We spend a third of our lives doing it, Napoleon, Florence Nightingale and Margaret Thatcher got by on four hours a night, Thomas Edison claimed it was a waste of time.' (BBC Science & Nature, 2014)
What is sleep?
Sleep is a natural, cyclical alteration of consciousness that is essential to our normal functioning and health. During this biorhythmic state of unconsciousness, the brain becomes less sensitive to external stimuli.
Why do we sleep?
Does it conserve energy or let the brain 'recharge'?
This is something of a misconception. Literature suggests that 'sleeping only reduces metabolism and energy use in humans by at most 5–10% overall' (Mastin, 2013a). Over an 8-hour period of sleep, this would equate to approximately 50 kCal (BBC Science & Nature, 2014).
Sleep is necessary for normal functioning and health. It plays a significant role in brain development and deficiency of sleep, especially long-term, can lead to serious health problems. Sleep deprivation hinders brain function, especially the regions controlling memory, planning, language and sense of time.
Judgement can also be affected. Research suggests that remaining awake for over 17 hours reduces cognitive psychomotor performance to the same extent as that caused by a blood alcohol concentration of 0.05%, the legal drink driving limit in the UK (Dawson & Reid, 1997).
Sleep deprivation impacts normal physiology, with consequences on emotional and physical health. Lack of sleep has many causes and is associated with several conditions, including: depression, anxiety, obesity, heart disease and type 2 diabetes mellitus.
How is sleep different to other states of unconsciousness?
Sleep occurs in a predictable pattern. During the shift from wakefulness to sleep, there is a progressive decrease in neurological response to environmental, auditory and visual stimuli from the brain (Moroz et al, 2011).