By sleep pressure, medicine understands a regulatory circuit that regulates fatigue and triggers physically induced sleepiness. During periods of wakefulness, metabolic products are deposited in the brain, triggering swelling sleep pressure. During sleep, the glymphatic system cleanses the brain of these deposits.
What is sleep pressure?
In medicine, sleep pressure is a regulatory circuit that regulates fatigue and triggers physically induced sleepiness. Sleep has essential tasks. These tasks include the regeneration of body cells, but also mental regeneration and the storage of learning experiences. Too little sleep therefore impairs physical and mental health. Persistent insomnia can therefore even be fatal for the human organism. In order for humans to get enough sleep on a regular basis and to avoid adverse health consequences, sleep and the need for sleep are subject to several physical regulatory circuits. In this context, medicine understands sleep pressure as a physically induced sleepiness. Together with the internal clock of the biorhythm, sleep pressure thus regulates the duration and timing of sleep. The regulation of the sleep-wake rhythm is the responsibility of the internal clock. Unlike the internal clock, however, sleep pressure does not depend on the diurnal rhythm, but increases consistently during the waking phase. Thus, the longer a person is awake, the more intensely he or she feels sleep pressure. The physiological cause of the increasing sleepiness is probably the metabolic products that accumulate in the brain during the waking phase. Above a certain level, therefore, these metabolic products make people sleepy. Sleep pressure thus regulates the purely physical need for sleep.
Function and task
Sleep pressure contributes in part to survival. By regulating sleep duration and controlling fatigue, for example, the mechanism ensures that sufficient cell regeneration can take place during sleep. During the day, all kinds of molecular metabolites accumulate in the brain. The brain has only limited energy at its disposal, and in its energy planning it decides on one of two functional states each time: the awake state or the state of sleep. In the waking state, the brain is able to concentrate on the environment and works. This work is conscious to the person and can be understood by him, for example, by his own thoughts. Although the person may not be consciously aware of any of this during sleep, however, the brain does not rest at all even in the sleep state – it continues to work and, unlike during the day, primarily tidies up at night. In sleep phases such as REM sleep, for example, the tidying-up work consists of sorting information. The sleeper can sometimes trace this sorting through dreams. However, this is not the only tidying up work the brain does during sleep. The glymphatic system is considered a kind of garbage disposal of the brain. It also cleans the control center of molecular metabolic products that accumulate during the day. The purification system is a network of tiny channels that contain the so-called cerebrospinal fluid and correspond to a kind of lymphatic system of the brain. As organizers, supporting and auxiliary cells of the nervous system, glial cells take control of the network. They ensure that all waste is collected in the channels during sleep and can thus be washed away with the cerebrospinal fluid into the bloodstream. Metabolic products are removed about twice as fast during sleep as during wakefulness, because the cerebrospinal fluid circulates faster during the resting phase. The nocturnal cleansing of the brain is closely related to sleep pressure. A person feels increasing fatigue as more metabolic products accumulate in the brain. The peak phase of sleep pressure is immediately before falling asleep. In the first three to four hours of the sleep phase, the sleep pressure decreases, because presumably the harmful metabolic products are also already broken down in this time period.
Diseases and ailments
Sleep disorders have not yet been conclusively researched. In recent decades, sleep medicine has established its own specialty that takes into account and documents the crucial tasks of sleep. Sleep pressure plays an important role in sleep disorders. For example, the reduction of sheep pressure makes people wake up momentarily after about four hours.However, many people with sleep disorders wake up far more frequently at night. Difficulty falling asleep despite high sleep pressure is also a common phenomenon. Somewhat less common is a general lack of sleep pressure. Sleep quality is directly related to sleep pressure. For example, if people go through too few deep sleep phases and their sleep remains generally superficial, metabolic products, and with them sleep pressure, can only break down at a slower rate. The result is daytime fatigue, inability to concentrate and reduced performance on the following day. Sleep disturbances due to reduced sleep pressure are often caused by irregular sleep-wake times. Sleeping late on weekends can, in some cases, reduce sleep pressure to such an extent that difficulties in falling asleep occur. The accumulation of metabolic products in the brain, which triggers sleep pressure in the first place and thus indicates the need for self-cleansing, is currently being researched. This research is devoted, for example, to the question of how sleep pressure might play a role in diseases such as Alzheimer’s and epilepsy, and what therapeutic options might be conceivable in this context.
