The human sleep structure includes two phases: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. During the sleep period, these phases are in rotation and replace each other several times (Hassan & Subasi, 2017). Sleep phases changes primarily are characterized by different brain waves, which are recorded using electroencephalography (EEG). Each stage of sleep has its features and gets operated by a different set of neurons.
NREM includes three stages; the first one begins immediately after the person falls asleep and lasts about ten minutes. Sleep is characterized by a decrease in alpha rhythms and the appearance of low-amplitude theta rhythms. The second stage lasts from 20 to 40 minutes, during which theta wave activity begins to appear on the EEG readings. During the third stage, delta oscillations of a frequency begin to predominate in brain activity.
REM starts after about 80 minutes from the moment a person falls asleep and lasts about 10-15 minutes. Muscle activity is minimal, and the person is in a state of complete immobility. At the same time, eyeballs often make sharp movements. According to EEG, the brain has the same activity level as during the first stage of NREM. During sleep, the duration of REM periods increases, and in the morning, it can reach up to 30-40 minutes.
There are three types of clusters of neurons, the excitation of which causes a change in sleep cycles. Sleep begins with the activation of the anterior hypothalamus. Sleep-promoting neurons suppress wakefulness neurons at the onset and during sleep. The development of non-rapid eye movement is ensured by the functioning of nonspecific thalamic nuclei and suture nuclei containing an inhibitory mediator. The second structure of neurons regulates REM. They include the locus coeruleus or “blue space,” the vestibular nuclei of the medulla oblongata, as well as the upper tubercles or “upper hills”. The third structure of neurons appears to be the centers that regulate the sleep cycle. These include the “blue space,” which controls the process of falling asleep and waking up and certain areas of the cerebral cortex.
To sum up, there are two sleep stages: non-rapid eye movement sleep and rapid eye movement sleep. Despite the EEG readings’ accuracy, the relationship between brain waves and dream structure has not been fully articulated. Three different categories of neurons operate sleep inside the human body.
Reference
Hassan, A. R., & Subasi, A. (2017). A decision support system for automated identification of sleep stages from single-channel EEG signals. Knowledge-Based Systems, 128, 115-124. Web.