**3.4 Sleep and aquaporin-4 in brain cleaning**

Attributed to the expression and function of the AQP-4 channels, the brain cleaning mechanism is predominant during sleep. Sleep increases the expansion of the extracellular spaces by up to 60% which allows for a maximal exchange of substances to and fro the CSF and the ISF compartments [11]. This phenomenon is particularly observed in the lateral position [12]. Therefore, the restorative properties of sleep may be linked to increased glymphatic clearance of the metabolic waste products that are generated by neural activity in the awake brain. This might underpin the beneficial effects of sleep, in clearance of metabolic byproducts, the phenomenon of jetlag, and the problems with lack of sleep.
