The science of sleep
We spend a third of our lives doing it.
Napoleon, Florence Nightingale and Margaret Thatcher got by on
four hours a night.
Thomas Edison claimed it was waste of time.
Why do we sleep?
So why do we sleep? This is a question that has baffled
scientists for centuries and the answer is, no one is really sure. Some believe
that sleep gives the body a chance to recuperate from the day's activities but
in reality, the amount of energy saved by sleeping for even eight hours is
miniscule - about 50 kCal, the same amount of energy in a piece of toast.
We have to sleep because it is essential to maintaining normal
levels of cognitive skills such as speech, memory, innovative and flexible
thinking. In other words, sleep plays a significant role in brain development.
What would happen if we didn't sleep?
A good way to understand the role of sleep is to look at
what would happen if we didn't sleep. Lack of sleep has serious effects on our brain's ability to function. If you've ever pulled
an all-nighter, you'll be familiar with the following after-effects:
grumpiness, grogginess, irritability and forgetfulness. After just one night
without sleep, concentration becomes more difficult and attention span shortens
considerably.
With continued lack of sufficient sleep, the part of the brain
that controls language, memory, planning and sense of time is severely
affected, practically shutting down. In fact, 17 hours of sustained wakefulness
leads to a decrease in performance equivalent to a blood alcohol level of 0.05%
(two glasses of wine). This is the legal drink driving limit in the UK.
Research also shows that sleep-deprived individuals often have
difficulty in responding to rapidly changing situations and making rational
judgements. In real life situations, the consequences are grave and lack of
sleep is said to have been be a contributory factor to a number of
international disasters such as Exxon Valdez,
Chernobyl, Three Mile Island and the Challenger shuttle explosion.
Sleep deprivation not only has a major impact on cognitive
functioning but also on emotional and physical health. Disorders such as sleep apnoea which result in
excessive daytime sleepiness have been linked to stress and high blood
pressure. Research has also suggested that sleep loss may increase the risk of
obesity because chemicals and hormones that play a key role in controlling
appetite and weight gain are released during sleep.
What happens when we sleep?
What happens every time we get a bit of shut eye? Sleep
occurs in a recurring cycle of 90 to 110 minutes and is divided into two
categories: non-REM (which is further split into four stages) and REM sleep.
Non-REM sleep
Stage one: Light Sleep
During the first stage of sleep, we're half awake and half
asleep. Our muscle activity slows down and slight twitching may occur. This is
a period of light sleep, meaning we can be awakened easily at this stage.
Stage two: True Sleep
Within ten minutes of light sleep, we enter stage two, which
lasts around 20 minutes. The breathing pattern and heart rate start to slow
down. This period accounts for the largest part of human sleep.
Stages three and four: Deep Sleep
During stage three, the brain begins to produce delta waves, a
type of wave that is large (high amplitude) and slow (low frequency). Breathing
and heart rate are at their lowest levels.
Stage four is characterised by rhythmic breathing and limited
muscle activity. If we are awakened during deep sleep we do not adjust
immediately and often feel groggy and disoriented for several minutes after
waking up. Some children experience bed-wetting, night terrors, or sleepwalking during this stage.
REM sleep
The first rapid eye movement (REM) period usually begins about
70 to 90 minutes after we fall asleep. We have around three to five REM
episodes a night.
Although we are not conscious, the brain is very active - often
more so than when we are awake. This is the period when most dreams occur. Our
eyes dart around (hence the name), our breathing rate and blood pressure rise.
However, our bodies are effectively paralysed, said to be nature's way of
preventing us from acting out our dreams.
After REM sleep, the whole cycle begins again.
How much sleep is required?
There is no set amount of time that everyone needs to sleep, since
it varies from person to person. Results from the sleep profiler indicate that people like to sleep
anywhere between 5 and 11 hours, with the average being 7.75 hours.
Jim Horne from Loughborough University's Sleep Research Centre
has a simple answer though: "The amount of sleep we require is what we
need not to be sleepy in the daytime."
Even animals require varied amounts of sleep:
|
Species
|
Average total sleep
time per day
|
|
Python
|
18 hrs
|
|
Tiger
|
15.8 hrs
|
|
Cat
|
12.1 hrs
|
|
Chimpanzee
|
9.7 hrs
|
|
Sheep
|
3.8 hrs
|
|
African elephant
|
3.3 hrs
|
|
Giraffe
|
1.9 hr
|
The current world record for the longest period without sleep is
11 days, set by Randy Gardner in 1965. Four days into the research, he began
hallucinating. This was followed by a delusion where he thought he was a famous
footballer. Surprisingly, Randy was actually functioning quite well at the end
of his research and he could still beat the scientist at pinball.
