What is a lucid dream?
A lucid dream is a dream in which the dreamer is aware that he or she is dreaming and is sometimes able to consciously influence the content of the dream (LaBerge, 1985). Some researchers extend this definition, for example Tholey (1985) who also considers aspects like clarity about the waking life as an indispensible prerequisite to call a dream lucid. In this thesis, I use the conventional minimal criterion for the definition (awareness of dreaming while dreaming).
How was lucid dreaming scientifically proven to exist?
A breakthrough in lucid dreaming research were the experiments by Hearne (1978) and LaBerge (1980a) in the late 1970s and early 1980s who showed that a lucidly dreaming person can give voluntary signals to the wake world using some muscle groups, for example by eye movements. The eye movements in lucid dreams largely correspond to the movements of the real eyes (supporting the scanning hypothesis mentioned before), which can be measured by EOG. These voluntary signals prove that the subject indeed knows during sleep of his mental state, and not only makes this up after awakening. Thus, it is possible to not only detect a lucid dream from the outside by dream report after the subject woke up, but to have the evidence that somebody is lucidly dreaming while this person is still asleep.
What parts of the sleeping body can be controlled from within a lucid dream?
Besides movements of the eyes, other physiological parameters of the subject’s sleeping body can be controlled from inside a lucid dream. These voluntary changes – including eye movements – are referenced to in the following as “body signals”. Respiration can be voluntarily controlled during lucid dreaming as shown by LaBerge and Dement (1982a): breathing faster and stopping breathing inside the lucid dream was detectable by nasal airflow recordings. The EEG of a sleeping person can be influenced during lucid dreaming (Erlacher et al., 2003). Muscle twitches measured by EMG can - to some extent - be controlled from within a lucid dream (Fenwick et al., 1984). Another study by LaBerge et al. (1983) found a significant correlation between subjectively experienced sexual activity during REM lucid dreaming and several autonomic parameters such as respiration rate, skin conduction, vaginal EMG, and vaginal pulse amplitude. There was a significant increase of these parameters during experienced lucid dream orgasm, but surprisingly no significant increase in heart rate.
In which sleep stage do most lucid dreams occur?
Lucid dreams occur typically, but not only, during REM sleep (LaBerge et al., 1981a; LaBerge et al., 1981b; Ogilvie et al., 1983; Fenwick et al.1984).
How often are lucid dreams?
There are mixed findings in literature regarding the frequency and prevalence of lucid dreams. Studies show that lucid dreams are on average very rare, less than 1% of all dreams are lucid; however, among regularly lucidly dreaming subjects, 17.3% of the dreams recalled are lucid (Barrett, 1991; Zadra et al., 1992). Concerning the prevalence, some studies show a high number of subjects (82%) to have had a lucid dream at least once in a lifetime (e.g., Schredl & Erlacher 2004), some lower numbers (26%, Stepansky et al., 1998). A recent study in a representative German sample with 919 adults by Schredl and Erlacher (2011) found an overall prevalence rate of 51%. Erlacher (2010) suggests different sampling procedures and methodological differences between the studies as possible explanations for the mixed results. In a study by Voss et al. it was shown that lucid dreaming is much more prevalent in children and adolescents than in adults. (Voss et al., 2012).
Can lucid dreaming be learned?
Lucid dreaming is learnable (LaBerge, 1980b) and there exist numerous techniques and methods aiming at inducing a lucid dream. One arbitrary example for such a technique called “Senses Initiated Lucid Dreaming” (SSILD) is described in Appendix A. Unfortunately, no existing technique is able to reliably and consistently produce lucid dreams, even though some look promising (Stumbrys et al., 2012). As a result, until today lucid dreaming studies face the problem of finding qualified participants being able to produce a lucid dream, especially in the sleep laboratory environment, and thus often have to settle for small participant numbers (Strelen, 2006).
What are typical lucid dreaming experiments?
Lucid dreams can be investigated by sleep experiments. In a classical study design, participants perform actions which they have been asked to perform before going to sleep, and mark specific time points such as the time point of becoming lucid, the start of a task or the end of a task, by eye movements. One example for a classical lucid dream study answered the question, how long it takes to count to 10 in a lucid dream (approximately as long as counting in wake state) (LaBerge and Dement, 1982b), another exemplary study confirmed these results and, moreover, found that executing motor activities (performing squats) requires more time in lucid dreams than in the waking state (Erlacher and Schredl, 2004). Some studies demonstrate how to benefit from lucid dreams during waking life. For example, it is possible to train motor tasks during lucid dreams in order to increase the wake life performance of these tasks (Erlacher & Schredl, 2010).