Sleep is an essential part of a day in everyone’s life. Everyone’s sleep pattern depends on their daytime engagements. It may importantly vary between individuals since the sleep quality plays an important role in everyone’s life. As we grow older sleep patterns change along with physical changes, which accompany the normal aging process. In general sleep disturbances are major problem in elderly people not only clinical patients but also in the normal population. For the past decades, some of the research findings show that sleep patterns play a vital role in the daytime cognitive functioning. In addition to this previous research has shown a 1.6 – 2 times higher mortality rate in elderly people with poor sleep quality than people with normal sleep quality(Asplund, 1999). This indicates comparing to other ages; sleep plays a crucial role in the elderly and most of them showing some kind of sleep disturbances. This paper aims to focus on the relationship between sleep patterns and daytime cognitive functions in elderly. Initially, this paper will focus on the general aspects of sleep and sleep disturbances.
Sleep in General:
“Sleep can be defined as ‘A period of diminished responsiveness to external stimuli’”(Lee, 1997). A good quality of sleep leads to a good quality of life. It has been proving good quality of sleep plays major part in healthy lifestyle. In normal, we spend the daytime involved in a lot of physical and mental activity, which requires a lot of energy both physically and mentally. It is a commonly known that the brain needs more energy, and it is thought to be refreshed when we have good quality of sleep. Furthermore, Sleep is a basic neurobehavioral state which is connected to essential areas of health and cognitive functioning which includes learning, memory, attention, mood regulation, and metabolic, immune, endocrine, cardiovascular functions(Rao, Hammen, & Poland, 2009). This provides that sleep is one of the essential parts in of life.
Stages of Sleep:
Sleep can be divided in to two major categories Non-Rapid Eye Movement (NREM) and Rapid Eye Movement (REM) sleep based on the electrical activities in the brain. There are five stages in complete sleep cycle, stage 1- 4 is NREM stage and stage 5 is REM stage (Maher, 2004). In NREM the first and second stages can be regarded as “light sleep”, third and fourth are “deep sleep” and “Slow-wave sleep” (Ancoli-Israel, Ayalon, & Salzman, 2008) in this stages body regenerates and repairs the tissues, builds muscles and bones and make the immune system strong(“What is Non-REM sleep?,” 2009). In normal sleep pattern first cycle will last up to 60 minutes in the initial stages and in the final stage 120 minutes(Maher, 2004). The pulse found to be short and fast in the REM stage of sleep. In this stage brain activity looks similar to awake state and is therefore, known as paradoxical sleep, this is the period of realistic dreams(“Health habits-Sleep well to age well,” 2002). During these stage brain areas which are connected with some kind of memory functions seem to be quite whereas those related to emotions are active(“Health habits-Sleep well to age well,” 2002).
Circadian rhythm and sleep:
An important factor which plays a vital role in everyone’s sleep is circadian rhythm, a 24 hour internal biological clock, which is also known as the circadian pacemaker. Circadian rhythm is exhibited by, body temperature cycle, secretion of hormone; mood and cognitive performance and most apparently by sleep and wake cycle and circadian rhythms are influenced by the external environmental and social cues. Thus any changes in the system of circadian timing or misalignments in the circadian rhythm and the external cues may result in Circadian rhythm sleep disorders(CRSD) (Lu & Zee, 2006). Circadian rhythm partly determines the time of sleep and wakefulness and any changes in the preferred time of sleep and wakefulness are gradually delayed as we grow old(Dijk, Duffy, & Czeisler, 2000). This indicates the importance of circadian rhythm in the sleep patterns in aging.
Sleep disorders in general:
According to the International Classification of Sleep disorders, the primary causality for obstinate sleep problems is thought to be the changes in the circadian timings or dysfunction between the external factors and visceral circadian rhythms. Disturbed sleep may result in insomnia and excessive sleepiness, which might have associated with the functional impairments (Lu & Zee, 2006). Sleep disturbances can occur commonly in some medical and psychological burdens(Someren, 2000). In addition, lack of sleep may result in poor cognitive symptoms like difficulty in paying attention, lack of alertness, lack of energy and poor reaction time(Ancoli-Israel et al., 2008). Specific REM sleep deprivation will cause emotional problems like irritability, suspiciousness and social withdrawal, which suggests that improvement in the facet of sleep could provide a psychological remedy which is especially important for the elderly people have a decline in REM sleep(Maher, 2004). In general, sleep deprivation will lead to excessive daytime sleepiness (Hawley et al., 2010) which might be regarded as a cause for poor daytime alertness. National Institute of sleep has found that during the deep stages of NREM sleep, the body repairs and regenerates tissues, builds bone and muscle, and appears to strengthen the immune system, and it suggests deprivation in this stage of sleep may lead to face medical consequences(“What is Non-REM sleep?,” 2009).
Sleep and aging:
“Aging accompanied by changes in sleep”(Hornung, Danker-Hopfe, & Heuser, 2005). Even though sleep changes are a result of the normal aging process, many elderly face difficulties in coping with the changes. A survey conducted by National institute on Aging in 1999, revealed that more than 50% of people from 9000 elderly reported at least one persistent sleep problems. In general, there is a false belief that we have less need for sleep duration as we grow old, but most of the recent studies suggest, that duration of sleep does not change(Ancoli-Israel et al., 2008), and one third of our adult life has been spent in sleep(Maher, 2004) and the total amount of sleep remaining the same while there is a change in the sleep architecture (Ancoli-Israel et al., 2008). The structure of sleep tends to be more fragmented, shallow and most of the epidemiologic studies in the past decades have found that 40% to 70% of elderly are suffering from recurrent sleep problems(Someren, 2000). Most of the Polysomnographic studies produces consistent result that, although elderly people are spending long hours in bed, they fall asleep for a very short period, they have also seen to awaken frequently over long periods of time thus they are very inefficient sleepers(Vitiello, 1997).
Some studies which have compared the sleep recordings of elderly people with younger and adult age groups have found a decrease in sow-wave sleep(3rd and 4th stage of NREM) and REM sleep and an increase in stage 1 and 2, namely light sleep(Ancoli-Israel & Ayalon, 2009). Further, changes in the circadian rhythm pursuant to as a result of aging may result in misaligned sleep timing, which may lead to either insomnia or excessive sleepiness or both, and finally it might affectthe functioning of the elderly(Lu & Zee, 2006). This suggests that elderly people are more sensitive to more sleep problems.
Sleep disturbances in elderly:
“Chronic sleep loss may not only hasten the onset but could also increase the severity of age-related ailments such as diabetes, hypertension, obesity, and memory loss” say Eve Van cauther, PhD, Professor of medicine at the university of Chicago (Gazella, 2009). Some sleep disturbances are commonly found in elderly, and they are more sensitive to insomnia, snoring, obstructive sleep apnoea, and some movement disorders like, restless leg syndrome, periodic limb movements, REM sleep behaviour disorder, circadian rhythm disorders like phase advancing and delayed phase, decreased nocturnal sleep time, and sleep deprivation lead them to have excessive daytime sleepiness and daytime napping(Wolkove, Elkholy, Baltzan, & Palayew, 2007a). In addition, sleep disorders in elderly is connected with medical one or more medical and psychiatric illness, and it is also related with high risk of falls, and walking difficulties(Ancoli-Israel et al., 2008).
Insomnia is the most common sleep disorder in elderly and some previous research studies found that aging process is not only the cause for insomnia but also social life dissatisfaction, less engagements, physical and psychological problems. Moreover, some previous studies assume that even healthy elderly people without any physical or psychological problems have some insomnia symptoms, which symbolize that having a satisfied and an active lifestyle might be a preventive factor against insomnia(M.M. Ohayon, Zulley, Guilleminault, Smirne, & Priest, 2001). Although it is acceptable that sleep disturbances are a result of the normal aging process, it was produced by the changes in the human circadian system(Monk, 2005), and there is an underlying mechanism would appear to be related with the elderly people’s sleep pattern, people who go to bed earlier in the evening spend more time on bed and sleep more than who go later(Monk et al., 2006).
Further, sleep difficulties are found to be more common in some somatic disorders like stroke, heart disease, Parkinson’s disease, psychiatric diseases like depression, Alzheimer’s and some studies found that some elderly people who have poor sleep parents are more prone to more sleep disorders, which indicate hereditary may also play a role in sleep disorders(Asplund, 1999).In addition, age-related changes in the sleep architecture results in light sleep, frequent awakenings during the night which results in less sleep duration and longer sleep onset(Natalie, Christina, & Meredeth, 2008).
In specific, REM sleep deprivation will cause emotional difficulties like suspiciousness, social withdrawal and irritability. This prescribes REM sleep deprivation can be a psychological remedy(Maher, 2004). When comparing to the younger ages studies found that elderly people may have less number REM sleep(Maher, 2004).
Daytime activities and napping in elderly:
Even all other factors given above are discussed, quality of sleep in elderly is depend on number of varies factors(Vitiello, 1997). Regular napping has a significant relationship with numerous chronic diseases, body mass index, pain and depression, nocturia, poor sleep quality, difficulties in maintaining sleep and excessive daytime sleepiness (EDS) and it provides that EDS will lead to cognitive impairments in elderly(M. M. Ohayon & Vecchierini, 2002). Apart from that sleep disturbances are found to be related with some daytime physical activities and habitual functions like heavy eating, high consumption of caffeine, and nicotine, which interferes with sleep and exercise before bedtime, cognitive functions like thinking, problem-solving, recollecting the daytime events may lead to have a disturbed sleep(Wolkove, Elkholy, Baltzan, & Palayew, 2007b) .
Further, some previous studies have been proven that the relationship between the level of daytime activity and the subsequent night sleep quality in the elderly(Shirota, Tamaki, Hayashi, & Hori, 2000). As an added point to this, some research found that good quality of sleep is related with taking a warm bath, breathing exercises, having bananas and carbohydrates, using some sort of relaxation techniques like yoga, music and meditation, and by maintaining the perfect time pattern for sleep all the days(Wolkove et al., 2007b). In addition, few other studies provided evidence for that having a meaningful physical and psychosocial functioning may assist for retaining a quality circadian sleep-wake rhythm(Sullivan & Richards, 2004).
Sleep and Cognition:
More Researches, found that chronic sleep deprivation will lead to have difficulty in attention, short time memory, reaction time, and it will affect the level of performance in all ages(Ancoli-Israel et al., 2008) and some studies provide that sleep deprivation, depression anxiety and aging are related to each other(Gazella, 2009). Some studies concluded that subjective alertness may vary in individuals based on their circadian rhythm and prior sleep-wake timing and in sufficient sleep may cause reduced alertness and performance(Dijk et al., 2000), and it is commonly known fact that maintaining the attention level is essential for optimal cognitive functioning(Blatter et al., 2006) and some studies have found that a quality night sleep plays a vital role in quality cognitive functions of good sleepers(Bastien et al., 2003).
Cognitive functions in the elderly and sleep:
Causes for the decline in the cognitive function may have number of reasons like, vascular diseases, depressions, neurological disorders, and diabetes mellitus sometimes and some other external factors like education and less social engagement (M. M. Ohayon & Vecchierini, 2002). In specific, a cognitive decline has been found more in the elderly people with sleep difficulties than the people with normal sleep control and most of the elderly people are having an unsatisfied sleep because of the changes in the sleep architecture caused by the aging process and majority of them are likely to be have a social dysfunction, substance abuse or having numerous medication for some other problems, self medications, physical illness and the occurrence of these factors are subjected to individual differences, some people may have the combination of these factors all together(Ancoli-Israel et al., 2008).
Further, changes in sleep as well as in cognitive functions may result in loss of ability to perform normal daily functions(Tinetti & Williams, 1997). Some studies proposed that distinguishing age related changes in sleep from those who occurs because of pathological factors like medical and psychological problems could help in finding appropriate remedy for the sleep problems(Vitiello, 1997), so individuals can have awareness about their sleep problems before it turns into major problem. Furthermore, studies found that the cognitive impairment is more prevalent in elderly people who have disturbed sleep pattern comparing to the elderly people who have good sleep control, and it is so problematic in elderly because it may provide chance to be mistaken as dementia (Ancoli-Israel & Ayalon, 2009)Thus, finding the sleep aspects and their impact on the daytime functioning may help to avoid those consequences.
Some studies found that quality sleep is related to good cognitive performance in the vigilance task(Altena, Werf, Stijers, & Someren, 2008). The term “Vigilance” includes wakefulness, alertness and attention(Mathis & Hess, 2009) and attention is the ability to focus on a task and a basic need to perform other elements of cognitive functions(Woodford & George, 2007). Further a study by Stoohs (2009), found that daytime sleepiness will develop reaction time deficits in time based tasks. Excessive sleepiness can be an underlying cause for the further cognitive decline and will lead to compromise in the quality of life in many elderly(Vitiello, 1997). Thus finding the sleepiness level and the daytime alertness of the non-clinical elderly people may help further to distinguish the impact of sleep and the pathological burdens in the cognitive functions of elderly.
Finally, all the evidence from previous studies provides knowledge about the sleep difficulties and their impact on the elderly people in the normal aging process. As a normal aging process provides various changes in both physical and mental process, elderly people are more sensitive to more sleep disturbances and cognitive impairments. Further, cognitive function is a complex process of higher order functioning like thinking, memory, learning(Killgore, Balkin, & Wesensten, 2006) but level of attention is a basic requirement for the higher order cognitive functioning(Woodford & George, 2007).
As the life expectancy increases, it found to be more important to have a quality life in the elderly and the sleep problems are found to be more prevalent in recent days(M. M. Ohayon, 2004). Thus it is essential to find the different patterns of sleep in elderly and comparing their alertness level which might help to avoid misinterpretations and may evoke an insight about the importance of sleep quality.
Most studies have suggested that sleep problems and the cognitive declines are common in elderly people and quality of sleep plays major role in daytime alertness, which is essential to perform other forms of cognitive functions(Woodford & George, 2007). Hence, several studies have looked at the relationship between the sleep and daytime alertness in older patients with diagnosed sleep disorder, but few studies have examined the link in groups of older people who have not gone to their doctor complaining of sleep. Thus finding the different aspects of sleep and the relationship between sleep patterns and the daytime alertness in non-clinical elderly people may help to describe the impact of sleep on the cognitive functions without any pathological factors which might evoke further studies in the area of sleep and aging in non-clinical aspect.On the whole, this study is keen to evoke an insight about the effects of sleep on cognitive functions in the non-clinical elderly people by finding the relationship between subjective sleepiness and the daytime alertness.
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