Yawning throughout life

Yawning is a behavior that begins in the first stages of life. It has not only been observed in infants and in newborns, but also in fetuses of 12-14 weeks' gestational age. Yawning frequency changes over the life span. In preterm infants, the number of yawns decreases between 31 and 40 weeks' postconceptional age, mainly during the day. In this period of life, yawning is an isolated behavior rarely occurring in bursts, and its frequency is quite low with respect to adults. The incidence of yawning seems to increase when children attend elementary school, whereas this is reduced in the elderly. Aged people yawn less than younger ones, mainly during morning and mid-afternoon. In adults, the time course of yawning is associated with the time course of sleepiness, except upon awakening when the high frequency of yawns is not associated with high sleepiness. In adults, yawning frequency increases in the early morning and in the late evening, whereas at the earliest stages of development (fetuses and preterm infants) yawning does not show diurnal variations. Yawning seems to be involved in the modulation of arousal process across the whole life span. In preterm infants, yawning is often followed by motor activation and it is more common during waking than sleep; in adults, yawning occurs mainly at sleep onset and upon awakening.