New born babies tend to sleep for about two thirds of the day which is 16 hours in every 24 hours. They display two kinds of sleep: quiet and active sleep which are immature version of REM and Slow Wave Sleep. At birth, there is more active sleep than quiet sleep but this gradually decreases. It has been suggested that babies sleep is an adaptive mechanism to make the parents lives easier. The greater amount of active/REM sleep may be explained in terms of the considerable learning and brain development that takes place. It is further supported by the fact that premature babies spend 90% of their sleep time in REM/active sleep.
Babies over one year of life have a gradual maturation of sleep in EEG patterns so they begin to look more like adult patterns. There is a decrease in active/REM sleep to about 50% and consolidation of sleep periods; rather than sleeping in short bursts, young children sleep through the night and may have one or two naps totally 10-12 hours of sleep.
Five years of age has shown on the EEG that full patterns of sleep are shown by the age of 5 but the frequency is different to adult patterns; there is more REM sleep, about 33% of the total sleep time. Most children of this age sleep for around 10 hours but the boys sleeping slightly more than the girls. There are more instances of parasomnias in this age.
Adolescence sleep for an average of 9-10 hours of sleep per night. The amount of REM sleep is slightly less than childhood. Circadian rhythms also change so that teenagers feel more awake later at night and have more difficultly getting up early, a delayed sleep phase. The changes in the sleep patterns may be linked to hormonal changes in the body. Hormones are generally released at night and so sleep patterns are disturbed leading to sleep deprivation. The hormonal changes can also explain the upset circadian clock which is described as the delayed sleep phased syndrome (Crowley et al, 2003). Wolfson & Carskadon (2005) have recommended that schools start their day later to accommodate poor attention spans of adolescents in the early morning.
Old age has a reduction in REM sleep to about 20% of the total sleep time with a corresponding increase of Stage 2 sleep which is about 60% of total sleep time. The amount of slow wave sleep is also considerably reduced to as little as 5% and may be non existent for some older people. Older people have more difficulty going to sleep and wake up more frequently at night times. They face a phase advance of their circadian rhythm as they fall asleep earlier in the evening and wake earlier in the morning. The reduced sleep in old age is partly a consequence of physiological changes but may also be explained in terms of actual problems staying asleep, such as medical illnesses or sleep apnoea. SWS is reduced in old age and so older people are easily woken up in their sleep. Van Cauter et al (2000) found that the reduction of SWS leads to reduced production of the growth hormone which may explain some of the symptoms associated with old age such as lack of energy and lower bone density.
Tynjala et al 1993 surveyed 40,000 11-16 year olds from 11 European countries. They found that Israeli children = 8.5 hrs on average whilst the Swiss children = 9.5 hrs on average. In addition, Shin et al 2003 found that Korean children = 6.5 hrs on average whilst Iranian children = 7.7 hrs on average.
This suggests sleep duration is shorter in Asia than Europe.
But, most evidence comes from Lab research using EEG recordings. These recordings are obtained by attaching electrodes to participants. This creates an unfamiliar sleeping environment which may disrupt their usual sleep patterns. However Empson (1989) suggests that after the first night participants adjust to conditions and their sleep is representative of their usual sleep patterns