Each one of us spends about one-third of our life asleep. Look at it this way, by the time you’re 75, you will have spent 25 years sleeping.
Sleep is part of the life of all higher vertebrates, a critical part. Suppressing sleep for an extended period has dramatic effects on our physiological equilibrium. This means sleeping is almost as important as eating or breathing.
This is where it is important to point out that the quality and length of sleep are individually and equally as important to the process.
Accordingly to scientists, sleep is defined by four criteria: reduced motor activity, diminished responses to external stimuli, posture (lying down with eyes closed) and relatively ready reversibility. These criteria distinguish sleep from comas and hibernation.
Compared with wakefulness and rapid eye movement (REM) sleep, non-REM sleep is characterized by an electroencephalogram (EEG) in which the waves have greater amplitude and a lower frequency. From the time you fall asleep to the time you reach the deepest non-REM sleep, about 1 ½ hours later, the amplitude of these waves increases continuously, while their frequency diminishes correspondingly.
I have been tracking my sleep for the past two years with the help of my Fitbit. Acknowledging the limitations of the device and the impact on the data those implications bring, I have learned quite a bit about my sleep behavior and what factors affect my sleep, both positively and negatively.
I also allow myself to ignore the data periodically. You see, the “quality” of sleep is determined by many factors. How restless am I, how many times do I toss and turn, or just re-position during the night?
There are times I have awoken feeling very rested and excited to see what the data said about the night’s rest only to be discouraged by a low quality due to repeated motion in the night.
Below is an example of such a night. The pink indicates times of restlessness. The teal is sound sleep. Though it says I was only fully awake twice during the night, I was restless 14 times leaving the quality at 72%.
There are four stages that provide a convenient means of describing the relative depth of non-REM sleep. There are times I can look at an analysis like the one above and see the stages clearly, and other times not so much.
Stage One non-REM sleep begins when you first lie down and close your eyes. After a few sudden, sharp muscle contractions in the legs, the muscles relax. Then, as you continue falling asleep, the rapid beta waves of wakefulness are replaced by the slower alpha waves of someone who is relaxed with their eyes closed.
Unfortunately this stage can take awhile to navigate. For me, that whole leg muscle relaxation thing is a challenge. Just ask the dog that sleeps at my feet.
Stage Two non-REM sleep is a stage of light sleep in which the frequency of the EEG trace decreases further while its amplitude increases. During Stage Two sleep, the EEG trace may also show a fast, high-amplitude wave form called a K-complex. The K-complex seems to be associated with brief awakenings, often in response to external stimuli.
I have found that this stage is actually the least frequent time I am awaken. That may be due to the sleep patterns of my spouse and dogs, and their unlikeliness to create ambient noise to disturb me. It also is likely because the bathroom break time isn’t for a few more hours.
Stage Three non-REM sleep marks the passage from moderately to deep sleep. Delta waves appear and soon account for nearly half of the waves in the EEG trace. This stage lasts about 10 minutes during the first sleep cycle of the night but accounts for only about 7 percent of a total night’s sleep.
Stage Four non-REM sleep is the deepest, the one in which we sleep the most soundly. The EEG trace is dominated by delta waves and overall neuronal activity is at its lowest. The brain’s temperature is also at its lowest, and breathing, heart rate and blood pressure are all reduced.
In adults, Stage Four lasts about 35 to 40 minutes during the first sleep cycle of the night and it accounts for 15 to 20 percent of total sleep time in young adults.
In the course of one night, you can experience 2-3 sleep cycles and therein the 4 different stages over and over.
Supposedly, the typical adult sleeps about 8 hours per night. Again I believe the definition of sleep is subjective. I may be in bed 8-9 hours, but accordingly to my data, I am lucky to get 5 1/2 – 6 hours sleep a night. It is not as simple as how much sleep we need at various times in our lives, our age also helps determine what type of sleep we get.
Sleep is one of those basic needs we can’t escape. But that doesn’t mean we’re planning our days to make sure we get our requisite hours of sleep each night. We live in a society where we’re expected to burn the candle at both ends, and even our best attempts at sleeping well can fail with early morning meetings, last minute projects, late night social gatherings, children who need night time attention, sleep problems, or a snoring spouse.
Sleep was once considered an inactive or passive state in which both the body and the brain turned off to rest and recuperate from the day’s waking activities. However, after scientists identified the characteristic patterns of activity throughout each period of sleep they realized that the brain is sometimes more active when we’re asleep than when we’re awake. So snooze away.
Melody K. Smith
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