Anesthesia, the reversible pharmacological suspension of conscious brain activity, despite being the cornerstone of modern surgery, is to this date a biological puzzle. The peculiar selectivity of general anesthetics towards consciousness, sparing most of the other brain functions essential for homeostasis, introduces the broad problem of finding the underlying biological mechanisms of conscious perception on one hand, and on the other univocally determining the neural correlates of consciousness to be able to quantitatively measure it. While scientific efforts still have not managed to frame both aspects in a convincing theoretical framework, over the years various theories of general anesthetic action have been proposed.