We do it every night and from time to time during the day, too. We sleep. But why actually? And what makes us fall asleep, how does the brain control our sleep? Prof. Anissa Kempf investigates sleep behavior using fruit flies as a model organism, since not only humans, but also animals such as worms, jellyfishes or insects, sleep.
Is sleep important?
Yes, of course. Sleep is absolutely essential. We sleep about a third of our lives. And unlike eating, we can hardly control our sleep behavior. We can, for example, decide to avoid carbohydrates or meat. And this works, without any major restrictions or consequences for our body. We can even survive several weeks without food. But if we decide to sleep a few hours less every night, this has a significant impact on our well-being and our entire organism already after one night. We die without sleep.
How is our sleep controlled?
That's still a mystery, and that's exactly what we're trying to find out. More specifically, we study what happens in the brain of sleepy flies. We know that certain nerve cells in the brain can trigger sleep. These are so-called sleep cells.
So sleep is not something passive that just happens?
No, absolutely not. In fact, sleep is one of our strongest motivational drives, like eating or reproducing. The motivation to sleep increases as the need to sleep builds up and decreases when the need is satisfied.
What exactly have you been able to find out so far?
In my work, I have been able to show that during the fly’s awake phases, free oxygen radical products accumulate in the mitochondria – the cell's power stations – of the sleep cells. This stimulates them. Above a certain threshold, this stimulation is enough to trigger sleep. These results showed how the brain is able to measure our need to sleep.
Does this also influence our sleep rhythm?
Well, it's not quite the same. We have the so-called circadian clock, an internal clock that determines that we are awake during the day and that we sleep at night. In parallel to this inner clock, there is a second system that measures our need to sleep and makes sure that we sleep in the first place. This is exactly what my team is investigating. This system detects when we haven’t slept enough at night, makes us tired, and thereby forces us to fall asleep.
So it's all about how the brain recognizes lack of sleep?
That’s right. The idea is that the body has to compensate for sleep deprivation. According to our hypothesis, certain processes can only take place in our organism at night when we disconnect from the environment. These seem to be vital for the organism, so that the body tries to catch up on sleep loss.
Why is it important to know more about our sleep?
Sleep is vital for the organism. Insufficient sleep has been identified by the World Health Organization as a major high-risk factor for several diseases, and sleep disorders are common in our society. It will be key to gain a better understanding of the physiological processes that control sleep in order to develop better treatments.