Sleep researchers have also found some remarkable consistencies with REM sleep across a number of different mammal species. At the human equivalent of between 2 and 3 years of age, the amount of REM sleep begins to drop significantly, replaced by more NREM sleep.
This suggests a major change in the purpose of sleep as we age. The research indicates the primary function of sleep for newborns to about age 2.5 is focused on brain growth and development. Thereafter, significantly more NREM corresponds to sleep being used more for brain maintenance and clearing of toxins.
The research also suggests the surge in more REM typically experienced during puberty corresponds with the growth of the brain's prefrontal cortex, usually associated with the development of higher thinking skills.
Use of the EEG opened a much broader understanding of sleep, with intense research still ongoing today. There still is much more that we don't know than we know about the hidden world we enter each night.
The time between sleep cycles is important to understand
Because sleeping is lightest between cycles, it’s common for normal sleepers to briefly awaken the five or six times between cycles per night, and then fall back asleep within seconds. Typically these very brief periods of awakening are so short they are forgotten by morning.
Moreover, even the best sleepers will awaken to some degree at least 10 to 15 times per night and forget about it by morning. Finer indications of arousal, such as brain wave activity measured in a sleep lab, show that normal sleepers actually awaken some 10 times or more per hour on average, although these arousals typically last less than 15 seconds. Transient awakenings like these are benign, and by themselves nothing to worry about.
So if you do wake up in the middle of the night – and you’re not awakened by some external noise or disturbance – there’s a good chance you’ve just completed one of these natural sleep cycles. You may also remember a dream from a just completed REM stage.
These brief periods between cycles are an especially important time to understand. Because sleep tends to be lighter as we age, instead of falling back asleep quickly between cycles some people may move the other way – toward an increased level of wakefulness. It may then take longer than a few minutes to fall back asleep.
For insomniacs, these brief wake-ups, even though normal, can become a cause for concern. That concern can then feed on itself, developing into something more – a self-perpetuating negative cycle of worry. In other words, worrying about falling back asleep keeps you up.
In this way, concern about being up can automatically trigger a heightened state of worried wakefulness, rather than the kind of drowsy state (Stage 1) that would be more conducive to falling asleep.
This is another example of how insomnia can inadvertently evolve from a conditioned response or learned behavior. But just as it can be learned, it can be unlearned. Bad habits can be broken, just as good habits can be intentionally cultivated. These are areas of emphasis in the STS we will soon be covering.
In the STS, you will learn how to relax and fall asleep when you want. You will learn relaxation tools and techniques that enable you to more easily let go, quiet your mind, and thereby move naturally back toward Stage 1, a drowsy state more conducive to sleep.
These are some of the key principles we will focus on; but for now just understand why, especially as you age, it’s not uncommon to find yourself up during the brief periods between one or more of the several sleep cycles you experience each night.
Sleep and body temperature
Another interesting finding from sleep research is that body temperature drops about 2 degrees during sleep, and rises during waking hours. Contrary to popular belief, your body is not always 98.6 degrees.