The Purpose of Sleep
Sleep is both universal and fascinating. Although we spend a third of our lives sleeping, scientists don’t fully understand its nature and purpose. The most precise definition available at this time is descriptive: It’s a natural behavioral state (another is wakefulness) governed by the nervous system that is characterized by perceptual disengagement and motor inactivity. The state is cyclical and reversible without intervention. Unlike a coma – a total lack of consciousness – sleep is actually a semi-conscious state. This means that a minimal level of environmental awareness allows an individual to react to certain triggers. For example, a sleeping mother will hear her crying baby; people wake up when hearing their name called; or danger such as a fire or an attack is present or imminent.
We know that sleep has a restorative function and has a major impact on physical health, cognitive performance and mood stability. It seems to be as important as air, food and water for sustaining life. Resting while awake is not a substitute for sleep.
Most animals sleep, but timing and duration vary tremendously across species. We’re not sure why.
Why Do We Need to Sleep?
Here’s the most simplistic answer: We need to sleep to avoid feeling sleepy.
Researchers have illustrated this need with a simple experiment that shows the impact of sleep debt. When healthy people are forced to stay awake continuously for one or two days, their waking state is eventually interrupted, involuntarily, by short episodes of sleep. Test subjects are incapable of avoiding them. Moreover, other adverse consequences can be observed at the same time:
- declining cognitive performance
- disrupted biological rhythms
- undesirable metabolic changes (e.g., hormone levels)
Scientists have observed, over longer periods of time, that a chronic lack of sleep
- may cause weight gain
- adversely impacts learning and memory
- reduces immunity
- shortens lifespans
On the other hand, quality sleep replenishes the body and mind in several ways. For example, sleep plays a crucial role in children’s growth and development. That’s a reason why young ones need more sleep than adults. Memory consolidation occurs during sleep. Body reserves and energy levels are restored while sleeping.
Interestingly, too much sleep is just as bad as too little sleep.
How much sleep someone needs is difficult to answer precisely, though statistically a majority of people need 7½ to 8 hours.