Activation of the glymphatic system during sleep – is the cerebral venous outflow a missing piece of the puzzle?

Until recently, mechanisms responsible for an activation of the glymphatic system of the brain, the system which is responsible for cleansing of this organ of waste products, were unclear. A recently published paper has finally shed some light on this problem. It has been demonstrated that there is a temporary decrease of the arterial cerebral blood flow during the deep phase of sleep, which is followed by an influx of the cerebrospinal fluid into the cranial cavity, and that this phenomenon is probably responsible for the activation of the glymphatic system. Although, of as yet, this issue has not been studied, it is likely that such a mechanism is not effective in the settings of disturbed cerebral venous outflow, and that in the case of venous congestion inside the cranial cavity, neurodegenerative lesions may develop. Therefore, the investigations on cerebral venous haemodynamics in the context of proper functioning of the glymphatic system should be one the directions of future research.