What is the reason why we sleep? It would be natural to conclude that we sleep to rest. However, if we measure the resting by the activity of the brain, 80% of the sleep time brain is as active as awake, consuming the same amount of energy like we are awake. Only 20% of sleep time our brain consumes less energy than awake, when it falls to the stage called deep sleep.

Given we sleep around 8 hours per day on average, brain activity indicator suggests we rest only 1.6 hours per night and the rest 6.4 hours is spent on something else. What is that something else? It must be something important, because, by cutting 6.4 hours of sleep every day for 80 years would mean extra 21 years of being awake! Also, just by looking at the early human life, it was very unsafe to sleep while many dangerous animals were hunting for food. It must have been a very important reason to keep sleeping despite risk of being hunted.

In order to understand the sleep, we must first say that the sleep is not uniform – there are several phases of sleep during the night, making it a one cycle, and there are several cycles with changing lengths of phases. Our sleep patterns change as we get older and are influenced by various external environment factors.

After rapid eye movement (REM, which is an active sleep phase) discovery, one sleep researcher went to live in a cave for 30 days to explore the effects. He discovered that irrespective of sunlight, our bodies had some sort of automatic sleep cycles, inner clocks. This experiment is not very scientific, but makes some sense that we have certain rhythms of waking and sleeping. They probably are deemed to change depending on many factors as said before, but the change probably does not take instantly.

Some researches say that people could be divided into three categories: early birds, regular and late birds. Early birds (larks) are the ones that wake up before alarm rings at 6am, feel most productive and creative in the morning and feel tired and wanting to go to sleep at 9pm. Late birds (owls) are those that hardly wake up before 10am, feel most creative from 6pm and don’t want to go to sleep before 3am. Some researches say that these two groups constitute 30% and these patterns come from early childhood and genes. One study show that if one of the parents is an early bird, half of the children would be also larks. In another study, however, a group of larks and owls were placed in a camp, where only natural light sources are available, and after 30 days owls started to raise with the sun and go to sleep with the sun down. It makes more sense that people modify and get used to the behaviour that are dictated by the environment they live in and the habits they form.

Another interesting phenomena is naps. Some researchers say that there are two opposite forces in our bodies: sleep regulating mechanism (circadian arousal controlled by light produces sleepiness) and awake regulating mechanism (homeostatic). Both of them push their own agenda continuously, awakening force being higher in the morning, but going down, while arcadian rhythm intensifies and takes over in the evening. Researches suggest that in the intersection of these two forces (around time 1:30-3:30pm) our bodies suggest to take a nap. The necessity to take a short sleep comes primarily from the natural causes, not from the food we eat, as we tend to think. One NASA study concludes that a 26 minute nap improved pilot’s performance by a significant 34%. Longer naps (more than 30 minute) can produce impairment of sleep inertia (which i also observed personally and thus would not go more than 45 minutes), but then produce improved cognitive performance for a longer period (some research say more than 6 hours). Naps are most valuable when they are done in the early afternoon and benefits are higher if they are done regularly.

In one sleep research 3 times more students solved the maths problems with a shortcut (easier solution) if they were allowed to sleep around 8 hours within 12 hours from the math training to solve in the traditional way and the math task initiation. Without a sleep only 20% of students found out a math shortcut, while with sleep 60% found a shortcut. It is found that sleep significantly improves learning a procedure. What is also important, disruption of the sleep eliminates all the learning benefit.

In the study of military soldiers, one night of sleep resulted in 30% loss in their overall cognitive skills and if the soldiers did not sleep two nights, the drop was by 60%. In the other testing mode, sleep restriction of 6 hours or less per night for five days straight caused cognitive performance to drop the same scale as for the person who did not sleep two nights.

In another study, researches found that 30 years old individuals, who a short of sleep (4 hours of sleep per night) utilize the foods by 30% less and age more rapidly. In six days some parts of the body were acting like 60 years old bodies. It took approximately the same time to recover to their normal functioning. It seems that sleep loss hurts attention, executive functions, short term memory, mood, quantitative skills, logic reasoning, math knowledge, motor skills.

Given all these researches, it seems that 80% of the time of sleep we digest, sort out, organize, rethink and perhaps even solve of what we were doing over the day and prepare for the next day a fresh start with available solutions to the problems of the previous day. Experiments with rats show that they consolidate the day’s learnings in the slow phase and have trouble remembering how to move along the maze if their sleep is disrupted at this stage. This suggests that the other 20% could be spent not only on body resting and physical recovering, but also on important memory processes.