Function of Sleep: RESTORATION (EXPLANATIONS)
A01: REM sleep is important for brain growth and repair whereas SWS is important for bodily restoration.
A02: Research support: Case studies of total sleep deprivation (Peter Tripp, Randy Gardner) have provided evidence for the body's resilience to deprivation of sleep.
A02: However... these case studies have three main limitations: Unique characteristics of the participants, contradictory findings and lack of scientific control.
EXPLANATION 1: REM SLEEP AND BRAIN RECOVERY (OSWALD, 1969)
A01: Drug overdose
Patients recovering from drug overdoses and CNS injuries show significant increases in REM sleep during their recovery period.
A02: However... research has found little evidence that intense physical exercise does anything other than make people fall asleep faster.
Large amount of REM sleep in babies reflects rapid brain growth.
A01: Replenishment of neurotransmitters
During REM sleep, neurons that have been active during the day cease firing but continue to synthesis new neurotransmitters for the next day.
A02: A problem with this explanation is that... REM sleep involve considerable neural activity, which uses up neurotransmitters. Their replenishment cannot, therefore, be the sole function of REM sleep.
A02: A further problem for this explanation is that... symptoms of severe depression are reduced in some people when deprived of REM sleep; also there is some contradictory evidence that complete REM deprivation has no significant ill effects.
EXPLANATION 2: SWS and BODILY RESTORATION (OSWALD, 1969)
A01: Hormonal Activity
- The increase in the body's hormonal activities during SWS suggests a restoration process in the body.
- A02: Supported by the finding that SWS deprivation in fibrositis sufferers leads to non-restorative sleep patterns.
- SWS is associated with the secretion of growth hormones, important for the synthesis of proteins, which need to be constantly restored.
- A02: However, HORNE (1988) highlighted the fact that amino acids are only freely available for 5 hours after a meal, making proteins synthesis during SWS unlikely.
A01: Increase in NREM sleep after deprivation
- BERGER and OSWALD (1962) found a marked increase in NREM on the first night after sleep deprivation while REM remained the same.
- A02: However... some research has found no differences in the effects of partial sleep deprivation (REM or SWS) or total sleep deprivation (REM and SWS)
Explanation 3: CORE SLEEP (HORNE, 1988)
A01: CORE SLEEP
- Core sleep = REM + SWS, which is responsible for normal brain functioning (HORNE, 1988)
- A02: This Explanation is supported by... HORNE (1988), who reviewed 50 studies where people had been deprived of sleep - very few reported that this interfered with the ability to perform physical exercise.
- A02: Also... runners slept for only an hour more after physical exertion (SHAPIRO et al., 1981)
A01: Lighter stages of NREM: These are not essential and are therefore optional sleep
A01: Bodily Restoration: This takes place during periods of relaxed wakefulness, while core sleep provides for restoration of brain systems.
A02: The view that sleep is necessary for bodily restoration is challenged by... the finding that participants given exhausting tasks went to sleep faster but not for longer (HORME AND MINARD 1985)
FUNCTION OF SLEEP: RESTORATION (STUDIES)
Sleep deprivation studies are used to test the assumption that sleep has an important restorative function.
STUDIES 1: TOTAL SLEEP DEPRIVATION
- Peter Tripp - After 3 days he becamse of abusive, after 5 days he hallucinated and became paranoid, after 8 days his brain waves resembled those of a sleeping state. After 24 hours' sleep he recovered.
- Randy Gardner - After 11 days no abnormal symptoms were present.
- There are 3 main limitations of these case studies: the unique characteristics of each participant, contradictory findings and lack of scientif control.
- However... it is impossible to prevent microsleep in these studies, so participants may not be completely sleep-deprived.
- In general... case studies show no significant effects of sleep deprivation.
STUDIES 2: REM SLEEP DEPRIVATION
REM sleep deprivation increases the tendency to enter REM sleep earlier and increase the proportion of REM sleep on subsequent nights (REM rebound) (EMPSON, 2002)
A02: However... symptoms of severe depression are reduced in some people when deprived of REM sleep.
A02: Some contradictory evidence... exists that complete REM deprivation has no significant ill effects e.g. one brain-injured patient who led a normal life without REM sleep (LAVIE et al., 1984)
STUDIES 3: SWS SLEEP DEPRIVATION - MOLDOFSKY et al. 1975 found that:
- Fibrositis patients experience tiredness and EEG patterns in SWS are faster (therefore SWS is not restorative)
- Volunteers deprived of SWS sleep experienced symptoms of fibrositis.
A02: However, some research has found no differences in the effects of partial sleep deprivation (REM or SWS) or total sleep deprivation (HORNE, 1988)
A02: Also... SWS effects are unlikely - proteins synthesis uses amino acids which are not available 5 hours after a mean (HORNE, 1988)
Studies 4: HORNE'S EXPLANATION
- BERGER AND WALKER (1972) found a large increase in SWS at the expense of the later stages on the first night after deprivation. There was an increase in REM on subsequent nights.
- A02: This supports the view that... stage 4 and REM sleep constitute 'core' sleep, as participants were almost completely recovered following deprivation, and that lighter stages have no restorative function.
- STERNE and MORGANE (1974) found no evidence of REM rebound following sleep deprivation for patients on anti-depressants.
- A02: This can be explained because... anti-depressant drugs increase levels of available dopamine and serotonin, so there is no need for an REM rebound.