October 16 is World Anesthesia Day, celebrating the 170th anniversary of the first successful demonstration of surgical anesthesia. Prior to then, surgery was really unpleasant, to put it mildly -- surgeons turned to alcohol, narcotics and even smacking their patients on the head to induce unconsciousness. Fortunately, anesthesia now allows tens of thousands patients every day to avoid the pain and memories of their procedures. But how does anesthesia work? This week, Reactions looks at scientists' current understanding of what happens when you go under.