Despite the astonishing fact that 234 million general anaesthetics are administered each year around the world, the way in which anaesthetics put you to sleep remains unknown. The phrase “put you to sleep” is synonymous with general anaesthesia, and recent evidence suggests this metaphor may be more accurate than we had ever imagined. At least some anaesthetics appear to act in part by hijacking sleep-promoting pathways in the brain to exert their effects.
While there are obvious similarities between natural sleep and general anaesthesia, there are also marked differences. Sleep is an active process in which our brain changes between states of high activity (REM sleep) and low activity (slow wave sleep). During general anaesthesia, the brain’s activity resembles only slow wave (or deep) sleep.
Another obvious but important difference is that while pain will waken someone from sleep it does not rouse the anaesthetised patient.
The intriguing phenomenon we have sought to explain is the common feeling after anaesthesia that time has not passed. While we often wake up just before our alarm sounds in the morning, aware that time has passed during the night, when people emerge from general anaesthesia they often report they have only just been put to sleep.
Our current lack of understanding of the effects of general anaesthesia on time perception...
