Functions of sleep Flashcards
Evolutionary explanation
The basic principle behind evolutionary explanations of behavior is that behaviors evolve and develop if they provide any advantages to the animal.
The evolutionary approach to sleep focuses on the ecological niche.
This refers to the lifestyle of animals.
This includes:
Their environment- aquatic or terrestrial. Animals sleeping patterns are often an adaptation to their environment.
Trophic level- preys are more vulnerable, especially when asleep
Diurnal or nocturnal
Sleep site- do they sleep in a safe place like a burrow or in a more exposed place
Size- large animals tend to sleep less than small ones
Hibernation theory Webb (1982)
evolutionary
Hibernation theory- Webb (1982) uses the comparison of hibernation to explain sleep. Some animals such as bears and squirrels hibernate over winter to conserve energy at times when hunting is impossible. Sleep is a time of relative inactivity when animals preserve energy resources, this is particularly important for small animals as they have a high metabolic rate.
Metabolic rate
The rate at which animals burn up resources. Animals with a high metabolic rate need more food, but also conserve more energy when they sleep.
Meddis (1975) predator-prey status
Evolutionary
Meddis (1975) proposed that animals have developed their sleeping patterns to protect them from harm. He believes that sleep keeps vulnerable prey animals safe at times when normal activities are impossible. Eg. Diurnal animals cannot hunt for food at night, hence they stay out of danger by sleeping.
His ‘waste of time’ theory suggests that animals sleep when they have nothing to do, as a way to stay still and out of the way fo predators.
Many disagree with this as sleep leaves an animal unreactive and vulnerable, so if safety was the sole reason then they would stay awake and alert instead.
Strength:
Siegal agrees with his ‘waste of time’ theory saying that being awake is more dangerous for preys as they are more likely to to get killed or injured.
Limitation:
Vulnerability- (Allison and Cicchetti)
reductionist- sleep is too complex and the theory ignores the physiological and psychological aspects of sleep. Doesn’t explain why theres different stages of sleep, or biological rhythms or the need to catch up with missed sleep.
Predation avoidance
Allison and Cicchett (1976)
(Research evidence weakness for Meddis, 1975)
This explanation suggests that the amount of time an animal sleeps for depends on its trophic position.
Allison and Cicchetti (1976) studied sleep in 39 animal species and found that prey animals sleep for significantly less time than predators. This contradicts Meddis’ ideas, and suggest that sleep is in fact a dangerous time for prey animals.
However, prey animals are often herbivores and research has shown that herbivores sleep for shorter lengths of times than carnivores (Lesku et al., 2006), so this might be a possible explanation for this.
Restoration theory
Oswald
The restoration approach suggests that sleep allows for the body to repair and replete cellular components necessary for biological functions that become depleted throughout an awake day.
Oswald presented one of the earliest restoration theories. He predicted that burning up more resources during the day should lead to longer sleeping hours. He later also found that people recovering from severe trauma to the brain, such as drug overdoses, spent more time in REM sleep. He also explained the rapid growth of new skin cells during sleep to be as a result of the increased release of the body’s growth hormone during deep NREM sleep.
He then proposed that REM sleep was for restoration of the brain, while NREM sleep was important for restoration of the body. For this reason, sleep deprivation would have an effect on brain functions and behavior.
Research evidence
Physical exercise and sleep
Strength: Shapiro et al. (1981) found that runners slept longer and spent more time in NREM after running a marathon, supporting Oswald.
Explains why newborn babies spend most hours of everyday asleep. It is because sleep is a time of massive brain growth and development that the baby’s body needs to go through.
Weakness: However, others, including Horne and Minard (1985) have found that tiring physical exercise leads to people going to sleep faster but not for longer than normal. This contradicts Oswald.
Horne and pettitt
Horne et al conducted a test to see if incentives would help participants (Pps) overcome the effects of sleep deprivation.
There were 3 groups:
Group 1- sleep deprived for 72 hours/ not given incentives
Group 2- sleep deprived for 72 hours/ given financial incentives to complete the task
Group 3- control group/ not deprived/ not given incentives
They were tested on tasks.
Findings:
After one night of deprivation Group 1 performed significantly worse than Group 2 and 3.
Even after two nights of sleep deprivation Group 2 still performed significantly better than Group 1.
Conclusions:
They concluded that incentives provided motivation and sleep deprivation mostly has an effect on motivation rather than cognitive abilities.
Limitations:
Methodological issues - sample was small (5 Pps in each)/ difficult to generalise
Some sleep Pps had occasional micro sleeps which could’ve acted as participants variables in some way.
Strength:
Ethical issue- sleep deprivation is stressful but the researchers followed appropriate ethical procedures and obtained full informed consent.
Memory consolidation
Another function of sleep is memory consolidation. This function suggests that when we learn a new skill at the start or middle of the day, at night we tend to forget that skill or knowledge, because of all the interfering tasks we did throughout the day. Therefore, learning in the evening and then going to sleep, avoids interfering tasks which means that knowledge will be retained better.
Research evidence:
Walker et al (2002) developed this approach and showed that motor learning improved if sleep followed training, but not if training was followed by similar period of wakefulness.
