Comment Re:Extremely variable sleeping periods (Score 2) 210
"Sleep is universal among vertebrates (9) and has been found in invertebrates (9, 10). The total number of hours of daily sleep varies from as much as 20 hours in bats to as little as 3 to 4 hours in giraffes and elephants (8, 11)—and there is currently no reasonable physiological hypothesis to explain this variation (11).Because CSF perfusion of the interstitial space is limited to the surface of the brain during waking, and brain volume increases faster than brain surface area [even with the folding of the cortical surface (12)], larger brains should have a relatively larger volume of interstitial space to “buffer” the accumulation of sleep-driving molecules, and thus might be able to withstand much longer periods of waking before the inevitable switch to the waste-clearing state of sleep occurs. If only neuroscientists could easily bring live, large-brained animals to the lab." (emphasis mine)