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mise à jour du
23 septembre 2001
1988, 1(8580), 300
cas chniques
Is yawning a brainstem phenomenon ?
Wimalaratana HS, Capildeo R
Regional Centre for Neurology and Neurosurgery, Oldchurch Hospital, Romford, Essex
a stroke patient who stretched his hemiplegic arm during yawning
Yawning occurs throughout the animal kingdom. Its purpose, physiological basis, and neuroanatomical pathways remain a mystery. There are few publications on yawning and only a brief account is to be found in most physiology textbooks. A yawn is a deep inspiratory movement with a wide-open mouth often accompanied by stretching of limbs. We describe a stroke patient who stretched his hemiplegic arm during yawning. Similar cases may help to postulate neuroanatornical pathways involved in yawning. [autres cas : Mulley , Blin : A single report of hemiplegic arm stretching related to yawning: further investigation using apomorphine administration ]

A 65-year-old man was admitted with acute onset of right-sided weakness. On examination he had a right upper motoneurone facial weakmess. The power in upper and lower limbs was 0/5 and 2/5, respectively. A computerised tomographic head scan showed an area of infarction in the left intemal capsule. His wife noted that he stretched both arms equally during yawning. A nurse saw similar movements on a subsequent occasion. The patient was also aware of this unusual movement of his arm but voluntary efforts to stretch the arm were unsuccessful, as were attempts to study power and tone of the limb during these involumary movements because he did not yawn in the presence of investigators. Limb movement during yawning faded away, apparently with the development of spasticity.

A case-report of a patient in whom "locked-in syndrome" developed after a pontine lesion commented that this patient could not open and close his mouth voluntarily but was able to do so when yawning (Gschwend).

These two cases demonstrate the involuntary nature of yawning. Our case indicates the non-involvement of pyramidal tracts in yawning, which appears to be operating from a point below the level of the pons, possibly in the medulla oblongata. Yawning is unassociated with other related physiological events and therefore must possess an indepenent medullary centre of its own which could be called a "yawning initiating centre YIC" Thus neuroanatomical patways involved in yawning should include non-pyramipal (or extrapyramidal) projections from YIC down to the brainstem nuclei and the anterior horn cells in the spinal cord, to share the common lower motoneurone pathway.

The infectious nature of yawning cannot be ignored. The probably indicates afferent patways to the YIC. Any further interpretation without more evidence of the complex process yawnig would be an over simplification.

Malcom Weller (Lancet, Vol 331 1988. Apr. 23: (8591): 950)

Dr Wimlaratana assert the purpose of yawning remains a mystery and Dr Forrester (mars 12p56) suggests that its purpose is to maintain lung compliance and inflate collapsed alveoli. I suggested third possibility . As Wimalaratana mention yawning is infectious. Animals would have a greater tendency to sleep together if the first to become weary was to signal and if the others were to respond. The infectious nature may therefore have a group cohesive function, which has survival implications for animals that hunt in packs or protect themselves in herds.

Dave Gilbert (The Lancet, 1988; Vol. 331 No. 8585 p 596)

Dr Wimalaratna and Dr Capildeo (Feb 6 p 300) discuss two cases which demonstrate the involuntary nature of yawning. In the rat, the stretch-yawn response bas been investigated pharmacologically and can be reliably induced with low doses of dopamine receptor direct agonists, such as apomorphine. Bouts of yawning, which occur during periods of hypomotility, are thought to follow stimulation of dopamine D2-autoreceptors in preference to postsynaptic dopamine D2-receptors, whose stimulation would result in hypermotility. The locus of dopamine receptor-mediated yawning has not been established.

Dopamine agonist-induced yawing is easily blocked with neuroleptics such as sulpiride, a dopamine D2-receptor antagonist widely used in the management of chronic schizophrenia. Studies where sulpiride is used to block apomorphine-induced yawning and hypomotility and related studies where dopamine autoreceptors have been blocked suggest that neuroleptic agents, especially at the low doses commonly used clinically, may cause increased stimulation of postsynaptic dopamine D2-receptors. This poses a serious question for the dopamine hypothesis of schizophrenia.

Thus, ironically, the stretch-yawn, which was described mystery by Wirnalaratna and Capildeo in its purpose, physiological basis, and neuroanatomical pathways, may prove a valuable tool for understanding how dopamine antagonists are effective in the treatment of schizophrenia.

 John M Forrester (Forrester, J.M. Is yawning a brainstem phenomenon? The Lancet 1988;331(8585):596.)

Wimalaratna and Capildeo suggest that yawning is organised by the medulla, but that its purpose remains a mystery, and that it is "unassociated with other related physiological events".

The link with the medulla was suggested as long ago as 1906 when Mosso stated: "Patients who suffer from cerebral anaemia or from certain affections of the medulla oblongata often yawn continually". What is the function of yawning ? Mead and Collier showed that lung compliance of anaesthetised dogs fell during about 2 h of spontaneous breathing to about 60% of its initial value, but could be restored rapidly by deep inflation of the lungs-most of it by a single deep inflation. These results were in accord with measurements in man and were later noted by anaesthetists.

There are two reasons for the loss of compliance. The surfactant film may get "old and weary" if not occasionally well stretched. Although this might add to the work involved in gentle breathing, in itselfit may be of little practical importance. Secondly, alveoli may collapse. Here besides the extra work, blood is shunted and arterial oxygenation is impaired. This surely matters. Yawning can prevent it, but so, of course can a sigh. In rats, yawning is associated with at least one other related physiological event, penile erection.

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Wimalaratna HS, Capildeo R. Is yawning a brainstem phenomenon ? a stroke patient who stretched his hemiplegic arm during yawning Lancet 1988;1(8580):300