Sleep has long been considered a ‘rinse cycle’ for the brain, with cerebrospinal fluid flushing out waste and toxins that accumulate during wakefulness. However, the mechanism behind this process was unclear until a recent study published in Cell shed new light on the subject. Researchers found that blood vessel contractions, stimulated by the release of adrenaline-like chemical norepinephrine, propel cerebrospinal fluid through the brain.
Studies have shown that glymphatic clearance – the removal of waste and toxins from the brain – is beneficial for overall health. However, research has also suggested that this process may be disrupted during sleep. To investigate further, scientists implanted electrodes into mice to track blood volume, electrical activity, and chemical levels during sleep. The results revealed that cerebrospinal fluid flow increased during non-REM sleep, when the body undergoes renewal.
The study found that norepinephrine oscillations – which occur every 50 seconds – triggered blood vessel contractions that propelled cerebrospinal fluid through the brain. This mechanism was not observed to the same extent when mice were awake or in REM sleep, when memories are consolidated. The researchers also discovered that zolpidem, a widely used sleep aid, impeded this process by reducing norepinephrine oscillations and cerebrospinal fluid penetration.
The findings suggest that the glymphatic system may be more active during non-REM sleep than previously thought. While the study’s results have implications for the development of new sleep aids, it is essential to note that zolpidem should not be stopped without consulting a doctor. Further research in humans is necessary to determine whether this medication affects brain clearance in the same way.
Neuroscientists Suzana Herculano-Houzel and Maiken Nedergaard, who were not involved in the study, praised the findings as “excellent science.” The discovery highlights an important neural circuit that regulates glymphatic flow and underscores the importance of continued research into this complex process.
Source: https://www.science.org/content/article/scientists-uncover-how-brain-washes-itself-during-sleep