A famous saying states that a good yawner
will induce yawning in seven people.
Contagiousness is often mentioned. This term,
though, is designed for infectious diseases
when, through direct or indirect contact, a
healthy individual becomes sick through the
transmission of a virus or microbe. The
replication of behaviour does not suppose the
presence of a transmission agent. It would
appear more appropriate, therefore, to refer
to mimetism, a term proposed by W. Baldwin in
1894, or to synchronous actions, rather than
imitation which could involve a voluntary
participation, which is not the case
here.
Ethological studies of non-human primates
show that at certain times an entire group
goes about yawning, without the possibility
for one member to be aware of another yawner,
either by sight, hearing or smell. One could
not consider this type of behaviour as
comparable to replication among humans, but
could link it, for instance, with a
synchronous trigger of activities related to
circadian rest-activity rhythms. Obviously,
in the case of human, these two variants can
be seen sometimes as one and the same. Given
the above and other ethological observations,
one can find that yawning replication is
found only in human.
This replication is triggered
involuntarily. Neither does the yawner want
to make others yawn, neither is the
spectator-receiver of the replication aware
of a need to yawn. The latter's yawn is also
triggered involuntarily, but only and only if
the level of vigilance allows for it. Indeed,
the involvement in a sustained intellectual
task (that is with high concentration or with
an optimum level of vigilance) will not allow
the triggering of a yawn. This point is
fundamental to the human ethological
explanation of the role of synchronisation of
vigilance states between two individuals
subjected to the transmission of
yawning.
How is this replication triggered? Sight
is a powerful stimulant. R.
Provine shows that 55% of spectators
viewing a video showing 30 successive yawns
will yawn within five minutes. The latency
period varies from a few seconds to five
minutes. The latency period and the duration
of the viewing have not allowed for the
precise identification of a rule, a type of
specific synchronisation. R. Provine has also
verified that there is no need whatsoever for
the face of the yawner to be in a precise
visual plane relative to the subject of the
contagion. Face to face, at 90°,
180°, 270° relative to one another,
contagion there is. The existence of a
susceptibility to contagion among blind
subjects confirms that sight is not the only
trigger. Viewing part of the face only, such
as a wide open mouth, does not trigger
replication. Therefore a multimodal
perception of the whole facial configuration
and of audible respiratory moments is needed,
along with coordinated dynamics for
replication to happen.
The replication of yawning seems to
originate at a basic level because it is
independent of knowing the triggerer
beforehand, independent of racial, education
or socio-cultural characteristics, which
indicates an absence of mnestic intervention.
There is no need of explicit characterisation
for the other party to be subjected to
replication. There is need for a vigilance
level situated between somnolence and
sustained concentration and for the
unconscious perception of the other party,
while in a position to notice the rigorous
chronology of the unfolding yawn via its
visual and/or audio components of mouth
opening, specific modifications of other
facial traits, ventilation activity and
sounds reflecting deep and prolonged
inspiration (the acme), and expiration, but
to a lesser degree.
Following such perception, the motor
trigger of the yawning reflex is also
involuntary and stems from the setting into
action of sub-cortical motor loops (gray
nucleus - brainstem). In parallel, there is a
conscious perception of the development of
this phenomenon, of its stimulus and of its
contextual valence through the interoception
pathways, which lead to a conscious hedonist
perception.
Ethology allows for the distinction
between two types of reactions regarding an
external stimulus:
1°) reactions qualifiable as common
programmes for the animal kingdom as a whole,
notably all mammals. These reactions seem
necessary for individual or group survival.
They are contagious through non-verbal
communication. This is a cognitive process of
direct, immediate and non-conscious
communication triggering innate or acquired
motor patterns such as escape or avoidance.
The replicated yawning in human can only be
partly related to this archaic behavioural
level. Its automatism is close to the latter.
But its random component and its possible
latency are quite different.
2°) reactions with cognitive
participation of an emotional nature. An
emotion expressed by a fellow being calls for
decoding through an analytical treatment of
the information. As a basis of social
cognition, facial expressions reflecting
emotions underly complex and flexible
cognitive processes. Only human primates
demonstrate the capacity to perceive others
as agents endowed with intention, along with
the ability to identify. This capacity to
think about others and their desires is
probably at the root of the complexity and
sophistication of Homo sapiens' social
bevaviour. (Theory of the mind). This is the
basis of conscious empathy: to understand the
feeling of the other, to feel personally what
the other feels. The replication of yawning
is akin to decoding an emotion, the other's
state of vigilance, but at an unconscious,
automatic level allowing for the
synchronisation of the state of vigilance
between individuals, which one could qualify
as an instinctive, involuntary empathy. This
capacity to in tune with unconscious affects
rests on implicit communications, developed
over the course of evolution, but whose
neurobiological mechanisms are just starting
to be understood.
Research by J.
Decety has helped identify participating
cortical structures when a subject imitates
the actions performed by an experimenter or
when the subject's actions are imitated by an
experimenter, in comparison to a situation
where actions are produced without imitation:
"As expected, over and above the regions
involved in motor control, a network of
activation common to the parietal cortex and
the frontal lobe (dorso-median prefrontal
regions) was detected between these two
imitation situations. This network of shared
activations is consistent with the hypothesis
of a common coding between the actions of
one's self and those of another individual.
When taken together, the neurophysiological
data pertaining to the neuronal
implementation of the three types of activity
(preparation, simulation and observation in
view of imitating) involving motor
representations show that there is a close
functional equivalence between them.
»
The activation of the inferior frontal
gyrus in the left hemisphere (which would
correspond to the F5 region in the monkey)
during the observation of actions can be
explained by a silent verbalisation among the
subjects. Indeed, this area belongs to
Broca's region, the lesion of which provokes
an aphasia. G.Rizzolati
discovered in the macaque's ventral premotor
cortex, in areas F4 and F5, groups of neurons
called mirror neurons whose activity is
correlated with the observation of another
individual's action in function of its
purpose, which shows the actions as being
volitional. These neurons seem to exist in
human. The bold speculation that supposes
their involvement in this in-tune, mimetic
yawning behaviour, is supported by the first
functional imagery study, done by R.
Hari (NeuroImage June 2003; 19, 2, Sup 1,
S1-S101), showing the activation of the
sulcus temporalis superior (STS) at the sight
of a yawner. In opposition to other banal
facial movements, the STS is specifically
stimulated by the viewing of a yawn. The STS
was identified long ago as the structure
involved in the perception of movement
involving facial characteristics and the
expression of the mouth. The activation
difference between non-specific facial
movements and a yawn points to the specific
activation of the STS during a yawn. It so
happens that the STS is an essential
component of the mirror-neuron system
identified by V.
Gallese et G. Rizzolatti, that is the
neurophysiological foundation of the ability
to imitate. Another interpretation is that
the STS is part of the analysis system of
visual behavioural information and, in the
typical case of yawning, recognises the
kinesodic pattern of this behaviour and its
contextual valence, enriched by the previous
emotional knowledge.
The perception of actions by another
party would involve a simulation process that
would lead to an understanding of intentions.
This tuning-in on the part of the observer
does not necessarily produce a movement or
action. An inhibiting mechanism, activated in
parallel and that can be located in the
frontal area, would block the triggering of
motor mimetic actions. Indeed, the study of
human neurological pathology of frontal
dysfunctions finds two circumstances where
uninhibited imitation disturbs
behaviours:
1°) The Gilles de la Tourette
disease, affecting the prefrontal cortex, the
basal limph nodes and the limbic system,
combines four major elements: tics, the rare
coprolalia behaviour, and the
echolalia/echopraxia, echokinesis.
2°) The prefrontal or premotor
syndrome is associated with a kinetic aphasia
(lesions to the left hemisphere) and
selectivity troubles of motor patterns,
leaving intact the superior functions:
de-automation of activities accompanied by
perseverance and rudimentary and erroneous
imitation, echokenesis and cetopraxia.
Could the replication of yawning be an
uninhibited behaviour, physiologically
speaking, that through its mechanisms would
be somewhat akin to these pathologies?
In human, at what age does the
replication of yawning start? As early as
1951, Piaget had shown that the sensitivity
to the replication of yawning in babies only
appeared during its second year, whereas
newborns yawn frequently, maintaining a
precocious behaviour developed during fetal
life. A.
Meltzoff proposes an ontogenic
interpretation of this discord. During its
first six months of life, the baby is able to
imitate hand movements because it perceives
surrounding hands as its own. However, it
does not have a conscious notion of itself as
an individual nor any perception of its own
facial movements. Once the mirror test shows
that the baby has self-perception as an
autonomous individual and has acquired the
capacity for self recognition in a mirror,
the mental development of imitation is
rounded out by the capacity to copy mimics,
which explains why it is only in the second
that the baby becomes sensitive to yawning
contagion.
To sum up, on the assumption that the
development of the frontal (motor) and
prefrontal (premotor) cortex is specific to
bipeds, it can proposed that yawning
replication is a real example of echokinesis,
a word coined by JM
Charcot, which is characterised by three
criteria:
- replication would be specifically
human, to be interpreted as a behavioural
mimetism,
- whereas upon observation of someone's
motor behaviour what was seen is mimed
through the motor areas of the observer and,
more often than not, is not followed by motor
actions consequent to frontal inhibition,
yawning for its part is the result of
uninhibited bevaviour, under certain
conditions pertaining to vigilance,
- replication would have provided a
selective advantage by allowing for an
efficient synchronisation of vigilance levels
between members of a group. It would be
instrumental in a type of involuntary
instinctive empathy, that would probably have
appeared late in the evolution of
hominids.
Alnwick: printed and published by W.
Davison, [1816]. Single sheet,
image 133x220 on paper 187x265mm. Printed in
black partly contemporary hand colour of a
yellow wash, dustsoiled and a little frayed
at the outer margins. (Isaac Some Alnwick
caricatures; a note and handlist 18) In the
period between 1812 and 1817, Davison
produced a number of caricatures, amusing if
somewhat crudely executed plates in the
manner of Gilray, Rowlandson and Bunbury. In
this instance, two men and a woman sit around
a table yawning widely, with - in a nice
example of product placement - a copy of
Davison's list of his pharmacy products lies
on the table.
