Looking at the groups closely interested in sleep disorders in Europe, they observed that there were apneas in sleep without being aware of each other; Tassinari, Gastaut and Duron working in France, Jung and Kuhlo working in Germany published their results in 1965 (Resource, 2011).
The sleep period, which is important for all living organisms, first attracted the attention of scientists about how and for what reasons dreams come into existence, which is the awareness of science. As a biological factor, sleep is the state of making the biological norms suitable for all levels by reviewing the biological structure in the formation of neural pathways that control the cognitive activities as tasks and functions and behaviors that activate the intercellular process states with the effect of genes. Carlson, 2013).
Sleep is a state experienced for many animal species. For many years, the effect of sleep on living species has been studied by scientists and is still being researched. Research on sleep is observed in sleep centers or in sleep laboratories in some universities. Revitalizing theories suggest that regeneration and repairs are significant in sleep, and the evolutionary perspective has suggested that sleep is an adaptive activity that ensures survival acquired over time (İtil, 2011).
In the studies carried out on sleep, the people who conduct the research are required to use some electronic devices. Some of these are: EEG (Electroencephalography), EMG (Electromyogram), EOG (Electro-occulogram) devices (Carlson, 2013). These electronic devices are necessary to follow the electrical waves (EEG) coming from the brain, eye (EOG) and muscle movements (EMG). In addition to these, devices that monitor the level of communication in the skin ((Skin Conductance), heart rate and breathing level are also used in research on sleep. The person to be researched is requested to come to the laboratory mostly at night. The benefit of this situation is that sleep can be normalized. EEG electrodes are placed in certain parts in contact with the scalp of the individual (Carlson, 2013).
In this sense, its effect on sleep is important in keeping the researches done on humans and animals stable. For this reason, based on effective data and analyzes on the microbiology of dreams and sleep, research on these words has increased its importance even more by using the keywords “sleep, neurobiology, memory, synaptic plasticity” in the theses and articles published in recent years (Carlson, 2013). ).
In humans, the sleep process takes place in four main stages, three parts of non-REM sleep and REM sleep. These parts can vary in terms of the pattern of brain waves.
Until the end of the first three stages, the brain waves gradually slow down and allow the REM sleep, the deepest sleep, to begin (Hobson, 2004). It is possible to list the four basic sleep stages and features mentioned here as follows:
This episode is a phase that we can count between sleep and wakefulness. When a normal person is awake, two different wave patterns can be observed in his brain. These are: Alpha and Beta Activities (Carlson, 2004).
This wave pattern, which is called alpha activity, manifests itself as a pattern in which the person is not cognitively engaged, for example, working at work, solving problems, or not being exposed to stimuli, that is, in a state of rest. It is observed that this fluctuation pattern comes regularly and is at medium frequency (between 8 Hz and 12 Hz) (Pace-Schott et. al. 2003).
Beta activity, on the other hand, can be observed during the period when the individual actively exhibits cognitive activities. During this activity, irregularity is seen in the brain waves and it manifests itself in the form of low frequency (13-30 Hz).
The brain of the individual in the 1st stage of sleep is 3.5-7.5 Hz. Theta started its activity by producing the wavelengths measured between This episode lasts for roughly ten minutes. At the end of this process, the individual transitions to the second sleep stage (Pace-Schott et. al. 2003).
When looking at EEG transcripts, Theta fluctuations, sudden fluctuations (Sleep Spindles) and increments per second (K-complex) are observed in the brain waves of the individual in the 2nd sleep stage. The state of brain waves, which are defined as Sleep Spindles, fluctuate with a shocking effect between two and five per minute and the wavelength is adopted as twelve to fourteen Hertz (Carlson, 2004).
On the other hand, the K-Complex is a second-long increase observed against a sudden sound. In their MRI experiments, Czisch et al. revealed that the function of the K-Complex is enhanced by preventing the individual’s sleep fragmentation (Czisch et. al. 2004). If the individual is warned during this period, he will claim that he has not fallen asleep.
Stage 3 and Stage 4
It is quite challenging to distinguish between these two phases. The third stage of non-REM sleep is considered intermediate to deep sleep. The fourth stage is the last and deepest stage among the Non-Rem sleep stages (Hobson, 2004).
About fifteen minutes after the second phase, Delta surges initiated by K-Complex waves begin to appear. When we look at the length of these waves, 3.5Hz. It can be easily seen that it is less than . In this stage, the individual is observed as having entered deep sleep (Hobson, 2004). It may be more difficult to awaken the individual during this process. During this phase, certain events take place in the body.
At this stage, the blood pressure of the individual drops considerably, decreases in breathing rate and relaxation occurs in the muscles (Hobson, 2004). From the first part of sleep to the end of the fourth stage, approximately one hour passes.
The brain wave movements recorded by EEG during the REM sleep period are similar to the brain wave movements that the individual will show when he/she is awake (Active Sleep). It is nervously active. The brain fluctuation in this universe is of low scale and high frequency (Carlson, 2004).
The duration of REM sleep in the initial sleep cycle ranges from one to five minutes, and this duration of REM sleep can be prolonged during cycles throughout the night.
During REM sleep, a person’s eyes move rapidly. This stage takes its name from this situation (Hobson, 2004). This phase is the phase in which the person dreams. Many scientists suggest that rapid eye movement in this phase is due to dreaming. The muscles in the body become paralyzed, and therefore the data presented by the EMG device seems rather stagnant (Hobson, 2004).
After the sleep cycle consisting of Non-Rem and Rem is defined for the first time, the individual begins a second sleep cycle (Carlson, 2004). During the sleep process, this sleep cycle lasts for about ninety minutes, of which about twenty minutes is REM sleep. From here, it would not be wrong to say that the person repeats this sleep cycle four to five times during an eight-hour uninterrupted sleep. When an awakening occurs here, these cycles start all over again (Pace-Schott et. al. 2003).