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    Ultradian rhythms are bodily rhythms that occur more than once in 24 hours. One example of this researched by Dement and Kleitman is the Non rapid eye movement (NREM)/ Rapid eye movement (REM) cycle. Otherwise known as sleep. This has 5 stages, and altogether lasts about 90 minutes. In stage 1, the heartbeat slows down, muscle tension is reduced and alpha waves are replaced by slower theta waves. It is also in this stage that a person may enter a state of hypnagogic hallucinations. Stage 2 sees the interruption of K-complexes, and occasional bursts of electrical energy known as sleep spindles. Stage 3 is the first stage of deep sleep, and is characterised by very slow delta waves with large amplitudes, in this stage the heartbeat continues to fall. Stage 4 is the deepest sleep and features the secretion of growth hormones to undergo repair work, reduction of metabolic rates and the slowest recorded brain waves. This is extremely hard to wake up from. Finally stage 5 see’s the occurrence of REM/paradoxical sleep after quickly going back through stages 3 and 2. This is the stage we are most awake. It features rapidly increasing and irregular brain waves, and an increase in the brains demands of glucose and oxygen.


    Researchers, have found by using a combination of methods (Electrooculography and Electroencephalogram) that as we age, changes in sleep rhythms and behaviours usually occur. One example of this is the high accumulation of rapid eye movement REM sleep as we are born, which gradually decreases to adult levels. This was researched by Zimbardo (1993) who found that new-borns need about 16 hours of sleep a day, 8 (50%) of which was to be spent in the REM stage. Compared to those above the age of 50 who spend on average 6 hours a day sleeping, one 1 (15%) of which is recorded in the REM stage of sleep. Similarly Floyd found through studying 400 sleep studies that our REM stage decreases 0.6% each decade. Therefore providing strong, objective evidence of the gradual decrease in overall sleep time, and the significant fall in deep Non rapid eye movement (NREM) sleep over a lifespan.
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