By Catherine A. Sanderson, Amherst College
In the words of author John Steinbeck, “It is a common experience that a problem difficult at night is resolved in the morning after the committee of sleep has worked on it.” Sleep truly is extremely important for our psychological and physical well-being.
Sleep Theories
One theory says that sleep evolved as an adaptation to conserve energy and provide protection from predators. According to this theory, sleeping helps people and animals stay safe. During sleep, we are quiet, don’t move, and are often hidden, so we aren’t drawing attention from potential predators.
A second view points out how sleep plays an important role in the process of growth and development. During deep sleep, the pituitary gland releases a growth hormone. Babies spend a substantial amount of time—about 12 to 16 hours a day—asleep, and of course they also show rapid growth during this age period.
Conversely, adults spend less time in deep sleep and also release less of this hormone.
A third theory explains why we sleep as a time for physical and mental recovery; a chance to repair muscles, replace essential chemicals, and rest the brain from the emotional and intellectual demands of the day.
In addition, sleep is also important for learning and memory and forgetting. On the one hand, sleep basically allows us to fix in our minds what we’ve learned that day; it’s a time when we consolidate, store, and maintain memories.
This article comes directly from content in the video series Introduction to Psychology. Watch it now, on Wondrium.
Pruning Unnecessary Connections
On the other hand, research with mice suggests that sleep also helps us to forget some things that we don’t need to remember.
When we learn new things, the brain grows new connections between neurons so that information can be transmitted faster. But over time, there can be too many connections and this interferes with learning and memory. So, during sleep, our brains may prune or pare back some of these unnecessary connections so that we can process what we do need to remember faster.
Stages of Sleep
Throughout the night, we pass through a series of four distinct sleep stages with brief periods of being more awake as we shift from one stage to the next.
In Stage 1 sleep, our breathing slows, our body relaxes, and our brain waves slow and show irregular alpha waves. Alpha waves are basically the resting state for the brain; they indicate calmness and quietly flowing thoughts, much like in the early states of meditation.
We may see fantastic images, like hallucinations, or experience muscle spasms and a sensation of falling, leading your body to suddenly jerk awake. This stage is the lightest sleep stage. Sleep in this stage can be disrupted easily by an alarm clock, phone ringing, doorbell, etc.
Stage 2 Sleep
Stage 2 sleep is actually the first stage of real sleep. One relaxes more deeply. Our body temperature decreases, our heart rate begins to slow, and our brain shows theta waves, which are slower in frequency and greater in amplitude than alpha waves.
Stage 2 also marks the appearance of sudden bursts of rapid brain waves called sleep spindles. One is now clearly asleep, although they can be awakened without too much difficulty.
Deep Sleep
Stage 3 is known as deep sleep. Our brain emits large, slow delta waves. These are the same types of brain waves generated during the deepest meditation. During this stage, it is difficult to wake someone up.
This is the stage in which sleepwalking—a behavior disorder typically caused by extreme sleep deprivation or alcohol use—occurs.
About an hour after one falls asleep, they transition from Stage 3 back to Stage 2 and then into rapid eye movement, or REM, sleep.
REM Stage of Sleep
REM (rapid eye movement) sleep is the stage of sleep in which most dreaming occurs. The REM stage of sleep is marked by active brain waves. This stage of sleep is often called paradoxical sleep, as one is definitely asleep, but their body is in a state of rapid arousal.
Their heart rate is elevated, breathing becomes rapid and irregular, eyes are darting around behind closed eye lids, and yet their muscles are so relaxed that they are virtually paralyzed.
Horses can sleep standing during the other phases but lie down for REM sleep because their muscles are too relaxed. This is the sleep stage in which dogs may whimper or twitch while asleep.
Dreaming
The most important characteristic of REM sleep is dreaming. This is thought to be the stage in which most dreaming occurs. Dreams that occur during REM sleep are often emotional, vivid, and usually story-like.
If one is awakened by an alarm clock during REM sleep, it may take them a minute to figure out that what they were just dreaming of, is real or not. The sound of the alarm might be part of the dream.
Sleep Cycles
Over the course of the night, we move from lighter sleep, Stages 1 and 2, to deeper sleep, Stage 3, and then the sleep cycle reverses back up to lighter stages of sleep before we enter REM sleep.
Thus, the cycle basically goes 1, 2, 3, 2, REM, 2, 3, 2, REM and so on throughout the night. This cycle then repeats itself about very 90 to 120 minutes, meaning one has about 4 to 5 sleep cycles over the course of the night.
And yet, interestingly, over the course of the night, the amount of time we spend in deep sleep gets shorter, and the amount of time we spend in REM sleep gets longer. This means that when we sleep for longer periods of time, we spend more time in REM.
One should never underestimate the importance of having a good sleep and should keep in mind that getting enough sleep actually leads us to feel better and think smarter.
Common Questions about Theories on Sleep and Sleep Cycles
Over the course of the night, we move from lighter sleep, Stages 1 and 2, to deeper sleep, Stage 3, and then the sleep cycle reverses back up to lighter stages of sleep before we enter REM sleep.
REM (rapid eye movement) sleep is the stage of sleep in which most dreaming occurs. The REM stage of sleep is marked by active brain waves.
Over the course of the night, the amount of time we spend in deep sleep gets shorter, and the amount of time we spend in REM sleep gets longer.
