Physiological Characteristics Of Lucid Dreaming

There are two distinct ways in which lucid dreams are initiated. In the usual case, subjects report having been in the midst of a dream when a bizarre occurrence causes sufficient reflection to yield the realization that they are dreaming. In the other, less frequent case, subjects report having briefly awakened from a dream and then falling back asleep directly entering the dream with no (or very little) break in consciousness (Green, 1968; LaBerge 1985a). Here is an example of a wake-initiated lucid dream:

I was lying awake in bed late in the morning listening to the sound of running water in the adjoining bathroom. Presently an image of the ocean appeared, dim at first like my usual waking imagery. But its vividness rapidly increased while, at the same time, the sound of running water diminished; the intensity of the internal image and external sound seemed to alter inversely (as if one changed a stereo balance control from one channel to the other). In a few seconds, I found myself at the seashore standing between my mother and a girl who seemed somehow familiar. I could no longer hear the sound of the bath water, but only the roar of the dream sea.... (LaBerge, 1980, p. 85)

Note that the subject is continuously conscious during the transition from wakefulness to sleep. This fact suggests that Foulkes (1985) is over-stating the case by claiming that it is "...a necessary part of the experience we call 'sleep' that we lose a directive and reflective self. You can't fall asleep, or be asleep, if your waking self is still regulating and reflecting upon your conscious mental state" (p. 42). 

Since lucid dreams initiated in these two ways ought to differ physiologically in at least one respect (i.e., an awakening preceding one but not the other), the SVLDs were dichotomously classified as either 'Wake-initiated' (WILD) or 'Dream-initiated' (DILD), depending on whether or not the reports mentioned a transient awakening in which the subject consciously perceived the external environment before re-entering the dream state. 

Fifty-five (72%) of the SVLDs were classified as DILDs and the remaining 21 (28%) as WILDs. For all 13 subjects, DILDs were more common than WILDs (binomial test, p < .0001). As expected, compared to DILDs, WILDs were more frequently immediately preceded by physiological indications of awakening (Chi-squared = 38.3, 1df, p < .0001) establishing the validity of classifying lucid dreams in this manner. See Figures 2 and 3 for illustrations of these two types of lucid dream. 

Figure 2. A typical dream-initiated lucid dream (DILD). Four channels of physiological data (central EEG [C3-A2], left and right eye-movements [LOC and ROC], and chin muscle tone [EMG]) from the last 8 min of a 30 min REM period are shown. Upon awakening the subject reported having made five eye movement signals (labeled 1-5 in figure). The first signal (1, LRLR) marked the onset of lucidity. Skin potential potential artifacts can be observed in the EEG at this point. During the following 90 s the subject "flew about" exploring his dream world until he believed he had awakened, at which point he made the signal for awakening (2, LRLRLRLR). After another 90 s, the subject realized he was still dreaming and signaled (3) with three pairs of eye movements. Realizing that this was too many, he correctly signaled with two pairs (4). Finally, upon awakening 100 s later he signaled appropriately (5, LRLRLRLR). [Calibrations are 50 microV and 5 s.]

As was mentioned earlier, momentary intrusions of wakefulness occur very commonly during the normal course of REM sleep and it had been proposed by Schwartz and Lefebvre (1973) that lucid dreaming occurs during these micro-awakenings. However, LaBerge et al.'s (1981,1986) data indicates that while lucid dreams do not take place during interludes of wakefulness within REM periods, a minority of lucid dreams (WILDs) are initiated from these moments of transitory arousal, with the WILDs continuing in subsequent undisturbed REM sleep. 

Figure 3. A typical lucid dream initiated from a transient awakening during REM (WILD). Six channels of physiological data (left and right temporal EEG [T3 and T4], left and right eye-movements [LOC and ROC], chin muscle tone [EMG], and electrocardiogram [ECG]) from the last 3 min of a 14 min REM period are shown. The subject awoke at 1 and after 40 s returned to REM sleep at 2, and realized he was dreaming 15 s later and signaled at 3. Next he carried out the agreed-upon experimental task in his lucid dream, singing between signals 3 and 4, and counting between signals 4 and 5. This allowed comparison of left and right hemisphere activation during the two tasks (LaBerge and Dement, 1982b). Note the heart-rate acceleration-deceleration pattern at awakening (1) and at lucidity onset (3), and the skin potential potential artifacts in the EEG (particularly T4) at lucidity onset (3). [Calibrations are 50 microV and 5 s.]

To summarize, an elevated level of CNS activation seems to be a necessary condition for the occurrence of lucid dreams. Evidently the high level of cognitive function involved in lucid dreaming requires a correspondingly high level of neuronal activation. In terms of Antrobus's (1986) adaptation of Anderson's (1983) ACT* model of cognition to dreaming, working memory capacity is proportional to cognitive activation, which in turn is proportional to cortical activation. Becoming lucid requires an adequate level of working memory to activate the pre-sleep intention to recognize that one is dreaming. This level of cortical and cognitive activation is apparently not always available during sleep, but normally only during phasic REM. 

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