- mise à jour
du
- 23 septembre
2001
- Lancet
- 1988, 1(8580),
300
- cas
chniques
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- 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
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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 1988. Apr. 23: 1
(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 Open University, Milton
Keynes MK7 6AA (The Lancet, march 596, 1988)
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 120 Morningside
Drive, Edinburgh EH 10 5NS (The Lancet, march 596,
1988)
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.
- Comprendre
avec l'aide de K Ezure la coordination
respiration - marche
- Convergence
of central respiratory and locomotor rhythms
onto single neurons of the lateral reticular
nucleus Ezure K, Tanaka I
Exp Brain Res1997; 113; 2;
230-242
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