from 13 birds over a one-hour period to track changes before and after yawns. Similar to previous findings in high-yawning rats, we identified significant cooling (_0.36°C) of the face 10&endash;20 seconds following yawning in budgerigars. Consistent with the hypothesis that yawns serve a thermoregulatory function, facial temperatures were slightly elevated just prior to yawning and then decreased significantly below baseline levels immediately thereafter. Similarly, birds that yawned during the trials had consistently higher facial temperatures compared to those that did not yawn. Moreover, yawn latency and overall yawn frequency were strongly correlated with the highest facial temperature recorded from each bird across trials. These results provide convergent evidence in support of a brain cooling function to yawning, and further validate the use of thermal imaging to monitor changes in skull temperature surrounding yawning events.

Introduction
 
Yawning or yawn-like mandibular gaping patterns have been documented across vertebrate classes, but it remains unknown whether the jaw stretching of fish, amphibians and reptiles is congruent with yawns observed in birds and mammals. Nonetheless, the ubiquitous nature of this reflexive behavior supports the view that it is an evolved adaptation. Many researchers have proposed hypotheses to explain the functional significance of yawning, but few have garnered empirical support. Comparatively, yawns appear to serve a role in promoting arousal and state change. The muscular contractions of the jaw and accompanying deep inhalation of air that characterize yawning produce significant changes in intracranial circulation, and recently it was posited that yawns function as a brain cooling mechanism. Brain temperature of homeotherms is determined by the rate of arterial blood flow, the temperature of arterial blood flow, and any metabolic heat production within the brain. In particular, the physiological consequences of yawning, i.e., enhanced blood flow to the skull and direct heat exchange with the ambient air, are predicted to alter the first two of these variables by cooling brain temperature through convective heat transfer. In addition, yawning could lead to ventilation of the sinus system, which would promote evaporative cooling of the sinus mucosa. The increases in localized circulation and changes in ventilation, which are associated with yawning, are well known mechanisms that cool brain temperature.
 
Since its conception, a growing number of reports have tested and confirmed the specific predictions derived from the brain cooling hypothesis. In particular, a growing number of studies have linked brain and/or body temperature changes to yawning events and shown that yawns can be effectively altered (i.e., selectively increased or decreased) through the manipulation of ambient temperature. According to this hypothesis, the onset of yawning should be preceded by rising brain temperature, and that once triggered yawns should produce a measurable cooling effect. Using thermocoupled temperature probes, Shoup- Knox et al. aimed to directly capture this association among freely moving Sprague-Dawley rats. Consistent with the brain cooling hypothesis, yawning events in rats were triggered during rapid increases in the temperature of the prelimbic cortex tissue (+.11°C), and following the execution of this response brain temperatures dropped precipitously down to baseline levels. Comparable temperature shifts, monitored through the use of an oral thermometer, have also been documented surrounding excessive yawning attacks in humans.
 
Recently, Eguibar et al. examined the extent to which the aforementioned reductions in intracranial temperature associated with yawning produced cooling at the surface of the skull. Using a high-yawning subline of Sprague-Dawley rats, thermographic images of the eye cornea and ear concha were captured before and after yawning events. Consistent with the brain cooling hypothesis, both cornea and concha temperatures significantly decreased (-0.32°C and -0.48°C, respectively) during and 10 seconds following yawns. These findings support the view that the physiological consequences of yawns provide a widespread cooling effect to the brain/skull, and not just internal tissues, and validate the use of thermal imaging to track changes in thermoregulation surrounding such events. While the use of high-yawning rats offered an effective model to initially assess this relationship, i.e., yawning frequency in high-yawning rats (20 yawns/h) is an order of magnitude higher than normal Sprague-Dawley rats (2 yawns/h) as well as after pharmacologically- and neuropeptide induced yawning, similar studies are needed to replicate these findings in animals with more typical yawning patterns.
 
Here, we investigated skull surface temperature changes as a function of yawning in an avian species: budgerigars (Melopsittacus undulatus). These birds served as an appropriate non-mammalian model to explore this relationship because much is known about their naturalistic and experimentally-induced yawn frequency, and yawning has previously been implicated in thermoregulation in this species. Following a similar methodology to Eguibar et al., thermographic images were continuously captured at 10 second intervals to track immediate shifts in facial temperature before and after yawns. In addition, based on previous research showing a strong correlation between body temperature and yawning following stress within this species, correlations were run to assess the relationship between both yawn latency and frequency and the maximum facial temperature measured across the trials.
 
Discussion
 
The motor action pattern of yawning produces profound changes in localized (i.e., intracranial) circulation and ventilation, which now have well documented thermoregulatory effects. As a follow- up to a recent report in which decreases in skull temperature were documented following yawns in a subline of high-yawning Sprague-Dawley rats, we show that yawning produces very similar reductions in the facial temperature of an avian species with more typical yawning patterns. In particular, budgerigars experienced an average temperature reduction of -0.36°C in the cere/eye region 10&endash;20 seconds after yawns, which is consistent with the temperature decrements detected at the eye cornea (-0.32°C) and ear concha (-0.48°C) within the high-yawning rats. In accord with the brain cooling hypothesis, facial temperatures differed considerably between birds that yawned compared to those that did not yawn during the experiment. Moreover, budgerigars with the highest facial temperature recordings yawned sooner following the onset of the recordings and more frequently across trials. These results are consistent with a previous study investigating stress-induced hyperthermia in this species, whereby a similar negative correlation was observed between body temperature and yawn latency. Given that the birds in the current study were briefly handled and placed in isolation for testing, we cannot rule out the possibility that the yawning and associated temperature changes reported here were also stress-induced.
 
Overall, these findings suggest that yawning is a thermoregulatory behavior in this species, and generally support previous research indicating a selective brain cooling function to the opening and closing of the beak in birds through the ventilation of the sinus system. In budgerigars, the sinus walls contribute to dissipation of heat through convection, conduction and heat loss by evaporation. Importantly, in birds the beak and surrounding tissue is an important dissipater of heat, because other areas are covered by plumage. Other mechanisms used in thermoregulation around this area include panting and gular fluttering, which are also closely related to yawning.
 
In summary, the current study provides convergent evidence supporting a widespread brain cooling function to yawning that can be captured through the use of thermographic images of the skull. We suggest that future research employ the use of thermal imaging to investigate the relationship between yawning and thermoregulation in other species, including poikilotherms.