Cortical Arousal during REM Sleep, LDEs and OBEs
REM sleep is sometimes called 'paradoxical sleep' because it is a state of high cortical arousal. During this state the brain sends out a signal paralyzing the body to prevent it from acting out dreams. But the eyes are not affected. Experienced lucid dreamers can send signals from the dream state by moving their eyes in the dream. This causes the physical eyes to move, an event that is recorded in the sleep lab. In one experiment the dreamer signaled upon becoming aware of the dream state. Then the team correlated the period of dream lucidity with other readings they were taking.
The H-reflex, which is normally suppressed in REM sleep, was found to be even more suppressed during lucid dreaming than during nonlucid dreaming; indicating that the body is even more paralyzed during lucid dreaming than during nonlucid dreaming. Why? Well, the team also found that the brain was more aroused than normal, too. [Brylowski, Andrew, Levitan, Lynn & LaBerge, Stephen. "H-Reflex Suppression and Autonomic Activation during Lucid REM Sleep: A Case Study". Sleep. 12(4):374-78.]
Lucid dreams are typically much more elaborate than non-lucid dreams. The experiencer is more active as well. The increased paralysis may well be required to keep the body still.
This paradox of high cortical arousal and decreased bodily mobility has been noted in at least one area of OBE research.
Ketamine, a drug consistently associated with OBEs, operates by stimulating the central nervous system. When it is used an anesthetic, other medications are commonly given to keep the patient from thrashing about. This simultaneous brain activation and bodily deactivation may explain why ketamine experience reports of OBEs frequently include typical NDE themes when it is used in a hospital setting, but only infrequently when it is used recreationally according to the late parapsychologist D. Scott Rogo. [Rogo, D. Scott. (1989). The Return from Silence. Wellingborough, Northamptonshire (England): Acquarian Press. p. 113-29.]
Perhaps recreational users do not simultaneously take the second medication. Or, perhaps, recreational users seek only the hallucinogenic 'trips' that occur at dosages far less than than those given by anesthesiologists preparing a patient for surgery. In any event, more research is clearly needed.
An Alpha Wave Continuum?
There may be a continuum where alpha wave activity is correlated with degree of dream consciousness or lucidity.
Both lucid dreaming and sleep paralysis are REM state phenomena and EEG traces taken from subjects in these states show similarities. Alpha waves are present in the EEG trace of both, although these waves are steady in LDE and intermittent during ASP. [Takeuchi, T., Miyasita, A., Sasaki, Y., Inugami, M., and Fukuda, F. (1992). "Isolated Sleep Paralysis Elicited by Sleep Interruption." Sleep. 15(3): 217-225.]
Other researchers correlating the degree of Alpha wave activity with lucidity found that non lucid dreams had a low level. Lucid dreams had more. Prelucid dreams (in which the dreamer reflected upon the status of the experience during the experience) had more alpha activity than lucid dreams. Tyson, P.D. et. al. (1984). Lucid, Prelucid and nonlucid Dreams Related to the Amount of EEG Alpha Activity during REM Sleep. Psychphysiology. 21(4): 442-51. This superficially surprising result may indicate that attempting to ponder the question 'Is this a dream' requires more brain activity than is required to experience the dream once the identification 'This is a dream' is made.
In any event, more research is needed to establish the reality of this continuum and the place of phenomena as False Awakenings and Out-of-Body Experiences on it.