The 5 phases of sleep

Why do we sleep? Why do we spend at least a third of our lives doing something that happens so fleetingly? To answer these questions, scientists have delved into the phases of sleep for decades. Understanding these cycles, this fascinating dream structure, can undoubtedly help us know more about ourselves.

On the other hand, something that we have been able to reveal is some of the vital functions that rest has in human beings. The brain needs us to sleep to carry out a series of processes. The first is to recover energy, the second is to reorganize information, take certain data to long-term memory, delete others that are considered useless, carry out metabolic and cleansing tasks…

Thus, and although Many of the purposes of sleep remain a biological enigma, We understand some aspects, those that we have managed to resolve thanks to electroencephalogram tests and rest deprivation studies. These and other investigations have in turn helped us to understand the phases of sleep in depth. Let’s see it below.

The phases of sleep

Sleep is divided into five phases. During this process, the brain carries out what neurologists define as neuronal integrity and remodeling of synaptic connections.

In fact, studies such as the one carried out at the Medical University of Lublin, in Poland, define sleep as a vital and neuroprotective necessity. It is like cleaning ourselves, like putting a tune-up on the most important and sophisticated organ in our body. From the beginning of sleep, these five phases appear in an orderly manner until we reach the REM phase. Then, throughout the night, periods of non-REM sleep alternate with periods of REM sleep. Each of these cycles lasts approximately 90 minutes. Therefore, In a sleep period of eight hours there will be four or five cycles.

The phases of sleep have been discovered through numerous studies in sleep laboratories. These are distinguished by mental activity recorded in an EEG (electroencephalogram) and by various physiological measures. Below we will detail what happens in each of these phases of sleep.

Phase I of sleep

This is the first phase of sleep. When the subject closes his eyes and notices that feeling of numbness is in this phase. Here we find that the conscious subject capable of reacting to stimuli in his environment. It is actually a transition phase between wakefulness and sleep.

At a physiological level, we find some theta brain waves. This means that EEG activity begins to be synchronized. Although it is still irregular, it is not as irregular as waking brain activity. If we observe a subject’s eyes in this phase, we observe how they open and close from time to time, and how they move up and down.

Phase II of sleep

After 10 minutes in phase I, the sleeping subject enters phase II. The subject is now fast asleep. But if the subject is awakened in this phase, he will not remember having slept. He will insist that he has been awake the entire time. Is a preparatory phase for true conciliatory sleep of phases III and IV.

At a physiological level, we find a Irregular EEG with episodes of theta waves. If an auditory stimulus is presented in this phase, a brain wave called the K complex appears; This wave seems to represent an auditory inhibition process that allows the individual not to wake up.

Slow wave sleep (Phases III and IV)

After 15 min in phase II, the individual begins phase III. Here It is the stage where restorative rest really occurs. Phase III and IV are quite similar, there is simply a change in sleep depth and sleep effectiveness.

In this phase, we find a slow wave EEG. This means that brain activity is highly synchronized and relaxed. We find strong inhibitory neuronal activity, to prevent the subject from waking up. This stage is also highly important for memory consolidation and learning processes.

REM phase (Rapid Eye Movement)

The REM phase comes after about 45 minutes in slow wave sleep. It is opposite to the other phasesin this we find a state similar to that of wakefulness. Brain activity is desynchronized and accelerated. Although it is difficult to awaken a subject in this phase, a significant stimulus (such as saying his name) will awaken him. It is much shallower than slow wave sleep.

In this phase we find that the subject’s eyes move rapidly in all directions (hence its name). And there is a marked loss of muscle tone, the subject is paralyzed. This paralysis is due to the fact that dreams appear during the REM phase. And to prevent the subject from imitating what he is doing in his dreams, there is a disconnection of the muscles.

Another curious fact about the REM phase is that genital activity appears in the form of vaginal lubrication in women and penile erection in men, without sexual arousal. This characteristic of REM sleep has been used in the clinical field to distinguish whether the causes of sexual impotence are psychological or physiological.

The function of the REM phase is still not entirely clear. Studies like the one published in the journal Neuroscience , They point to a function related to memory consolidation and learning. But even so, there is still much to discover about this paradoxical phase of sleep.

To conclude, as we see, we still have many mysteries to solve about rest and sleep phases. As more techniques and sophisticated engineering become available, we will reveal more aspects about this dream universe.

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