Fluid dynamics during sleep

During non–rapid eye movement sleep, low-frequency oscillations in neural activity support memory consolidation and neuronal computation. Sleep is also associated with increased interstitial fluid volume and clearance of metabolic waste products. It is unknown why these processes co-occur and how they are related. Fultz et al. simultaneously measured electrophysiological, hemodynamic, and flow signals in the human brain (see the Perspective by Grubb and Lauritzen). Large oscillations of fluid inflow to the brain appeared during sleep and were tightly coupled to functional magnetic resonance imaging signals and entrained to electroencephalogram slow waves. Slow oscillatory neuronal activity thus leads to oscillations in blood volume, drawing cerebrospinal fluid into and out of the brain.

Science, this issue p. 628; see also p. 572