Your brain doesn’t sleep at night!
The point of sleeping is to get restorative sleep so you can recharge your batteries, but one of your organs remains constantly active nonetheless: the brain. In fact, it is even the brain’s electric activity (EEG or electroencephalogram) which defines the two major phases of each sleep cycle, slow wave sleep and paradoxical sleep (dreams). How does the brain function during the night and why do we suffer sleep disturbances?
How does an electro-encephalogram (EEG) work?
To analyze sleep quality, sleep specialists need to record numerous parameters.
By measuring cerebral activity with an EEG, they can gauge a lot of information about how the brain works.
What are brainwaves?
Both nerve tissues and muscle tissues work on the basis of cellular polarization and depolarization, which basically creates an electric current. So we can use different devices with electrodes to record these types of electric activity in the form of waves. The electromyogram records muscle activity, the electrocardiogram is for cardiac muscle and the electroencephalogram (EEG) is used for the brain.
What are the different types of brainwaves?
The different types of waves tell us about the nature of our cerebral activity. We can characterize them in terms of frequency, duration and the amplitude tells us how coordinated the neurons are (synchronization).
During wakeful hours, the brainwaves measured are very small, which indicates the neurons are multitasking, so there are multiple activities going on.
In contrast, the neurons become synchronized during sleep, meaning there is only one activity going on: sleeping!
We can distinguish 5 types of brainwaves which each reflect the workings of the brain:
- α waves (alpha 8-12 Hz), the creativity and relaxation waves
- ß waves (beta 12-30 Hz), alertness and activity waves
- γ waves (gamma 30-60 Hz), waves for information processing
- δ waves (delta 0-4 Hz), sleep waves
- θ waves (theta 4-8 Hz), deep relaxation waves
What are the phases of sleep?
The brain is very active at night: measurements of its electric activity have proven that sleep is roughly divided into 90 minute cycles. There are 4 to 6 cycles per night depending on the individual.
We can distinguish two major phases:
- Slow wave sleep, or non-paradoxical sleep (75 % of time spent sleeping), which consists of a light sleep phase of around 20 minutes and a deep sleep phase of around 60 to 75 minutes.
- Paradoxical sleep (25 % of the time spent sleeping, or about 15 to 20 minutes) with significant eye movement (the REM, or Rapid Eye Movement phase).
What is the role of slow wave sleep?
This phase has two distinctive parts: slow wave sleep, which is light sleep, the phase in which you are falling asleep, and slow wave deep sleep which is recovery sleep. It is during this time that a number of hormonal mechanisms kick in to regulate the activity of our organs and major physiological functions like growth, weight and blood sugar…
Slow wave light sleep, the most fragile phase
This phase is about preparing you for the next phase of sleep, by slowing down your mental and metabolic activity.
At this stage, the slightest external signal wakes us up.
Body temperature also progressively drops, cerebral activity decreases, breathing and cardiac frequency slow down while our muscles relax.
Slow wave deep sleep, the best for recovery
The deep sleep stage is the one where we recover.
An EEG will show the presence of waves with a big amplitude and a low frequency, and functional imaging (fMRI) will show reduced oxygen consumption, proof that the brains’ metabolism is slowing down. Even though cerebral activity is lessened, the brain is at work is focusing on one key task, memorization.
A multitude of connections are formed between neurons to fix new knowledge and memories in the brain’s memory region. Also, during this stage the secretion of the growth hormone is at its highest, its maximum level in the circadian cycle, and numerous toxins are eliminated too.
This deep sleep phase represents around ¼ of the total duration of sleep, and essentially occurs during the first part of the night.
What is the role of paradoxical REM sleep?
We call this phase paradoxical sleep because it is like a state of deep sleep in which the individual also shows signs of alertness. At this time, our cerebral activity is intense, causing rapid and incessant eye movements. At the same time, our muscles are completely lax; our body is in the opposite state to our mind, as though it were paralyzed. This is the phase in which we have the longest and most elaborate dreams, mainly occurring as the night comes to an end.
The way the brain functions during paradoxical sleep
Brainwaves during paradoxical sleep tend to be smaller and closer together than during slow wave sleep, and the contrast is particularly marked when compared with deep sleep. This reflects multiple neural activities going on, almost like when we are awake.
Some parts of the brain like the primary visual cortex remain totally relaxed, a part of the brain involved in processing information from the retina. This is true even though there is rapid eye movement happening at the same time.
Another area which remains relaxed is the prefrontal cortex, responsible for reasoning and logic.
On the other hand, there is marked activity in other regions, like the sensory regions: the associative visual cortex which produces images, the amygdala which is responsible for emotions, and the hippocampus which aids in memory processing are 3 regions which are especially solicited. This is why our dreams are so full of images and emotions, fear and joy.
What is the point of paradoxical sleep?
For a long time it was thought that the essential role of paradoxical sleep was to consolidate procedural memory (the memory of movements and physical know-how). This has been partially confirmed by the intense cerebral activity observed in the hippocampus.
Today, this theory has been fine-tuned though, and neuroscientists are trying to better explain the role our dreams play. For a long time, we thought dreams only occurred during this paradoxical phase of sleep, but it turns out this is false.
Nevertheless, it is true that we remember dreams we have during the paradoxical phase of sleep better than those we have during slow wave sleep.
As it happens, researchers were able to identify the region of our brain dreams come from in 2017 using EEG. They discovered that the regions which were activated were actually linked to the themes of the dreams. For example, dreaming about people will activate the region of the brain involved in facial recognition, and the same region is also activated for that task when we are awake. It seems that the main reason why we dream is so we can assimilate emotions felt over the course of a day, which explains in turn why sleeping badly has an effect on our emotions and our mood.
How can EEG be used to get better sleep?
Sleep specialists often use EEG combined with other sensors (forehead muscles, ocular movements…) to diagnose sleep disorders.
We call this polysomnography.
Although not quite as thorough, some connected devices can allow you to begin this analysis at home, and they are already available today.
You can use helmets, headbands, mattresses equipped with sensors or bracelets to record different parameters and find out if you are getting good restorative sleep, or poor sleep. The most advanced devices study movement, cardiac and respiratory frequency, brainwaves, body temperature etc.
Neurofeedback, a solution to restore sleep
New technologies aren’t just used to make diagnoses; they can also help you to treat sleep issues naturally.
Indeed, in order to remain in a life sustaining state of equilibrium, living organisms are constantly making internal readjustments. We receive information and treat it by giving feedback. The two principal forms of feedback are hormonal and cerebral (Neurofeedback).
Doctors naturally thought that they could use this innate technique to treat sleep issues, and they were right. The objective of Neurofeedback is to produce the right brainwaves to stimulate the right regions of the brain and teach yourself how to sleep better.
It’s a way to relearn healthy sleeping patterns which works just like other kinds of re-education exercises. As a consequence, connected devices which provide Neurofeedback allow us to treat insomnia without using sleeping pills.
Sounds interesting? Find out more here