Yawning: unsuspected avenue for a better understanding of arousal and interoception.

Almost all the vertebrates yawn, testifying the phylogenetic old origins of this behavior. Correlatively speaking, yawning shows an ontogenical precociousness since it occurs as early as 12 weeks after conception and remains relatively unchanged throughout life. Thus, it is contended that these common characteristics and their diencephalic origin allow to model an approach from which emerges a pivotal link between yawning and REM sleep. Yawning and stretching reverse the muscular atonia of the REM-sleep and reopen the collapsed airways. Yawning appears as a powerful muscular stretch, recruiting specific control systems particularly the paraventricular nucleus of the hypothalamus, the locus coeruleus and the reticular activating system from which the vigor of this ancestral vestige, surviving throughout evolution with little variation, may increase arousal. On the other hand, the James-Lange theory proposes that afferent feedback from muscles and viscera provides the brain with a feeling that characterizes the active motivational state and arousal. On this basis and using selected supporting findings from the literature and from data provided by daily life, it is contended that yawning takes part in interoceptiveness by its capacity to increase arousal and self-awareness. Adaptative behaviors depend on interactions among the nervous system and the body by a continuous feedback between them. The body's schema is a main component of the self, and interoceptive process is essential to awareness of the body and arousal. Yawning contributes to bodily consciousness as a behavior affiliating a sensory motor act and his perception from which pleasure is derived. Yawning can be seen as a proprioceptive performance awareness which inwardly provides a pre-reflective sense of one's body and a reappraisal of the body schema. The behavioral consequences of adopting specific regulatory strategies and the neural systems involved act upon attention and cognitive changes.Thus, it is proposed that yawning is a part of interoceptiveness by its capacity to increase arousal and self-awareness.