When an adult falls asleep, her higher brain functions decelerate which allows her to enter the phase known as deep sleep. During this time her body hardly moves, breathing is slow and regular, and her muscles become relaxed and loose. After around an hour and a half later and her brain becomes more active and she enters into a period called light sleep. It is during this time when she may slip into REM (rapid-eye-movement) sleep where most dreams occur. These deep/light cycles continue throughout the night, at around two hours intervals, so that the average adult spends around 6 hours in deep sleep and 2 in light sleep.
Babies need to be parented to sleep because, unlike adults, they only go into a deep sleep after an initial period of light sleep. Let’s see how many of you can relate to this: Imagine you’re performing your bedtime ritual with your baby:you’re rocking, walking, nursing etc until she falls asleep in your arms. Her eyes are completely closed, her eyelids may be fluttering and she may be twitching or showing momentary smiles (called sleep grins). Just as you think it’s safe to place your baby in her crib and sneak away, she wakes and starts crying! Why does this happen? It’s because she wasn’t properly asleep and only in a state of light sleep. Next time you attempt your bedtime ritual, carry on past this first stage of sleep (usually takes around 20 minutes). Wait until the twitching and smiling cease, the breathing becomes more regular and the muscles relax so that her limbs dangle weightlessly. These are the tell-tale signs that the baby is in the deep stage of sleep and your chances of being able to put her down and sneak away successfully are dramatically improved (Sears 2005).
Like adults, babies’ sleep cycles continually change from light to deep throughout the night. However, their cycles are significantly shorter than those of adults. They will enter into a period of light sleep every hour or so. During this time the baby is prone to awakening easily if an uncomfortable stimulus occurs, such as hunger (Sears 2005).
Some new parents will often spend time just watching their baby sleep. If you do this, you may notice the tell tale signs that she is about to awaken. You may be able to get your baby through this period of light sleep, without waking, if you place your hand on your baby’s tummy, whisper a comforting word or play her favourite lullaby quietly. Sometimes letting baby know that you’re there will comfort her enough to enter back into deep sleep without waking. Fathers may have more luck with this technique if the baby is breast fed because often the baby will pick up on the scent of breast milk and will automatically awaken for a feed.
W. Sears (2005). The Baby Sleep Book: How to Help Your Baby to Sleep and Have a Restful Night.” Harper Thorsons.