What happens in the brain when we sleep

What happens in the brain when we sleep

The brain is not passive during sleep. On the contrary, there are lots of things happening there…

A night is made up of 3 to 6 cycles per night. Each lasts approximately 90 minutes and is broken down into 4 phases: falling asleep, slow-wave sleep (which includes light slow-wave sleep and deep slow-wave sleep), REM sleep, and a latency/wake-up period. Throughout these phases of sleep, the brain remains active and reacts in different ways.

1. The brain plunges into a “haze of consciousness”

During the day, the hypothalamus, a small region located in the heart of the brain, secretes serotonin and small proteins “hypnogens” which inhibit the neurons of the arousal system. They are what help you fall asleep in the evening. The eyelids become heavy, the eyes sting, the yawns increase and ideas get confused : this “fog of consciousness” as scientists call it, are the signs that we are going to sleep. The team of Dr Hélène Bastuji from the Neuroscience Research Center in Lyon analyzed the different brain waves occurring in succession in the brain when falling asleep which reflect the activity of neurons, using intracranial electrodes. These researchers showed that the thalamus (located just above the hypothalamus) falls asleep before the cortexHeadquarters consciousnessand could explain some hallucinations or sensations felt (free fall, jolt) when falling asleep.

2. He slows down more and more

In the second phase of the sleep cycle, “during slow-wave sleep (50-60% of the night), the electrical activity of the brain gradually slows down explains to us Dr Marc Rey, neurologist and President of the National Institute of Sleep and Vigilance (INSV). The sleeper is then in a sort of half-sleep and can wake up easily. In the deep slow-wave sleep phase (20% of the night), the electrical activity of the brain slows down more and more, “until reaching 1 hertz whereas normally, when we are in a calm waking state, the brain has electrical activity with a frequency of 8 to 12 hertz. continues our interlocutor. Breathing and heart rate are regular. It is at this moment that we secretes growth hormone in particular. The sleeper plunges into a state where his brain is increasingly insensitive to external stimulation such as noise or light. He wakes up with difficulty.

3. The brain produces inconsistent and complicated dreams

In the third phase of the cycle, “during paradoxical sleep (20% of the night), the electrical activity of the brain is close to waking while we are sleeping. Brain waves are fast. From a cerebral point of view, the sleeper is barely asleep and is easily “wake up”. Behaviorally, he is sleeping and his muscles are paralyzed.” describes the specialist. This is why this phase is called “paradoxical” sleep because the individual simultaneously presents signs of deep sleep and signs of wakefulness. Many areas of the brain are very activatedlike the visual areas, those of emotion… On the other hand, the “executive control” areas, active when awake, are there deactivated” completes the Dr Philippe Beaulieu, somnologist. During paradoxical sleep,he most productive, abundant, pictorial, incoherent and complicated dreams occur. The content of a dream during REM sleep could “translate the emotional conflicts of the moment, in a symbolic way“, explains the somnologist.

4. When you wake up, the brain gradually reactivates

At the end of the night, the cycles consist almost exclusively of paradoxical sleep. This is why the “lucid dreams” or more concrete seem more numerous in the early morning. Daylight or outside noise causes the brain to gradually reactivate and must make the transition from sleep to consciousness. During this time, it is possible (and normal) to feel a little groggy and confused. “A kind of sleep inertia or“drunkenness of sleep“, image Dr. Andrew McHill, director of the Sleep, Chronobiology and Health Laboratory at Oregon Health and Science University.