REM Sleep &
Remembering Dreams
(...Continued
From REM Sleep & Remembering Dreams Pt 1)
Now let us take a look at the mechanics behind REM sleep.
Early ideas about sleep inclined to a 'passive' theory that
sleep occurs to prevent fatigue or is caused by a lack of
sensory stimulation. To support that notion, certain experiments
showed that if incoming nerves in the mid-brain were severed,
the organism remained virtually in constant sleep.
Some theories propounded that
the brain was actively inhibiting consciousness in order to
achieve sleep, and some experiments showed that cats could
be put to sleep by electrical stimulation of a part of the
brain.
It gradually became accepted
that the reticular formation in the brain stimulates the cortex
of consciousness. There seems to be an inherent rhythmic sleep-wake
cycle, but wakefulness is aided by external sensory stimulation.
Several factors assist in
maintaining wakefulness by stimulating the reticular formation,
such as a decrease in blood oxygen level, excess of carbon
dioxide or excessive warmth. The cortex itself is capable
of exerting a strong effect on wakefulness - worries or excitement
can keep us awake.
When the electrophysiological
monitoring of people during sleep began, the distinct states
of slow-wave sleep, (SWS), and REM became known. Research
has shown that the two sleep states are governed by the ebb
and flow of neuro-transmitter substances at the base of the
brain.
It is fascinating, in a sleep
laboratory, to observe that inevitable alternation, in a roughly
90 minute cycle. Typically, the subject is 'wired up' with
sensors called electrodes, that are stuck by tape or glue
to the body to detect electrical signals accompanying muscular
or nervous activity.
Two electrodes on measured
positions, (for consistency between laboratories), of a few
millionths of a volt are used. Four other electrodes, placed
above and below the outer edge of each eye record eye-movements,
(EOG), in any direction, and two others on the jaw measure
muscular tonus, (EMG).
Those measures provide enough
information for a standardised evaluation of sleep state,
but often other measures, such as respiration and body temperature,
are also recorded. The data formerly appeared on chart paper
emerging from the recording instrument - termed a polygraph
- but it is more likely nowadays to be stored in a computer
and displayed on a screen.
SWS has been arbitrarily divided
into four stages, according to the amount of slow waves of
a certain amplitude that are present. At sleep onset, in stage
one, the eyes begin to roll slightly in many subjects and
the waking alpha rhythm, (about ten cycles per second), of
the EEG disappears. In stage two, there are sudden 'k-complexes'
in the EEG in response to external or internal stimuli. Stage
three exhibits definite large slow waves and if over half
the record consists of such a pattern, stage four is registered.
After perhaps 20 minutes or so of stage four sleep, the sequence
is reversed, to perhaps stage two, and then REM sleep suddenly
makes an entry.
The EEG of REM sleep is active
- showing saw-toothed waves. The EMG trace is very narrow,
reflecting the amazing bodily paralysis which afflicts the
subject for the duration. REM sleep is associated with dreaming.
Occasionally, the eyes shift about - in 'REM bursts'. The
movements seem to be a mixture of both involuntary and scanning
actions.
Another feature of REM sleep
is of penile erections in males - and clitoral erections in
females. All men are conscious of the connection between erections
and dreaming and it may have been that link which led Freud
to assume the sexual nature of dreams. However, it is unwise
to assume anything whatsoever in science, and experiments
have shown that if subjects are woken repeatedly from REM
sleep, the erection cycle gets out of phase with the REM cycle.
Thus the two phenomena are linked, but there is not necessarily
any cause and effect between them.
Each REM period increases
in length during the night, and the amount of SWS correspondingly
decreases, so that the first half of the night consists mostly
of SWS and the second half predominantly REM.
More recent theories about
sleep and dreaming have stressed the evolutionary background
and have tried to explain either SWS or REM sleep, but no
one idea is fully accepted. Generally, it has been hypothesised
that SWS keeps us still and out of harm during darkness and
that bodily growth and repair can occur at that time.
REM sleep is seen by some,
looking at the computer analogy, as a time when memories are
updated and filed, and redundant information discarded - not
true! (see common misconceptions).
A few decades ago, it was
thought that to be deprived of REM sleep would result in mental
disturbance - it was an erroneous belief. It is understood
now that some drugs, such as certain anti-depressants, completely
abolish REM sleep - and yet there are no noticeable deleterious
effects in users.
The surprising conclusion
is that REM sleep does not seem to be necessary in adults.
However, it may be very important
to the developing foetus. This is conjectured from the fact
that sleep of a new born baby is about 50% REM. That type
of sleep, then, may be significant in programming or even
providing some kind of genetically coded imagery to the foetus.
Not many psychologists believe now that the mind of a new
born baby is a complete tabular rasa or blank state.
A person who is deprived of
sleep will, on eventually resting, experience non-dreaming
SWS in preference to dreaming sleep, (REM), so dreaming is
a bit of a luxury to those short on sleep.
Interestingly, the 90 minute
SWS/REM 'ultradian' cycle has been seen to persist into day-time
activities, for instance when observing oral activity.
DREAM DURATION
The greatest myth about dreams
is that they are over 'in a flash'. It is surprising how many
people today accept that idea as true. It stems from the Frenchman,
Maury, who reported having had a long and involved dream which
culminated in his execution by guillotine. At the moment the
blade fell, he was woken by part of the bed collapsing on
his neck. He reasoned that the whole dream construction must
have occurred in that moment.
It sounds a plausible notion,
but we know that expectation certainly affects dreams and
it may have been that his bed often collapsed and perhaps
gave warning creeks. The facts of that case cannot now be
known. As there was no counter evidence that dreams occurred
in 'real time', Maury's theory stayed around and gained considerable
ground.
However, Dr Hearne was the
first person to show that dreams do actually take as long
as they appear to do. In his sleep-laboratory, studies of
lucid dreams, where subjects signalled information from within
the dream by making coded eye movements, Dr Hearne found that
the estimated passages of time between signals corresponded
to the actual measured durations in the polygraphic chart
record.
FURTHER INFORMATION ON DRUGS
There are different effects
alcohol can have on sleep. In addition, it is interesting
for the analyst to note that, in small quantities, it acts
as a stimulant, but in larger doses, it has the opposite effect
- that of being a depressant. Tobacco is also a stimulant
and smokers tend to fall asleep after a longer period than
non-smokers.
Barbiturates used to be prescribed
for insomnia. They were very powerful and suppressed REM sleep.
The body then adapted by tolerance so that the baseline level
of REM sleep recovered. However, if the user stopped taking
the drug, a massive 'REM rebound' effect would occur, for
several weeks, during which vivid nightmares might result.
DREAM FORGETTING AND RECALL
The reason for rapid evaporation
of dream memories is probably to prevent confusing dreams
with reality. The memories do not seem to be actually erased
- because something the following day can trigger the recall
of an entire dream. It is more a case of them being filed
away somewhere marked 'Not normally to be accessed'. Of course,
those seeking self-insight and self development from their
own dreams have to overcome that obstacle.
Recall is best immediately
after the dream. The brain is very active in REM and the thought-processes
can function on waking. However, waking from SWS can be quite
different - especially from stage four sleep. Often the individual
woken from that condition is disoriented, and 'sleep-drunk'.
DO WE DREAM IN COLOUR?
Finally, let us briefly consider
the big differences between individuals as regards colour
in dreams. In general surveys on dreams, colour is usually
referred to in about a third of cases. If, however, subjects
in the sleep lab are asked to report any colours in dreams
on being woken from REM sleep, nearly three-quarters can recall
colours. The content of the dream seems to be remembered in
preference to any colour factors.
Authors Details: David
F. Melbourne Web
Site
David F. Melbourne, who lives on a remote Scottish island,
has been studying dreams for 25 years and is known all
over the world for his accurate dream interpretations.
Apart from the general public, he has analysed dreams
for celebrities and famous authors, all of whom have
admitted a high degree of accuracy. |
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