Lulu Xie et al write in their paper Sleep Drives Metabolite Clearance from the Adult Brain:
Using real-time assessments of tetramethylammonium diffusion and two-photon imaging in live mice, we show that natural sleep or anesthesia are associated with a 60% increase in the interstitial space
Do we have technology to do the similar measurements in humans and not only in mice? Have those measurements been done?