The mechanics of the unique psychedelic mindstate remain tantalizingly unclear, but there are several interesting clues. For instance, LSD enhances REM sleep associated with dreaming. During a typical night, we experience about four or five periods of REM sleep, increasing in duration toward the end of the night. During REM sleep, the activity of the brain’s neurons is very similar to the activity during waking hours, but the body is paralyzed and cannot move. It was dubbed “paradoxical sleep” when it was first discovered, as this brain activity seemed to indicate that the subject was not sleeping at all.
A subject was observed during a normal sleep cycle of approximately seven hours, which was interrupted briefly one hour after she fell asleep in order to administer a placebo or 30ug of LSD. First, the inactive placebo was given. Her progression through the four stages of sleep may be seen in the top graph, with periods of REM sleep indicated by the dark black bars. We can see that most of her REM sleep occurs during lighter Stage 1 sleep.
While the initial REM episodes a half hour or so after waking are similar, after 30ug of LSD the second REM episode occurs much earlier and lasts almost three and a half times longer than the corresponding REM episode after placebo. Many more micro-REM episodes lasting only ten to twelve seconds burst into sleep for several hours after the LSD has taken effect.
In general, LSD can prolong the first or second REM episode and cause these REM micro-bursts, but only if given in low doses immediately before sleep or one hour after sleep begins. Doses that are too high simply cause the sleeper to awaken as they are about to transition to REM sleep.
Joseph N. Muzio, Howard P. Roffwarg, Edward Kaufman, Alterations in the nocturnal sleep cycle resulting from LSD, Electroencephalography and Clinical Neurophysiology, Volume 21, Issue 4, October 1966, Pages 313-324.