The importance of good sleep
If it can be tempting to shorten our nights to make the most of our days, it is ultimately a very bad calculation. The importance of good sleep for health no longer needs to be demonstrated. Neuroscience has long studied its influence on memory, learning, metabolism or even immunity.
When we are in the arms of Morpheus, our body works in slow motion, our cells are renewed, our heart rate and our blood pressure drop, and our brain assimilates the many information stored throughout the day.
Insufficient sleep causes short-term irritability, fatigue, lassitude and impaired immediate memory. And an accumulation of sleep debt increases the long-term risks: cardiovascular illnesses, of diabetesand even of certain cancers.
An adult needs an average of 7 hours of sleep per day, with a range ranging from 6h to 9h depending on the person. A full night’s sleep ensures that the body benefits from the three phases of sleep in sufficient quantity, all of which play an important role in the body’s recovery.
Sleep cycles: a division into 3 phases, light, deep and paradoxical
Every night, our sleep is divided into 3 to 6 successive cycles which each last between an hour and a half and two hours. Each sleep cycle is articulated in a phase of light slow sleepa slow-wave deep sleep phaseand an REM sleep phase. To study the activity of the brain during these different phases, sleep specialists carry out electro-encephalographies, which trace the electrical waves traversing the brain and testify to neuronal activity.
During the light slow wave sleep phase at the beginning of the cyclethe waves are slow but interspersed with transition phases between wakefulness and sleep: we are not yet sleeping deeply and can be easily woken up. “It is this slow-wave sleep that constitutes the majority of our sleep, since it represents 50 to 60% of our sleep time” indicates the expert.
During the deep slow-wave sleep phase, the waves are slowvery large amplitude and of low frequency : brain activity is significantly reduced.
Finally, during REM sleep – which represents approximately 1/4 of total sleep time – brain activity is exactly the same as when awake. Only our muscle tone is zero.
When do we dream?
Pascale Ogrizek, sleep doctor: If we are likely to dream during all the phases of sleep, it is during the REM sleep phase that the dreams are the deepest and most elaborate.
If something wakes us up during this phase, we are usually able to remember our dream very clearly.
What is the most restorative sleep?
“It is slow, deep sleep that is the most recuperative, especially from physical fatigue, because it promotes the secretion of growth hormones, which participates in cell renewal,” explains Dr. Ogrizek. Slow-wave sleep accounts for approximately 20 to 25% overnight.
REM sleep, or REM sleep
While during slow-wave sleep, breathing is regular, heart rate decreases and blood pressure drops, paradoxical sleep is marked by a irregular breathing and heart rateand by the presence of rapid eye movements say REM for “rapid eye movement”. “You can see the movement of the eye sockets under the clause eyelids” describes Dr. Ogrizek. During this phase, our muscle tone is on the other hand completely abolished: we are therefore paralyzed, in order to prevent us from living our dreams.
How long does this phase last?
REM sleep lasts approximately 25% of total sleep time, in small phases of 15 to 20 minutes. “Over a full night, we are in the REM sleep phase for a little over an hour and a half on average” indicates the specialist.
When does REM sleep occur at night?
REM sleep only occurs after an hour to an hour and a half of sleep, and is more important in the second part of the night. At the beginning of the night, it is the phases of slow sleep – light and deep – which predominate, in order to ensure the good recovery of the body.
What is the role of REM sleep: what is it for?
REM sleep was discovered relatively recently, in 1959, by doctor Michel Jouvet. He defined REM sleep as a kind of third state of the brain between wakefulness and sleep. Since then, many studies have been carried out on the subject, in particular to seek to understand its role.
But the function of this REM sleep is the subject of many hypotheses.
“One of the most supported hypotheses is the hypothesis of the genetic programming of behavior” explains the specialist.
Pascale Ogrizek, sleep doctor: REM sleep would therefore be a state of sleep during which the behavioral patterns specific to the human species, but also specific to the individual, would be repeated blankly. Like a re-programming that would limit the influence of the environment on the nerve connections, and limit their influence on our behavior and our personality.
In psychoanalysisthe Freudian theory suggests that the dream is the expression of a “liberation of instinctive drives” normally blocked by the preconscious.
According to other theories, this paradoxical sleep would play an important role, either in memorization or in forgetting.
It would therefore seem that unlike deep sleep, which is useful for recharging the body’s batteries, paradoxical sleep is more useful for recharging the mind.
REM sleep disorders
If they are rather rare, REM sleep disorders exist.
This pathology is characterized by irrepressible bouts of sleep during the day, sometimes even in full activity. “These bouts of sleep are of short duration (about 15 minutes), and their specificity is that they occur directly in the paradoxical sleep phase” describes Doctor Ogrizek. Narcolepsy is a very rare pathology that affects only one in 5 thousand births.
The sleep paralysis is a parasomnia of REM sleep, which manifests during the transitions between REM sleep and wakefulness. “The person wakes up and is conscious, while his body is still paralyzed as it is in the REM sleep phase” describes the specialist. This state lasts only a few seconds and is totally safe, but it is extremely distressing for those who live it.
The absence of paralysis during REM sleep
Conversely, it sometimes happens in the elderly that the body can continue to move during this phase of REM sleep, allowing them to live their dream. “These people can then carry out sometimes violent movements, with increased physical strength. This disorder is sometimes the precursor of a degenerative disease, such as Parkinson’s disease,” says the doctor.