Reptiles, birds and mammals all sleep. That is, they become unconscious to their surroundings
for periods of time. Some fish and amphibians reduce their awareness but do not ever become
unconscious like the higher vertebrates do. Insects do not appear to sleep, although they may become
inactive in daylight or darkness.
By studying brainwaves, it is known that reptiles do not dream. Birds dream a little. Mammals all dream
during sleep. Fun fact - cows can sleep while standing
up but they only dream if they lie down!
Different animals sleep in different ways. Some animals, like humans, prefer to sleep in one long
session. Other animals (dogs, for example) like to sleep in many short bursts. Some sleep
at night while others sleep during the day.
How much sleep do you need?
Most adult people seem to need 7 to 9 hours of sleep a night. This is an average, and it is also subjective.
You, for example, probably know how much sleep you need in an average night to feel your best.
The amount of sleep you need decreases with age. A newborn baby might sleep 20 hours a day. By age 4
the average is 12 hours a day. By age 10 the average falls to 10 hours a day. Senior citizens can
often get by with 6 or 7 hours a day.
Sleep and the brain
If you attach an electroencephalograph to a person's head, you can
record the person's brainwave activity. An awake and relaxed person generates alpha waves,
which are consistent oscillations at about 10 cycles per second. An alert person generates
beta waves, which are about twice as fast.
During sleep, two slower patterns called theta waves and delta waves take over.
Theta waves have oscillations in the 3.5 to 7 cycle per second range and delta waves are those
below 3.5 cycles per second. As a person falls asleep and sleep deepens, the brainwave
patterns slow down. The slower the brain wave patterns, the deeper the sleep - a person deep
in delta wave sleep is hardest to wake up.
At several points during the night, something unexpected happens - Rapid Eye Movement (REM) sleep occurs.
Most people experience 3 to 5 intervals of REM sleep per night, and brainwaves during
this period speed up to awake levels.
If you ever watch a person or a dog experiencing REM sleep, you will see their eyes flickering
back and forth rapidly. In many dogs and some people, arms, legs and facial muscles will twitch
during REM sleep. Periods of sleep other than REM sleep are know as NREM - non-REM - sleep.
REM sleep is when you dream. If you wake up a person during REM sleep, the person can vividly recall dreams.
If you wake up a person during NREM sleep, generally the person will not be dreaming.
You must have both REM and NREM sleep to get a good night's sleep. A normal person will spend about 25% of the night
in REM sleep, and the rest in NREM. A REM session - a dream - lasts 5 to 30 minutes.
Medicine can hamper your ability to get a good night's sleep. Many medicines, including most sleeping medicines,
change the quality of sleep and the REM component of it.
Why do we sleep?
One way to understand why we sleep is to look at what happens when we don't get enough:
A person who gets just a few hours of sleep per night can experience many of the same problems over time.
- As you know if you have ever pulled an all-nighter, missing one night of sleep
is not fatal. A person will generally be irritable during the next day and will either
slow down (become tired easily) or will be totally wired because of adrenalin.
- If a person misses two nights of sleep it gets worse. Concentration is difficult and
attention span falls by the wayside. Mistakes increase.
- After three days a person will start to hallucinate and clear thinking is impossible.
With continued wakefulness a person can lose grasp on reality. Rats forced to stay awake
continuously will eventually die, proving that sleep is essential.
Two other things are known to happen during sleep. Growth hormone in children is secreted during
sleep, and chemicals important to the immune system are secreted during sleep. You can become
more prone to disease if you don't get enough sleep, and a child's growth can be stunted by sleep deprivation.
But the question remains - why do we need to sleep? No one really knows. There are all kinds of theories,
What we all know is that, with a good night's sleep, everything looks and feels better in
the morning. Both the brain and the body are refreshed and ready for a new day!
- Sleep gives the body a chance to repair muscles and other tissues, replace aging or dead cells, etc.
- Sleep gives the brain a chance to organize and archive memories. Dreams are thought by some to be part of the process.
- Sleep lowers our energy consumption, so we need three meals a day rather than 4 or 5. Since we
can't do anything in the dark anyway, we might as well "turn off" and save the energy.
- According to this article, sleep may
be a way of recharging the brain, using adenosine as a signal that the brain needs to rest.
"Since adenosine secretion reflects brain cell activity, rising concentrations of this
chemical may be how the organ gauges that it has been burning up its energy reserves and
needs to shut down for a while." Adenosine levels in the brain rise during wakefulness and decline during sleep.
Things you can do to improve sleep
- Exercise regularly. Exercise helps tire and relax your body.
- Don't consume Caffeine after 4:00 or so. Avoid other stimulants like cigarettes as well.
- Avoid alcohol before bedtime. Alcohol disrupts the brain's normal patterns during sleep.
- Try to stay in a pattern with a regular bedtime and wakeup time, even on weekends.
What about dreams?
Why do we have such crazy, kooky dreams? Why do we dream at all for that matter? According to
Joel Achenbach in his book Why Things Are:
The brain creates dreams through random electrical activity. Random is the key word here.
About every 90 minutes the brain stem sends electrical impulses throughout the brain,
in no particular order or fashion. The analytic portion of the brain - the forebrain -
then desperately tries to make sense of these signals. It is like looking at a Rorschach
test, a random splash of ink on paper. The only way of comprehending it is by viewing the
dream (or the inkblot) metaphorically, symbolically, since there's no literal message.
Here are some other things you may have noticed about your dreams:
This doesn't mean that dreams are meaningless or should be ignored. How our forebrains choose
to "analyse" the random and discontinuous images may tell us something about ourselves, just as
what we see in an inkblot can be revelatory. And perhaps there is a purpose to the craziness:
Our minds may be working on deep-seated problems through these circuitous and less
threatening metaphorical dreams.
Dreaming is important. In sleep experiments where a person is woken up every time he/she enters
REM sleep, the person becomes increasingly impatient and uncomfortable over time.
- Dreams tell a story. They are like a TV show, with scenes, characters and props.
- Dreams are egocentric. They almost always involve you.
- Dreams incorporate things that have happened to you recently. They can also contain deep
wishes and fears.
- A noise in the environment is often worked in to a dream in some way, giving
some credibility to the idea that dreams simply are the brain's response to random
- You usually cannot control a dream (in fact, many dreams emphasize your lack
of control by making it impossible to run or yell), but proponents of
dreaming try to help you gain control.