Background: Yawning is a phylogenetically old behavior of ubiquitous occurrence. The origin and function of this conspicuous phenomenon have been subject to speculation for centuries. A widely held hypothesis posits that yawning increases the arousal level during sleepiness; thus, providing a homeostatic regulation of vigilance.
Methods: This chapter reviews experimental data on the relationship between yawning and vigilance that allow testing of the components and predictions of this hypothesis.
Results: Behavioral studies and electroencephalographic (EEG) recordings of brain activity before and after yawning have provided 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 specific autonomic activations or increased arousal levels after yawning.
Conclusions: The data therefore do not support an arousing effect of yawning or a role in regulation of vigilance or autonomic tone.
Copyright 2010 S. Karger AG, Basel.