No. 105: May-Jun 1996
The first paragraph of this long review article defines the anomaly well.
"A patient undergoing surgery with general anaesthesia can reasonably expect to remember nothing about the operation on recovery. Cases of direct recall of intraoperative events have been reported, but these are rare and are nearly always attributable to faulty anaesthetic technique or apparatus failure. However, a study by Levinson in 1965 alerted people to the possibility that information processing may continue despite clinically adequate anaesthesia: In this study, he subjected 10 dental surgery patients to a mock crisis in which, mid-operation, the anaesthetist exclaimed, 'Stop the operation, I don't like the patient's colour. His/ her lips are much too blue. I'm going to give a little oxygen'. Subsequently, patients had no recall for the 'crisis'. However, under hypnosis one month later, four of them repeated verbatim the anaesthetist's exclamation and four showed evidence of partial recall."
Such experiments suggest strongly that perception and some sort of learning occurs even when a person is clinically unconscious. Does this mean that consciousness is not essential to the learning process?
(Andrade, Jackie; "Learning during Anaesthesia: A Review," British Journal of Psychology, 86:479, 1995)
Comment. The foregoing supports those anecdotes in which a person "sleeps on a problem" and awakes with the solution. From personal experience, this works with crossword puzzles and cryptograms.