Sleep is a vital stage of a day cycle in humans. Even though modern scientists have conducted numerous studies of sleep, the functions of sleep remain unknown. According to various studies, sleep bares restorative, adaptive, and cleansing functions, as it helps the body to dispose of toxins (Garrett & Hough, 2018). The effects of sleep become apparent under conditions of sleep deprivation, as the human brain starts to experience significant difficulties performing its cognitive functions. Therefore, the importance of sleep is difficult to overestimate.
There are four stages of sleep divided into rapid eye movement (REM) sleep and non-REM sleep. During the first stage of sleep, the EEG shifts to theta waves, with a frequency of 4–7 Hz (Garrett & Hough, 2018). During this phase, the eyes are closed, but a person is easy to wake up. After 5-10 minutes, a person falls into the second stage of sleep, or light sleep, which is characterized by a decrease in heart rate and a drop in the body temperature. This stage is associated with the emersion of K complexes and sleep spindles (Garrett & Hough, 2018). K complexes are large waves in EEG that appear every minute, and sleep spindles are brief bursts of 12- to 14-Hz, which prevent disruptive stimuli from reaching the cortex and waking up the person (Garrett & Hough, 2018). The third stage is known as slow sleep and characterized by delta waves at a frequency of 1–3 Hz (Garrett & Hough, 2018). During this stage, a person is difficult to wake and can feel disorientated if he or she wakes up. These three stages are non-REM sleeping stages.
REM sleeping stage is also known as a paradoxical sleeping stage, as the EEG looks similar to a relaxed waking stage (Garrett & Hough, 2018). The sleeper is difficult to arouse but can react to meaningful inquiries (Garrett & Hough, 2018). According to research, 80% of the time during the REM stage, people report dreaming, which is not frequent during non-REM stages.
Waking and sleeping are controlled by complex processes as there is no center that controls it. Wakefulness is promoted by brainstem areas and hypothalamus by sending arousal signals to the cerebral cortex (Garrett & Hough, 2018). These signals are chemicals called neurotransmitters, which induce the arousal of different parts of the brain (Garrett & Hough, 2018). Neurons in the ventrolateral preoptic nucleus (VLPO) are responsible for shutting down the arousal centers promoting sleep (Garrett & Hough, 2018). Thus, sleeping and waking controls are complex processes that require further research.
Disruption of sleep can cause a problem with cognitive functions. The article by Maski et al. (2017) studied one of the central functions of sleep, which is memory consolidation. Previous research demonstrated that sleep spindles during the second stage of sleep could be used as mediators for the cognitive abilities of children. The researchers hypothesized that children with primary snoring (PS) and obstructive sleep apnea (OSA) had decreased cognitive abilities due to impairment of declarative memory consolidation. An experimental study was conducted, which confirmed that the hypothesis using rigorous scientific methods. Therefore, the intensity of sleep spindles can be biomarkers of risk for cognitive dysfunction.
Narcolepsy is a neurological disorder that involves problems controlling sleeping and wakefulness. Patients with this disease fall asleep suddenly during the daytime and fall directly into the REM sleep. As a result, patients may experience excessive daytime sleepiness, hypnogogic hallucinations, cataplexy, and sleep paralysis (Bhattarai & Sumerall, 2017). There is no cure for the condition; however, its symptoms can be treated with amphetamine-like stimulants to fight sleepiness and antidepressant drugs to lessen cataplexy (Bhattarai & Sumerall, 2017).
In summary, the functions of sleep remain unknown even after excessive research. Sleep has four different stages, which are divided into REM sleep and non-REM sleep. There are numerous sleep disorders, which can affect the well-being of a person.
References
Bhattarai, J., & Sumerall, S. (2017). Current and Future Treatment Options for Narcolepsy: A Review. Sleep Science, 10(1). Web.
Garrett, B., & Hough, G. (2018). Brain and behavior: An introduction to behavioral neuroscience (5th ed.). Los Angeles, CA: SAGE Publications, Inc.
Maski, K., Steinhart, E., Holbrook, H., Katz, E., Kapur, K., & Stickgold, R. (2017). Impaired memory consolidation in children with obstructive sleep disordered breathing. PLOS ONE, 12(11), e0186915. Web.