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- mise à jour
du
- 21 mai
2026
- Respir
Physiol Neurobiol.
- 2026;343:104575
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- Biomechanics
of contagious yawning: Insights into
cranio-cervical fluid dynamics and kinematic
consistency
- Martinac AD, Waters S, Lloyd RA, Bilston
LE.
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- Tous
les articles sur la contagion du
bâillement
- All
articles about contagious
yawning
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- Abstract
- Yawning is a stereotyped
orofacial&endash;respiratory behaviour whose
physiological role remains uncertain. Because
cerebrospinal fluid (CSF) movement contributes
to solute transport and waste removal and is
strongly influenced by respiratory pressure
dynamics, the study evaluated whether contagious
yawning alters neurofluid flow relative to
normal and gaping deep breathing, and whether
contagious yawning kinematics are reproducible
within individuals. In a single MRI session in
healthy adults, real-time phase-contrast imaging
at the upper cervical level (C3) was combined
with mid-sagittal real-time cine imaging to
quantify CSF and internal jugular venous flows
during normal breathing, forceful oral
inspirations (gaping deep breaths), yawns, and
stifled yawns, and to derive tongue-motion
trajectories.
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- Both gaping deep breaths and yawns increased
CSF and venous flow compared with normal
breathing; despite similar flow magnitudes,
yawns more frequently produced co-directional
caudal CSF and jugular outflow during
inspiration, whereas gaping deep breaths
typically showed counter-directional
CSF&endash;venous flow. Contagious yawning also
elicited a marked internal carotid inflow
increase (up to 43%) during the gaping/early
expiratory phase that was not apparent during
both deep and normal breathing. Yawning
kinematics were highly reproducible within
individuals across repeated events, indicating a
stable motor sequence consistent with brainstem
pattern-generator control. These observations
show that yawning is not simply an intensified
breath but a distinct cardiorespiratory
manoeuvre that reorganizes neurofluid flow.
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- The inspiratory alignment of CSF with venous
outflow during yawns suggests a transient caudal
advection that could influence solute transport
and heat exchange within the
cranial&endash;cervical system, motivating
targeted mechanistic studies with simultaneous
airway pressure, thoraco-abdominal motion, and
cervical venous pressure measurements.
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- Résumé
- Le bâillement est un comportement
orofacial et respiratoire
stéréotypé dont le
rôle physiologique reste incertain.
Étant donné que la circulation du
liquide céphalo-rachidien (LCR) contribue
au transport des solutés et à
l'élimination des déchets, et
qu'elle est fortement influencée par la
dynamique de la pression respiratoire, cette
étude a cherché à
déterminer si le bâillement
contagieux modifie le flux du liquide
cérébrospinal par rapport à
la respiration profonde normale et au
bâillement, et si la cinématique du
bâillement contagieux est reproductible
chez un même individu. Au cours d'une
seule séance d'IRM chez des adultes en
bonne santé, l'imagerie par contraste de
phase en temps réel au niveau cervical
supérieur (C3) a été
combinée à l'imagerie
cinématographique sagittale
médiane en temps réel afin de
quantifier les flux de LCR et veineux jugulaires
internes pendant la respiration normale, les
inspirations buccales puissantes (respirations
profondes avec bouche grande ouverte), les
bâillements et les bâillements
réprimés, et de déterminer
les trajectoires des mouvements de la
langue.
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- Les respirations profondes et les
bâillements ont tous deux augmenté
le débit du LCR et le flux veineux par
rapport à la respiration normale ;
malgré des amplitudes de débit
similaires, les bâillements ont plus
fréquemment produit un écoulement
caudal du LCR et un débit jugulaire dans
la même direction pendant l'inspiration,
tandis que les respirations profondes montraient
généralement un écoulement
du LCR et un flux veineux en sens inverse. Le
bâillement contagieux a également
provoqué une augmentation marquée
de l'afflux carotidien interne (jusqu'à
43 %) pendant la phase de bouche grande
ouverte/début de l'expiration, qui
n'était pas apparente lors de la
respiration profonde ni de la respiration
normale. La cinématique du
bâillement était hautement
reproductible chez les individus lors
d'événements
répétés, indiquant une
séquence motrice stable compatible avec
le contrôle par un
générateur de schémas du
tronc cérébral.
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- Ces observations montrent que le
bâillement n'est pas simplement une
respiration intensifiée, mais une
manœuvre cardiorespiratoire distincte qui
réorganise le flux du liquide
cérébrospinal. L'alignement
inspiratoire du LCR avec le débit veineux
pendant les bâillements suggère une
advection caudale transitoire qui pourrait
influencer le transport des solutés et
les échanges thermiques au sein du
système crânio-cervical, ce qui
justifie des études mécanistiques
ciblées avec des mesures
simultanées de la pression des voies
respiratoires, des mouvements thoraco-abdominaux
et de la pression veineuse cervicale.
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- Introduction
- Yawning is a stereotyped orofacial behaviour
characterised by a prolonged jaw gape and
coordinated oropharyngeal movements, and in
terrestrial vertebrates is commonly (though not
invariably) accompanied by a deep inspiration.
It is observed across a wide range of mammals,
amphibians, reptiles, and other vertebrates
(Moyaho et al., 2017, Palagi et al., 2019,
Gallup, 2022, Gallup and Wozny, 2022). Yawn-like
behaviour in aquatic mammals, including beluga
whales, Indo-Pacific bottlenose dolphins, and
dugongs, show that similar gape-associated
behaviours can occur in submerged animals in the
absence of a clear respiratory component (Ames,
2022, Enokizu et al., 2022, Enokizu et al.,
2023). This broader comparative literature
supports the view that jaw gaping and associated
craniofacial movements are defining features of
yawning, whereas a deep inspiratory component is
common in terrestrial vertebrates but not
universal across yawning-like behaviours.
Although yawning is a common behaviour, it
remains poorly understood and experimental data
on its mechanics are limited (Corey et al.,
2012, Gupta and Mittal, 2013). Most yawns appear
to be comprised of an initial deep inspiration,
followed by a pause and then rapid expiration. A
range of hypotheses have been proposed:
physiological hypotheses suggest that yawning
may play a role in regulating blood oxygen/CO_
levels and airway patency (hypoxia/ventilation;
Provine et al., 1987; Doelman and Rijken, 2022),
brain thermoregulation (Gallup and Gallup, 2007,
Gallup and Eldakar, 2013, Eldakar et al., 2015),
arousal/attentional state (Guggisberg et al.,
2007, Guggisberg et al., 2010, Thompson, 2014,
Krestel et al., 2018), and cerebral metabolic
waste clearance (Dolkart, 2017). In contrast,
social hypotheses focus on the social and
communicative aspects of yawning; see Massen and
Gallup (2017).
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- CSF movement is critical for solute
transport and metabolic waste removal, yet the
influence of yawning on CSF and blood dynamics
is largely unexplored. In general, CSF is
thought to be produced by the choroid plexus in
the brain's ventricles, flowing through various
pathways before exiting via the ventricular
system and entering the subarachnoid space. The
movement of the jaw and the act of inhaling can
impact circulation within the skull.
Specifically, any behaviour that compresses the
jugular vein in the neck can immediately raise
CSF pressure (Walusinski, 2013). Research by
Lloyd et al. (2020) has shown that CSF flow is
influenced by the pressures in the thoracic and
lumbar spinal regions, which fluctuate during
respiration, along with cranial and spinal blood
flows. An increase in caudal CSF has been
observed in the cervical spine and ventricles
following the inspiratory phase of yawning,
accompanied by an increase in venous blood
outflow through the internal jugular vein (Klose
and Schröth., 1992). This suggests that the
physiological impacts of yawning might be
reflected in the flow profiles of CSF and
blood.
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- The highly stereotyped nature of yawns has
led to the proposal that they are coordinated by
a brainstem central pattern generator (CPG),
like those controlling breathing and locomotion
(Erkoyun et al., 2017). Because a brainstem CPG
orchestrates a stereotyped, modulable sequence
of inspiratory drive and
orofacial&endash;pharyngeal muscle activation,
it could plausibly contribute to intrathoracic
pressure transients and cervical venous pressure
gradients that influence neurofluid (CSF and
blood) flow. Swallowing is likewise organised by
brainstem patterning circuitry and recruits
overlapping oropharyngeal&endash;laryngeal
effectors (Jean, 2001, Jean and Dallaporta,
2006), raising the possibility of temporally
linked expression of yawns and swallows.
Consistent with this, prior
behavioural/physiological work has reported an
association between yawning and subsequent
swallowing, with swallows frequently occurring
within seconds of yawn termination (Abe and
Weisz., 2015; Ertekin et al., 2015).
Accordingly, we treated swallow timing relative
to yawns as an exploratory measure of
swallow&endash;yawn functional coupling, defined
here as a non-random temporal association
between behaviours.
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- Building on evidence that deep breathing
strongly modulates blood and CSF flows in the
cranium and spine (Yamada et al., 2013,
Dreha-Kulaczewski et al., 2015,
Dreha-Kulaczewski et al., 2018, Lloyd et al.,
2020, Kollmeier et al., 2022), our study
investigates how contagious yawning influences
CSF and blood flow through the cervical spine.
In parallel, this study aimed to examine the
intra-individual reproducibility of yawning
kinematics. Real-time phase-contrast magnetic
resonance imaging (PC-MRI) and real-time
sagittal scans were used as non-invasive methods
to quantify both fluid velocities and anatomical
movement during the respiratory manoeuvres. We
hypothesised that the effect of yawning on CSF
and blood flow would resemble the effect of a
gaping deep breath. An additional hypothesis was
that tongue motion patterns during repeated
yawns would exhibit highly consistent,
stereotyped patterns within individuals.
Evidence of highly consistent stereotyped
yawn-related tongue and jaw motion would add
weight to existing evidence for the existence of
a yawning CPG.
- This study had two primary aims: (1) to
quantify changes in cerebrospinal fluid (CSF)
and cervical blood flow at C3 during contagious
yawning, relative to within-session normal
breathing and a yawn-mimicking gaping deep
breath manoeuvre; and (2) to test
intra-individual reproducibility of yawning
kinematics using real-time sagittal cine
imaging. Additional analyses of stifled yawns,
post-manoeuvre swallow timing, and possible sex
variability of yawning, were treated as
secondary exploratory observations to aid
interpretation of the primary outcomes and are
presented as such in the results and
discussion.
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- Discussion
- Although respiration is a dominant driver of
CSF movement, the effects of yawning on CSF and
blood flow have not been previously
characterised. In this study, we show that yawns
and gaping deep breaths produce comparably large
CSF and venous flow magnitudes to normal
breathing, but they differ in flow
directionality. Deep inspirations generally
increased cranial CSF flow with
counter-directional IJV outflow, whereas yawns
more often produced co-directional CSF and IJV
outflow during inspiration. In addition, yawns
within individuals also exhibited highly
stereotyped orofacial tongue kinematics across
repeated events, compatible with, but not proof
of, control by a central pattern generator. This
has not been previously identified.
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- 4.1. Comparison of neurofluid flow
between gaping deep breathing and
yawning
- The magnitude of CSF flow during gaping deep
breaths and yawns was found to be similar, and
both were greater than normal breathing. These
findings align with the spirometry results,
which also showed comparable airflow rates for
yawning and gaping deep breathing. During gaping
deep inspiration, there was an increase in
cranial CSF flow, while expiration prompted a
caudal movement of CSF. The IJV flow magnitude
during gaping deep breaths were greater than in
normal breathing and flowed in the
counter-directionally to CSF. These patterns
align with prior reports that forced breathing
increases CSF flow compared with eupnoea and
introduces physiological variability across
sites (Yamada et al., 2013, Dreha-Kulaczewski et
al., 2015, Dreha-Kulaczewski et al., 2018,
Gutiérrez-Montes et al., 2022, Kollmeier
et al., 2022). However, during yawning, CSF flow
direction differed from both normal and deep
inspiration. In the respiratory-CSF literature,
"forced/deep breathing" protocols typically
involve voluntary, larger-than-eupnoeic
inspirations (often repeated) that amplify
intrathoracic pressure swings and venous return,
thereby increasing cranial&endash;spinal CSF
oscillation amplitude relative to eupnoea. Our
yawn-mimicking deep breath shared the key
feature of a large voluntary inspiration but
differed from sustained hyperpnoea (deep
breathing) protocols in that it was a single
oral, jaw-gaping inspiratory effort, implemented
to better approximate yawning airway
configuration while avoiding baseline drift from
repeated deep cycles. Although the protocols
were not identical, our comparison focused on
their shared mechanical effects, particularly
the net decrease of intrathoracic pressure and
increased intra-abdominal pressure.
- Venous&endash;CSF coupling during gaping
deep breathing likely reflects changes in
intrathoracic and intra-abdominal pressures
(Lloyd et al., 2020). In our data, IJV outflow
during inspiration was consistent across
participants for both gaping deep breaths and
yawns. In contrast, CSF directionality during
yawning differed from gaping deep breaths:
despite similar peak magnitudes, yawns
frequently produced co-directional CSF and IJV
outflows (Fig. 2, Fig. 4). Pressure differences
between the cranium and thorax are the driving
force for CSF and venous blood flow during
respiration yet direct measurements of
intrathoracic/cervical pressures during human
yawns are not available. However, a plausible
mechanism to explain the differences between
gaping deep breathing and yawning is that
ribcage expansion and diaphragmatic descent
generate negative intrathoracic pressure
(enhancing venous return) (Agostoni and Rahn,
1960, Kono and Mead, 1967), while
pharyngo-laryngeal dilation, mediated by
activation of upper-airway dilator muscles, can
lower upper-airway resistance (Pierce et al.,
2007). Together with orofacial&endash;pharyngeal
muscle recruitment, this may transiently bias
CSF caudally during yawning (Lloyd et al.,
2025a). This remains hypothetical and warrants
simultaneous pressure&endash;flow recordings in
future studies.
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- 4.2. Comparison of manoeuvre
duration
- An additional distinction between the
manoeuvre was duration. Contagious yawns and
stifled contagious yawns lasted approximately
twice as long as the gaping deep breaths
(12.08_±_3.64_s and 11.23_±_4.07_s vs
6.62_±_2.84_s), whereas yawns and stifled
yawns did not differ in duration. This
reinforces that yawning is not merely a
higher-amplitude respiratory effort, but a
longer, multi-phase patterned behaviour that
sustains the orofacial&endash;pharyngeal
configuration and respiratory patterning over
several seconds. Cross-species comparative work
further indicates that yawn duration covaries
with brain size and neuron numbers (Gallup et
al., 2016, Massen et al., 2021), and the
durations observed here are consistent with a
full yawn sequence rather than truncated events,
supporting the interpretation that the measured
CSF and vascular responses reflect robust
yawning-linked physiology. Notably, stifled
yawns showed comparable durations to uninhibited
yawns, suggesting that voluntary suppression
predominantly alters the external expression of
the manoeuvre (e.g., jaw excursion/oral
aperture) rather than its overall timing;
consistent with this, stifled yawns retained key
tongue kinematics once initiated (Fig. 7),
implying that suppression acts on the periphery
of the motor pattern rather than aborting the
sequence entirely.
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- 4.3. Sex differences in CSF flow
direction during yawns and peripheral nerve
stimulation
- Analysis of CSF flow during yawning revealed
possible sex-specific differences (Fig. 4C). In
males, CSF and IJV flows were typically
counter-directional, whereas females more often
exhibited co-directional flows. All males
reported strong PNS sensation (mean PNS score of
3.17_±_1.03) while 7/11 females reported
none, and the remainder reported only occasional
faint sensation (PNS score of 1.46_±_0.69).
This PNS induced abdominal activation may have
increased intra-abdominal pressures and
restricted diaphragmatic excursion, and
disrupted normal breathing coordination,
potentially influencing CSF flow directionality
in males (Agostoni and Rahn, 1960, Lloyd et al.,
2020, Lloyd et al., 2025a). Because PNS was
rated once at the end of the session and was not
manoeuvre-specific, the apparent sex difference
should be interpreted cautiously: the much
stronger PNS response reported by male
participants could have altered
abdominal/thoracic mechanics during scanning and
thereby influenced CSF&endash;IJV coupling. The
female data may be less affected by MRI-related
peripheral nerve stimulation and may therefore
more closely reflect typical yawning physiology,
although this inference remains cautious (see
Limitations). Future studies should minimise PNS
or quantify it per manoeuvre to more
definitively assess sex-related effects.
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- 4.4. Evidence that yawning is controlled
by a central pattern generator (CPG)
- Despite inter-individual variation,
consistent stereotyped behaviours were observed
across multiple yawns for a given individual
(Fig. 7). Intra-individual similarity in yawning
patterns was high, with cross-correlation
coefficients ranging from 0.75 to 0.97 for
tracked tongue movements (group mean was
0.86_±_0.062). Even when yawns were
stifled, the tongue exhibited movements quite
like those seen in full yawns, indicating that
the yawning motor pattern, once initiated, is
automatic and difficult to suppress or alter
(Fig. 7). This balance between intra-subject
consistency and inter-subject variability
indicates that yawning displays
individual-specific motor patterns, consistent
with, but not definitive evidence of, a yawning
CPG. CPGs operate autonomously, generating
patterns of neural activity that drive rhythmic
behaviours (Dzeladini et al., 2014, Katz, 2016,
Krestel et al., 2018). In the case of yawning,
the CPG would autonomously initiate and execute
the yawning cycle, explaining the consistent
intra-individual flow and tongue movement
pattern (Walusinski, 2010). Despite their
autonomous nature, CPG outputs can be modulated
by external stimuli or internal states (Traub,
Draguhn, 2024). This flexibility might account
for the variations in inter-participant yawning
patterns while still maintaining a recognisable,
individual-specific pattern; and implies that
the patterns of yawning are not learned but are
an innate aspect of neurological
programming.
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- The preservation of overall yawn duration
under voluntary stifling further suggests that
suppression modifies outward expression more
readily than it terminates the underlying motor
program. Together with the high intra-individual
reproducibility of tongue trajectories, this
supports the idea that once initiated, yawning
proceeds as a structured sequence that can be
partially masked but is difficult to fully
interrupt.
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- This hypothesis is bolstered by observations
(Fig. 6) which show that in _81_±_14% of
induced yawns, and in 68_±_8.4% of stifled
yawns, a swallow followed within one breath
(Fig. 5), suggesting close functional coupling.
Yawning and swallowing, though outwardly
appearing as distinct physiological behaviours,
may be closely interconnected through their
underlying neurological mechanisms since
spontaneous yawning is frequently associated
with spontaneous swallows (Abe et al., 2015) and
are hypothesised to be influenced by a network
of brainstem regions that includes CPGs
responsible for both behaviours (Ertekin et al.,
2015). Swallowing is organised by a medullary
CPG with a dorsal swallowing group in the
nucleus tractus solitarius and a ventral
swallowing group near the nucleus ambiguous
(Jean, 2001, Ertekin and Aydogdu, 2003). This
network interacts with the respiratory pattern
generator to coordinate brief swallow apnoea and
airway protection (Jean and Dallaporta, 2006,
Bianchi and Gestreau, 2009). The frequent
yawn&endash;swallow pairing therefore likely
reflects interacting pattern generators and
shared orofacial&endash;pharyngeal synergies,
which may contribute to the reproducible and
distinct CSF&endash;IJV flow alignment observed
in our data during yawning.
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- 4.5. Implications of directionality of
CSF and blood flows during yawning: brain waste
clearance and thermoregulation
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- 4.5.1. Waste clearance
- Yawning is a coordinated neuromuscular
activity that impacts fluid dynamics in the
cranial and cervical regions. On this basis,
yawning has been proposed to facilitate brain
waste clearance via the glymphatic system (or
cerebral waste clearance generally) potentially
by augmenting venous return and promoting
transit of cervical lymphatic fluid into central
venous system during neck flexion (Dolkart,
2017). The glymphatic system refers to the
proposed perivascular pathway by which CSF
exchanges with interstitial fluid and may assist
removal of metabolic waste from the brain (Iliff
et al., 2012, Mestre et al., 2020). However, to
date there has been limited direct evidence for
this. Gaping deep breathing increases
intracranial arterial and venous volume
displacement (Burman and Alperin, 2024),
supporting a respiratory mechanism; our data
extend this by showing that yawning, while
comparable in magnitude to gaping deep
breathing, differs in CSF&endash;IJV coupling,
with frequent co-directional outflows during
yawning inspiration. In this context,
co-directional outflow refers to CSF and venous
blood moving in the same direction at the same
time. We interpret these as transient, jointly
directed outflow that could favour caudal
advection toward the spinal canal and thereby
enhance macroscopic CSF mixing or clearance,
particularly around sleep&endash;wake
transitions (Guggisberg et al., 2007, Zilli et
al., 2007). However, this remains an indirect
inference: whether such changes in velocity and
directionality translate into greater
parenchymal waste removal has not been
demonstrated in humans and needs to be evaluated
in future work.
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- 4.6. Thermoregulation
- The thermoregulatory hypothesis for yawning
suggests that yawning helps dissipate excess
brain heat by increasing airflow and heat
exchange (Gallup and Gallup, 2008, Gallup and
Eldakar, 2013). A distinct feature of contagious
yawning in our results was internal carotid flow
increasing by an average of up to 43% in yawns
compared to gaping deep breaths across the cycle
of a yawn (Fig. 2, Table 1). This complements
the concurrent displacement of venous blood and
CSF, providing a plausible haemodynamic
component for thermoregulatory accounts of
yawning. Prior behavioural and thermal-imaging
studies report decreases in brain and/or
cranial&endash;facial temperature surrounding
yawning in non-human animals (Shoup-Knox et al.,
2010, Eguibar et al., 2017, Gallup et al.,
2017). Clinical observations in humans also
support a possible thermoregulatory function of
yawning (Gallup and Gallup, 2010, Gallup and
Hack, 2011). Recent animal work further suggests
that thermoregulatory aspects of yawning may
also be linked to centrally mediated
state-dependent mechanisms, with melanocortin-4
receptor signalling shown to potentiate yawning
and to be associated with elevations in brain
temperature preceding yawning/stretching
episodes (Alam et al., 2025). However, cranial
temperature was not measured in our study, so we
interpret the present arterial finding as
supportive but indirect evidence.
-
- We also found that both yawning and
gaping deep breathing increased CSF and venous
blood outflow compared with normal
breathing. Furthermore, the co-directional flow
of CSF and venous return could increase heat
transfer from the brain to the lungs. This
coordinated respiratory and vascular response
during yawning appears optimized for maximal
fluid exchange, producing the largest combined
displacement of venous blood and CSF of any
spontaneous respiratory manoeuvre. The human
brain operates at a higher temperature
(0.3°C to 0.93°C_±_0.5°C)
than the body's core (McIlvoy, 2004, Oh et al.,
2020). The alignment of CSF, venous blood flow,
and internal carotid inflow, could facilitate
increased (compared to normal and gaping deep
breathing) heat transfer during inspiration
where hotter CSF and venous blood leave the
brain, while arterial flow from the thorax would
cool the brain. This process could not only
enhance thermal regulation but also adheres to
the Monro-Kellie doctrine, which posits that the
volume inside the cranium is fixed; thus, any
increase in one component requires a decrease in
another, maximising the capacity for heat
exchange through blood and CSF.
- Evidence from behavioural studies supports a
thermoregulatory role for yawning through a
hypothesized thermal window effect: yawning
frequency increases when ambient temperatures
are below body temperature but declines when
conditions approach or exceed it (Gallup et al.,
2009, Gallup et al., 2010, Gallup and Eldakar,
2011, Gallup et al., 2011, Massen et al., 2014).
Yawning frequency has also been reported to
increase during experimentally induced sickness
and fever, consistent with sensitivity to
thermal load (Marraffa et al., 2017). This
pattern reflects that cooling efficiency is
greatest when inspired air and circulating blood
can absorb excess heat, and least when ambient
temperatures are too high for heat exchange.
Experimental studies found that applying neck
and facial cooling over the carotid regions,
which facilitates cranial heat loss, reduced
spontaneous yawning frequency (Gallup and
Gallup, 2007; Ramirez et al., 2019). Taken
together, the alignment of CSF and venous
outflow observed here, and previously by Klose
& Schröth, (1994), as well as increased
arterial carotid inflow, could be a
physiological mechanism that augments the
cooling potential of yawning beyond that of
ordinary respiratory manoeuvres. These data
situate yawning within broader homeostatic
functions without implying a single purpose.
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