title: Circadian variation of yawning behavior.
abstract: Circadian variation of spontaneous yawning is demonstrated in a line of Sprague-Dawley rats, genetically selected for high frequency of this motor pattern. Yawning is highest in late light and early dark hours, both under natural and artificial illumination. The hypothetical neurotransmitters underlying this physiological rhythm in yawning are discussed.
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012018:Reflex / Q000502:physiology*