So what is normal sleep?
Let’s begin this by explaining what normal sleep is not. Firstly, sleep is not the opposite of wakefulness. The idea of on/off would suggest that when we are awake we are on and when we sleep we are off. However, when we sleep we constantly move from one phase to another and different sleep phases fluctuate during the night. There are variations within sleep just as there are variations within wakefulness. We are not always ‘wide awake’ as we not always ‘fast asleep’. Secondly, sleep is not a passive process. On the contrary, the body’s activities during sleep are absolutely vital for living. Normal sleep is not like sleeping a log.
Animal experiments have showed that when rats were kept constantly awake for approximately 10 days they undergo a profound deterioration in their basic bodily systems such as temperature control and they die. Unfortunately we have also read stories about using sleep as torture method in wars. Sleep loss can have serious psychological and physical effects. Without regular periods of rest, animals are unable to function properly in all sorts of ways.
Russell Foster is a circadian neuroscientist and he studies the sleep cycles of the brain. He asks: What do we know about sleep? Not a lot, it turns out, for something we do with one-third of our lives. In this talk, Foster shares three popular theories about why we sleep, busts some myths about how much sleep we need at different ages.
How to describe normal sleep?
Research studies have shown us that sleep is very complex yet organised process. There are complex brain processes involved in going to sleep and in switching from one stage of sleep to another. An internal biological clock controls our periods of being asleep and awake, and also changes the levels of alertness and sleepiness within each 24 hours (circadian rhythm). Scientists have discovered the nature of sleep by studying the activity of the brain and recording in sleep laboratories. In short: sleep is made up of different stages and sub-types. These stages of sleep are organized in a series of cycles that repeat throughout the night.
Sleep is an active process. During the night our body system renews itself and our body tissue is repaired. Proteins and hormones are produced during the night so we literally do grow during the night! Furthermore, brains organise new information at night and therefore sleep has tremendous impact on mental processes.
Human sleep also shows interesting differences compared with other animal species. The duration of sleep within each 24-hour period varies from 3 hours in a horse to almost 20 hours in bats. These variations can probably be partly explained by differing vulnerability to attack by predators.
There has been debate about the function of sleep with different suggestions. It’s evident that there’s no single answer to this question. Sleep serves many different, often related functions from mental and bodily restoration and recovery to organising memories and learning new experiences. Sleep can also be seen as essential ‘tool’ for resolving emotional problems and conflicts.
Normal sleep graph
Typical sleep graph for more irregular sleep
Last but not least, it’s good to remember that bad nights belong to everyday, normal life and that even the very best sleepers occasionally sleep poorly.