How and why do we sleep, why do we dream?
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Sarah Messenger (0801595) SJPS5004 How and why do we sleep, why do we dream? Considering the functions of sleep and dreams, it has been suggested that humans spend approximately one third of their lives asleep (cited in Goldsmith, 2005). However, there still remains no clear agreement on what the function of sleep is. This essay focuses on exploring how humans sleep, and possible explanations for why we sleep and why we dream. It is believed that sleep follows a circadian rhythm, effecting sleep onset and stages (cited in Sanei & Chambers, 2007). The human biological circadian rhythm is roughly a 24 hour cycle, which is controlled by a circadian pacemaker. This "pacemaker" is the section of the brain known as the suprachiasmatic nucleus (SCN), which is situated in the hypothalamus (cited in Stickgold & Walker, 2009). Signals produced by the SCN travel to different regions of the brain which controls the sleep-wake cycle within humans (cited in Kramer et al, 2001). The SCN regulates other functions associated with the sleep cycle such as body temperature, hormone secretion, urine production, and changes in blood pressure, which are all known to decrease during the sleep process. The SCN controls and is entrained to the sleep-wake cycle which is dependent on the cycle of light and dark, and on body temperature. A change in these could shift or disrupt the cycle. One internal factor affecting the circadian rhythm is melatonin (cited in Bermudez, Forbes & Indiji, 1983). The SCN regulates the pineal gland's secretion of melatonin, which has a day/night function. Melatonin is a hormone that helps to regulate sleep. The release of melatonin is dependent on the availability of light on the ganglion cells which contain the photopigment melanopsin. The ganglion cells receive light information through receptors known as rods and cones. This information travels along the retinohypothalamic pathway, where the SCN receives and interprets the environmental light, which determines the release of melatonin (cited in Hannibal & Fahrenkrug, 2002).
Meddis offers this explanation on the grounds that humans would have been more likely to fall or hurt themselves, or be at increased risk of danger. The protection theory suggests that that it is an evolutionary advantage to sleep during the night as it keeps humans protected from harm and danger. Meddis proposes a genetic explanation as part of an evolutionary approach, suggesting that those who slept during the night were more likely to have survived to maturity and passed on their genes, ensuring that as an activity, sleep would have been retained in our behavioural response. The protection theory is however open to criticism. It is suggested that if the protection theory is to be accepted then it would be expected that those who are exposed to more risk of danger and predation would sleep more (cited in Moorcroft & Belcher, 2005). However this is does not appear to be the situation in some cases. Research indicates that species such as herbivores, who are at most risk sleep less, whereas big cats such as lions who are at little risk of danger, tend to sleep for longer periods of time (cited in Moorcroft, 1993). As a result of these findings, Meddis concluded that food intake has an influence on the amount of time an individual spends asleep, suggesting that those who spend more time eating have less time to sleep and vice versa . Although the protection theory suggests that sleep serves an important adaptive function, it is not clear why such a complex physiological mechanism as sleep would evolve simply to keep vulnerable individuals safe. It is suggested therefore that a state of behavioural inactivity, would serve much the same purpose (cited in Schedlowski & Tewes, 1999). In addition, the adaption hypothesis, put forward by Webb 1974 can also be criticised for its suggestion that sleep is a function of energy conservation.
The transformation of hidden desires and anxieties into the manifest symbolism of the dream is called 'dream work'. Several mechanisms may be involved, including condensation (refers to the way in which a particular dream symbol acts as a focus for several hidden thoughts), displacement (occurs particularly with emotional reaction which may be disproportionate to the event itself) and representability (involved in the visual representation of underlying thoughts within dreams. In order to interpret the latent content of dreams, Freud developed a vocabulary of dream symbols, drawing on cultural symbols found in mythologies, stories and jokes, as examples. He suggested, for instance, that dreams of flying represented sexual intercourse. Freud emphasised also that dream imagery tends to contain representations of the day's events, which can be used to disguise the latent content. He did accept however that dream imagery could be accepted at face value, where certain imagery did not have underlying meaning. Freud's theory has been criticised however, as it relies on the subjective reports of the dreamer which may be inaccurate (cited in Mattoon, 1984). However, as dreams are personal and inaccessible, it is impossible to carry out such interpretation in any different manner. One general criticism of dream research is that many studies are carried out using participants who are deprived of REM sleep. As a result, it is suggested that the content of dreams within these studies may not be valid, and the imagery and content may be influenced by the deprivation of such stages of sleep (cited in Schwartz, 1978). Although there are many different views with regards to the function of sleep and dreams, many theories have offered sound explanations of the processes. However, there is still no clear-cut, widely accepted explanation as to why humans sleep and dream. As a result, more intense and extensive research into these areas may assist in offering more conclusive theories that may offer more concise explanations as to the functions of sleep and dreams.
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