Detection of Artefacts in Sleep Studies Data - Literature review Example

?Introduction Dement (1999, p34) defines sleep as a “condition of unconsciousness from which a person can be aroused into consciousness”. During sleep, the brain is less responsive to external stimuli, but very receptive to internal stimulus (Dement, 1999). Many people confuse other neurological states with sleep. One of these states is coma, but unlike sleep, a person who is in coma cannot be aroused. Numerous research studies have been carried out for long periods to investigate sleep and its importance to the human body. The studies have yielded different findings and this implies that scientists are yet to comprehend the phenomenon fully. However, empirical studies have established that sleep is important for enhancing normal and healthy performance of physical and mental aspects of the human body. In addition to these findings, sleeping process has been exclusively studied to establish the various stages involved and the brains level of activity during the process. This paper investigates the various stages of sleep and the role of sleep to human beings. Recent scientific studies have discredited the common misconception that regarded sleep as a dormant mental state. Scientists have established that the brain maintains a high level of activity during sleep. In addition, sleep influences the physical and mental functioning of our bodies in various ways that continue to attract numerous studies in order to enhance our understanding about the phenomenon (Baddely, 2000). Nerve-triggering chemicals called neurotransmitters determine whether we are awake or sleep by stimulating various groups of nerve cells and neurons in the brain. In the brainstem that links the brain with the spinal cord, neurons produce various neurotransmitters such as norepinephrine and serotonin that ensures that some parts of the brain remain active while in a wakeful state. When we begin falling asleep, neurons at the base of the brain start signalling and they suppress the neurotransmitters that keep us awake (Espana and Scammel, 2011). According to Espana and Scammel (2011), the state of wakefulness is enhanced by neurons present in the midbrain, pons, and in the posterior hypothalamus that produce various types of neurotransmitters, including histamine, serotonin, dopamine, acetylcholine, orexin and norepinephrine. The neurotransmitters that determine wakefulness and sleep diffuse actively in the brain, activating the targeted regions of in the cortex and forebrain. The reciprocal inhibition that occurs between sleep and wake controlling regions in the brain helps in the production of sleep and wakefulness with quick transitions between the states (Espana and Scammel, 2011, p 847). Scientists use three basic measures to classify sleep into different stages. The three measures include the gross brain activity, muscle tone and the eye movement (Carlson, 2001). Electroencephalograph (EEG) machine detects gross brain wave activity from which it produces summary of electrical action from the brain. The muscle tone is measured using an electromyogram (EMG) machine while eye movements during sleep are recorded using electro- oculogram (EOG). According to Harvey and Bruce (2006), electroencephalograph (EEG) is the most widely applied measure of distinguishing the different sleep stages while electromyogram (EMG) and electro-encephalograph are crucial in differentiating rapid eye movement (REM) sleep from the other types. Two different states alternate in cycles when a person is asleep and they portray the varying levels of neural activity in the brain. The states that constitute sleep are non-rapid eye movement (NREM) and rapid eye movement (REM) (Zhang, 2004). According to Zhang (2004), each of these states is associated with a unique and different form of brain wave activity. Non -rapid eye movement (NREM) is subdivided into four different stages that include stage 1, 2, 3 and 4. Therefore, typical sleep is made up of five stages, where NREM constitute 75% and the rest is REM (Carlson, 2001). The stages of REM sleep and NREM rotate and recur during sleep where stages 1, 2, 3 and 4 are succeeded by REM sleep to make a complete sleep cycle. A complete sleep cycle takes about one and half hours (Carlson, 2001). Stage 1 non REM sleep occurs immediately after falling asleep. The sleep is light and Myers (1999) argues that the stage is a transition between sleep and wakefulness. During stage 1, muscles begin relaxing while breathing becomes slow and even. In addition, the heartbeat becomes regular accompanied by a drop in the blood pressure. Other physical changes occurring during this stage include little or no body movements, reduced flow of blood into the brain and reduction of temperatures in the brain. Stage one account to about ten minutes of the total sleeping time and it is easy to arouse a person sleeping at this stage. Moreover, the brainwaves are small, slow and irregular with low voltage and fast EEG (Patrick, Nunn, and Barton, R 2006, p175). According to Huang, et al (2011), a person sleeping in the first stage experiences drifting thoughts and dreams accompanied by floating feeling. The feelings range from fantasy to real life experiences. Stage 2 non-REM sleep happens on the entire sleeping period and it accounts to about 40-50% of the sleeping time (Huang, et al (2011). Just like the stage 1, the brain waves continue to slowdown but sometimes, rapid burst of waves occurs. During this stage, the eye movements cease. Both the first and the second stage of sleep are associated with theta waves that are slower in frequency than alpha waves. Theta waves continue to the second stage where they are accompanied by sleep spindles and K complexes. Both the sleep spindles and K complexes are characterised by sudden increase in the frequency and the amplitude of theta waves (Patrick, Nunn, and Barton, 2006, p182). The onset of stage 3 is demonstrated by the appearance of delta waves that have longer amplitudes than the theta waves. According to Pagel and Perumal (2007), delta waves are the slowest and have the highest amplitude among the brain waves. Both the third and fourth stages are very similar to each other and are mainly distinguished by the proportion of the delta waves. According to Harvey and Bruce(2006, p63), the third stage comprises of other faster and smaller waves besides the delta but in the fourth stage, delta waves are more dominant, accounting to over 50% of the waves recorded. Deep sleep occurs in both the third and the fourth stages. All muscle movements stops and it is very difficult to rouse someone in both of these stages from sleep. When people in both of these stages are awoken, they are normally sleepy, disoriented and take some time to adjust to the immediate environment (Espana, and Scammel, 2011). In spite of the deep sleep, sleepwalking and sleep talking mainly occur during these stages (Carlson 2001). REM sleep is the final stage of sleeping cycle and it accounts to about 25% of the total sleeping time (Dement, 1999). REM sleep succeeds non-REM and unlike the latter, it is characterised by rapid eye movements. In spite of the darting eye movements, there is little muscular activity and skeletal muscles are in the state of paralysis. In addition, the heart and breathing rate increases while the blood pressure rises (Espana and Scammel, 2011). According to Harvey and Bruce (2006), the brain metabolism increases dramatically by as much as 20% resulting to a heightened brain activity. REM sleep has unique brain waves that are identical to waking sleep and it comprises of beta, alpha, and desynchronous waves. Psychologists associate REM sleep with dreaming. Experimental observations have shown that when a sleeping person shows characteristics of REM sleep and is aroused, the individual reports to having had a vivid dream. Moreover, the person is able to recall the dream with high degree of accuracy and clarity absent from other stages of sleep (Carlson, 2001) Therefore, in a typical sleep at night, people begin in stage one and move through other stages consecutively up to stage 4. The cycle repeats itself but in the second phase, REM sleep replaces the first stage and the person undergoes the same stages again. The entire cycle from stage 1 to REM takes about one and half hours and the cycle repeat itself throughout the sleeping period. As the sleep progresses, Zhang, (2004, p50) notes that the duration utilized by REM sleep increases and that of delta sleep reduces until the last cycles where there is absolutely no delta sleep. Research on the importance of sleep to human beings is continuing and experiments on animals have demonstrated that sleep is crucial for survival. Empirical studies have shown that depriving sleep to rats reduces their life expectancy dramatically and it lowers their immunity (Huang, et al 2011). These findings indicate that sleep plays an important role in promoting the immune system and enhancing life expectancy of human beings. Sleep is necessary for optimum mental and physical performance in human beings. Lack of enough sleep reduces the ability to concentrate on particular tasks and impairs the functioning of the memory (Harvey, and Bruce 2006). According to Zhang, (2004, p48), sleep is essential in processing the data stored in the temporary memory, encoding and transmitting the information to long-term memory. Lack of sleep interferes with the performance of the nervous system causing drowsiness and slowed psychomotor coordination. According to Harvey and Bruce (2006), sleep deprivation is one of the major causes of accidents in roads and in workplaces. If sleep deprivation persists, people become moody and could suffer from hallucinations. In addition, insufficient sleep leads to high prevalence of chronic disease such as depression, diabetes, obesity and cardiovascular ailments. Lack of sleep accelerates their onset and it interferes with the management of these diseases (Harvey, and Bruce 2006). In this respect, promoting sufficient sleep is important for prevention of chronic diseases and health improvement. Deep sleep is associated with production of growth hormones especially in infants and young adults (Patrick, Nunn, and Barton, 2006). Most somatic cells are produced during sleep and there is low rate of protein metabolism. Proteins are essential structural compounds necessary for cellular growth and repair of damaged tissues and their reduced breakdown during sleep provides favourable environment for the cellular growth. This explains why young children spend longer time sleeping than elderly persons. During deep sleep, the brain section that controls emotions, decision making and social interactions records drastic reduction in its activity (Pagel and Perumal 2007). Therefore, deep sleep helps in the maintenance of optimum physical, social and emotional performance while awake. REM sleep plays an important role in brain development especially in young children. REM sleep stimulates the cerebral cortex that helps the brain develop learning ability (Patrick, Nunn, and Barton, 2006). All functions of sleep in human beings are not yet established and this undermines the exact determination of the exact hours that a person should sleep. According to Carlson (2001), the amount of sleep that a person needs mainly depends on age, state of health, sleeping habits and diet. Infants require an average of about 16 hours while toddlers and young children below ten years require an average of about 10 hours. As people grow older, the duration required to get enough sleep reduces. However, pregnant women require more sleeping hours than adults who require an average of seven hours (Carlson, 2001 p 29). Different neurotransmitters affect sleep and wakefulness in the brain. However, some substances affect the concentration and the equilibrium of these chemicals in the brain causing sleep impairments. Caffeine, nicotine, and diet pills are some substances that cause difficulties in sleeping. In addition, pharmacological studies have established that some anti depressive drugs repress REM sleep. Other drugs that suppress sleep include alcohol that deprives people REM and stages of deep and restoring sleep (Huang, et al 2011). Because of the critical role that sleep plays in human memory, sleep deprivation causes significant physical, and psychological disruptions depending on the duration that sleep is lost. Empirical evidence shows that sleep deprivation ultimately results into sleep rebound to enable recovery of memory lost during the period of sleep deficiency (Patrick, Nunn, and Barton, 2006). It is apparent that sleep is important for maintaining and improving health in people of all ages. In view of the adverse effect caused by sleep deprivation, it is important to create favourable physical and emotional environment to get sufficient sleep. There are various methods of promoting good sleeping habits to avoid adverse consequences of sleep deprivation. These methods include maintaining a regular habit of going to sleep at particular time and waking at specific time in the morning. The sleeping environment should be kept clean, well ventilated, dark, quiet, and with favourable temperature that is neither too cold nor hot to provide a relaxing conditions. Activities such as listening to music, reading, watching television should not be carried out in the bedroom. Therefore, electronics such as computers and television sets should not be used in the bedroom while sleeping. Moreover, maintaining good eating habits by avoiding overeating, drinking coffee and other sleep repressive substances is important to have a pleasant sleep (Pagel and Perumal 2007). Conclusion Sleep consists of five stages that are distinguishable from each other by the sleep intensity, eye movements and the type brain waves recorded during sleep. Neurotransmitters play a great role in determination of sleep and wakefulness. Certain chemical substances present in drugs, food and drinks cause disruptions in the performance of neurotransmitters leading to sleep disruptions in various stages. Sleep plays an important role in enhancing life expectancy of human and providing favourable environment for growth and development during infancy and childhood. In addition, it promotes learning and enhances optimum physical and mental performance in human beings. References Baddely, A. (2000). The episodic buffer: a new component of working memory. Trends in Cognitive Sciences. 4(11), pp 413-426 Carlson, N. (2001). Sleep and biological rhythms. In: Physiology of behaviour. 7th ed. Boston: Allyn and Bacon Publishers. Dement, W.(1999). The promise of sleep. London: Delacorte Press. Espana, R., and Scammel, T. (2011). Sleep neurobiology from a clinical perspective. Sleep.34(7), pp 840-859. Harvey, R., and Bruce, M. Eds.(2006). Sleep disorders and sleep deprivation: an unmet public health problem. Washington, DC. 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