What are sleep stages?
Sleep is divided into three stages of NREM sleep (light N1 sleep, N2 sleep, deep N3 sleep) and REM sleep. A person usually falls asleep in about 15 minutes, first falling into a light N1 sleep followed by N2 sleep shortly. After about half an hour the person goes into a deep sleep N3. During deep sleep, the brain recovers and the waste products are removed from the brain.
About 90 minutes after falling asleep, deep sleep changes into REM sleep, during which the human autonomic nervous system is activated, breathing may become uneven, and heart function accelerated. Intermittent arrhythmias and occasional respiratory arrest are also possible. The striated muscles are completely flabby and only involuntary muscles, such as the respiratory muscles, work. During REM sleep, the brain’s metabolism is even faster than when awake.
After a while, REM sleep changes again to a N2-N3 sleep, either after a short wake or a light sleep.
In a healthy person, the various sleep phases are repeated 4 to 6 times during the night, with each cycle lasting approximately 90 minutes. A kind of rhythm of about 90 minutes is also noticeable during wake and is called the BRAC (basic rest-activity cycle). In practice, some people may have noticed that if you do not go to bed at night when you are tired, it may take those 90 minutes for the next fatigue to appear.
In a newborn child, most sleep consists of REM sleep. Respectively in old age both REM sleep and deep N3 sleep amount decrease.
All night long sleep polygraphy is needed to identify and classify sleep phases, which simultaneously records brain electrical activity (EEG), jaw muscle activity (EMG), and eye movement (EOG).
Classification of sleep stages
- N1 light sleep
The first phase of NREM sleep is equivalent to a light snooze. And is transition stage between wakefulness and being fully asleep. The electrical activity of the brain slows down. In N1 sleep, alpha activity changes to 3-7 Hz theta. Muscle tension (EMG), measured in the jaw muscles, decreases and slow wavy eye movements are detected in the eye movement channels (EOG). One can hear sounds from the environment and does not necessarily feel like he is sleeping in N1. In a good sleeper, N1 sleep is only about 2 to 5 percent of sleep. With poor sleep, the proportion of N1 sleep increases.
- N2 sleep
This sleep phase is equivalent to light sleep. The N2 sleep phase is characterized by sleep spindles of 1 to 2 seconds in length and 12 to 14 Hz in frequency.
In addition, K-complexes (a waveform that may be seen on an EEG) in response to external stimuli can be detected in this sleep phase. N2 stage sleep typically makes up the majority of our sleep: 40–55% in healthy young adults.
- N3 deep sleep
Deep sleep on NREM also called as delta sleep or slow wave sleep. The predominant activity is slow ½ to 2 Hz delta frequency. No K complexes are present. Breathing and heart function are regular and calm. N3 sleep is revitalizing and regenerative sleep phase. Normally, a person has deep sleep at least 15-25 percent of the night’s sleep.
- REM sleep
The name of the REM sleep phase refers to the rapid eye movements that are typical of this sleep phase. The EEG is somewhat reminiscent of alertness, which is why this sleep phase is also called paradoxical sleep or desynchronized sleep. Potential alpha activity is slower than during wake. No K-complexes. During tonic REM sleep, muscle tension (EMG amplitude) is at its lowest. During phasic REM sleep, rapid eye movements and small muscle spasms are observed. Heart rate and breathing are often irregular. REM sleep is also referred to as the phase when dreaming occurs. REM sleep averages about 20 to 25 percent of the night’s sleep.
Sleep stages are currently classified by the American Academy of Sleep Medicine as three stages of NREM sleep (N1-3) and R sleep (REM). The previous Rechtschaffen and Kales sleep ratings had four NREM sleep phases (S1-4) and REM sleep. Steps S3 and S4 of the previous classification are combined in the new classification into the same N3 dream. Thus, according to the previous classification, the combined number of S3 and S4 sleep estimates is equivalent to N3 sleep. Previously used S1 sleep corresponds to N1 sleep and S2 sleep corresponds to N2 sleep.
Everyone dreams, and yet everyone also knows someone who never dreams and who doesn’t remember any of the dreams they saw. However, we each spend a few hours each night dreaming. Dreams are also seen in sleep phases other than REM (rapid eye movement), but this phase involves fast eye movement and lively sleep. The actual REM episode occurs during the last three sleep cycles of the morning.
Theories of seeing dreams
REM sleep is associated with rapid and sharp eye movements and is the name of this sleep phase (Rapid eye movement sleep). However, the same phase is also called paradoxical sleep because during this period muscle tension and reflexes are absent, but the brain is active. During REM sleep, acetylcholine secretion is increased while serotonin and adrenaline secretion are decreased. Blood circulation increases, heart rate increases and blood pressure fluctuates. The sleep curve shows theta waves, which are linked to the activity of the hippocampus, and thus to memory and space perception.
A study published by a hospital based on studies from the 1980s focused on sleep and sleep disorders. Studies in the psychodynamic frame of reference on the restoration of dreams are interesting.
Because the restoration of dreams has played a role in psychodynamic psychotherapy even after Freud, it has also been studied why some people are unable to recall their dreams afterwards. This led to interesting theories, caused by patients’ sleep registrations:
- People who forget their dreams deny their anxiety and are more defensive.
- In one study, individuals who were unable to recall their dreams had more eye movements during REM sleep, which was combined with more vigorous prevention. On the other hand, eye movements can also refer to sleep-time thinking, making the more abstract content of dreams in itself more difficult to recall.
- In addition, conditions that interfere with a good night’s sleep can also reduce your dream memory. These include stressful conditions, for example.
Experimentally, it has been shown that when a sleeper is awakened from the REM sleep phase, is able to restore the dream, at least visually more accurately than a person, who has already passed the REM phase of the sleep cycle. There are various theories about the importance of seeing dreams, and while one theory suggests that REM sleep is about balancing emotional life, the research evidence does not explicitly support it.
Seeing dreams is associated with procedural or implicit memory. This means that the skills learned during being awake are stored in memory during REM sleep. This implicit memory can also be called emotional memory. Newborns see dreams about half the time they sleep, while adults only dream about a quarter of their sleep. We remember better the things we associate with stronger emotions, and it is these events that get stronger during REM sleep.
Because animals also see dreams, dreams are thought to simulate coping with threats. During sleep, the best coping strategies are stored in memory, which can then be found in the event of a real danger.
How does the mind work during sleep?
Dreams can also be used to deal with threats or traumas that you have already experienced. When a person sees dreams of such situations, the intense emotional charge associated with the situation weakens and they are organized into memory without much emotion. This explains why the emotional component of powerful experiences diminishes over time, even though the events themselves are well remembered.
REM sleep is also associated with search activity concept. This theory, developed by Vadim Rotenberg and associates, is an adaptation theory, a biological behavioral model that thrives on animal experiments. The theory is that an individual – animal or human – constantly monitors their environment without a predetermined goal. Searching refers to the ability to change a situation or attitude at any given moment without knowing the outcome in advance. Adaptation leads to the successful functioning of the individual and the body’s resistance to stress, illness and other harmful factors.
The dream of REM sleep is related to the theory of exploration so that, according to the theory, REM sleep provides a search activity that is functioning while awake, that is, an environmentally adaptive activity. Sometimes, in times of stress, the search activity of an individual is blocked: for example, an animal may become paralyzed and may not choose to fight or flee. This is called freezing. In humans, similar blocking can occur in anxiety neurosis. Anxiety occurs when a person suppresses unacceptable influences that come to consciousness. After such a situation, the amount of REM sleep is increased and the sleep acts as a recovery activity.
According to Allan Hobson, dreams reveal more than conceal. His neurochemical theory presents the REM sleep phase as changes in neurotransmitter levels and concomitant electrical activity.
While awake the brain constantly checks the content of our thoughts for reality, and therefore our thoughts, actions and feelings are logical. However, during REM sleep, closure of the serotonin valve and concomitant high acetylcholine levels cause the sleep consciousness to be dominated by intense emotions and strange sensations. Because our mind wants to find logic in everything, it weaves a coherent story from dreamlike images, which is not necessarily coherent, but rather dreamlike. When one wakes up from sleep, the secretion of serotonin increases and the sleep experience is flushed out of consciousness. This explains why dreams are difficult to remember.
One professor’s threat simulation theory is a biological model that assumes that functions, including dreaming, are selected to promote species survival. Most of the dreams that are recalled have some sort of threatening content, even if they are not medically defined as nightmares. We practice or simulate such a threat situation in our dreams. Even the most neutral sleep contents can be simulations of social situations for reality, because our existence depends on our fellow human beings. Therefore, seeing dreams has no direct purpose in promoting or maintaining mental health.
What are lucid dreams?
I was climbing the ladder. They were set against a high stone wall, and they were narrow and shaky. Suddenly, for some reason, they began to lean back, and for a moment I was terrified. Suddenly, however, I knew this was a dream, and I knew that I wouldn’t get hurt, even if I fell from high down. It was as if I was watching the ladder fall from the side. I got up from the ground unharmed. After that, I never again saw that dream again. – Woman, 42
Most adult people have sometimes seen a lucid dream. During this, the dreamer realizes he is asleep and follows the dream as if he were a bystander. Sometimes he may also consciously direct his sleep in some direction.
Seeing lucid dream is considered a dissociative state, which in this context means the simultaneous action of two different functions, sleep and wake. Lucid dreams are significantly more common in children and adolescents than those over the age of 16 and are therefore thought to be involved in brain development.
A German study specifically surveyed school-age children through a lucid dream questionnaire. The study found that 6-14 year olds see a lot of lucid dreams, but after the age of 16 they become rare. In addition, lucid dream was found to be associated with a higher level of knowledge among school children as well as in connection with nightmares. In a nightmare-threatening situation, the sleeper may have begun to monitor the situation from the outside and may have guided her sleep to a safer direction.
In another study, adult subjects were trained to see lucid dreams by self-suggestion. After a few months of training, they were able to see lucid dreams more often and communicate about those with eye movement. They were then subjected to sleep registration over several nights in a sleep laboratory. Measurements showed that during lucid dreams, the electrical function of the brain was different from that during wake or REM sleep. The transition to lucid dream went from REM sleep, not wake, and during this time the forebrain and the anterior lobes of the brain were active. These areas are inactive during REM sleep and are associated with, among other things, human will function and self-perception