Stress

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Circadian Rhythm
Infradian Rhythm
Ultradian Rhythm
Jet lag
Shift Work
Evolutionary Theory of Sleep
Restoration Theory of Sleep
Sleep Deprivation Studies
Lifespan Changes in Sleep
Insomnia and OSA
Narcolepsy and Somnambulism
Child behaviour linked to sleep
 

 

 

 

 

Restoration theory

Oswald (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 awake too!

Evidence in support of restoration theory

Further support is provided by Shapiro (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 of cats). 

 

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!

REM 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. 

Note: restoration 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 biological state of REM sleep and makes no mention of the psychological state of dreaming.  Therefore it is not to be used in a question that asks for theories of dreaming.

 

 

 

 

 

 

 

 

 

 

 

Research in support of restoration theories

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 new tissues

 

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)

Research against restoration theories

·         Protein synthesis occurs 24 hours a day, not just during stage 4 - although it does seem to peak in stage 4.

·         Amount 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.

·         The brain is very active during REM so runs counter to the idea that it is an ideal time for repair.

·         The model is over simplistic since in fact neuro-chemicals appear to be produced throughout a night’s sleep and not just during REM.

·         When we 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 endogenous purpose. 

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.

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