Safely Switching Consciousness Off and On Again; September / October 2012; Scientific American Mind; by Christof Koch; 2 Page(s)

We take it for granted that any kind of surgical procedure, whether extracting a wisdom tooth or replacing a heart valve, will be painless and won't leave any bad memories. Every year tens of millions of patients worldwide remember being prepared for an operation—then nothing, until they wake up in the recovery room. This is the magic of general anesthesia, which safely knocks out that most precious of life's possessions, conscious experience, then reliably restores it without any lasting consequences. Of course, it was not always thus. Until the discovery of nitrous oxide as an anesthetic in the mid-19th century, surgery was an extreme and dangerous intervention of last resort whose effects could, at best, be blunted by opium or alcohol.

Today anesthesiologists can choose from an astonishing variety of chemicals to separately and independently eliminate pain (analgesia), memory (amnesia), mobility, and responsiveness to the cutting, scraping, drilling or cauterizing of the surgical procedure, and, most important from the point of view of the patient, awareness (loss of consciousness). Two types of anesthetics exist: intravenous agents that are injected into the bloodstream for the rapid induction and maintenance of anesthesia, such as barbiturates, propofol and ketamine, and inhalation agents, such as laughing gas (nitrous oxide) or vapors of volatile liquids, including isoflurane and sevoflurane.