What happens when we sleep?
We spend one third of our lives asleep. That's about twenty five years.
Whilst we sleep, our brains do not. Nerve cells in the brain are constantly firing and
transmitting information. We can measure this electrical activity on a machine called an
electroencephalograph (EEG) - this records the electrical activity in the form of a wave pattern.
Sleep follows a regular cycle throughout the night and the EEG traces change in a very
predictable way, (see the trace opposite). There are four distinct stages per cycle with  about
five cycles per night. There are two basic forms of sleep; slow wave sleep (SWS) and rapid
eye movement (REM) sleep. When we are fully conscious and going about our daily routines
the brain shows a pattern known as beta waves, (8-25Hz). When we're very relaxed, as when
we've settled ourselves down to sleep, this activity turns into alpha waves, (6-8Hz). Stage 1
sleep soon follows and shows typical theta activity. The second stage of sleep is also
characterised by theta waves, (4-7Hz) but also shows sleep spindles and K complexes. This is
a sort of no man's land between waking and sleeping. Quite often, in this stage of sleep you
become aware of vivid images in your mind's eye. Providing you don't immediately fall into
Stage 3 sleep you might find yourself startled back into full consciousness by the vividness
and reality of these images. They are known as hypnogogic images and seem to be nothing to
do with dreaming. Some psychologists believe that such images are responsible for reports of
UFO sightings, ghosts and other supposed paranormal activity. However, most people pass
through this stage of sleep so quickly that the images seen are rarely remembered in the
Theta waves lead into very low frequency delta waves (Stages 3 and 4, 1-3Hz) and it is these delta waves that characterise the deepest
stages of sleep. A person in this stage of the sleep cycle is very difficult to rouse. The pulse rate has slowed right down, the breathing is
deep and slow. Stages 3 and 4 together are known as Slow Wave Sleep (SWS).
And then, approximately 90 minutes after you've fallen asleep, something quite extraordinary starts to happen. The electrical activity of your
brain reverts to the beta waves characteristic of full, waking consciousness - actually it's a mixture of theta and beta activity as shown on the
trace. But you are still very much asleep. Your breathing and pulse rate become irregular and you experience almost total muscle paralysis.
The only things that move are your eyes, and they dart backwards and forwards beneath your closed eyelids. This is REM sleep, (Rapid
Eye Movement), sometimes known as paradoxical sleep because we cannot explain how or why this can be. This is the period when most
dreaming is thought to occur, although not exclusively. Becoming conscious or semi-conscious during this stage of sleep can be a terrifying
experience. Often there are accompanying feelings of someone being in the room or footsteps coming up the stairs, or being attacked by an
unseen presence. Sometimes these experiences are so clear and so terrifying, that we may try to move and find we cannot. This makes the
terror worse.  Later, when we try and understand what happened to us, we will  often conclude that it was the result of some paranormal
experience or haunting. It's certainly an experience you won't forget in a hurry. At present, the cause of this phenomenon is unknown.
After a few minutes of REM sleep, you fall back down into delta sleep and this marks the end of the first sleep cycle.

We experience four or five sleep cycles every night, each cycle lasting approximately 90 minutes, (see diagram opposite). The amount of
time spent in REM sleep gets longer with each cycle, the last REM period may last as long as 40 - 60 minutes.
So, if my calculations are right, we spend at least two and a half hours, out of every twenty four, dreaming. Over an average lifetime of 75
years this works out at 68,500 hours, or nearly 3,000 days, or approximately 8 years! So, we spend 25 years sleeping and 8 years dreaming.
This is a huge investment of time that could be spent doing other things. So why do we sleep? It must be important to our survival or
presumably we would not do it. Unfortunately we don't yet know the answer to that question.
What we do know is that sleep patterns change as we age. New born babies sleep about 16 hours per day and will spend half of that time in
REM sleep. This gradually decreases with age until, at about age 50 we may find we need only  6 or 7 hours sleep and will only spend
approximately 15% of the sleep period in REM sleep. The reasons for this are not known and until we actually figure out why we sleep, we
will not find the answer. It is likely that sleep is a restorative or adaptive process; or may be both. Some researchers have found that REM
sleep deprivation causes us to be anxious and irritable, but other studies have concluded that there are no deleterious effects. Deprivation of
nonREM sleep, on the other hand, has been shown to cause acute physical tiredness and a deterioration in cognitive ability. It may be that
sleep, (particularly REM sleep) is important for learning and memory but this is, as yet unproven. It is interesting to note that, in some cases,
too much sleep has been accused of causing or worsening depression. Many of the  antidepressants used today, reduce the amount of time
spent in REM sleep.  However, we must be careful in drawing conclusions from such studies; it may be that the REM periods of sleep are a
way of assimilating information and perhaps healing emotional difficulties. This can be a painful process but would seem to be essential if the
person is to achieve mental and emotional health again. A person on anti-depressants may be less depressed because the issues giving rise
to the depression are being avoided or the memory of them is lessened. If REM sleep causes or worsens depressive states, do older people
only rarely suffer from depression because they spend so little time in REM sleep? And why are not all babies and toddlers depressed?
Copyright J.C.Harthan 2002
My own thoughts on the function of REM were presented in a paper at the 21st Annual
IASD Conference in Copenhagen in June 2004.
Click here to read the Abstract.