The circadian rhythm is a kind of daily biological clock of creatures, on which sunlight has the most important impact. This ‘clock’ can be found in the so-called suprachiasmatic nucleus in the hypothalamus of mammals. The hormone melatonin is also important in the process: it is produced to the effect of darkness, and helps fall asleep. If this part of the brain were injured, the cycle of sleep-wake would be damaged too. Probably, this was the case with Pál Kern, who had been shot in the head during WW I and he could not fall asleep for 40 years afterwards. Now we will never know, but the temporary disorder of the circadian rhythm can be experienced personally. When you travel to a distant country in east-west direction, you have to fight against jetlag, the tiredness due to crossing time zones rapidly.

However, be very careful, because the disturbed sleep-wake cycle might cause cerebral and cardiovascular diseases. For example, geologist Michel Siffre spent months in a cave in voluntary exile during the 1960s and ‘70s to examine the circadian rhythm, and finally he had depression and mental disorders.

During the sleep cycle, we can separate two phases: the Non-Rapid-Eye-Movement (NREM) and the Rapid-Eye-Movement (REM). NREM is the phase of deep sleep characterised by slow brainwaves, decreasing blood pressure and slowing respiration. It is difficult to wake up from this phase. In REM, the brain is active, the eyeballs move, we dream and it is easier to wake up. One sleep cycle lasts about 90-120 minutes and consists of several NREM phases and one REM phase. If you suffer from constant tiredness, you can set the alarm of a smartwatch that wakes you up nicely during an REM phase.

The daily sleeping need of an adult is eight hours on average, but you may not manage to sleep that much. However, it is important to sleep through at least three, four or five sleep cycles. It increases the cell division, relaxes the main organs that do not deteriorate in as quick pace as during wakefulness; and memories are stored in the brain. Lack of sleep spoils the ability of concentration, the state of the immune system and it might lead to death in extreme cases. Sleep deprivation as a method of torture has been used for hundreds of years, keeping the tortured person awake in unnatural uncomfortable positions.

As people grow old, their need for sleep decreases: while a baby sleeps about 16-19 hours a day, elderly people sometimes can hardly sleep 5-6 hours a night. In addition, there are some successful people, who do not waste their time on sleeping, which may cause the problem of being overdriven. Steve Jobs was said to need only 4-5 hours of rest daily, and Nikola Tesla contented himself with only 2 hours of sleep, allegedly. There are also a couple of curiosities in the animal world about dozing. The best sleeper’s prize would go to koalas among mammals with a daily average of 22 hours. The best wokens are giraffes making their daily 2 hours in few-minute naps.

Let’s sleep like a baby, like a log or like a top. Let us fall into a slumber as the Sleeping Beauty does. Let’s see again the film classics that examine the world of dreams: Michel Gondry’s The Science of Sleep or Christopher Nolan’s Inception. But first, let’s skim through our photo gallery in the topic of sleeping, including visual and photographic works of art inspired by napping, and objects like our great-grandmothers’ sleeping bodices and great-grandfathers’ nightcaps.

TEJ

Translated by Zita Aknai