The Sleep Cycle: Stages of Sleep

On a daily basis, everyone experiences a significant shift in consciousness.

We spend about a third of our lives sleeping. Dreaming gives us yet another state of consciousness.

People have studied dreams since the time of the ancient Egyptians. Proper systematic dream and sleep research has gained currency over the past fifty years. As technology advances, so does our ability to analyze how and why we dream.

Three distinct characteristics of the state of rest that is sleep are:

  1. Reduced activity
  2. A drop in our responsiveness to stimuli
  3. Distinct brain wave patterns

REM and NREM Sleep

cycles of sleep

Back in 1950, a graduate student working alongside a researcher at the University of Chicago got the opportunity to monitor sleeping infants. He observed very noticeable changes in their eye movements.

There were stages where the eyes moved extremely swiftly then intervals with little to no eye movement at all.

  • REM: Rapid Eye Movement
  • NREM: Non-rapid Eye Movement

Following this observation, the researchers noted that when adults are awakened during REM sleep, they almost always reported dreaming. If they lurched into consciousness during NREM sleep, on the other hand, they usually did not recall any dreams.

Since the 1950s, this research has been expanded upon considerably.

We now know two facts:

  1. Dreaming is not limited to REM sleep only
  2. REM sleep is not synonymous with dreaming

This makes it extremely tough to accurately estimate the proportion of dreaming between these two stages of sleep. Some people who come to during REM sleep don’t outline any dreams. Others exiting NREM sleep will demonstrate some vague recall of an event.

To generalize, NREM sleep is more dream-free than REM sleep. Any reported dreams in the REM stage tend to be more vivid, longer-lasting and visual.

Complex measuring devices like the EEG, EOG and EMG help to monitor movements of the eye and electrical activity in the muscles.

The Stages of Sleep


When we are awake, our brain waves include:

  • Gamma
  • Beta (high and mid)
  • Beta Sensory Motor Rhythm
  • Theta
  • Alpha

These beta waves are low-amplitude and high frequency.

As we reach a drowsy state, our breathing and heart rate slow down. Body temperature drops as muscles relax. We edge towards alpha waves.

Stage 1

The first, light stage of sleep is very brief.

Drifting off and moving through alpha and theta waves, we experience a state almost like daydreaming. It’s quite possible to fall into this kind of stage during the day, some being more prone than others.

During stage 1, we tend to get more hypnogocic hallucinations. Vibrant feelings like falling or hearing our names being called are accompanied by abrupt muscle contractions.

We then coast toward theta waves. This is a light period when we are neither properly awake nor asleep.

We normally fall asleep within 10 minutes although this varies considerably from person to person.

Stage 2

Another truncated period of maybe 20 minutes, we fall deeper into sleep during this stage.

Sleep spindles are very short bursts of brain activity produced during stage 2.

Our body temperature drops further and our heart rates slow up.

The K complex is another brain wave pattern experienced in this stage of sleep. It occurs in response to either an internal stimulus (stomach cramps, for example) or external stimuli like the sound of voices or vehicles.

Stage 3

This is a transitional period as we edge toward deeper sleep.

Delta waves – deep and slow brain waves – begin to emerge. When these waves make up 20-50% of any EEG tracing, we are in stage 3 heading toward dreamland.

Stage 4

This is also known as Delta Sleep.

Delta waves continue to build proportional to other brain waves. After the 50% mark has been reached, we are in stage 4, the deepest sleep of all.

Stage 4 lasts for about 30 minutes.

Problems like bedwetting or sleepwalking tend to manifest themselves toward the end of our deepest period of sleep.

It is quite difficult to be woken during this sleep segment. If you are roused by an alarm clock while in stage 4, there’s every chance you’ll feel groggy and disoriented.

There are virtually no eye movements during either stage 3 or 4.

Stage 5: REM

We now leave NREM behind and move into REM sleep.

As well as rapid eye movement, our respiration rate and brain activity both surge upwards.

Other body systems become more active while muscles relax. Voluntary muscles become paralyzed. The rise in brain activity leads to dreaming.

The body features an inbuilt method of self-paralyzing to protect us. If you dream of being trapped, you in many senses are, unable to move of your own volition.

Sleep Cycles

When we sleep, the above documented stages do not always happen sequentially.

Initially, we move from the first to fourth stage in order. Then, we repeat stage 3 and 2 before entering REM sleep. After REM, we normally go back to stage 2.

We experience 4 or 5 of these sleep cycles during the course of a night.

REM kicks in after about 90 minutes of sleep. The first REM cycle is often brief but becomes progressively longer. This can extend up to an hour at times.

Explaining Sleep

Although sleep has been extensively studied and researched, it might be clear that we need to sleep. What is not so clear is why we need to sleep.

What is not so clear is why we need to sleep.

There are 4 main theories:

Sleeping To Restore Depleted Resources

Over the course of a day, our bodies expend a great deal of energy.

When we sleep, our body has the chance to rest and recuperate.

In a study, subjects were monitored after running a 57-mile race. They slept for longer than normal afterward as you would expect. They also enjoyed much more deep sleep.

Sleeping To Save Energy

Linked to this idea is the concept that we sleep in order to conserve energy.

By taking ourselves out of commission for one-third of each day, we protect ourselves from exhaustion.

If we look back in history, in times where resources were more limited, sleeping was a great way to make these stretch further.

Sleeping To Clear The Mind

Each day, we are exposed to a colossal amount of information.

From the moment we wake until bedtime, we are bombarded with multimedia and a lot of this is clutter.

One school of thought suggests that we sleep in order to clear our minds of extraneous data. By sleeping and getting rid of this unwanted information, our brains are then more receptive to new learning.

Sleeping In Order To Dream

Almost every subject every studied has exhibited signs of dreaming.

Since we all dream, this separate state of consciousness is highly likely to serve some important function. We are just not clear yet on what that, precisely, that function is.

Perhaps we really do need to dream…

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