Sunday, October 2, 2011

Research Paper: Effects Of Sleep Deprivation

Literature Review - Effects Of Sleep Deprivation

Normal, healthy individuals need adequate sleep for optimal cognitive functioning (Himashree et al., 2002). Without adequate sleep, humans show reduced alertness (Penetar et al., 1993) and impairments in cognitive performance (Thomas et al., 2000, 2003). Prolonged sleep deprivation is associated with decrements in elementary cognitive abilities such as vigilance and sustained attention (Doran et al., 2001; Wesensten et al., 2004), as well as impairments in complex, higher-order cognitive processes such as verbal fluency, logical thought, decision making, and creativity (Harrison & Horne, 1997, 1999, 2000). In occupational settings such as aviation, air traffic control, and sustained military operations where constant vigilance is a necessity, extended periods of sleep loss have been associated with catastrophic accidents (Mitler et al., 1988) and may have been a factor in some friendly fire incidents (Belenky et al., 1994). Studies of sleep-deprived individuals show that errors attention begin to emerge by 19 h of continuous wakefulness (Russo et al., 2004) and cognitive performance declines at a rate of approximately 25% for each 24-h period of wakefulness (Belenky et al., 1994).

Sleep deprivation produces global decreases in cerebral metabolism and blood flow, with the greatest declines evident in those regions critical for higher order cognitive processes (Thomas et al., 2000). These regions, the heteromodal association cortices, are associated with attention, vigilance, and complex cognitive processing, and reductions in activity within these regions are associated with decrements in these higher-order cognitive process (Mesulam, 1999). As a global blood flow and metabolic activity decline during prolonged periods without sleep, the brain appears to compensate by recruiting cognitive resources from nearby brain regions within the prefrontal and parietal cortices in order to maintain cognitive performance at acceptable levels (Drummond et al., 2001). Some evidence suggests that these compensatory activities may be particularly prominent within the right cerebral hemisphere (Drummond et al., 2001). Consistent with these reports, other studies suggest that cognitive  processes mediated by the right hemisphere are more adversely affected by sleep deprivation than those mediated by the left (Johnsen et al., 2004; Pallesen et al., 2004).
Neuropsychological evidence suggests that the right cerebral hemisphere is dominant for attentional processes (Heilman&Van DenAbell, 1980; Mapstone et al., 2003). Much of the evidence supporting the dominance of the right hemisphere in attention comes from studies of patients with unilateral brain damage (Heilman & Van Den Abell, 1980; Weintraub & Mesulam, 1987). Lesions to the right cerebral hemisphere are more likely to produce contralateral hemispatial neglect than similar lesions to the left hemisphere (Behrmann et al., 2004; Mapstone et al., 2003, Mesulam, 1999). Further evidence supporting the prominent role of the right hemisphere in attentional processing comes from several functional neuroimaging studies that reveal greater right hemisphere activity in response to tasks requiring allocation of spatial attention (Fink et al., 2001; Macaluso et al., 2001). The accumulating evidence suggests that the left cerebral hemisphere allocates its attentional processing predominantly toward the contralateral (i.e., right) hemispace, whereas the right hemisphere appears to distribute attentional processing more equally between both hemispaces, and is therefore considered dominant for attention (Mesulam, 1999). Consequently, the phenomenon of contralesional neglect occurs nearly exclusively following lesions to the right hemisphere.
Given the apparently greater role of the right hemisphere in attentional processing and the preliminary evidence that the cognitive processes mediated by the right hemispheremay be more sensitive to the detrimental effects of sleep deprivation, it was hypothesized that prolonged sleep loss results in greater impairment of right hemisphere visual attention mechanisms oriented toward the contralateral (i.e., left) perceptual hemispace. Participants were assessed several times each day while remaining awake for 40 h. During each 15-min testing session, participants monitored a 150◦ arc of lateral visual space for periodic occurrences of brief flashes of light while simultaneously performing a continuous serial addition task.
Adequate sleep is important for both good mental and physical health. Poor sleep quality is a significant predictor of depressed mood (Mendlowicz, Jean-Louis, von Gizycki, Zizi & Nunes, 1999). Sleep deprivation has been shown to worsen depressive symptoms in some individuals (Benedetti, Zanardi, Colombo & Smeraldi, 1999; Beutler, Cano, Miro & Buela-Casal, 2003) and increase disturbed mood (Crabbe, 2002; Dinges et al., 1997). Sleep deprivation can also result in increased anxiety (Miro, Cano-Lozano, Espinosa & Buela-Casal, 2002), fatigue, confusion, and tension (Dinges et al., 1997). Furthermore, sleep deprivation affects mood to a greater degree than either cognitive or motor performance (Pilcher & Huffcutt, 1996). Regarding physical health, poor sleep quality and sleep loss are associated with decreased immune function (Cruess et al., 2003; Irwin, 2002), the pathophysiology of cardiovascular disease and diabetes (Roost & Nilsson, 2002), and also the development of overweight/obesity (Agras, Hammer, McNicholas & Kraemer, 2004).

Sleep deprivation also influences food consumption in studies of animals, although these studies have shown some conflicting results. For example, studies with rats have shown that sleep deprivation may lead to over eating (Brock et al., 1994; Tsai, Bergmann & Rechtschaffen, 1992). On the other hand, Johansson and Elomaa (1986) found a reduction in the amount of food consumed by rats when deprived of rapid eye movement (REM) sleep. In addition, some studies also demonstrated that sleep deprivation disturbs the light/dark eating pattern in rats rather than simply increasing or decreasing food intake (Elomaa, 1981; Martinez, Bautista, Phillips & Hicks, 1991). Overall, sleep deprivation seems to alter eating patterns among animals. There are relatively few studies on the effects of sleep on food consumption or food choice in humans, but several pieces of indirect evidence exist to suggest a link between sleep and food consumption. Hicks, McTighe and Juarez (1986) found that short-sleeping college students (e.g., 6 h per night) were more likely to eat more small meals or snacks than long-sleepers who averaged 8 h or more of sleep per night. There is also evidence showing that individuals with eating disorders display abnormal sleep patterns. For example, Latzer, Tzischinsky, Epstein, Klein and Peretz (1999) found that women with bulimia nervosa reported more difficulty falling asleep, more early waking, more headaches on awakening, and more daytime sleepiness than women without bulimia.

Additional evidence for an association between sleep and eating comes from studies of the hypothalamic pituitary adrenal (HPA) axis stress hormone cortisol and other studies of psychosocial stress. There is a negative association between amount of REM sleep and cortisol levels (Lauer et al., 1989) and a positive association between cortisol levels and calories consumed (Epel, Lapidus, McEwen & Brownell, 2001). In addition, sleep loss may be thought of as a source of stress for some individuals, which may subsequently influence food choice and food consumption as well. Increases in stress lead to more snacking and a decrease in the consumption of typical meal-type foods (Oliver & Wardle, 1999). In sum, there is some evidence that loss of sleep, as a stressor, may influence eating patterns, but, to date, no study has examined the effects of sleep restriction on food choice and consumption. A study examined the association between self-imposed sleep deprivation and eating among a sample of college students. We hypothesized that individuals would change their pattern of calorie consumption on the day following partial sleep deprivation. Due to the lack of conclusive evidence, as discussed above, we did not make an a priori hypothesis regarding the direction of change in calorie intake. We also predicted that individuals would choose foods differently following partial sleep deprivation; specifically, in concordance with the Oliver and Wardle (1999) study mentioned above, we predicted that they would choose foods based less on health and weight control and based more on mood and convenience.

In that study, the effects of self-induced partial sleep deprivation among an undergraduate sample were examined. The results showed significant differences in food consumption and food choice following partial sleep deprivation as compared to nights of normal sleep. As expected, there was a change in food consumption, as measured by calories consumed, following a night of partial sleep deprivation. We found that consumption of calories decreased after sleep loss as shown in Johansson and Elomaa’s (1986) study with rats. It is noteworthy to point out that the decrease in calories did not become statistically significant until two days after sleep deprivation rather than the day after. It could be argued that this indicates that sleep deprivation was not the cause of this decline in calories, but that some other factor played a role. One possible explanation is that people consume more calories following the weekend and eat less as the weekend approaches. However, it is important to note that the decrease in calories did not begin until after sleep loss. Also, some participants began the diaries on Monday while others began on Tuesday, making it less likely that the finding was due only to the time frame of the study. Other explanations for the observed decrease in calorie consumption could include diary fatigue and increased awareness of intake. Diary fatigue could have resulted in the participants eating the same amount but recording less in the diary or they could have actually consumed less because of an aversion to writing in the diary. Similarly, a heightened awareness of calorie intake could have led to a decrease in food consumption due to health or weight concern reasons. Due to the fact that there was no control group that kept diaries but did not experience sleep loss, the decrease in calories cannot be attributed solely or exclusively to sleep deprivation.


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1 comment:

  1. I would like to appreciate your work and would like to tell to my friends.