How the Brain Takes Out the Garbage While You Sleep

Oleg Kritsky -

Evidence suggesting that sleep is crucial to your health continues to pile up. A recent finding published in Science has shed light on one of the mechanisms behind the restorative function of sleep. It seems that while we sleep, our brain is tidying up. During wakefulness, the body’s metabolism produces a host of neurotoxic waste products, including beta-amyloids (Aβ), which are cleared from the brain during sleep.

The accumulation of Aβ in the interstitial space leads to the buildup of plaques associated with Alzheimer’s disease and dementia.  These improperly functioning protein structures are toxic to the cells that make up the central nervous system (CNS).

The exact mechanism by which Aβ plaques lead to neurotoxicity is not well understood. One hypothesis is that Aβ may compete for insulin receptors, causing inadequate glucose metabolism, which eventually leads to neurodegeneration – a landmark feature of Alzheimer’s disease.

In addition, research has shown that Aβ is detrimental to glutamatergic synaptic transmission and intracellular calcium homeostasis. Collectively, these adverse effects of Aβ presence in the interstitial space lead to irreversible neuronal damage.

Because of their neurotoxic effects the CNS needs to process and remove metabolic byproducts such as Aβ. The CNS lacks a conventional lymphatic system that would otherwise perform this task. It is, however, bathed in another solution: cerebrospinal fluid (CSF). CSF allows the brain to float without collapsing on itself, protects it from mechanical stress, facilitates proper blood flow to the brain, and acts as a “dumpster” that collects metabolic waste produced in the CNS.

Sleep is associated with a whopping 60% increase in the interstitial space volume, which provides for a dramatic increase in exchange of material between the CSF and interstitial fluid (ISF). At the onset of sleep, the increased ISF volume allows for improved clearance of Aβ by “dumping” it into the CSF, where Aβ is eventually passed to the general blood circulation to be degraded by the liver.

Nearly every study suggests that sleep is required to restore the body and the brain and improve function. This study shows that, in addition to the many benefits conferred by sleep, it is also important in regulating clearance of waste products that are linked to neurodegenerative diseases such as Alzheimer’s and dementia – a powerful reminder that our brains need a time to have their garbage taken out.

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