(1966) suggested that sleep restores depleted resources of
energy, removes waste from muscles and repairs cells. For example
during the day waste chemicals build up in the muscles following
physical exertion and neurotransmitters used for communication
throughout the nervous system are likely to be used up. Sleep therefore
might be an ideal time for the body to remove this waste and
restock/replenish its levels of neurotransmitters in preparation for
activity the next day. As some have put it…life disrupts homeostasis;
sleep restores it.
In addition the body could carry out repairs to damaged
cells and growth could occur the young
Non REM sleep
According to Oswald, NREM sleep is a time for replenishing
the body. Oswald points out that most NREM sleep, especially stages 3
and 4, occur at the start of the night when the body is most tired.
During stages 3 and 4 we secrete greater levels of growth hormone into
the blood which would help in the repair process, seeming to offer
support to his theory. (Good evaluation phrase!). We do know that
many restorative functions appear to occur during sleep, for example
digestion, removal of waste from muscles etc. and protein synthesis for
repair and growth. However, these processes also occur whilst we are
Evidence in support of restoration theory
Further support is
(1981) who studied ultra marathon runners who had completed a 57-mile
run. It was found that they slept for 90 minutes longer than usual for
the next two nights. REM sleep decreased whilst stage 4 of quiet or
NREM sleep increased dramatically from 25% of nights sleep to 45%.
However, lack of
exercise does not reduce amount of deep sleep as this model would predict.
Ryback and Lewis (1971) got healthy students to spend 6 weeks in bed and
observed no change in their sleep patterns. (Note: Carrying our sleep research
on student sleep patterns seems to be as valid as research on the sleep patterns
Other evaluation points
When we lose sleep
and are given the opportunity to make it up we only catch up on a small
proportion of it. This suggests that not all sleep is needed. Why
therefore would we need non-essential sleep?
Amino acids are not
stored in the body and only remain in the bloodstream for about eight
hours before being broken down or excreted. As a result we would expect
protein synthesis to stop half way through a night’s sleep. This would
explain why deep sleep occurs in the irst half of a night’s sleep. Of
course this also assumes that we eat just prior to going to sleep!
Oswald (1980) and Hartman (1984), built on the theory to
include restoration during REM sleep. They believe that REM is for
restoration of the brain. Stern & Morgane (1974), believed that
neurotransmitter levels within the brain may be restored during REM
sleep. The young brain is growing and developing at its fastest rate so
young children, especially babies sleep for much longer than adults. In
the newborn about 9 hours a day is spent in REM compared to about 2
hours in adults.
theories of sleep make cognitive sense since we suffer so many
unpleasant consequences when deprived of sleep
It is important to
remember that this seeks to explain the
state of REM sleep and makes no mention of the psychological state of
dreaming. Therefore it is
to be used in a
question that asks for theories of dreaming.
Research in support of
The most obvious
support comes from aspects of the sleep deprivation studies to be
discussed in the next section. First some other evidence:
Disruption of stage 4 sleep can cause fibrositis, a
condition of the lower back caused by muscle wasting.
Babies sleep for much longer than adults and spend up to 9
hours in REM. This would allow time for growth and development
of the brain.
Following brain insults i.e. damage caused by ECT,
strokes, drug overdoses etc. Patients spend longer in REM
for an average of 6 weeks. This suggests time is being
spent carrying out
repairs by laying down new proteins and building
Growth hormone, essential for production of amino acids
and proteins is secreted during deep sleep.
It has been suggested that neurotransmitters are
replenished during REM. When patients are prescribed
antidepressants e.g. tricyclics or monoamine oxidase inhibitors
(MAOIs) they spend less time in REM.
This is not
easy so I shall spend time explaining it in class
However, when treatment is stoppedthere is no REM
rebound. Perhaps this is due to the drugs providing whatever
chemical REM sleep usually provides. Antidepressants increase
levels of serotonin and dopamine. Stern and Morgan (1974). So
perhaps REM is a time for the brain to replenish its supply of
neurotransmitters that it has used up during the day.
According to Oswald and Horne loss of these
neurotransmitters would explain problems in perception memory and
attention experienced following sleep deprivations e.g. Randy Gardner
and Huber-Weisman (1976)
synthesis occurs 24 hours a day, not just during stage 4 - although it
does seem to peak in stage 4.
of sleep does not appear to decrease when our level of daytime activity
decreases, (as shown by Ryback & Lewis, and others).
Following great physical exertion the amount of additional sleep we need
may only be negligible. Horne & Millard (1985) found that although we
usually fall asleep quicker we do not usually sleep for longer.
brain is very active during REM so runs counter to the idea that it is
an ideal time for repair.
model is over simplistic since in fact neuro-chemicals appear to be
produced throughout a night’s sleep and not just during REM.
miss out on sleep it doesn’t seem to affect our physical well-being. A
good night’s sleep and we’re back to normal.
Other research contradicting the theories
Returning briefly to animal studies; this theory predicts
that more active species will sleep longer. However, one of the least
active creatures, hence its name, the sloth, sleeps for about 20 hours a
day, whereas some very active humans get by on a few hours only. At the
other end of the scale, shrews are very active and presumably would need
plenty of restoration, nut only sleep a couple of hours a day.
Whilst looking at other species. Oswald assumes a single
and essential purpose for sleep. If this is the case why are there so
many different patterns of sleep across other species. Why do lions
need to sleep so long and herbivores sleep so little? It seems unlikely
that big cats suffer so much more damage on a daily basis.
The different patterns of sleep in other species do seem to
be related more to their differing lifestyle needs rather than a more
If sleep served only one purpose we would expect the results
of sleep deprivation studies to show similar results. This is not the
case; we only need to look at the very different outcomes of Peter Tripp
and Randy Gardener.
One final comment on this section that is always worth
making: Horne (1988) distinguishes between core and non-core sleep.
Core sleep (stages 4 and REM) appear to be essential and present in all
species, whereas non-core sleep (stages 2 and 3) appears not to be so
vital. Evidence for this is: following sleep deprivation we spend
longer in REM and stage 4 suggesting that we need to catch up on these.