Sleep Science Made Simple

Sleep.

We spend a third of our lives doing it.

Napoleon, Florence Nightingale, and Margaret Thatcher got by on just 4-hours a night! Thomas Edison claimed it was waste of time... but those who go for long periods without it will experience some very obvious and progressively dangerous effects:

• Inability to concentrate.
• Irregular body temperature.
• Grumpiness.
• Reduced muscle tone and skin appearance; “bags” under the eyes.
• Memory loss.
• Lack of physical endurance.
• Immune system impairment.
• Incoherence in speech and movement.
• Unstable metabolic rate.
• Irrational thoughts and actions.
• Personality changes.
• Brain impairment.
• Visual and auditory hallucinations.
• Death (!)

Nobody knows for sure how long humans can go without sleep: In 1980, Californian Robert McDonald went without sleep for nearly 19-days, or 452-hours, to be exact. Earlier, in 1965, Randy Gardner went without sleep for 11-days but, after just 4-days, he started to hallucinate... he began thinking he was a famous footballer! Laboratory rats have been shown to literally drop dead after 3-weeks without sleep.

And, yet, in spite of all these terrible effects, nobody really knows why we sleep at all! Until the 1939 publication of “Sleep and Wakefulness” by sleep researcher Nathaniel Kleitman, it was thought that nothing happened during sleep; your mind and body simply turned themselves off. However, it’s now known that the mind and the body are, in fact, highly active during sleep.

Scientists have proposed a variety of reasons for this: The body rests after the days activities... growth and other important hormones are released into the body in greater quantity... the body sets about repairing any damage; muscle tissue, for example, is rebuilt and restored... mental energy is replenished... new memories are consolidated and old ones are pared... dreams may be a means to process thoughts and new experiences had during the day...

All of these are probably true, to some extent.

The amount of sleep an animal needs varies: For example, giraffes sleep for less than 2-hours a day; pythons sleep for 18-hours. Humans tend to sleep between 4 and 10 hours, with most sleeping about 7 or 8 hours.

The 5-Stages Of Sleep

Humans sleep in 5-stages, each of which are independent of one-another and, yet, they are also very much connected as part of a grand “sleep cycle”: all the stages repeat over-and-over in a cycle that starts off at approximately 100 minutes long, and then gets gradually longer with each successive stage.

This sleep-cycle actually begins at the end of another “6th stage” of sleep: Waking!

Actually, I don’t mean “waking” as in ‘being awake while standing-up and walking about’; I mean a period of 'relaxed wakefulness' that occurs when your body is preparing itself for sleep.

When you get into bed after the day’s activities, your muscles are tense... your heartbeat is elevated... your eyes are darting about: You’re simply not relaxed at all!

As you begin to fall asleep though, your muscles begin to relax... your heart slows... your eye movement slows down. You are still awake but are now much more relaxed - that’s relaxed wakefulness!

Now the sleep cycle can begin...

Stage 1 Sleep:

This is simply a state of drowsiness.

Polysomnography (the analysis of the electrical and muscle activity of the body during sleep) shows that, even though your body functions have slowed during your period of “relaxed wakefulness”, they reduce even more (by about 50%) when you enter stage 1 sleep.

Your eyes are closed during this stage but, if somebody woke you up, you might feel like you weren’t asleep at all.

This stage lasts for about 5 to 10 minutes.

Stage 2 Sleep:

Stage 2 is a period of light sleep during which your body relaxes even more.

Polysomnography readings show irregular tensing and relaxing of the muscles during stage 2 sleep.

This is the longest sleep stage - it can occupy up to 60% of the total sleep-cycle time.

Your heart rate becomes very slow and, significantly, your body temperature drops; your body now prepares to enter a deep sleep.

Sleep Stages 3 & 4:

Both of these are stages of deep sleep (called delta sleep), with stage 4 being much deeper than stage 3.

During these stages, your body is almost immobile and your brain slows right down to a virtual crawl; it’s almost like you were in a coma.

The Sleep-Cycle

Stage 1, 2, 3, and, 4, when taken together, are known as non-R.E.M. sleep.

Since there are 5 sleep stages, you might expect number 5 to come right after 4... but you would be quite wrong: You see, your body doesn’t care about correct number sequence. What actually occurs is that, once stage 4 is complete, your body goes back to stage 3, and then stage 2, before going on to stage 5.

The cycle happens like this:

Waking... Stage 1... 2... 3... 4... 3... 2... Stage 5

(After stage 5 in the first sleep-cycle is complete, you go back to stage 2 and every repeated cycle begins from there instead).

Approximately 90 minutes after you first fall asleep, you enter:

Stage 5 Sleep:

Stage 5 of sleep is also known as R.E.M. sleep.

R.E.M. stands for “Rapid Eye Movement”: If somebody was watching your eyes while you were in R.E.M. sleep, they would see your eyes moving rapidly beneath your eyelids.

Other significant changes happen in this stage: your breathing quickens... your heart beats faster... your brain becomes highly active... and you start to dream.

Also, your face, fingers, and legs might twitch but (in most people) all of your major muscles will become paralyzed...  possibly to stop you from acting out your dreams for real!

R.E.M. sleep typically lasts for about 10 minutes but gets much longer as each successive sleep-cycle gets longer.

The Most Important Type of Sleep

In terms of how “deep” your sleep is, the sleep stages look like this:

• Stage 1: Not deep at all; nearly awake.
• Stage 2: Very light.
• Stage 3: Much deeper.
• Stage 4: The deepest of all.
• Stage 5: Very light.

Stages 3 and 4 - delta-sleep - are the “deepest” stages of sleep and they are the most invigorating and restorative. If you're sleep-deprived, it’s this type of sleep your body is screaming out for.

During the first sleep-cycle that happens right after you fall asleep, stages 3 and 4 are the longest. However, as the sleep-cycles repeat throughout the night, they will get shorter and shorter.

Also, during the first sleep-cycle, stage 5 (R.E.M. sleep) is the shortest. However, as the sleep-cycles repeat throughout the night, they will get longer and longer.

In other words, you get most delta-sleep when you first go to sleep and the least just before you wake up... and you get the least R.E.M. sleep when you first go asleep and the most just before waking up.

This is very significant: When you’re deprived of delta-sleep you experience huge problems: severe drowsiness... nausea... aches and pains... difficulty concentrating... even bad coordination and balance.

If this happens, your body will sacrifice all the other stages of sleep in order to gain as much delta-sleep as possible... this is why it tries to get as much of this type of sleep as possible during the first few hours of sleep.

When deprived of R.E.M. sleep we also experience problems, mainly concentration difficulties and some amount of drowsiness.

Although it’s not known for sure what function R.E.M. sleep serves, the fact that our own bodies will sacrifice it in order to catch up on delta sleep is very telling:

Deep sleep - delta sleep - is clearly the priority!

Three or four hours of deep sleep is far more valuable than 10 hours of light, disturbed sleep.

As you might have now realized, the key to getting quality sleep is being able to slide into delta-sleep as soon as possible and staying there for as long as your body deems it necessary!

The Circadian Rhythms

Although your core body temperature remains pretty much the same (at 98ºF/ 37ºC), there is, in fact, a slight variation over the course a 24-hours day, whereby it increases or decreases by about 3ºF/ 2ºC.

In general, your temperature is at its lowest just before you wake up... it then rises all morning... drops again in early afternoon...  and then rises again to it highest in the late afternoon/ early evening... it then starts dropping again and reaches it’s lowest point about 4 or 5 o’clock in the morning. These variations occur at different times for different people but, for each individual, remains very constant.

These daily temperature changes are part of what’s known as your circadian rhythm (from the Latin “circa” meaning “about” and “dies” meaning “day".)

The circadian rhythm is controlled by a very real “biological clock” in your brain... it’s called the suprachiasmatic nucleus... a little bunch of pin-head sized structures located just where your two optic nerves cross near the back of your eyes.

There are other bodily changes associated with the circadian rhythm: a rise in temperature is accompanied by increased alertness and a fall in temperature is accompanied by lethargy and tiredness.

The Sleep Hormone

The suprachiasmatic nucleus also controls the production of a hormone called melatonin by your pineal gland, a small pea-size organ located at the front of your head, between the two halves of your brain.

The more melatonin it produces, the more sleepy and tired you feel.
 
When light reaches the back of your retina, it creates signals that travel along your optic nerves and interact with the suprachiasmatic nucleus which, in turn, tells your pineal gland how much melatonin to produce... large amounts of light reduce production of melatonin (while darkness increases it’s production).

Summary of Important Facts

This is a summary of the 3 important factors - sleep stages, circadian rhythm, and melatonin - that comprise your body’s “sleep system”:

1. Stages of Sleep:

Sleep stages 3 and 4 (delta-sleep) are the most invigorating and restorative. Delta-sleep happens more immediately after you go asleep and less immediately before you wake up. When sleep deprived, your body will sacrifice other sleep stages in order to get more delta-sleep.

2. Circadian Rhythms:

Your body temperature varies by about (plus or minus) 3ºF/ 2ºC over the course of a 24-hour day. When temperature rises, you become more awake and alert. When temperature decreases, you become more sleepy and tired.

3. Melatonin:

When you are exposed to darkness, your body makes melatonin which makes you tired and sleepy. When you are exposed to light, your body stops making melatonin and you become more awake and active.

Take careful note of these three facts... you can use them to create a simple, but devastatingly effective, 4-step strategy to dramatically enhance your sleep quality.