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bout the role of sleep in the development of such conditions.

Another theory reported by Yang et al., 2014 highlighted sleeps important told in memory consolidation. They examined how sleep affects the remodelling of postsynaptic dendritic spines induced by motor learning in the mouse primary motor cortex. They found that when mice were allowed to sleep following a motor learning task displayed an increased formation of postsynaptic dendritic spines on a subset of branches of individual layer

V pyramidal neurons as opposed to rats who were not allowed to sleep. These findings indicate that sleep has a key role in promoting learning-dependent synapse formation

and maintenance on selected dendritic branches, which contribute to memory storage.

Chronic sleep deprivation may be required to reveal the most serious physiological consequences of sleep loss, but it usually requires strong stimulation which can obscure the interpretation of effects. The disk-over-water method permits chronic sleep deprivation of rats with gentle physical stimulation that can be equally applied to yoked control rats. Results showed that rats eventually died; survival was 11-32 days in totally sleep deprived rats and 16-24 days in PSD rats. Furthermore, rats showed a progressively debilitated, scrawny appearance with brownish disheveled fur and severe ulcerative and hyperkeratotic skin lesions localised to the tails and the paws developed. There was a startling increased food intake and energy expenditure despite consistent weight loss and drop in body temperature. Thirdly, there was in crease in plasma norepinepherine and plasma thyroxine. Despite the researchers controlling for confounding variables such as the physical environment, physical stimulation and exercise, stress could be a major factor in the deterioration of the rats health. One of the strongest pieced evidence for this was that adrenal weights in rats carried to death was 59% greater in TSD rats than PSD rats and controls.

A few case study approaches have investigated the effect of total sleep deprivation in humans. Randy Gardner is the holder of the scientifically documented record for the longest period a human has intentionally gone without sleep not using stimulants of any kind. He stayed awake for 264.4 hours (11 days 24 minutes). By day 2 he had difficulty focusing his eyes and showed signs of astereognosis. As the days progressed he displayed moodiness, ataxia and memory lapses. By the 5th day he had begun hallucinating, this was where is become more serious. As the days went on he showed slurred speech and fragmented thinking and by day 10 he displayed extreme paranoia and an expressionless appearance. After the 11th day Randy fell asleep for 14 hours and appeared to recover from his loss of sleep, with follow up sleep recordings showing no significant differences. He displayed no long term psychological or physiological effects. However, Gardner is an individual with unique characteristics and so the results cannot be generalised to the wider population, therefore lacking population validity. Furthermore, there were no explicit measurements in this study, such as the paranoia. Finally, there appear there may have been findings related to micro-sleep, suggests he could have had undetected sleep in this way.

Sleep deprivation is still used as a torture and interrogation technique, with prisoners kept awake for over one week causing at least 5 to experience disturbing hallucinations.

When determined polysomnographically, there are two distinct types of sleep - rapid eye movement (REM) and non-rapid eye movement (NREM) sleep -which alternate every 45 minutes to form a NREM-REM sleep cycle approximately every 90 - 100 minutes. Depending on the sleep episode duration, there are usually 4-5 sleep cycles per night. The proportion of NREM and REM sleep in each cycle changes throughout the night with a higher proportion of NREM sleep in each cycle in the latter half of the night. NREM is generally associated with more stable physiology - regulating breathing patterns, lower heart rate, lower temperature - whereas REM is a more active state with a more variable but generally higher breathing patterns, lower heart rate, blood pressure, brain temp.

Brain activity, as measured by EEG, is very active during REM sleep, exhibiting irregular, low amplitude, high recency waves very similar to those seen during wakefulness. During NREM sleep the EEG activity is more synchronous, with higher amplitude, lower frequency waves.