Restoration Explanations of sleep function Flashcards
Explain what theories into restoration suggest
These theories suggest that sleep helps to maintain health and homoeostasis by allowing us to build up energy reserves (used up during wakeful activity), remove waste products, and repair damage. REM and NREM probably have different functions.
Discuss REM in terms of restoration
Oswald - suggests that REM restores brain function by replenishing neurotransmitters levels and allowing neurons to regain their sensitivity to them. REM sleep may also play a role in memory consolidation. Crick and Mitchison - suggested that during REM sleep unwanted memories are disposed of - thus making more important memories easier to access. Stickgold - later refined this idea suggesting REM may be particularly important to consolidate procedural memory so memories of certain procedures like playing a melody on a piano, can actually improve while you sleep.
Discuss evidence that REM restores brain function
1) The proportion of REM is much greater in babies than adults. This may be because brain growth and development requires protein synthesis to take place in REM.
2) People have more REM after ECT or drug overdoses, both of which damage the brain and so need repair
3) Some antidepressant drugs abolish REM - perhaps the increase in serotonin levels they cause means there is no need for REM sleep to replenish levels of this neurotransmitter
Discuss Non REM in terms of restoration
The important part of NREM sleep seems to be slow wave sleep. This occurs in deep sleep, stage 3 and 4, when the body is very relaxed and delta waves appear in EEG records. It seems that SWS restores bodily functions as growth hormone is produced, allowing protein synthesis and cell growth including production of antibodies in the immune system. this explains why lack of SWS is associated with reduced immune function. Stickgold suggests that SWS is also important for consolidation of semantic memory (understanding meaning) and episodic memory (events). The non-REM stages of sleep seem to prime the brain for good learning the net day. If you haven’t slept your ability to learn new things could drop by up to 40% (walker et al). Lack of sleep affects the hippocampus which is involved in making new memories.
Discuss evidence for the restorative role of NREM
1) Growth hormone (which is needed for repair of tissues as well as for growth) is released in stage 4 sleep.
2) Adults deprived of stage 4 suffer fibrositis symptoms (back ache), as muscle fibres in the back do not repair themselves.
3) Walker et al found that adults older than 60 have a 70% loss of deep sleep compared to young adults ages 18-25. Older adults had a harder time remembering things the next day, and memory impairment was linked to reductions in deep (slow wave) sleep.
Horne calls stage 4 and REM “core sleep” and claims that these are essential for normal brain function, and without them cognitive activities will suffer. He claims that the other stages of Non-REM are not essential, and lack of them is not damaging. Some evidence for this view is that., after a period of sleep deprivation we catch up by having more REM (called “REM rebound”) and more SWS when able to sleep uninterrupted, but there is no increase in the other stages of sleep.
Evaluate the restoration theory: part one
Restoration theory predicts that slep deprivation would have serious consequences because necessary repair and restoration would not happen without it. This is supported by findings from sleep deprivation studies e.g the case study of Peter Tripp, who stayed awake for 201 hours and suffered fairly severe short term effects, such as low body temperature, paranoia, hallucinations and abusive behaviour. In animals it is possible to ensure even longer periods of sleep deprivation; Rechtscaffen - found that rats prevented from sleeping died after 33 days. It is questionable however whether such animal studies can tell us much about human sleep behaviour and some researchers have suggested that birds have much more similar sleep patterns to humans than rats do. In fact total sleep deprivation studies on pigeons have found no ill effects after several weeks (Rattenborg 2005). Indeed many studies suggest no serious problems as a result of sleep deprivation; e.g. Horne - reviewed 50 studies of sleep deprivation and found very few of them showed serious effects. This suggests that there may be ways to restore brain and body without sleep, and so casts doubt on the Restoration Theory of Sleep.
Evaluate the restoration theory: part two
Restoration theory also predicts that people would sleep more after exertion/. The evidence here is mixed. Shapiro - found that Super-Marathon runners slept on average 1 and a half hours longer on the next 2 nights sleep after a 57 mile road race, and that there was a greater proportion of SWS (45% compared to the normal 25%). However several studies suggest that intense exercise may cause us to fall asleep more quickly, but not to sleep for longer. Also, Ryeback and Lewis’ asked healthy volunteers to spend 6 weeks in bed; they found that sleep time was similar to normal. This goes against Restoration Theory as spending all your time in bed should mean that need for restoration and repair is reduced leading to less sleep.
There is increasing evidence that cancer (particularly breast cancer), heart disease, diabetes, obesity and infectins are all linked to reduced sleep. Studies at the University of Surrey have shown that people can become pre-diabetic even after a few weeks of shift work. This supports the restoration theory as it suggests these disorders arise when the body is prevented from maintaining optimum health due to sleep disturbance.
What are the problems with restoration theories?
Amino acids needed for protein synthesis may only be available for about 5 hours after a meal (Horne). Since most people east several hours before going to sleep, for most of the night protein synthesis would not be possible. This therefore casts doubt on the suggested mechanisms of restoration during a night’s sleep.
What are the real life applications with the restoration theory?
Restoration theory has important applications for a culture where entertainment, employment and communication is increasingly available on a 24 hours basis. Consequent lack of sleep could have a negative impact on our health and immune systems, making us more vulnerable to illness and infection. Similarly, insufficient sleep could affect ability to retain and recall information, which clearly has important implications for those taking exams. If psychologists can promote greater awareness of the importance of sleep this could help tackle many of the health issues currently facing society, particularly the rapid increases in obesity and diabetes.
