During deep sleep phases (NREM 3–4), a special brain cleansing mechanism is activated – the so-called glymphatic system. It was described relatively recently and serves as a "sanitation network" for the central nervous system.
How it works. In a waking state, the intercellular space of the brain is relatively narrow, and the circulation of interstitial fluid is limited. During deep sleep phases, under the influence of decreased norepinephrine levels and overall relaxation of the body, the intercellular gaps expand almost twice. This allows cerebrospinal fluid to actively wash the brain tissues, flushing out metabolic byproducts: excess ions, toxins, damaged proteins, including β-amyloid and tau proteins.
It has been established that it is during the night that the brain eliminates up to 60% of the metabolites accumulated during the day.
Why this is important. Amyloid proteins are normally constantly formed as a byproduct of neuronal activity.
If the glymphatic system is not functioning well (for example, due to chronic sleep deprivation, sleep apnea, or disruption of deep sleep phases), amyloids begin to accumulate in the brain tissues.
These deposits form amyloid plaques, which are considered a key pathological factor in Alzheimer's disease and other neurodegenerative disorders.
Similarly, the accumulation of pathologically altered tau proteins is associated with the development of so-called tauopathies.
Implications for health. Lack of sleep, especially a deficit in phases 3 and 4, sharply increases the risk of cognitive decline.
Studies have shown that even one night of poor sleep leads to a measurable increase in β-amyloid concentration in the cerebrospinal fluid.
Chronic sleep deprivation exacerbates inflammation, reduces neuroplasticity, and accelerates degenerative processes.
Thus, deep sleep is not just "rest," but an active phase of neurodetoxification. It is critically important for the prevention of memory diseases and the maintenance of long-term cognitive health.
