We love that morning feeling that makes us say: “I woke up feeling refreshed today.” But that’s not the norm. Among other things, because there are so many things that worry us in our daily lives that sometimes, when it’s time to go to sleep, no matter how tired we are, we are unable to sleep.
We count sheep, do breathing exercises, and try to put to the test any advice that will help us fall asleep. And, in this way, we wake up wanting to take on the world or, at least, to be as rested as possible for our daily tasks. We are in search of the longed-for restful sleep. And describing it as “restful sleep” is not just a metaphor.
If we do the math, we can easily see that we spend a third of our lives sleeping. There must be a reason why our body needs it. With sensations and warnings, sooner or later, the moment arrives when signals are activated to encourage us to rest.
We sleep to repair the DNA of neurons.
The most intimate origin of the signals that induce sleep is in our cells. These signals are activated in a precise way to repair the damage that occurs within them, in a natural way, during daily activity.
The molecular mechanisms that lead us to sleep have been unmasked in a very recent study in animal models since sleep is essential in all organisms with a nervous system. And it has been shown that the ultimate goal of sleep is to repair the damage that accumulates in DNA while we are awake. Yes, just like it sounds.
When we are awake, the homeostatic pressure that induces sleep, that is, fatigue, builds up in the body. We accumulate fatigue when we are active and we deplete it when we sleep. And we reach a minimum of fatigue after a full night of good sleep.
The main cause of increased homeostatic pressure is the accumulation of damage to the DNA of neurons. During the normal functioning of all our cells, reactions occur whose products can damage DNA and, therefore, the genes that make us who we are.
All cells have molecular mechanisms to combat damage, day and night. But neurons are more susceptible to damage accumulation when we are awake, reaching dangerous levels that we cannot afford. Science has revealed that sleep recruits DNA repair systems, which fix it so efficiently that we wake up feeling refreshed, and that is the perfect way to say it. Using the metaphor “a good night’s sleep” makes perfect sense.
PARP1 sends us to sleep
One of the first molecules to respond and activate the mechanisms that induce sleep is the protein PARP1. Its mission is of vital importance: it is responsible for marking the sites of DNA that have been damaged and recruiting the appropriate systems to repair them.
An interesting result was that if PARP1 is prevented from acting, the feeling of sleepiness disappears. But this inhibition also means that the DNA mutation repair systems are not activated, something that you can already guess is not good.
How many hours of sleep are necessary?
To try to find out if there is a minimum number of hours of sleep that leads to the desired restful sleep, the study used the zebrafish, an animal model commonly used in brain studies and with a sleep pattern similar to that of humans.
What if we go to a party?
Motivation is also one of the many and very different neural mechanisms that regulate sleep-wake cycles.
Motivation, without a doubt, modulates whether we are more likely to stay awake or to get out of the way and go to sleep if the situation requires it. When we are motivated we can maintain good physical and mental performance, for example by writing an interesting article, reading a good book, or dancing at a fun party. And all this far beyond our usual schedules and ignoring homeostatic pressure.
In nature, establishing relationships with other conspecifics, mating opportunities and the presence of predators clearly generate motivational responses and modulate states of arousal. There are animals that can remain awake or asleep much longer than normal, and even keep only half of their brain awake, and only one eye open.
Something similar happens to humans when we sleep in a bed that is not our own during a trip. This is what is known as the first night effect. It is, therefore, more than interesting to understand as well as possible the processes that modulate arousal and its relationship with staying awake or going to sleep since they can lead to complicated situations, even conflict.
For its meaning and relationship, let us end with the beginning of the poem “The Dream” by Jorge Luis Borges: