Essay \"Sleep and the Importance Of It.\" - Grade A PDF

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Sleep and the importance of it....

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Critically evaluate the competing theories for why we sleep? Sleep is a process that is extremely natural like eating. All vertebrates probably sleep including birds, fishes and reptiles and sleeplike states have been observed in all invertebrates like flies and bees (Cirelli & Toroni, 2008). Sleep is often defined as as a natural and reversible state of reduced responsiveness to external stimuli and relative inactivity, accompanied by a loss of consciousness. Sleep occurs in regular intervals and is homeostatically regulated, i.e., a loss or delay of sleep results in subsequently prolonged sleep (Borbély & Achermann, 1999). Researchers have found that sleep deprivation causes impairment in daily routine functions and cognitive problems (Brown, 2012; Killgore, 2010; Vanderkerckhore & Cluydts, 2010). There are two core stages in mammalian sleep. These are the Slow Wave Sleep (SWS) or Non Rapid Eye Movement (NREM) and Rapid Eye Movement or REM sleep and these stages keep alternating throughout the night. Even though sleep has been studied for many years, the function of sleep is still not clear and there is no consensus among researchers. This essay critically evaluates the different theories of why we sleep. It include the restorative or recuperative, evolutionary and information processing theories of sleep. Some researchers believed that sleep was a state required for enhanced tissue growth and repair (Sherington, 1946). The main purpose of sleep according to the restoration theory is to recharge and repair the brain and the body by reinstating energy resources, growth and repair of tissue cells and muscles and restocking neurochemicals (Benington and Heller, 1995). It involves establishing homeostasis in the body after periods of wakefulness (Gennaro et al, 2002). It has been concluded that certain body and cerebral deficits occur due to wakefulness and sleep permits bodily processes to be repaired or restored which would allow normal daily functioning (Oswald, 1974; Hartmann, 1974; Adam, 1977). In 1974, Oswald claimed that NREM sleep restores the body whereas REM sleep refurbishes the brain through protein synthesis. However Horne suggested that there were two kinds of sleep needed by organisms that is core sleep and optional sleep. He suggested that stage 4 of NREM and REM comprised core sleep and this was critical as it was essential for brain development. He

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explained that only core sleep was critical for brain restoration and that body restoration would occur simply through restful wakefulness (Horne, 1989). Evidence for the restoration theory comes from a variety of sources. It has been discovered that Growth Hormone which is essential for protein synthesis is released during sleep (Dattilo, 2011; Adam, 1983; Rudman, 1981). The amount of anabolic hormones such as prolactic, testosterone, luteinizing hormones are highest during sleep (Juneja et al, 1991; Touitou et al 1990) while catabolic hormones like corticosteroids are generally low during sleep (Lindhom, 1990; Weitzman, 1974). It has also been observed that there is high brain activity during REM sleep suggesting that a brain recovery process and restitution of neurochemicals is taking place (Boly et al, 2012; Babloyantz, 1986). Babies provide evidence for REM sleep and brain restoration. Babies do not have highly developed brains or strong synaptic connections and as a result they spend approximately two-thirds of their day asleep and eight hours in REM (Ornitz et al, 1970) suggesting that their brains have a lot of protein synthesis contributing to much needed cell and synaptic growth (Peirano et al, 2003; Chokroverty, 1994). It has also been found that cognitive development during the first year is incredibly rapid (Chokroverty, 1994). A major portion of evidence comes from sleep deprivation studies. Many studies conducted have demonstrated a clear link between physiology and sleep deprivation (Bruce, 2015; Morselli, 2011). It has been observed that slow wave sleep increases following sleep deprivation (Oswald, 1972). Rechtschaffen et al demonstrated that sleep deprivation in rats can cause a reduction in body temperature, deterioration of the immune system with white blood cells reducing to up 20% (Zager et al, 2007) and can eventually led to death. Increased mitosis in the lymphocytes has also been observed along with an increase in bone growth during sleep (Valk, 1974). Sleep deprivation in humans can have a similar effect (Bonnet, 2003). Peter Tripp who stayed awake for 201 hours towards the end showed symptoms of paranoia, hallucination, slurred speech and became extremely uncooperative with observers (Dement, 1976). Randy Gardner who went without sleep for 206 hours showed symptoms of blurred vision, memory problems and became mildly paranoid (Corren, 1998). Another finding is that wound healing is hindered by sleepdeprivation (Gumustekin et al, 2004). These studies that sleep is extremely important for the mental well being and proper functioning of individuals. Another striking finding is that, individuals who have experienced physiological assaults on their brains from severe 1

electroconvulsive therapy or excessive amounts of drug intake spend more time in REM sleep probably to produce brain proteins or neurotransmitters that have been damage and are imperative for repair. Some researchers have also exclaimed that extra activity causes an individual to sleep longer than usual in order to establish homeostasis in the body (Shapiro et al, 1981). Moreover, it has been found that slow wave sleep increases when the need for rest is high such as in hyperthyroidism (González et al, 2012; Dunleavy, 1974), during pregnancy or after strenuous physical activity (Griffin, 1978; Otto et al, 2015). On the other hand, when less energy is used such as in hypothyroidism, the amount of slow wave sleep is reduced (Hearson et al, 2015). Stern and Morgane in 1974 also demonstrated during sleep neurotransmitters such as acetylcholine, serotonin and noradrenalin are rebalanced (Stern & Morgane, 1974). Evidence for this comes from individuals who take anti-depressants as they contain these neurotransmitters and tend to spend more time in REM. These evidences suggest that sleep is imperative from brain and body restoration. However contrasting evidence exists as well. For example, the availability of amino acids is only about four hours after eating food hence protein synthesis could occur only for a short duration within the night’s sleep (Halson, 2014; Adam, 1980). Moreover, increased mitosis is also confirmed after a night without sleep which is positively influenced by oral glucose overload and negatively influenced by cortisol secretion (Everson and Crowley, 2004). It is important to note that when a person is sleep deprived, not all lost sleep is recovered (Oswald, 1974) and there is also a fluctuation in the level of neurochemicals suggesting that they are not simply being restocked during REM (Mehta, 2015; Huang et al, 2012). Increased activity should lead to longer sleep according to the restoration theory; however Horne and Minard concluded that participants that were exhausted from high activity fell asleep faster but not for a longer duration (Horne, 1989). Another issue with the restoration theory is that all research can be subject to researcher bias therefore the findings of experiments by Shapiro and Stern’s may be limited. Another important question is that if sleep’s major function is in fact restoration, then why haven’t there been consistent results from sleep deprivation. For example both Peter Tripp and Randy Gardner were sleep deprived however their effects were different where Tripp suffered more severe effects than Gardner (Durmer and Dinges, 2005). Therefore the reliability and validity of these 2

studies can be questioned. Another criticism is that these theories do not account for variations in sleep patterns unlike the evolutionary theories which explain these variations through adaptation to different environment places. Therefore to conclude, restoration theories can provide a minor explanation for the function of sleep. It has great face validity and the physiological variables can be measured easily however further research is needed to answer questions like if the brain is only restored in the few stages of sleep what is the purpose of the other stages? Hence the restoration theories cannot be a major explanation of why we sleep. The evolutionary or adaptive theories of why we sleep focuses on increasing the chances of survival and passing genes to offspring (Webb, 1974). Evolutionary theories explain that animals sleep in order to conserve energy (Webb), to protect themselves from predators (Cicchetti, 1976), spending time looking for food hence sleeping lesser (Lima & Rattenborg 2007; Stephens & Krebs, 1986) or simply because they have nothing else to do (Meddis, 1975). Warm blooded animals utilize enormous amounts of energy to preserve a constant body temperature as a result, the inactivity during sleep helps to conserve energy in the body (Siegel, 2009). Furthermore smaller animals with higher metabolic rates such as rodents require more energy and therefore sleep more. This is the energy conservation theory as proposed by Webb in 1974. While sleeping, the body experiences a drop of 1-2degrees in temperature and this drop can reduce energy consumption up to 10% in humans and even more in endotherms (Heller & Edgar, 2010; Hammel & Pierce, 1968). Such a reduction is cost-effective (Walker and Berger, 1980) and sleep helps in preserving energy since little is being gained from being awake and active (Obal, 1984). The body conserves energy during sleep in two ways-By lowering body temperature and through inactivity in the brain. Sleep also enables animals to balance speciesspecific energy budget to keep it at affordable levels. A definite negative correlation between metabolic rates and amount of sleep have been found in a number of studies (Petit et al, 2014; Rechstaffen, 1974). In order to protect themselves and survive, animals sleep. The stillness during sleep attracts less predator attention and therefore increases chances of survival. Moreover, in the nighttime most animals are unable to perceive their environment as their sensory receptors such as the eyes may not function to optimum level making them vulnerable.

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To avoid this danger animals sleep at night. Studies have also concluded that animals that are likely to be captured sleep lesser to watch out for themselves. (Allison and Ciccheti, 1976). Evidence for the evolutionary theories of why we sleep mainly come from sleep deprivation studies. Rechstaffen et al in 1989 found that rats die if they are sleep-deprived (Rechtschaffen et al 1989). A meta- analysis of sleep deprivation studies concluded that humans who are sleepdeprived have a difficulty in coping with environmental demands (Huber Weidman, 1976). Similarly, a patient with brain damage who was unable to sleep had difficulty in functioning and eventually died (Lugaressi et al 1982). Likewise, a person can develop fatal familial insomnia which comprises of normal sleep patterns till middle age and then no sleep. A person usually dies within 2 years after contracting this disorder (Schenkein & Montagna, 2006). Therefore sleepdeprivation can be fatal and interfere with normal daily functioning of an individual. Partial sleep-deprivation leads to cold, flu, depression, diabetes, obesity, strokes and also Coronary Heart Diseases (Knutson & Cauter, 2008; Dettoni et al, 2012). It has also been found that animals with a low energy diet sleep lesser than animals with a high metabolic rate. For example cows sleep for 3 hours but squirrels and shrews sleep longer (Siegel, 2005). Predator and prey sleep patterns have also been observed-Lions and tigers tend to sleep more than cattle (Campbell & Tobler, 1984) as well as variations in sleeping patterns such as nocturnal and diurnal patterns to keep animals safe from predators has also been observed (Acerbi & Nunn, 2011). A fairly recent study also found that animals that slept in dangerous locations tended to sleep lesser and there was a positive correlation between tropic positions and overall sleep, that is, carnivores slept more than herbivores (Lesku et al, 2006). However a lot of contrasting evidence has been found. For example, the correlation between body size and sleep is not perfect, negative correlations between small animals and higher metabolic rates which contradict the energy conservation theory (Capellini et al 2008). Moreover the negative correlations found are merely co-relational and cannot explain a proper cause and effect relationship. Animals that are small in size but have a safer place to sleep, sleep for longer durations (Lesku et al, 2006). Additionally, animals that consume food with high calorific density spend more time sleeping as they do not have to spend more time looking for food (Everson & Wehr, 1993; Nedeltcheva, 2010). Studies have also found that only a small amount of energy is restocked during sleep. Glycogen restoration is increased only during early sleep with little 4

change during rest of the sleep (Moorcroft, 2013). Also while observing preys and predators, according to the energy conservation theory, preys should sleep longer however the opposite occurs. It is also important to note that sleep only provides slightly more energy conservation than behavioral inactivity. Energy gain of sleep can be equivalent to energy provided by a slice of bread (Horne, 2006). Evolutionary theories also fail to explain the need to be unconscious while sleeping and they don’t explain why animals show rebound sleep following sleep deprivation while rebound patterns are clearly observed in cats, dogs and humans (Pedrazzoli et al, 2008). The distinction between REM and NREM sleep is also not made clear in evolutionary theories. It should also be noted that even though the evolutionary theory aims at increasing chances of survival while sleeping, the state of unconsciousness would increase the risk and the chances of being attacked. Behavioural inactivity would provide the same protection as sleep in being not noticeable. Some species have also gone through extreme lengths to sleep. For example, the Indus dolphin sleeps unilaterally (Horne, 1988) while the wildebeest sleeps out in the open plains of Africa where it is completely exposed to predators (Green, 2011). This suggests that sleep isn’t simply about adaption but serves some complex function. Another issue with the evolutionary theories is that it lacks scientific validity. It has been presented Post-hoc and they lack empirical support. Therefore it is difficult to authenticate yet cannot be discarded as well hence they are neither valid nor falsifiable. It has also been argued that evolutionary theories are determinist and reductionist in nature. Determinist as they do not take free will into account. Moreover they are reductionist because the function of sleep is much more multifaceted and intricate rather than solely for protection purposes. Evolutionary theories also cannot explain exceptions. An advantage of the evolutionary theory is that it aims to provide a more generalized explanation for all species however there are many confounding variables involved making it very difficult and non-valid. Therefore the evolutionary approach can be regarded as one of those theories that lack depth and insight. The information consolidation theory provides a cognitive perspective to the function of sleep and this theory suggests that sleep enables people to process and strengthen the information that has been acquired during the day. This theory was first proposed by Müller and Pilzecker. It is 5

presumed that there are two types of consolidation processes-synaptic consolidation and systems consolidation (Dudai, 2004). Several researches and studies have confirmed the positive effect of sleep on memory (Barrett & Ekstrand, 1972; Benson, 1977). Evidence for the information consolidation theory was first provided by Ellenbogen and colleagues. They found that a 90-min and even a 60-min sleep period improved word recall and was likely to protect memory against future interference (Alger, Fishbein & Lau, 2012; Diekelmann, Biggel, Rasch & Born, 2012; Seth, Varghese & Truong, 2012). Compelling evidence has also been provided by studies in animals such as mice, cats and rats in tasks such as classic, aversive and classical conditioning (Block, Hennevi & Leconte, 1977; Smith & Wong, 1991). Enhanced REM sleep has been higher in rats living in enriched as opposed to impoverished environments (Deneberg, Desantis, Waite & Thoman, 1977; Tagney, 1973). Increasing REM pharmacologically by administration of carbachol into the pontine reticular formation and of corticotrophin-like intermediate lobe peptide (CLIP) as well as a REM sleep rebound after prior REM deprivation, all improved memory for a Y-maze discrimination task when applied after learning of the task (Wetzel, Wagner & Balschun, 2003). Whereas deprivation of REM sleep impaired memory construction on complex tasks like two-way shuttle box avoidance (Youngblood, Smagin, Elkings, Ryan & Harris, 1999). Stronger evidence for REM sleep involvement in humans was acquired from procedural memory tasks such as learning a new language or Morse code (Guerrien, 1994; Koninck, Christ, Hebert & Rinfret, 1990; Verschoor, Holdstock, 1984). However, evidence for REM sleep in memory processing in humans is incoherent. Most studies are unable to conclude any effects of REM sleep deprivation on memory with uncomplicated verbal materials (Bertini & Torre, 1973; Tilley, 1981). Only complicated materials like meaningless sentences proved that REM sleep deprivation impaired memory formation (Empson, 1970). REM sleep deprivation studies have been criticized as stress can be a major confounding variable on memory formation (Born & Gais, 2000). Another major criticism is that this theory does not account for why different species spend different amounts of time in REM. For example, ferrets spend 6 hours in REM by humans spend only 2 hours in REM per day (Rasch & Born, 2013). The other criticism is that, even when REM sleep is completely absent in

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humans, such as while consuming antidepressants, no obvious harm have been concluded (Rasch, Pommen, Diekelmann & Born, 2009; Vertes & Eastman, 2000). Therefore, the information consolidation theory is a good explanation of why we sleep however further research is required to understand REM-sleep associated biological and molecular mechanisms which are a mystery. Keeping in mind the various different conclusions from each theory, no affirmative conclusion as to why we sleep can be made. Each theory has its own advantages and disadvantages and different answers to the mystery of why we sleep. The restoration theory explains the physiological needs of sleep. The evolutionary theory highlights the different patterns of sleep and the information processing theory tells us how sleep enables us to improve our memory yet no theory is successfully able to establish the desire to sleep even after sleep deprivation in species. Therefore further research should be conducted with advancing technology and increasing literature, variables can be measured more efficiently; the methods of research can be more unbiased. Moreover no study documents that sleep cures anything and therefore concrete evidence is needed (Rechtschaffen, 1979). The function of sleep is still an unsolved mystery of science.

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References 1. Acerbi, Alberto, and Charles L. Nunn. 'Predation And The Phasing Of Sleep: An Evolutionary Individual-Based Model'. Animal Behaviour 81.4 (2011): 801-811. Web. 2. Adam K (1980) Sleep as a restorative process and a theory to explain why. In: Adaptive capabilities of the nervous system (McConnel PS,Boer GJ, Romijn HJ, Van de Poll NE, Corner MA, eds), pp 289–305. Amsterdam: Elsevier 3. Alger SE, Lau H, Fishbein W. Slow wave sleep during a daytime nap is necessary for protection from subsequent interference and long-term retention. Neurobiol Learn Mem 98: 188–196, 2012. 4. Allison, T, and D. Cicchetti. 'Sleep In Mammals: Ecological And Constitutional Correlate...