Theories of sleep WJEC PY4

One theory of the function of sleep is the energy conservation theory (Webb). Warm – blooded animals, such as humans use up a lot of energy to maintain a constant body temperature. This is especially difficult for small animals with a high metabolic rate. All activities use energy and animals with a high metabolic rate use even more energy when scavenging and hiding or escaping from predators. Sleep, however, provides a period of enforced inactivity (therefore using less energy), much like hibernation. This means that it is a way of conserving energy and may provide explanation towards the function of sleep.

This has a certain amount of face validity if we compare sleep patterns in different species. It has been noted that the percentage of sleep varies according to the size of a species. The amount of sleep is further affected by two other external factors: food requirements and predator avoidance.

For example, cows and horses (grazing animals) have to spend a lot of their time eating because the food that they eat, such as grass and plants, is low in nutrients and so they need to eat a lot of the time and therefore have less time to sleep. However, carnivores such as cats and dogs eat a more balanced and healthy diet and so do not need to spend all of their time eating. This means that they can have afford to have more sleep and can therefore conserve more energy. 

Sleep is also affected by the status of predator or prey. If an animal is a predator, then it can spend more time sleeping because they don’t need to worry about being hunted. Animals that are preyed on spend more time being vigilant to avoid predators. In an ideal situation, these animals would not sleep at all because it is dangerous, but realistically, they must sleep when they are in the least amount of threat. Meddis (1975) even suggested that sleep helps prey animals to avoid the predators when they are most vulnerable. This can suggest why some animals are nocturnal and choose to sleep during the day and hunt at night-time and may be used to explain the function of sleep.

However, when considering energy conservation, we should acknowledge that there is a distinct difference between REM and NREM sleep. The brain uses up a lot of energy and the amount of energy it uses up only drops significantly in NREM sleep, as REM brain waves remain very similar to those of a fully active and functional brain. This means that the theory cannot be used to fully explain the function of sleep and may only explain why we have NREM sleep.  This view was supported by Allison and Cicchettie (1976) who found that larger animals had less NREM sleep, because they don’t need to conserve as much energy as those with a high metabolic rate. This shows that it is NREM sleep that is important for energy conservation and can therefore partially contribute to the explanation of the function of sleep.

On the other hand, it has been found that sleep does not conserve a great deal more energy than when resting, sleep reduces energy rates by 5-10%. This suggests that rest would be just as adaptive as sleeping. Further criticism would suggest that it would be safer for prey animals to rest and not sleep, as it does not come with certain dangers that sleep has, such as loss of consciousness, which further endangers the animals. This means that the “energy conservation” explanation is not sufficient to explain the function of sleep. As well as this, the unilateral sleeping habits of marine mammals and some birds also indicate that the sleep function can be fulfilled while an animal is still partially awake. This suggests that conserving energy cannot be the key feature of sleep. It may be that inactivity serves another purpose such as lowering core body temperature and not energy conservation.

Oswald believed that the function of sleep was to re-group our resources after expending them all during the day. In particular, that REM sleep was important for brain growth and repairs whereas slow wave sleep (SWS) was important for bodily growth and repair. In order to support this theory, Oswald observed patients who were recovering from injuries to their central nervous system (CNS). He found that there was a significant increase in the amount of REM sleep and that this was suggestive of recovery processes going on in the brain. This supports the theory of restoration, implying that in a time where severe recovery is needed, the brain will allow more REM sleep to occur in order to speed up recovery. This has strong implications in the function of sleep.

However, this is a correlational study, which means that we cannot infer cause and effect. We don’t know if the increase in REM sleep was because the brain needed to recover or if it was simply just caused by the injury to the CNS. It may even be due to a third factor, which may have caused both the injury and the increased REM sleep. 

 The findings are also questionable because the participants were only those who had suffered from injury to their CNS, which means that we do not know if we can generalise it to perfectly healthy people who have not had an injury. It may just be that only people with injuries to their CNS use REM sleep as a means of recovery. Overall, this research can only, at best, make limited contributions to the explanation of the function of sleep, as we do not know if we can apply the findings to everyday life.

On the other hand, a study by Adam and Oswald (1983) found that tissue growth of new cells in the skin takes place more quickly when we are asleep. This is strong research to suggest that restoration does occur and seems to provide a more valuable contribution to explaining the function of sleep.

Oswald also suggests that sleep is important for conserving and replenishing biological substances such as neurotransmitters and hormones. For example, over the course of the day, our neurotransmitter levels fall. During REM sleep, some neurons synthesize new neurotransmitters for release during waking. This suggests that we sleep in order to replenish key brain chemicals in order for us to be able to function normally again once we are awake.

This is also true of hormones and SWS. SWS are related to the secretion of growth hormone, which stimulates protein synthesis to take place. This reaction is fundamental in the re-growth and repair of body tissues because proteins are fragile and must be continuously renewed. This continuous restoration of essential proteins is part of the body’s natural healing process. For growth hormone to be secreted, uninterrupted SWS are vital. This also suggests that sleep is imperative for the body to function properly, providing a valuable explanation for the function of sleep.

In order to test the theory that sleep is necessary for the restoration of the bodily processes, many studies of sleep deprivation were carried out, most of which split into two categories. Studies were either of totals sleeps deprivation or partial sleep deprivation.

One case study consisted of an American DJ named Peter Tripp who stayed awake in a 201 hour “wakeathon”. It was found that, 3 days into the experiment, Tripp became abusive. After 5 days, he claimed he began to hallucinate (for example, he kept seeing spiders in his shoes and mice and kittens in random places) and became extremely paranoid (he accused people of drugging his food and accused a technician of putting a “hot electrode” in his shoe). By the end of the study, his body temperature had dropped and his waking brain wave patterns were practically identical to sleeping brain waves. It was then reported that, after 24hours of sleep, he awoke and felt fine.

This shows that going without sleep, even for lengthy periods, does not result in long term damage according to self-report. There is also no indication that you need to recover anything like the amount of sleep lost.

However, friends and family of Tripp said that after the stunt, he was never quite the same again, which may cause us to be unsure about the extent of damage that the stunt may have produced. It may just be that Tripp was psychologically affected by the lack of sleep and not biologically damaged or that the friends and family were affected by certain demand characteristics, which caused them to expect that Tripp had suffered some serious damage as a result of the experiment.

However, in 1965, Tripp’s record was smashed by 17-year-old Randy Gardner, who managed to stay awake for 264 hours (11 days) for a supposed science fair project. Dr. Dement and some of Randy’s high school friends kept him awake and tracked his condition by administering a series of tests, keeping him active at night by going for drives, playing loud music and long games of basketball and pinball. Unlike the study with Tripp, the one thing they didn’t do was give him any drugs, not even caffeine. To make sure he wasn’t causing himself brain damage or otherwise injuring his health, his parents made him get regular checkups at the hospital. The doctors found nothing physically wrong with him, though he did intermittently appear confused and disoriented.

 However, there are many contrasting reports of Gardner’s condition during the experiment. According to some sources, as more days passed, Gardner suffered certain physiological symptoms of sleep deprivation e.g. speech began to slur, he had trouble focusing his eyes, he had trouble remembering what he said from one minute to the next, and some sources even state he, like Tripp, experienced hallucinations. Other sources state that he experienced no such symptoms and that he was physically and psychologically fine.

As of 2007, Gardner remains alive and well, having suffered no long-term ill effects from his experience, showing that sleep deprivation has no severe effects on the human body. This may suggest that sleep is not as vital for the body as was originally thought.

However, one limitation of these studies is that they are only studies of individuals. We do not know that the average human being would behave in the same way and so we cannot generalise this research to the rest of the population. The research is also limited because a lot of the findings contradict each other. Some say that Gardner experienced no psychological symptoms at all and that Tripp did. Others say that Gardner did in fact experience problems, such as hallucinations just like Tripp. This means that we cannot justifiably generalize the findings to all human behaviour.

Further evidence to criticise this research comes from Williams et al. (1959) who found that, after 72 hours of sleep deprivation, it was impossible to prevent short episodes of micro sleep while they are awake. EEG recordings show that micro sleep was the same as sleep in terms of brain waves. This explains why Tripp’s EEG readings showed the same brain wave patterns as a sleeping person, suggesting that he was in fact getting micro amounts of sleep that were undetectable. This may explain why there were no long-term effects for the body and may suggest that sleep is as important to restoration as Oswald originally thought.

One theory that explains what they believe as the functions of sleep is the restoration theory.  This theory believes that the main function of sleep is to save energy and to restore psychological functions. 

Oswald and Horne put forward this theory.  They believe that slow wave sleep is useful for the recovery of processes in the body.  In this type of sleep there is a release of growth hormone from the pituitary gland that stimulates protein synthesis that helps repair tissues in the body. 

They also believed that in REM sleep recovery processes also occur.Another theory is the evolutionary approach, this theory says that the main function of sleep is the need to survive i.e. we must sleep in order to survive.  The theory suggests that a species will only be successful in survival if it adopts an appropriate pattern of sleep that is compatible with where the live and how much they are predated upon.  Meddis believes that sleep evolved in order to carry out the function of survival by keeping animals inconspicuous and safe from predators.  A factor that the theory believes influences the main function is the metabolic rate that we have as they found that as smaller animals have a high metabolic rate they need more sleep to preserve some of the energy they use. 

These theories are both very different for example their research is different as the evolutionary approach is mainly based upon animals that they have then generalised to humans.  They mainly use the idea of animals as prey or predators as a means of explaining the theory.  This is a problem, as it is generally believed that humans are far more complex than animals even though we evolved from apes.  Also we do not have the same cycle as animals in terms of prey and predators.  This means that the generalisation is not always accepted.  The restoration theory however has more humans based research therefor is often seen as more reliable.

There has been evidence found that babies sleep for longer periods of time than adults do.  This however has been explained differently by both approaches.  The evolutionary approach believes this is to give the parents some time to rest but the restoration theory says this is because they need more REM sleep to restore the active brains that babies have during the enormous brain growth that they experience.