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When people talk about sleeping like a baby they usually mean that they slept deeply and soundly. But how similar to the sleep of an adult is the sleep of an infant? Are there significant differences? Do babies have the same kind of sleep as children, teenagers and adults?
As it turns out, the answer is no. Sleep in infants is quite different from that of adults. In fact, there is a clear developmental process by which the sleep of infants develops first into the sleep seen in children, then adolescents, and then adults. In this post I will briefly describe some of the qualities of sleep during infancy and how it differs from sleep in older individuals.
Even before birth sleep patterns begin to develop. Six or seven months after conception Rapid Eye Movement (REM) sleep first appears. About a month later the first evidence of non-REM sleep appears. Because these states are not as clear-cut in infants as in adults they are referred to as active sleep (REM) and quiet sleep (non-REM). Both types of sleep are clearly present about a month before birth.
You can tell an infant is in active sleep by noting twitches, irregular breathing and eyes movements under the eyelids. Interestingly, active sleep is the first stage of sleep to emerge. While active sleep makes up about 50% of the sleep of full term infants, in premature infants it is about 80%. During this stage of sleep the higher areas of the brain are stimulated by deeper centers of the brain. We do not know if infants actually dream but this stimulation allows higher levels of the brain to begin to experience the neural activity associated with seeing and hearing - even before birth! It is also true that while in the uterus the fetus makes breathing movements during REM sleep that allow for practice at breathing prior to birth and the actual inhalation of air. For these reasons, REM sleep may be most important early in life and decreases with age as the brain matures. REM declines to about 30% of sleep by age 3 and by adulthood only 20% to 25% of sleep is REM.
Deep breathing, stillness, occasional fast sucking movements and occasional sudden body jerks characterize quiet sleep. This type of sleep takes additional brain maturation beyond that which is required for REM sleep to occur. Quiet sleep in infants is unlike that in children and adults in that clear stages (currently called N1, N2, N3) are not seen in the EEG. Instead of the ongoing pattern of slow wave activity seen in children and adults, infants have bursts of high amplitude slow waves. Over the first month after birth these slow waves become continuous and the sudden jerks cease. Following the first three months of life, non-REM sleep gradually becomes more differentiated so that lighter and deeper stages of sleep can be detected. By six months of age more complex patterns emerge that are characteristic of stage 2 (N2) sleep in children and adults.
Overall infants in the first week of life spend about 16 hours asleep each day - the amount of time adults usually spend awake during a day. About 8 hours of this occurs at night and another 8 hours as naps during the day. By two years of age, children are sleeping about 11.5 hours per day with most of that at night. At age 18, the nightly sleep requirement is about 9 hours, although few teens are actually getting that much.
Sleep changes throughout the life span and serves to help the brain function properly for the day-to-day challenges of life, whatever your age. Like that of a baby, may your own sleep be restful and refreshing.
