The
interplay between yawning and vigilance: a
review of experimental evidence
Adrian G. Guggisberg
Department
of Clinical Neurosciences, University of Geneva,
Switzerland
Yawning is a
phylogenetically old behaviour of ubiquitous
occurrence. The origin and function of this
conspicuous phenomenon have been subject to
speculations for centuries. A widely held
hypothesis posits that yawning increases the
arousal level in case of sleepiness, thus
providing a homeostatic regulation of vigilance.
This article reviews experimental data on the
relationship between yawning and vigilance that
allows testing the components and predictions of
this hypothesis.
Behavioural studies and
electroencephalographic (EEG) recordings of
brain activity before and after yawning provide
consistent evidence that yawning occurs during
states of low vigilance, thus substantiating the
notion that it is provoked by sleepiness.
However, studies analyzing autonomic nervous
activity and EEG based indices of vigilance in
yawning subjects did not find persistently
increased arousal levels or specific autonomic
activations after yawning. The data therefore
does not support an arousing effect of yawning
or a role in regulation of vigilance or
autonomic tone. Instead, yawning has been shown
to have contagious effect on others, and to
activate brain regions responsible for social
interaction and self-processing.
We therefore suggest that
yawning has an intrinsically social role rather
than a homeostatic function in the individual,
i.e., it is a non-verbal (and potentially
subconscious) form of communication, which is
crucial for synchronizing the behaviour of a
group of individuals.
