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Biological Rhythms

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Biological Rhythms, Sleep and Dreaming a) Biological Rhythms A biological rhythm is a biologically driven behaviour that is periodically repeated. These rhythms are governed by both internal (endogenous) and external (exogenous factors). There are three types of biological rhythm. These are: Circadian, Infradian and Ultradian rhythms. Circadian Rhythm Circadian rhythms take place once every 24 hours. The Sleep-wake Cycle The best example of a circadian rhythm is the 24 hour sleep-wake cycle, associated with which are many cyclical changes with active and dormant periods, for example body temperature. Research has studied whether circadian rhythms are natural and triggered internally (endogenous) or whether they rely upon external cues in the environment (exogenous). Research has involved participants being deprived of possible zeitgebers (an external event that partially controls biological rhythms - literally means 'time-giver'), such as sunrise and sunset and temperature changes during a 24 period. Siffre (1972) was removed from the normal light-dark cycle, by being kept in a dark cave for 2 months. There were no zeitgebers such as natural light or sounds and he had no idea what time it was. He had food and drink and so on. His behaviour such as when he slept/woke and when he ate his meals was monitored. At first the findings showed there was no clear pattern in his sleep-waking cycle. However, later his sleep-waking cycle settled down to a regular pattern of about 25 hours i.e. longer the normal 24 hour cycle. This suggests that our internal biological clock must have a 25 to 30 hour cycle and that that our zeitgebers must reset the clock to our normal 24 hour day. This study is supported by and Wever (1979) who discussed studies on participants who spent several weeks or months in an underground bunker without any cues to light or dark. The findings showed that most of them displayed circadian rhythms of about 25 hours. However, this is not a universal finding. Folkard (1996) studied one individual who had a 30 hour cycle. ...read more.


Nevertheless, with this study it is difficult to separate the effects of sleep deprivation and the methods used to keep the animals asleep i.e. constant stress. However, there are inconsistencies in relation to the Restoration theory. We can argue that if sleep does have a restorative function we would expect that people who are more active would require more sleep. But we have seen the research evidence does not support this view i.e. Rosenzweig et al (1999). Furthermore, there is need for multi-perspective evidence that explains sleep as a psychological and physiological function. Also, the Restorative theory doesn't explain why there are so many differences in the way animals sleep. It may be that sleep serves an ecological function instead. Ecological theories Ecological theories take the view that sleep is an adaptive function. They presume that sleep occurs in all animals because it promotes survival and reproduction. Predator Avoidance Meddis (1975) proposed the predator avoidance theory which claims that the function of sleep is to keep animals inconspicuous and safe from predators at times of the day when there are most vulnerable. For most animals, this means sleeping during the hours of darkness. It follows that those species in danger from predators should sleep more of the time than those species that are predators. However, Allison and Cicchetti (1976) pointed out that in fact predators tend to sleep more than those preyed upon. This might seem inconsistent with ecological theories of sleep. However, species that are in danger from predators might benefit from remaining alert most of the time and sleeping relatively little. Interesting evidence which supports the claim that the pattern of sleep is often dictated by the environmental threats faced by animals was reported by Pillieri (1979). Dolphins living in the River Indus are in constant danger from debris floating down the river. As a consequence, these dolphins sleep for only a few seconds at a time to protect themselves from debris. ...read more.


Research Evidence Webb and Cartwright (1972) described a study which provides support for their theory, in which participants were given problems to solve and then allowed to go to sleep. Some were then woken when they entered REM sleep. They found those that had been allowed to sleep uninterrupted were able to provide more realistic solutions to the problems the next day, suggesting that there REM sleep had given them the opportunity to work through their problems. In another study Cartwright (1984) interviewed women who were undergoing divorce and were either depressed or not depressed. He then compared them with a non-depressed married group who has never considered divorce. All participants were studied over a 6 nights in a sleep laboratory. The non-depressed divorcing women reported having longer dreams which dealt with marital status issues. This apparently helped the individuals cope better. Such issues were absent from the dreams of the depressed groups. Presumably the depression was associated with an inability to deal with problems The above findings are supported by Hartmann (1973 who found that people who were experiencing various kinds of problems had more REM sleep than the less troubles individuals. Evaluation The problem solving theory seems to be a reasonable account of dreaming and is supported by some research studies. However, this approach doesn't explain why people and animals have dreams not related to the solution of problems. Also, the problem solving theory implies that it would be useful to remember our dreams. But, it seems puzzling that we forget about 95% of our dreams. There is also the question of why sleep is necessary because we can also solve problems by engaging in another task for a while, as indicated by the saying 'a change is as good as rest'. The most reasonable conclusion is that the problem solving theory helps to explain some dreams, but does not provide a comprehensive account of all dreams. Finally, this approach is uninformative about the physiological processes involved in dreaming. ...read more.

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