Contagious yawning, in which yawning is
triggered involuntarily when we observe another
person yawn, is a common form of
echophenomena&emdash;the automatic imitation of
another's words (echolalia) or actions
(echopraxia). The neural basis for echophenomena
is unknown; however, it has been proposed that
it is linked to disinhibition of the human
mirror-neuron system and hyper-excitability of
cortical motor areas.
The authors investigated the neural basis
for contagious yawning using transcranial
magnetic stimulation (TMS). Thirty-six adults
viewed video clips that showed another
individual yawning and, in separate blocks, were
instructed to either resist yawning or allow
themselves to yawn. Participants were videoed
throughout and their yawns or stifled yawns were
counted.
They used TMS to quantify motor cortical
excitability and physiological inhibition for
each participant, and these measures were then
used to predict the propensity for contagious
yawning across participants.
They demonstrate that instructions to resist
yawning increase the urge to yawn and alter how
yawns are expressed (i.e., full versus stifled
yawns) but do not alter the individual
propensity for contagious yawning. By contrast,
TMS measures of cortical excitability and
physiological inhibition were significant
predictors of contagious yawning and accounted
for approximately 50% of the variability in
contagious yawning. These data demonstrate that
individual variability in the propensity for
contagious yawning is determined by cortical
excitability and physiological inhibition in the
primary motor cortex.
Résumé
Le bâillement « contagieux
», celui qui est déclenché
involontairement quand nous observons une autre
personne bâiller, est une forme de
comportement en écho comme il en existe
d'autres tels la répétition
involontaire des paroles d'autrui
(échalolie) ou des actions
(échopraxie). La base neurale des
comportements en écho est mal connue ;
cependant, il a été proposé
qu'ils soient liés à la
désinhibition du système ses
neurones miroirs et à
l'excitabilité des zones motrices
corticales.
Les auteurs ont étudié la base
neuronale du bâillement « contagieux
» en utilisant la stimulation
magnétique transcrânienne (TMS).
Les mesures ont cherché à
quantifier l'excitabilité motrice
corticale d'une part et l'inhibition
physiologique d'autre part.
Trente-six adultes ont regardé des
clips vidéo montrant un bâillement.
Ils ont reçu comme consigne de
résister au besoin de bâiller ou au
contraire de se laisser aller.
La TMS a été utilisée
pour quantifier l'excitabilité corticale
motrice et l'inhibition physiologique pour
chaque participant. Les mesures ont ensuite
été utilisées pour
prédire la propension à la
contagion de chacun des participants.
Les auteurs démontrent ainsi que les
instructions pour résister au
bâillement augmentent l'envie de
bâiller et modifient la façon dont
les bâillements sont
extériorisés (c.-à-d.
bâillements francs ou
étouffés), mais ne modifient pas
la propension individuelle à la contagion
du bâillement.
En revanche, les mesures du TMS de
l'excitabilité corticale et de
l'inhibition physiologique sont des
prédicteurs significatifs de contagion du
bâillement et représentaient
environ 50% de la variabilité à la
susceptibilité à la contagion. Ces
données démontrent que la
sensibilité individuelle à la
contagion du bâillement est
déterminée par le seuil à
l'excitabilité corticale et une
inhibition physiologique dans le cortex moteur
primaire.
Discussion
We investigated the neural basis for
contagious yawning, an example of echophenomena,
using non-invasive brain stimulation (TMS)
techniques. Contagious yawning can be triggered
by seeing another individual yawn, but the
propensity for contagious yawning, although
stable over time, is known to vary across
individuals. Here we provide evidence that the
propensity for contagious yawning may be
triggered automatically and is strongly linked
to the cortical excitability of the primary
motor cortex. Specifically, TMS was used to
quantify baseline cortical excitability and
physiological inhibition within the primary
motor cortex and to predict behavioral measures
of contagious yawning, and we tested the
hypothesis that the propensity for contagious
yawning was linked to the balance of cortical
excitability and physiological inhibition within
the primary motor cortex.
The key findings from the study can be
summarized as follows. First, the instruction to
resist yawning proved to be only partially
successful. Although it led to a significant
decrease in the number of full yawns observed,
there was a significant increase in the number
of stifled yawns recorded. Furthermore, when the
numbers of full and stifled yawns were combined
into a single measure, the difference between
the resist and allow conditions was not
statistically significant. Nonetheless,
urge-to-yawn estimates increased significantly
when participants were instructed to resist
yawning. This is consistent with the proposal
that urges for action are chiefly associated
with actions that cannot be realized immediately
and must be held in check. Together, these
findings demonstrate that the instruction to
resist yawning significantly increases the urge
to yawn and alters how the yawn may be expressed
(i.e., stifled yawns rather than full yawns),
but it does not alter the individual's
propensity for yawning.
Second, the propensity for contagious
yawning was shown to be strongly predicted by
individual variability in TMS measures of
cortical motor excitability and physiological
inhibition recorded from the hand area of the
primary motor cortex.
We suggest that these findings may be
particularly important in understanding further
the association between motor excitability and
the occurrence of echophenomena, observed in a
wide range of clinical conditions, e.g.,
epilepsy, dementia, autism, and Tourette
syndrome, that have been linked to increased
cortical excitability and/or decreased
physiological inhibition.
Stephen Jackson, Professor of Cognitive
Neuroscience, in the School of Psychology, led
the multidisciplinary study. He said: "We
suggest that these findings may be particularly
important in understanding further the
association between motor excitability and the
occurrence of echophenomena in a wide range of
clinical conditions that have been linked to
increased cortical excitability and/or decreased
physiological inhibition such as epilepsy,
dementia, autism, and Tourette syndrome."
Echophenomena isn't just a human
trait
Contagious yawning is triggered
involuntarily when we observe another person
yawn &emdash; it is a common form of
echophenomena &emdash; the automatic imitation
of another's words (echolalia) or actions
(echopraxia). And it's not just humans who have
a propensity for contagious yawning &emdash;
chimpanzees and dogs do it too.
Echophenomena can also be seen in a wide
range of clinical conditions linked to increased
cortical excitability and/or decreased
physiological inhibition such as epilespsy,
dementia, autism and Tourette syndrome.
The neural basis for contagious
yawning
The neural basis for echophenomena is
unknown. To test the link between motor
excitability and the neural basis for contagious
yawning the Nottingham research team used
transcranial magnetic stimulation (TMS). They
recruited 36 adults to help with their study.
These volunteers viewed video clips showing
someone else yawning and were instructed to
either resist yawning or to allow themselves to
yawn.
The participants were videoed throughout,
and their yawns and stifled yawns were counted.
In addition, the intensity of each participant's
perceived urge to yawn was continuously
recorded.
Using electrical stimulation they were
also able to increase the urge to yawn.
Georgina Jackson, Professor of Cognitive
Neuropsychology in the Institute of Mental
Health, said: "This research has shown that the
'urge' is increased by trying to stop yourself.
Using electrical stimulation we were able to
increase excitability and in doing so increase
the propensity for contagious yawning. In
Tourettes if we could reduce the excitability we
might reduce the ticks and that's what we are
working on."
The search for personalised
treatments
TMS was used to quantify motor cortical
excitability and physiological inhibition for
each participant and predict the propensity for
contagious yawning across all the
volunteers.
The TMS measures proved to be significant
predictors of contagious yawning and
demonstrated that each individuals's propensity
for contagious yawning is determined by cortical
excitability and physiological inhibiton of the
primary motor cortext.
The research has been funded by ESRC
doctoral training award to Beverley Brown and is
part of Nottingham's new Biomedical Research
Centre (BRC) leading research into mental health
technology with the aim of using brain imaging
techniques to understand how neuro modulation
works.
Professor Stephen Jackson said: "If we can
understand how alterations in cortical
excitability give rise to neural disorders we
can potentially reverse them. We are looking for
potential non-drug, personalised treatments,
using TMS that might be affective in modulating
inbalances in the brain networks."
This latest research follows the publication
of their study 'On the functional anatomy of the
urge-for-action' which looked at several common
neuropsychiatric disorders associated with
bodily sensations that are perceived as an urge
for action.
