The Biology of Bedtime
How Children Sleep (and How to Make It Better)
• Review the normal development of sleep in infancy.
• Understand how you can help your baby develop good sleep habits from birth.
• Learn about using a baby monitor, the timing of sleep training, and more.
Although this book is focused on helping the parents of children one year old and up, understanding the evolution of sleep in infancy is critical to understanding how your child’s sleep problems evolved, whether you have an infant, a toddler, or a school-age child. Many of the children I see in the Pediatric Sleep Center have “never been good sleepers,” according to their parents. This chapter will help you understand why your toddler has been struggling with sleep since he came home from the hospital, and it will also help you set your newborn up for good sleep. Don’t worry if you want to sleep train your baby. I’ll show you how to do that too.
Sleep in the First Six Months of Life, and Beyond
When my older son was about six months of age, he had been sleeping through the night for a month or so. My wife and I were relieved to have so easily moved out of the sleep-deprived newborn months, during which he had slept in short bursts, waking at two- or three-hour intervals for feeding and diaper changes. At least half of infants naturally grow out of this pattern by five to six months and achieve what scientists have defined as “sleeping through the night”--sleep without interruption from 10:00 p.m. to 6:00 a.m. Then our son started to wake up first once and then two to three times a night to nurse. We were perplexed: What had happened to sleeping through the night?
Our routine had grown naturally out of the soothing techniques we’d used when he came home as a newborn: my wife would nurse our son to sleep, then place him in his crib. He could sleep through the night because he had reached an age where he did not need middle-of-the-night calories anymore and he was old enough to self-soothe. But we had become so comfortable in our little routine of nursing and rocking him to sleep that we missed the opportunity to put him to bed drowsy but awake. We’d created a bad sleep habit (technically called an “inappropriate sleep onset association”), which often causes these nocturnal awakenings. In Chapter 2, we’ll talk about how this problem obeys the logic of habits, and in Chapter 7, I’ll tell you what we did (in the section called “My Sleep-Training Mistakes”).
Although my day job is dealing with the biology of sleep (and sleep problems) in children, I was still surprised to discover how quickly developmental changes in sleep can trip parents up. Understanding how your child’s sleep changes as he grows will help you recognize why your child’s sleep pattern changes so quickly in the first year. It will also help you understand the reasons behind the process in this book, and help you anticipate problems with your next child.
I’m not the first doctor to find my own experience in parenting useful. One of the fathers of sleep medicine, Nathaniel Kleitman, wrote a seminal paper on the development of sleep in infancy. In it, he included an illustration that, at first glance, looks like a series of lines and dots, almost like Morse code (see page 18). It was a different sort of code, however, one that tired parents have been trying to crack ever since: the sleep patterns for a child during the first six months of her life.
This particular child, Kleitman reports, “was a first child, and her parents were sufficiently indulgent to permit her to set her own sleep-wakefulness pattern.” Rumor has it that the indulgent parent was Kleitman himself. (This illustration was clearly dear to him, as he used it to illustrate the cover of his book Sleep and Wakefulness, published ten years later.)
His study demonstrates some important truths about sleep in the first six months of life.
First, sleep is pretty chaotic in the first month or two. Do you clearly remember the first few weeks after you brought your child home from the hospital? I sure don’t. Babies are physiologically hungry at night, leading to an apparent reversal of day and night. Fortunately, this resolves by about three weeks of age. After this, your child fairly quickly settles into a three- or four-hour cycle that typically follows a pattern of wake--feed--sleep. In the first few months, there is a wide range of normal sleep durations. Some babies may sleep twenty hours a day. Others may sleep ten to twelve hours per day, but these twelve hours usually don’t occur together. Longer periods of wakefulness are distributed randomly--sometimes during the day and, unfortunately, sometimes at night.
Around three to four months of age, as they grow larger and need less frequent feedings, babies can start having longer periods of sleep through the night. At this age, six to seven hours of continuous sleep is a pretty good stretch. It does not always occur during the nighttime hours, an effect of the dreaded day-night reversal. (Note to parents: This can be difficult to avoid. The best thing to do is make sure that your baby is exposed to natural light during the day and darkness at night, which will help her adjust to a natural rhythm.)
Around four months (weeks 16 and 17 on the graph), Kleitman’s baby has a set pattern of persistent night sleeping and daytime waking. However, it’s not until weeks 23 and 24 (around five months) when the child in the illustration has finally achieved the holy grail--pretty consistent nighttime sleep with minimal interruptions.
Kleitman’s graph shows us a significant fact: after the first six months of life, most healthy children are able to sleep through the night. Many parents are racked with guilt about sleep training. But sleep research shows that children naturally move toward long periods of sleep at night. By following the plan in this book, you will be supporting your child’s development by helping her to independent, uninterrupted sleep.
Six Months and Beyond: Settling into “Typical” Sleep
One of the most interesting things about sleep in infants from six months of age onward is how much their sleep resembles ours. When we study children in the Pediatric Sleep Center, we use electroencephalography (EEG) to study the different brainwave patterns that occur during the night. We use these patterns to classify the types (or stages) of sleep. The amount and timing of different stages of sleep in newborns differ significantly from what’s seen in grown-ups like you and me, but by six months of age, the brainwave patterns of babies look a lot like yours or mine, with a few subtle differences. Even children who struggle with sleep have the same brainwave patterns, and they sleep just like other children for most of the night (although their exhausted parents would say otherwise).
The stages of sleep are:
Stage 1: This is a brief stage, typically about 5 percent of the night, that occurs as you pass from wakefulness to sleep. It is very light, and during it a sleeper can be awoken easily. If you ever nod off and then jerk awake, you are in stage 1 sleep.
Stage 2: This is the most common stage, constituting about 50 percent of the night in children and adults. It is relatively light and dreamless.
Stage 3: This is also known as slow-wave or delta sleep, due to the large, slow waveforms noted on the EEG tracings. This is the deepest type of sleep, and the most refreshing. This is usually about 25 percent of the night in children and young adults, and is reduced in the elderly--this is why old people often endure insomnia. It is very difficult to wake a child in stage 3. If you have ever picked your child up from his car seat, changed his diaper, put him in his pajamas, and laid him down in his crib without waking him up, he was in stage 3. Since this stage tends to occur in the first half of the night, it explains why many children with sleep problems eventually go to sleep but then wake up and need Mom or Dad two to three hours later, just as their parents are climbing into bed. Stage 3 is also when sleepwalking and night terrors occur.
Rapid eye movement (REM) sleep: This stage accounts for about 20 percent of the night, and it is when vivid dreams occur. If you wake up out of REM sleep (for instance, if you hear your alarm in your dream and then you awaken), you’ll feel wide awake, with none of the grogginess that occurs if, say, your screaming child wakes you up during stage 3. It is also when nightmares occur. During REM sleep, all of your skeletal muscles are paralyzed except for your diaphragm (the main breathing muscle) and your eye muscles. In the first few months of life, babies enter sleep through REM sleep. The paralysis during REM sleep in young infants is incomplete. That is why young babies frequently twitch, grunt, sigh, and briefly cry out right after they fall asleep. It is the characteristic back-and-forth eye movements that give REM sleep its name.
Note a few things: First, that deep period of slow-wave sleep in the beginning of the night. That’s when you can transfer your child from car seat to crib without incident. The second is the vertical bar over the first REM period. During REM sleep, awakenings are both natural and common. We all experience them at night, but if your sleep environment is the way you arranged it to fall asleep at night, you usually go right back to sleep. (If you fell asleep in your bed and woke up on the floor of the bathroom, you would likely not just go back to sleep.) If you are only awake for five minutes, you won’t remember this the next day.