Sleep is a crucial component of our daily life that interacts with human mental and physical health.
What is sleep?
Sleep is controlled by two primary mechanisms and is a biological process in which our response to various stimuli gradually decreases throughout the day. It varies according to gender, age, events, and situations we are exposed to during the day and is influenced by these factors.
Sleep consists of sleep cycles lasting 90 to 120 minutes. Within a sleep cycle, there are three subsections, N1, N2, and N3 with slow eye movements (NREM) and a phase with rapid eye movements (REM) characterized by dreams. The repetition of sleep cycles (NREM-REM) during the night makes up our total sleep time, and about 4-6 cycles are observed in one night (Carskadon, & Demen, 2005; Malhotra, & Avidan, 2013).
Sleep Mechanisms:
Sleep is controlled by two biological sub-mechanisms: the circadian rhythm (process C) and the homeostatic process (process S). Process C refers to the circadian rhythm, also known as the body's biological clock. This cycle lasts about 24 hours. During this cycle, some hormones (melatonin and cortisol) and body temperature are regulated by the action of daylight. The center of the circadian cycle is the suprachiasmatic nucleus in the hypothalamus of the brain (Borbély, 1982; Luyster et al., 2012).
Process S refers to the initiation of sleep depending on the amount of adenosine accumulated during the day. Adenosine remains an end product of the use of adenosine triphosphate (ATP), our body's energy unit, and its accumulation during the day creates homeostatic pressure. In electroencephalography recordings, there is a correlation between the strength of activity in the theta band and the amount of adenosine. Caffeine consumed during the day can block adenosine and postpone sleepiness (Borbély et al., 2016).
Detecting the existential rhythm and interpreting it in different situations is our main approach to the data set.
Is sleep a passive process?
The question of whether sleep is an active or passive process can be clarified by dividing it into different domains. In this sense, sleep can be classified as a passive process, physically speaking. There is relative immobility in the NREM and REM sleep phases caused by different systems. In the NREM phases, sensory inputs are filtered by the thalamus, and motor activity is reduced (Tubbs et al., 2019). Specifically, during the REM phase, which is associated with the influence of vivid dreams, muscles are inhibited to prevent movement. This state is also referred to as sleep paralysis. In contrast, the maintenance of brain electrical activity, the decrease in cerebral blood flow by only 20% during sleep, and the overlap of the N3 phase of sleep with the maximum release point of growth hormone suggest that this is a biologically active process (Honson, 2005).
Poor sleep quality may predict a higher risk of anxiety conditions later in life.
Sleep & Health:
Sleep is closely related to mood, cognitive performance, and daily activity levels. Sleeping more or less than necessary leads to various health problems and death. For example, glucose tolerance has been reported to be impaired, cortisol levels to increase, leptin (satiety hormone) levels to decrease, and ghrelin (hunger hormone) levels to increase in individuals whose sleep has been restricted for several consecutive days. Similarly, when sleep duration is reduced, antioxidant defense responses decrease, and we have lower immunity to various diseases as the body is less able to ward off and fight them (Luyster et al., 2012). Another study of 686 male university students highlighted that poor sleep quality was associated with mental health problems (e.g., depression, anxiety), that individuals with stress, anxiety, and depression symptoms slept less well, and that there was a strong association between sleep quality and mental health problems (Zou et al., 2020).
Observational and prospective studies have shown an association between sleep duration and type 2 diabetes, body mass index, obesity, and metabolic disease!
According to the above information, experts believe that at least two nights of sleep monitoring are essential for the diagnosis and detection of a sleep disorder. However, it is known that in today's hospital environment, it is difficult to fall asleep with electrodes and cables (polysomnography/sleep recording devices) attached to several parts of the body. On the other hand, it is not possible for people from different social classes to make an appointment at a hospital and/or pay for sleep data recording at a private clinic. Therefore, it is important to record individual sleep at home with a validated sleep monitoring device that is suitable for everyday use. We are pleased to introduce our "sleep and stress monitoring device" that we are working on, which falls into the domain of wearable technologies!
REFERENCES:
Borbély, A. A. (1982). A two process model of sleep regulation. Hum neurobiol, 1(3), 195-204.
Borbély, A. A., Daan, S., Wirz‐Justice, A., & Deboer, T. (2016). The two‐process model of sleep regulation: a reappraisal. Journal of sleep research, 25(2), 131-143.
Carskadon, M. A., & Dement, W. C. (2005). Normal human sleep: an overview. Principles and practice of sleep medicine, 4(1), 13-23.
Hobson, J. A. (2005). Sleep is of the brain, by the brain and for the brain. Nature, 437(7063), 1254-1256.
Luyster, F. S., Strollo Jr, P. J., Zee, P. C., & Walsh, J. K. (2012). Sleep: a health imperative. Sleep, 35(6), 727-734.
Malhotra, R. K., & Avidan, A. Y. (2013). Sleep stages and scoring technique. Atlas of sleep medicine, 77-99.
Tubbs, A. S., Dollish, H. K., Fernandez, F., & Grandner, M. A. (2019). The basics of sleep physiology and behavior. In Sleep and health (pp. 3-10). Academic Press.
Zou, P., Wang, X., Sun, L., Liu, K., Hou, G., Yang, W., ... & Chen, Q. (2020). Poorer sleep quality correlated with mental health problems in college students: A longitudinal observational study among 686 males. Journal of psychosomatic research, 136, 110177.