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- Fetal
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- Bâillements
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révélée par
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- Fetal
yawning : a behavior's birth with 4D US
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- Sonography
Edited by: Kerry Thoirs
- Fetal
Yawning
Olivier
Walusinski
- Chapter 18 Pages
325-332
-
- Development
of Fetal Yawn Compared with Non-Yawn Mouth
Openings from 24-36 Weeks Gestation.
Reissland N
- Seemingly
Trivial Fetal Motions: Yawning and Hiccups.
Piontelli A
-
- According to Dorland's Medical Dictionary,
"A yawn is a deep, involuntary inhalation with
the mouth widely open, often accompanied by the
act of stretching". Yawning is composed roughly
of an active wide opening of the mouth followed
simultaneously by a deep inhalation, a
dilatation of the pharynx, larynx and thorax,
and by a lowering of the diaphragm. The oral
cavity becomes amply visible, the tongue is
retroverted, the eyes halfclose, the nostrils
dilate, the eyebrows rise and the forehead
wrinkles slightly. Finally, the mouth passively
closes again with a deep expiration.
-
- Fetuses yawn.
- Some authors claim that they do so from 12
weeks. However, we did not detect the first
yawns earlier than 15 weeks. Fetal yawns do not
correspond completely to the above description.
Up until 25 weeks the eyes are kept closed, and
the dilation of the nostrils as well as the
lowering of the diaphragm are too difficult to
evaluate.
-
- At around 25 weeks fetuses open their mouth
widely, blink, raise their eyebrows, wrinkle
their forehead and retrovert their tongue.
Dilation of the larynx, pharynx and thorax have
been ascertained in fetal animals such as
sheeps.
-
- Yawns last on average 8-10 s and occur
principally as occasional and isolated events.
However, in three cases (at 20, 21 and 25 weeks
respectively), one fetus yawned in a series of
five and two in a series of six yawns with an
interval of 8-10 s between the closure of the
mouth and the next yawn.
-
- Most, but not all yawns emerge before a
cycle of rest. However when fetuses start
yawning, they stop all previous activities, and
only resume any other motion when the yawn or
yawns are over.
-
- Yawning fetuses do not display apparent
signs of distress. Cerebral blood flows were
checked during and immediately after yawning,
but these were well within the normal
range.
-
- On the whole, we are still far from
understanding the functional significance of
yawning, whether before or after birth.
Nevertheless, one cannot but wonder why fetuses
yawn. In life after birth, yawning is mostly
connected with tiredness, sleepiness, boredom,
irritation, interruption of sleep and rousing.
However, yawning can also be related to pleasure
and relaxation as well as hunger. It is
difficult to ascribe complex emotions such as
boredom or irritation to fetuses. Hunger is
another stimulus which may hardly be experienced
in utero, save perhaps in extreme circumstances.
Hedonic feelings are hard to demonstrate at this
early stage, too, though fetuses may begin to
function on a pleasure/displeasure base. Some
motions and positions are "preferred" to others,
but one cannot go much further beyond this
simple fact. Anyway, even assuming fetuses could
begin to experience some form of pleasure or
displeasure after the first half 4 pregnancy,
why should this be expressed through yawns?
-
- In life after birth yawning has a
"contagious", social nature. Seeing someone
yawning triggers a yawn. Yawning also has an
ideational component as even just thinking of
yawning makes one yawn. None of this, however,
can be associated with fetal life. Fetuses can
hardly be regarded as social beings, though they
increasingly prepare to enter a social world. In
utero they clearly never see someone yawning,
nor were the fetal yawns we studied preceded or
followed by their mothers' yawning. All mothers
(and fathers) were very attentive and laughed
during and after the fetal yawn. It is also
difficult to assume that fetuses could have such
complex forms of ideation as to think about a
yawn, and start yawning as a consequence.
-
- After birth, yawning is not a necessary
event, in the sense that it does not invariably
accompany any of the above-mentioned states, and
displays large variations both within the same
individual and amongst different individuals.
The same quality of apparent non-necessity
applies in fetal life. After birth, frequent
yawning is linked with a variety of medical
conditions. Neurological conditions are often
associated with frequent yawning. Viral
infections, diseases directly affecting the
trunk or its compression due to intracranial
hypertension, diseases of the thalamus, of the
region of the hypophysis, brain tumours,
cerebral haemorrhage, multiple sclerosis,
myasthenia gravis and more are all coupled with
excessive yawning. All sorts of non-neurological
conditions can also cause excessive yawning.
These range from diabetes to profuse bleeding,
liver cirrhosis and heart attack. However,
nonexcessive yawning is a perfectly normal
phenomenon in man during all phases of life, and
fetuses can hardly be defined as excessive
yawners. Furthermore, all fetuses who yawned
were perfectly healthy at birth and at
subsequent follow-ups.
-
- Though yawning is readily and easily
recognizable at all ages, including the fetal
stage, various modes of yawning and their
possible significance may change with age. In
the neonate, yawning is almost invariably
accompanied by stretching. In the adult,
stretching especially occurs when yawning is
associated with awakening, and as such has been
related with a kind of re-setting in motion of
the organism after the relative stillness of
sleep. In the fetus, some tentative form of
stretching can be observed only from 24 to 25
weeks. One or both arms can be slightly
stretched outwards and the forearm stretched
either upwards or downwards. However, at this
stage stretching is barely perceptible.
-
- The neural mechanisms controlling yawning
have been to some extent clarified. A primary
"yawning centre" is located in the bulbopontine
regions of the cerebral trunk. Anencephalic
children born with the cerebral hemispheres
missing or reduced to small masses attached to
the base of the cranium, and without the
cerebellum and the flat bones of the skull, yawn
and stretch just like all of us. In other words,
we don't need a cortex in order to yawn. In man
and in some mammals a second pathway is thought
to be represented by the ill-defined limbic
system, an assemblage of interrelated,
phylogenetically old, deep brain structures
commonly regarded as involved in emotions,
motivation, processing of sensory and motor
functions, memory and even cognitive
information.
-
- Given its link with sleep, and especially
with the transitions between sleep and
wakefulness and vice versa, yawning has elicited
a special curiosity in those involved in sleep
research. The main experts in the field can be
considered to be the American psychologist
Robert Provine and the neurologist and
psychiatrist Piero Salzarulo in Italy.
-
- The association between yawning and
sleepiness has been explained by the anatomical
proximity between the bulbopontine region
involved in yawning and the ascending reticular
formation discovered in 1949 by Moruzzi and
Magoun. This latter system acts diffusely on the
cerebral cortex and activates it, regulating
arousal and sleep.
-
- Awakening is very rare before 34-36 weeks,
and fetal sleep prior to this age is considered
by many to be a preparatory function only akin
to sleep. Fetuses do not yawn because they feel
sleepy.
-
- Besides in man, yawning is widespread
throughout the animal kingdom. Darwin in his
famous book The expression of emotions in man
and animals mentioned yawns in various species
of monkeys, including the baboon, the macaque
and the cercopithecus. Following his lead, other
scientists have investigated yawning in animals.
When monkeys yawn, they display acuminate teeth.
"Alpha males" have been found to yawn more
frequently not only than females, but also than
less high-ranking males. For this reason, this
display and consequently yawning have been taken
to indicate dominance, aggression and
territorial defence.
-
- Besides monkeys and mice, all sorts of
animals, including snakes, fish, penguins,
crocodiles, and parrots yawn. Given its
widespread nature within the animal kingdom,
yawning could have different functions in
different species.
-
- All sorts of explanations have been given to
explain yawning in man, ranging from oxygenation
to brain cooling. Yawning has been suggested to
foster wakefulness, or to communicate relaxation
after a period of high vigilance. By being
contagious, yawning indicates empathy,
appreciation of other people's behavioural and
physiological states. Many more explanations
have been offered. However, none of the above
could apply to the fetus.
-
- Yawning: a Form of
Communicating?
-
- Finally, a few additional words on yawning.
Provine, the researcher who studied many of its
facets, considered it a facial expression with a
communicative function after birth. Jean Piaget
was the first to make an important observation
in 1951: that children started yawning in
response to seeing a yawn only during the 2nd
year of life. Subsequently, Provine and Anderson
and Meno [271 proved experimentally that
contagiousness of yawning did not start reliably
in children under 6 years old. This finding
aroused a lot of interest from two main points
of view. Following the seminal studies of
Meltzoff and Moore, it has long been known that
newborns are capable of recognizing and
imitating most facial expressions. Many
scientists wonder why they do not do the same
with such a dramatic facial expression as a
yawn. Recently, yawning has met with renewed
interested linked with studies of mirror neurons
and autism.
-
- So-called autistic spectrum disorders are
characterized by a more or less profound
impairment in communicative capacities and
shared social interactions. Autistic individuals
have problems in relating to others and in
reading other people's emotional states. In
particular, they are unable to display empathic
reactions when others show pleasure, fear or
pain. Empathy is connected with the capacity to
recognize, understand and share the emotions of
others. A number of anatomical and functional
studies all seem to point to disfunctioning of
the above-mentioned mirror neuron system in
autism. The fetus and the neonate generally are
not 'autistic', yet, as Piaget pointed out, they
cannot imitate and possibly decode yawns in
others.
-
- This is just an hypothesis, but what if one
turned the matter round and saw yawning as an -
albeit unconscious - form of communicating
various states to the caregiver. When mothers
see a neonate yawning, they assume, depending on
the context, that the child must be sleepy,
waking up, or even hungry. In other words, at
the neonatal stage yawning could be an important
tool for directing the efforts of the caregiver
onto "the right track".
-
- Up to 2 years of age, and before they become
fully verbal, children need a lot of empathic
understanding on the part of those caring for
them. Furthermore, sleep and hunger are two
basic and vital states. A caregiver can miss
many other nuances, but not these vital
needs.
-
- Yawning, unlike crying and screaming,
elicits empathy and sympathy, not irritation,
anxiety or exasperation, thus simplifying the
task. Furthermore, in children yawning would not
need to be bidirectional. When babies and
children are tired, and they communicate this by
yawning, the caregiver usually takes the
initiative to put them to bed. At such moments
they may like to be lulled to sleep, or be read
a repetitive story, but clearly are not willing
to engage in complex social interactions. On the
other hand, though, babies (and young children)
are not keen to recognize fatigue or boredom in
their caregiver's face when she or he yawns
while they may be needing or demanding some
action or interaction. As the saying goes,
"Children's needs come first". Mother or father
may be tired, but still have to prepare some
food or be asked to participate in some
story-telling or preparatory ritual for
sleep.
-
- If this were the case, fetuses yawning in
utero would be displaying a preparatory and
anticipatory function, helping them to have
their vital needs better understood and more
easily met by those caring for them after
birth.
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