Can people dream under anaesthetic?

Kat asked Chris this question...

Chris - Almost certainly not. The reason is that when you go to sleep and you have what's called physiological, normal sleep, this is a very organised process of brain activity. Dreaming occurs when you go through a phase of which is called REM (rapid eye movement) sleep and you can see when this happening to somebody because, if you look at them when they are sleeping. you will see their eyelids flickering because their eyeballs are moving around underneath their eyelids. If you wake someone up when they're doing that and ask them do you remember anything, do you recall anything, they will almost overwhelming say "I was just having a dream". And as you go through the night your dreams become longer, they become more detailed and you tend to have your best, richest and most memorable and recallable dreams right at the end of a night's sleep. We don't know what dreams do, but they're very important for psychological well being. If you deprive people of restful sleep and dream sleep, then they don't feel rested the next day, they don't remember things, they can't form new memories properly, and that kind of thing. So it's probably got some kind of brain cleansing or memory consolidation role. But when you put people to sleep with an anesthetic agent, anesthetics disrupt the membranes of nerve cells and what they do is make nerve cells become less active than they should be. They increase the activity of inhibitory nerve signals in the brain and they decrease the excitation in the brain and, as a result, they basically just shut down your brain for the most part. There are some that work slightly differently but that's the general process. And so all they do is just turn you into an unconscious individual with very low levels of brain activity, not this organised pattern of dream activity, so you do not dream when you're under an anaesthetic, although, when you're waking up, you may have some bizarre experiences because your brain is just beginning to kick-in and return to consciousness. And so some people do describe some rather strange memories as they wake up from an anaesthetic, but that's not when they were actually anaesthetised.