Physiological Characteristics Of Lucid Dreaming 1

The preceding studies have shown that lucid dreams typically occur in REM sleep. However, since REM sleep is a heterogeneous state exhibiting considerable variations in physiological activity, of which two distinct phases are ordinarily distinguished. In its most active form, REM is dominated by a striking variety of irregular and short-lived events such as muscular twitching, including the rapid eye movements that give the state one of its most common names. This variety of REM is referred to as 'phasic,' while the relatively quiescent state remaining when rapid eye movements and other phasic events temporarily subside is referred to as 'tonic.' On first thought, one might expect lucid dreams to be associated with decreased phasic activity (Pivik, 1986). However, research by the Stanford group, detailed below, has shown lucid dreaming to be associated with, on the contrary, increased phasic activity. 

LaBerge, Levitan, and Dement (1986) analyzed physiological data from 76 signal-verified lucid dreams (SVLDs) of 13 subjects. The polysomnograms corresponding to each of the SVLDs were scored for sleep stages and every SVLD REM period was divided into 30 s epochs aligned with the lucidity onset signal. For each epoch, sleep stage was scored and rapid eye movements (EM) were counted; if scalp skin-potential responses were observable as artifacts in the EEG, these were also counted (SP). Heart rate (HR) and respiration rate (RR) were determined for SVLDs recorded with these measures. 

For the first lucid epoch, beginning with the initiation of the signal, the sleep stage was unequivocal REM in 70 cases (92%). The remaining six SVLDs were less than 30 s long and hence technically unscorable "by the book" (Rechtschaffen & Kales, 1968). For these cases, the entire SVLD was scored as a single epoch; with this modification, all SVLDs qualified as REM. The lucid dream signals were followed by an average of 115 s (range: 5 to 490 s) of uninterrupted REM sleep. Physiological comparison of EM, HR, RR, and SP for lucid vs. non-lucid epochs revealed that the lucid epochs of the SVLD REM periods had significantly higher levels of physiological activation than the preceding epochs of non-lucid REM from the same REM period. Similarly, H-reflex amplitude is lower during lucid compared to non-lucid REM (Brylowski, Levitan, & LaBerge, 1989). 

In order to study the temporal variations of physiology as they correlated with the development and initiation of lucidity, for each SVLD REM period the physiological variables were converted to standard scores and averaged across dreams and subjects. Figure 1 is a histogram of the resultant mean standard scores for the five minutes before and the five minutes after the initiation of lucidity. Note the highly significant increases in physiological activation during the 30 s before and after lucidity onset. 

Figure 1. Histograms of grand mean z-scores for EM, RR, HR, and SP.Bins are 30 s in length with t=0 representing the signaled onset of lucidity. Ns vary with variable and bin, but all values are averaged across lucid dreams and subjects. (* p<.05) 

Physiological data (EM, RR, HR, and SP) were also collected for sixty-one control non-lucid REM periods, derived from the same 13 subjects, in order to allow comparison with SVLDs. Mean values for EM and SP were significantly higher for REM periods with lucid dreams than non-lucid control REM periods (RR and HR did not differ). 

Given the finding that lucid dreams reliably occur during activated (phasic) REM, measures of central nervous system activation, such as eye movement density, should contribute something to the pattern of lucid dream distribution. Since it had been previously observed that eye-movement density starts at a low level at the beginning of REM periods and increases until it reaches a peak after approximately five to seven minutes (Aserinsky, 1971), we (LaBerge et al., 1986) hypothesized that lucid dream probability should follow a parallel development and accordingly found that mean eye-movement density correlated positively and significantly with lucid dream probability (r = .66, p < .01). 

Lucid dreams have been frequently reported to occur most commonly late in the sleep cycle (Green, 1968). LaBerge et al. (1986) tested this hypothesis by first determining for each of their 12 subjects the time of night which divided their total REM time into two equal parts. All but one of the subjects had more lucid dreams in the second half of their REM time than in the first half (binomial test; p < .01). For the combined sample, relative lucidity probability was calculated for REM periods one through six of the night by dividing the total number of lucid dreams observed in a given REM period by the corresponding total time in stage REM for the same REM period. A regression analysis clearly demonstrated that relative lucidity probability was a linear function of ordinal REM period number (r = .98, p < .0001). 

lucidity

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