Why Do We Sleep?

Why do we sleep? Why do we dream? How conscious are we during sleep and dreams? Neurologist Mélanie Boly explains the important ongoing studies at The Center for Sleep and Consciousness at University of Wisconsin.


My name is Melanie Bolli, and I’m a neuroscientist and neurologist.

So what we do is in the laboratory. There are two main topics as the title of the lab is saying the other set of experiments in humans and animals about the functions of sleep. And we also work on neural correlations of consciousness and find mechanisms more likely to get a broad it’s all work in progress.

But Giulio Tononi has a very promising theory called the synaptic homeostasis theory of sleep, shy. And this hypothesis says that we need to sleep to learn during wakefulness because what happens during wakefulness is that we are constantly exposed to new situations, and we learn all the time. And we mainly learn by strength, strengthening connections, making connections tight and stronger in the brain. But then you cannot do that continuously without a renormalizing process.

Because if you were like making the connection stronger all the time, you could increase your energy consumption, even increase the brain’s volume, and that’s not sustainable because then your brain will explode. And then you cannot hold that, right. So they hypothesize that sleep is that particular period it is crucial to renormalize to decrease the weight of the signups.

And in the morning, when we wake up, we’re again ready to learn. As I said, there are different theories of sleep. And this one is very promising. But they are still testing it experimentally, although there is a lot of data to support it now. So they have done experiments in animals looking at the strength, and the number of signups shows that you have more signups when you go to sleep and then when you wake up in the morning, right?

But then what they try to do is also finding a way to improve the quality and like if you want to be the efficiency of sleep, like they think that slow waves, the electroencephalography, big slow waves we have during sleep are involved in that plasticity process. And there are investigating if you induce slow waves with sound, for example, in human subjects. And then you would need to sleep, let’s hear.

I guess my biggest surprise was I’m working for 11 years in vegetative state patients. And these patients have their eyes open. But they don’t show any signs of consciousness. So my biggest surprise working in the field was that experiment with Adrian, who wasn’t before Cambridge now is in Canada. And so we designed a program together to detect consciousness in patients that kind of move in. And so what you do is you ask them to imagine some things like imagine playing tennis while they are in the scanner, and you record the brain activity.

And personally, I designed a paradigm, but I never thought it would work, right? Because I thought, well, these patients, they don’t move they, you know, maybe they’re just too weak to have some high, you know, like very abstract restaurants to come in. But it works in one out of 10 patients, maybe, but they do. So, yeah, it is really useful. And that was a very big surprise for me.

It tells you a lot about the dissociation between behavior and actually what someone can experience. The patients we have that responsibility to like we do imagine playing tennis show activation of the motor cortex when we ask them at the bedside that you don’t see any behavior. So that tells you a lot about the difficulties of accessing consciousness clinically and how, like for dreams, Yeah, like how from the outside someone can be no sign of consciousness completely asleep or unresponsive and then still a lot is going on. So I think it’s very striking.

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