Psychology A2 - A Grade Essays - Biorhythms Part 2
Discuss the consequences of disruption to biological rhythms (24 marks)
One cause of disruption to biological rhythm is shift lag which is defined as scheduled work outside of the normal working hours of 7am to 7pm. Shift work can either be fixed (e.g. regular evening/night work) or rotating (e.g. a cycle of evening and night shifts). Endogenous pacemakers and exogenous zeitgebers (such as light, noise and temperature) ensure that the body is active during the day and inactive during the night, because shift work requires the worker to be awake when the body is not meant to shift workers often experience sleep problems which prevents them from having quality sleep. This could cause symptoms such as depression, immunosuppression and hypersomnia. It has been suggested that forward rotating shifts (phase delay) are the less harmful and easiest to cope with than backwards rotating shifts (phase advance) as it means there is more time to sleep between shifts.
The importance of shift direction was demonstrated in a study that looked into police officers working a backwards rotating shift who had reported significant sleep and work problems. It was found that when their shifts were altered so that they were clockwise rotating shifts accidents at work dropped by 40% and the officers reported more satisfaction in their personal life. This supports the idea that forwards rotating shifts are less harmful because it goes in the direction of your natural body clock and also leaves more time between shifts to sleep. However, despite these findings it has also been found that fixed shift work is better for you than rotating shift work. If a person works+ night shifts for a period of time then their body will eventually adjust to the altered patterns and symptoms of shift lag decrease.
As well as being worse for you than fixed shifts, research suggests that people working rotating shifts are particularly prone to cancer. A study that looked at over 14,000 male, Japanese shift workers found that those with rotating work shifts were four times more likely to develop prostate cancer. This study has good internal validity because it measures what it is supposed to and takes into account extraneous variables such as age, whether the individual smokes, type of work and stress levels – all things that could contribute to the development of cancer. However, because the study was conducted only on Japanese men it has both beta gender and culture bias. There are male specific things, such as hormones, that could influence the development of cancer. The culture and gender bias means that the results of the study cannot be generalised to women or other, non-Japanese, cultures which reduces the ecological validity of the study.
Jet lag is another cause of disruption to biological rhythms which occurs when normal circadian rhythms are disrupted by travelling across time zones. When we cross times zones there is a shift in zeitgebers which causes a conflict between external cues and endogenous circadian pacemakers. Generally flights going west to east (phase delay) are worse for you than flights going east to west (phase advance) because you lost hours in the day and thus have less time to sleep. People with jet lag show a wide range of symptoms such as fatigue, concentrating problems, memory difficulties and impaired cognition.
A study that supports the idea that jet lag is a cause of disruption to biological rhythms looked at the games of major league baseball teams. Teams on the east coast of the US had to travel to the west coast to play some games and the west coast teams had to travel to the east for others. It was found that the east coast teams won 44% more of the games than the west coast team, presumably because they were experiencing jet lag which reduced their performance levels. However, it could be argued that there are a number of extraneous variables that could have affected the team’s performance that hadn’t been taken into account by the study. For example, the low oxygen concentration and noise of other passengers on the plane, humidity, drinking caffeine or even just not being as good as the other team at baseball. This suggests that the internal validity of the study is reduced because it doesn’t measure specifically what it wanted to measure (i.e. how much jet lag actually disrupts biological rhythms) as there are too many extraneous variables that could affect the results.
Jet lag, much like shift lag, has been found to be associated with the development of cancer. One study used data collected from 1,500 female flight attendants and found that those who had been flying for over 5 years had double the risk of breast cancer. However, it has been argued that the women could have been more prone to breast cancer because of high altitudes, being exposed to cosmic radiation and flight dehydration and not necessarily because of the disruption to their biological sleep patterns.
Discuss the restoration theory of the function of sleep (24 marks)
Sleep is divided into two different stages – slow wave sleep (SWS) and rapid eye movement sleep (REM). The restoration theory suggests that these two stages both have different functions that are necessary for humans to live. According to the theory, the function of SWS is to release growth hormone, which is particularly important in childhood, and also to promote protein synthesis. Proteins need constant renewing, for example the proteins that are involved in the immune response. When SWS was reversed by 12 hours the release of growth hormone was also reversed which shows that the release of growth hormone is controlled by neural mechanisms related to SWS. The theory also suggests that the function of REM sleep is to provide a period of reduced neural activity so that neurones can regain their sensitivity to neurotransmitters in order to allow them to function properly. This has been demonstrated by the use of MAOI’s which have been found to abolish REM sleep, it has been suggested that this is because with more monoamines (e.g. serotonin) in the neurones the receptors don’t need to be revitalised and thus there is no function of REM sleep. Another function of REM sleep suggested by the restoration theory is the idea of brain growth. Species that are born immature (such as humans) have more REM sleep than species that are born fairly mature. This may be because there isn’t as much neural development needed in species that are born more mature and thus the need for REM sleep is decreased. The restoration also suggested that REM sleep may play a role in consolidating procedural memory whereas SWS may play a role in consolidating semantic memory. This would explain why children sleep more than adults, because they are constantly experiencing new things that then need to be consolidated during SWS and REM.
Research evidence supports the idea’s proposed by the restoration model, for example a study that looked at the effects of sleep deprivation in rats. The rats in the study were kept on a moving disk and not allowed to sleep and it was found that after 33 days all of the sleep deprived rats had died. However this study has been criticised, not only because it involved experimenting on (and ultimately killing) animals, which raises ethical concerns but also the fact that rats will have different sleep cycles to humans and thus any data collected from them cannot be generalised to humans. Also it has been argued that the rats may have died from the stress of being in an unusual environment and being kept awake rather than dying from the lack of sleep itself. This ultimately reduces the face validity of the study and means that the results cannot be generalised to humans.
There has also been research evidence that has supported the claims made by the restoration theory that protein synthesis occurs during SWS and also the idea that REM is necessary for neurone receptors to regain sensitivity. During exercise individuals use a lot of neurotransmitters and proteins and thus you would expect for them to sleep longer after periods of exercise. This has been found to be the case, for example one study found that after a marathon individuals slept around 1 hour more than they usually would for a couple of days after. This suggests that they needed more SWS and REM sleep in order for their body to produce proteins/regain neurone sensitivity so that they could function normally again. However, some studies have found that exercise only shortens the amount of time people take getting to sleep rather than increasing the amount of time actually sleeping. This therefore suggests that SWS/REM may not be important as the restoration theory suggests.
The restoration theory, and research into the theory, is deterministic as it suggests that sleep is necessary for a person to survive and to function normally, however it has been argued that this is not the case. For example, case studies have found that people can go prolonged lengths of times without sleep – for example one man didn’t sleep for 260 hours and reported no ill effects and displayed no psychological or physical symptoms of the sleep deprivation. However this is a case study which, despite giving rich data, can be bias to individual differences and thus any results found may just be due to the individual and their sleep needs. For example some people may be able to go without sleep without suffering from any consequences, whereas others may miss a couple of hours sleep and suffer from symptoms of sleep deprivation. As everyone’s sleep cycles are different you cannot generalise the results of one case study to the general population as it may have just been an anomaly. This ultimately decreases the ecological validity of the study and thus the restoration theory as an explanation of the function of sleep.