ON YAWNING AND ITS FUNCTIONS

The forms and behavioral correlates of yawning are described, and the phylogenetic and ontogenetic aspects of the act are examined with part icular attention to its possible functions. Much evidence supports the view that yawning is an important mediator of behavioral arousal leve ls, a view that is further strengthened by a review of endocrine, neur otransmitter, and pharmacological mechanisms of yawning: A major funct ion of yawning appears to involve maintenance or increase of arousal w hen environments provide relatively little stimulation.