The Glymphatic Influx and Slow Delta Waves in Sleep and Anesthesia

Investigation of the mechanisms and pathways of waste clearance in the brain has received much attention lately because of their functional significance and clinical implications (1,2). In a recent study (3), Hablitz et al. made an attempt to bring us one step forward in tackling the puzzling question of how and when the brain clears its waste. Here, the authors studied the influence of different anesthetics (known to emulate sleep like conditions) on the glymphatic influx, which subsequently promotes waste clearance. It is the first study to demonstrate that the rate of glymphatic influx can be correlated to the prevalence of high EEG delta power and low heart rate variability. This relation also seems to vary uniquely based on the type of anesthetic substance administered. Analyzing the findings, they propose that the prevalence of the slow delta waves of highly synchronized neuronal activity promotes glymphatic influx. But we suggest, while assigning such role to the delta waves alone, findings may benefit if analyzed and interpreted in relation to a recent observation of the presence of regional delta oscillations in REM sleep; which hitherto is considered as the characteristic hallmark of non-REM sleep (4).