Sleep cause discovered by scientists

Sleep feels refreshing and we're groggy without it - but what actually causes it?
27 March 2019


girl yawning whilst seated


Individual brain cell repairs is what causes sleep, scientists discover...

Yaaaaaaawn… Feeling the tiredness creeping in as you read this? Has it been an early start or a long day? We all know we need sleep and we don’t function well without it but, until now, it has not been known why it’s so essential.

The key reason for sleep is to allow cells that create connections in your brain to have their DNA repaired, which allows them to function better the next day. This repair process happens continuously at all times, but is much more efficient at night, according to Lior Appelbaum, from Bar-Ilan University, who observed this in zebrafish.

These little, striped fish you often see in a pet shop are perfect to use in brain observation experiments due to their transparency.  Appelbaum’s team used the fluorescent proteins found in jellyfish and coral to mark specific areas of the zebrafish’s brain and observe the DNA-containing chromosomes’ movement, which increased whilst they slept.

Appelbaum compares this night-time movement to repairing potholes in a city road: “During the day traffic creates a lot of activity that causes damage to the road. During the night, when the city is more quiet and there is less traffic on the roads, we have the time to fix all the holes and damage to the road, to prepare it for the next day.”

The busy roads are like the connections in your brain. So it’s only during sleep when they aren’t being used that enough repairs can be made to the chromosomes within the brain cells and the chromosomes move around when this happens.

By highlighting the chromosomes, his team were able to watch this damage-reversing process happening because they moved around more at night than during the day. But why does damage happen in the first place?

It’s caused simply by being awake and using brain cells. Plus, oxygen compounds created by bodily processes and natural radiation from our surroundings are also having an effect. But don’t panic, these effects aren’t anything to worry about.

“All cell resources and energy are attributed to wakefulness and dealing with all the brain inputs and learning we do during the day” continues Appelbaum. But it does explain why we and all animals have developed such a counter-intuitive behaviour, to shut down our bodies like this.

He explains that in evolutionary terms “sleep is a very dangerous state of behaviour because if you sleep you reduce your sensory input. If you are in a field a tiger could eat you, or if you’re on the road driving a car you risk an accident”. So even though the risks might have changed over time, and drowsiness on an evening drive could be lethal, the effect of sleeping is not just limited to night-time.

When day-time DNA damage was increased artificially, the fish then fell asleep despite the daylight. It shows how sleep-deprivation affects animals and humans alike, and why we all have to sleep.

“If we chronically lose sleep for several days, months or even years perhaps we gain DNA damage in specific neurons and even damage our brain”, Appelbaum explains. “We always see sleep disturbance in neurodegenerative diseases or ageing and it eventually even causes cell death in a specific region.”

Appelbaum finishes by emphasising that “it’s not news that we have to sleep and sleep well, but what we now know is why. That we have to sleep well to prevent this accumulation of DNA damage.” So if taking a nap wasn’t on your mind before reading this, perhaps now’s the time to call it a night…


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