What’s the neurological difference between anaesthesia and sleep?

If a neuroscientist used electroencephalography (EEG) to record your brain’s electrical activity while you were under anaesthesia, the results would look different from how they appear when you are sleeping. In fact, your brain waves under anaesthesia would more closely resemble those seen were you to have the terrible misfortune of falling into a coma after brain illness or injury. Doctors often tell surgery patients that they will be ‘put to sleep’ during the operation, but in terms of the neurological effects of the anaesthesia, it would be more accurate (and more unsettling) to tell them that they will be put into a reversible coma.