How sleep synchronises the brain

Why do we sleep?

“It is a mystery, but there are plenty of theories. In the past people believed that the body went into hibernation. But today we understand more about why sleep is so important. The brain simply slows down and get time to synchronise. This way the brain rebuilds the communication between the neurons. Sleep helps the brain to work properly,” says sleep research expert and Associate Professor Janne Grønli at the University of Bergen’s (UiB) Faculty of Psychology.

What happens to the body and the brain when we sleep?

“The muscles relax, our breath slows down and our heart rate and body temperature sink. Sleep is divided into different periods, non-REM and REM sleep, which alternate through a sleep cycle. There are about four or five sleep cycles a night, lasting about 90 minutes each. Non-REM sleep is characterised by slow activity in the brain. During REM sleep, however, the brain is very active. The body is completely calm and muscles are paralysed. Hence the sleep feels very deep despite the brain’s activity. REM sleep is rare early in the night, but increases towards the end of the sleep cycle. When we sleep the brain only registers a minimum of outside stimuli and uses less energy than when we are awake.”

What happens if you decide not to sleep?

“The first thing you will notice is an increased reaction period. In a former study, people who had been awake for 16 hours were surveyed. They performed as poorly as someone who was on 0.5 parts per thousand of alcohol. There is also research on people who have cut their average nightly sleep back to five hours. After a while they scored highly on a depression scale. So if you don’t sleep, most likely you will not be so happy. Sleep deprivation also increases the risk of cardiovascular disease in the long term, according to another study.”

Can you die if you don’t catch sleep?

“No, there is little evidence of this. Some people claim they can stay awake for weeks, but this probably not correct and these people have probably fallen asleep without begin completely aware of it themselves. In lab tests, rats died after two weeks without sleep. This is because their immune system was extremely poor. Sleep enhances the immune system and growth hormones are released, cell division peaks and the body is strengthened.”

What is the longest anyone has gone without sleep?

“The world record was set by a boy who managed to stay awake for eleven days. Afterwards he slept for fourteen hours. There is no correlation between sleep lost during the time one has been awake; the body will catch the sleep it needs.”

But why do we sleep at night?

“As we are mammals, we need the daylight to scavenge for food. Man’s circadian rhythm is set by the sun. Melatonin is the body’s circadian rhythm hormone and is secreted into the body when it is dark, with a peak in the middle of the night. When it is light this process does not happen. This partly explains why it is so important to catch enough light in wintertime so as to maintain the circadian rhythm, whilst during summer it may be wise to try and shut the light out to catch enough sleep.”

How would you describe a good night’s sleep?

“A good night’s sleep is when you sleep for a long enough and undisturbed period so that you feel refreshed when you wake up the next day. If you are tired during the day, it is most likely because you suffer from not enough sleep or poor sleep quality.”

(Translated from the Norwegian by Sverre Ole Drønen.)