Biographies de neurologues
Nouvelle Iconographie de La Salpêtrière
 L'histoire des neurosciences à La Pitié et à La Salpêtrière J Poirier
The history of neurosciences at La Pitié and La Salpêtrière J Poirier 

mise à jour du
19 novembre 2006
27 dec1958 p1585
31 jan 1959 p304 
anonymous 1958
PR Bromage 1959


J. Barbizet has done a useful service in reminding us how little is known about the everyday occurrence of yawning. In a short article he concisely and clearly covers almost all that can be said about it from the physiological, psychological, and clinical points of view. The act of yawning is involuntary and unfolds itself in a fairly consistent way, beginning with an active inspiratory movement that is chiefly remarkable for the enormous dilatation of the pharynx. At the height of the inspiration there are associated facial movements and then very often generalized stretching of the limbs. This is followed by the third phase of passive expiration. Such movements are seen also in many animals, and there is possibly a connexion between it and, for example, certain movements of birds' beaks accompanied by the flapping of wings.
Drowsiness and boredom are the usual precipitating causes of yawning. It has been observed in some neurophysiological experiments but usually in association with sleep. No "centre" for yawning has been detected by direct stimulation, nor have the conditions been defined that will invariably produce it. Barbizet considers it likely to be related to the activity of the brainstem reticular formation, whose function is intimately related to the level of wakefulness of the brain. In support of this is the fact that yawning is commonly observed in association with lesions of the brainstem or lesions indirectly compressing it. It is among the sequelae of encephalitis lethargica, and is occasionally seen as an aura of epilepsy. However, A. P. Heusner cites various authors who describe the complex yawning-stretching act in anencephalic infants, which would put the controlling centre, if it exists, at the level of the lowest centre of respiration.
The possible functional significance of yawning is unsettled. The movement may increase venous circulation to the heart, and as a result of increased cardiac output the brain might benefit, but direct observations of the effect of yawning on the cerebral circulation are missing. Heusner finds a systemic vasoconstriction and transient tachycardia, probably the same as that obtained by any deep inspiration.
In many ways the most interesting and tantalizing aspect of yawning is its relation to psychological factors and in particular the way in which it seems to be infectious in a group. The act is a part of the complex language of gesture that long preceded speech as a means of communication in the prehistory of man, a subject greatly enlarged by the work of ethologists such as Lorenz and Tinbergen. In some unknown way animals are tuned to respond to significant signals of their own species. Yawning is a relatively simple signal, and the perception of its social meaning-boredom, presumably-may hardly require any learning by environmental experience. We seem to know more about the social significance of yawning than the part, if any, it plays in the homoeostasis of the body.

SIR.-Your annotation (Journal, December 27, p. 1585) on the article by Dr. Barbizet about yawning does not quite cover all the ground. There is the psychological conflict which Dr. Barbizet hints at: the conflict between the need to remain within an irksome environment and the desire to escape from it (to sleep or other activity). But aside from this there is also a functional respiratory consideration.
Yawning may be considered as a paroxysmal sigh, combining the thoracic and abdominal muscles of respiration with the phylogenetically primitive glossopharyngeal elements. By thinking of a yawn in this way, one aspect of its functional significance may be clearer, for occasional sighing is a regular and necessary accompaniment to the muscular hypotonia of sleep.
Without an occasional sigh the compliance of the chest falls and the work of breathing is increased. This fall of compliance is readily observed in cases of prolonged apnoea treated by mechanical artificial ventilation. If a pressure-controlled machine is used and the pressure of the inspiratory phase is kept constant for an hour or so a gradual fall of tidal volume is observed. However, if a few artificial sighs are interposed, by increasing the inflating pressure for two or three breaths (so that the tidal volume approaches the inspiratory capacity), then the compliance reverts to its previous level. Presumably the act of sighing opens up alveoli which had become shut by surface tension forces, restoring the lung volume to its normal value.
It is of some interest that this restoration of compliance does not occur if the patient is receiving noxious stimuli while under light general anaesthesia, with or without complete curarization. Here the attempted reaction is the opposite of a sigh or a yawn, the patient responding to noxious stimulation from without by an expiratory rather than an inspiratory effort.-I am, etc.,
Royal Victoria Hospital, P. R. BROMAGE. Montreal.
BROMAGE PR. Total respiratory compliance in anaesthetized subjects and modifications produced by noxious stimuli. Clin Sci (Lond). 1958;17(2):217-36.