SLEEP: Why do we sleep one third of our time?

Home Q&A SLEEP: Why do we sleep one third of our time?

We spend one third of our time sleeping, but scientists still don’t know why. A prominent researcher reviews the most likely explanations. 

Hans Foerstl

Eat, sleep, repeat – it’s what humans do to survive. Scientists know a lot about our general state of health from how we sleep, but many mysteries remain. For an overview Technologist spoke to Hans Förstl, director of the Department of Psychiatry and Psychotherapy at the Technical University of Munich (TUM).

TECHNOLOGIST What is sleep anyway?

HANS FÖRSTL It’s a highly organised and active cerebral state with decreased awareness of ongoing external events. It offers the brain an opportunity to rework and reconnect the information we collected throughout the day. It’s like a computer working off-line.

TECHNOLOGIST Why do we do it?

HANS FÖRSTL Several theories exist. Exhaustion – physical and mental – may play a role. But even if we don’t know the exact answer, it’s a fact that all higher animals sleep. Even phytoplankton that dive into the ocean at night use neurotransmitters similar to those of people delving into sleep. Organisms need to balance their energy and adapt their structure in order to prepare for the challenges of the next circadian stage. In the case of the human brain this adaptation consists of a more economical rewiring in neuronal networks.

TECHNOLOGIST How much sleep is enough?

HANS FÖRSTL Five to 7 hours. But if you continuously sleep for less than four or more than 10 hours, you should see a doctor to rule out a pathological condition. Some people claim that we – as a society – are not sleeping enough due to all the modern temptations like TV and the Internet, but in my view our modern life is just too interesting to sleep longer. And before we compare ourselves to our ancestors and their “healthier” sleeping habits, we should remember that they had to climb up trees and cling to branches in order to avoid the worst – but not all – of the imminent dangers. Generally, I believe that it all depends on preferences, demands and satisfaction. If someone is satisfied with his or her personal sleeping pattern – however unconventional – it’s fine.

TECHNOLOGIST What happens if we don’t sleep?

HANS FÖRSTL Important functions like healing and memory decrease, because sleep is necessary to maintain our cognitive functions and control inflammatory processes. But generally we tend to get the sleep that is urgently needed – even if it means dozing off at inconvenient times. Microsleep – brief periods of dozing off – can probably keep us going over a couple of days, even if it’s with slow heads and a terrible mood.

TECHNOLOGIST Do we stress too much about getting the right amount of sleep?

HANS FÖRSTL A lot of my patients develop a “sleep neurosis”. This is characterized by the gross societal misconception that everyone has a natural right to spend at least eight to 12 hours of sweet slumber in a cosy bed before waking up rejuvenated and happy as a puppy. The great disappointment that comes with these high expectations is the first step on the way to sleeping-pill addiction and eventually depression.

TECHNOLOGIST What regulates our sleep?

HANS FÖRSTL The most important factors to determine our personal sleeping pattern are our internal circadian rhythm and what is known as the sleep/wake homeostasis. These two internal factors are then influenced by external physical and social “time indicators”, like the amount of light around you and your cultural setting. The circadian rhythm is the reason we can get jetlagged; it’s a biologically regulated span of approximately 25 hours during which we experience different stages of sleepiness and wakefulness, also known as the internal clock. Even though the circadian rhythm differs from person to person, our urge to sleep is generally strongest between 2 am and 4 am as well as between 1 pm and 3 pm, explaining why you become so tired after lunch.

“Modern life is just too interesting to sleep longer”

Interview by Line Emilie Fedders @LineFedders

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