1. Read the following article: Fultz NE, Bonmassar G, Setsompop K, Stickgold RA, Rosen BR, Polimeni JR, Lewis LD. Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleep. Science. 2019 Nov 1;366(6465):628-631. doi: 10.1126/science.aax5440. PMID: 31672896; PMCID: PMC7309589. Click here to download: csf oscillation in human sleep paper.pdf Download csf oscillation in human sleep paper.pdf Summarize this article in 3-4 sentences. 2. Why do we sleep?