Elsevier

Consciousness and Cognition

Volume 21, Issue 3, September 2012, Pages 1456-1475
Consciousness and Cognition

Review
Induction of lucid dreams: A systematic review of evidence

https://doi.org/10.1016/j.concog.2012.07.003Get rights and content

Abstract

In lucid dreams the dreamer is aware of dreaming and often able to influence the ongoing dream content. Lucid dreaming is a learnable skill and a variety of techniques is suggested for lucid dreaming induction. This systematic review evaluated the evidence for the effectiveness of induction techniques. A comprehensive literature search was carried out in biomedical databases and specific resources. Thirty-five studies were included in the analysis (11 sleep laboratory and 24 field studies), of which 26 employed cognitive techniques, 11 external stimulation and one drug application. The methodological quality of the included studies was relatively low. None of the induction techniques were verified to induce lucid dreams reliably and consistently, although some of them look promising. On the basis of the reviewed studies, a taxonomy of lucid dream induction methods is presented. Several methodological issues are discussed and further directions for future studies are proposed.

Highlights

► We carried out a systematic review of lucid dream induction techniques. ► Induction means include cognitive methods, external stimulation and drug application. ► None of the induction techniques work on demand but some look promising. ► Taxonomy of induction methods is presented with the effectiveness evidence levels. ► Methodological considerations and future directions are provided.

Introduction

A lucid dream is a dream during which the dreamer is aware of the fact that he or she is dreaming and therefore often can consciously influence the dream content (LaBerge, 1985). Although awareness of dreaming while dreaming is usually considered an adequate criterion for lucid dreaming, some discussions have been held whether this is sufficient (Gillespie, 1984, Tart, 1984, Tart, 1985). Tart (1984), for example, separates dreaming-awareness dreams and lucid dreams, for which he poses an additional criterion that overall clarity of waking consciousness should also be retained. Tholey (1985) describes seven aspects of lucidity (clarity) in dreams: (1) clarity about the state of consciousness (that one is dreaming); (2) clarity about the freedom of choice; (3) clarity of consciousness; (4) clarity about the waking life; (5) clarity of perception; (6) clarity about the meaning of the dream; (7) clarity recollecting the dream. According to him, (1)–(4) are indispensible prerequisites of lucid dreaming. While in this paper we will follow the conventional minimal criterion for the definition (awareness of dreaming while dreaming), it is important to acknowledge that dream lucidity is not an “all-or-nothing” phenomenon but rather a continuum with different degrees: some dreams can be more lucid than others (Barrett, 1992, Moss, 1986).

Despite the fact that the phenomenon of lucid dreaming was known since the times of Aristotle (see Aristotle, 2007), only 30 years ago it was successfully verified in a sleep laboratory by measuring eye movements during REM sleep corresponding with dreamed gaze shifts (Hearne, 1978, LaBerge, 1980a, LaBerge et al., 1981). Since then, numerous studies have been conducted and research (overview: Erlacher & Schredl, 2008a) indicates that lucid dreaming is mainly a REM sleep phenomenon, although it can also occur during NREM sleep (see Dane, 1984).

During REM dreams the skeletal muscles of the sleeping body are actively suppressed by neural structures in the brain stem, keeping dreamers from actually acting out actions in their dreams (Hobson, Pace-Schott, & Stickgold, 2000). One obvious exception is eye movements. In accordance with the scanning hypothesis, eye movements during REM sleep correspond with shifts of gaze in dream imagery (cf. Roffwarg, Dement, Muzio, & Fisher, 1962). Since lucid dreamers have access to their waking memories (cf. Erlacher, 2009), it is possible for them to move their eyes during the dream according to a prearranged pattern of eye movements (usually: left–right–left–right, LRLR) and produce a distinct electrooculagram (EOG) recording during REM sleep; i.e., they can communicate from within the dream (cf. LaBerge et al., 1981). Then the lucid dreamer can be awakened and asked for a dream report to match the recorded eye signals with the dreamed gaze shifts. In such way, REM lucid dreams were successfully verified by subjective dream reports and objective EOG data in a number of different sleep laboratories across the world (e.g., Dane, 1984, Dresler et al., 2012, Erlacher and Schredl, 2008b, Fenwick et al., 1984, Hearne, 1983, Hickey, 1988, Kueny, 1985, LaBerge et al., 1981, Ogilvie et al., 1983, Voss et al., 2009, Watanabe, 2003).

Most frequently, lucid dreams are initiated from REM sleep (so called “Dream-Initiated Lucid Dream” – DILD), however sometimes they can also be initiated from the waking state (“Wake-Initiated Lucid Dream” – WILD) (LaBerge, Levitan, & Dement, 1986). Physiologically, lucid dreams are associated with elevated levels of automatic nervous system activity (LaBerge et al., 1986), but also with higher H-reflex suppression (Brylowski, Levitan, & LaBerge, 1989). According to recent findings, lucid REM sleep when compared to non-lucid REM sleep is associated with increased EEG 40 Hz power, especially in frontal and frontolateral regions (Voss et al., 2009). Another recent fMRI study found increased activation during REM lucid dreaming in several brain regions, including the bilateral precuneus, cuneus, parietal lobules, and prefrontal and occipito-temporal cortices (Dresler et al., in press). This specific pattern of activation might explain the presence of higher order cognitive skills involved in lucid dreaming. The prefrontal cortex is associated with metacognitive regulation and self-assessment, executive function and top-down control of behaviour, attention regulation (Arnsten and Li, 2005, Fernandez-Duque et al., 2000, Miller and Cohen, 2001, Schmitz et al., 2004), while the precuneus is associated with self-processing operations, such as first-person perspective taking and experience of agency (Cavanna & Trimble, 2006). In lucid dreams the dreamer has to observe and evaluate his or her present experience to recognise the dream state and become lucid, then to take a first-person perspective and agency and guide behaviour and attention according to one’s intentions in order to influence the dream content (see also Kahan & LaBerge, 1994).

Although frequent lucid dreaming is considered to be a rare skill, the estimates of lucid dreaming incidence within the general population suggest that about a half of the population have experienced a lucid dream at least once and about one out of five people are experiencing lucid dreams regularly, i.e. at least once a month (Schredl and Erlacher, 2011, Snyder and Gackenbach, 1988; but cf. Stepansky et al., 1998). Recent studies found that the prevalence of lucid dreaming in children is similar as in adults, however younger children seem to have lucid dreams more frequently (Schredl et al., 2012, Voss et al., in press). Differences across different cultures also exist (e.g., Erlacher, Schredl, Watanabe, Yamana, and Gantzert (2008) found significantly lower incidence of lucid dreaming in Japanese student sample in comparison with other countries). Since the onset of lucid dream research it was demonstrated that lucid dreaming is a learnable skill (LaBerge, 1980b; see also Saint-Denys, 1867/1982) and a number of practical applications were suggested (e.g. LaBerge & Rheingold, 1990). Lucid dreaming, for example, was successfully applied in nightmare treatment: several case studies (Abramovitch, 1995, Brylowski, 1990, Spoormaker et al., 2003, Zadra and Pihl, 1997) and a controlled trial (Spoormaker & van den Bout, 2006) demonstrated that the development of lucid dreaming abilities can decrease nightmare frequency and nightmare intensity. Lucid dreaming can also be used to enhance and perfect motor performance and motor skills (Erlacher and Schredl, 2010, Tholey, 1981) or employed for creative problem solving (Stumbrys & Daniels, 2010). Furthermore, lucid dreaming is an invaluable tool for scientists to explore the mind–body relationship during REM sleep (see e.g. Erlacher & Schredl, 2008a) and its uniqueness warrants lucid dreaming a special place within the whole area of consciousness research (Hobson, 2009). However, in order to utilize the advantages offered by lucid dreaming and make them available both to the scientific community and a wider population, reliable induction techniques must be established to increase the frequency of lucid dreams. This is the main challenge currently facing lucid dream research.

By the term “lucid dream induction” we refer to any means aiming to increase the frequency of lucid dreams. A plethora of various techniques (e.g. Gackenbach, 1985, LaBerge and Rheingold, 1990, Price and Cohen, 1988, Tholey, 1983) has been suggested for lucid dream induction and several attempts were made to classify them.

One of the first classification systems was suggested by Gackenbach (1985–1986), who classified induction techniques into two broad categories: (1) presleep induction and (2) sleep induction. The first category, presleep induction, includes intentional techniques and “unintentional considerations”. According to Gackenbach, intentional techniques focus on the present moment (e.g. reflecting whether one is dreaming right now, engaging into other focused activities, such as meditation or alpha feedback training) or are focused on the future (e.g. autosuggestion, post-hypnotic suggestion or intention to remember that one is dreaming). Furthermore, some techniques might combine both aspects, e.g. Tholey’s (1983) combined technique, which includes elements of reflection (present focussing) and intention with auto-suggestion (future focussing). “Unintentional considerations” include situations during the day (e.g. interpersonal interactions, emotions) and individual propensities (e.g. field independence, creativity; for overview of individual differences associated with lucid dreaming see Snyder & Gackenbach, 1988) that are not directly related to the attainment of dream lucidity but increase the likelihood of having a lucid dream. The second category, sleep induction, can be divided into external cues and internal cues. External clues are various environmental stimuli (e.g. auditory, tactile) that can be applied during REM sleep to be incorporated into a dream and recognised as a cue by the dreamer that he or she is dreaming. Internal cues can be unusual events or inconsistencies within a dream, a sense of “dreamlikeness” or just a spontaneous insight occurring in a dream which leads to the awareness that one is dreaming.

Another classification of lucid dreaming induction techniques was suggested by Price and Cohen (1988), who grouped them into three broad classes: (1) lucid-awareness training, (2) intention and suggestion techniques and (3) cue “REM-minding” techniques. Lucid-awareness training aims to cultivate a proper waking attitude to promote lucidity, such as critically reflecting on a frequent basis whether one is dreaming or not, heightening perceptual awareness, alpha feedback or waking fantasy training. Intention and suggestion techniques aspire to trigger a lucid dream through an act of will or suggestion. Examples of such techniques include intentions to carry out a specific action while dreaming (e.g. flying), to remember that one is dreaming and post-hypnotic suggestions. The third class of induction methods described by Price and Cohen (1988), cue “REM-minding” techniques, resembles Gackenbach’s (1985–1986) external cues category and includes tactile, auditory and other external stimuli presented during REM sleep to trigger lucidity. Price and Cohen (1988) also acknowledge that there are some other methods that do not fit into their three major classes described, such as Tholey’s combined technique or hypnagogic techniques that aim to enter lucid dreams directly from the waking state at sleep onset.

Although both these classification systems were useful and provided an adequate coverage of lucid dream induction techniques presented in literature, they seem to be fragmentary, not including all techniques. Over the recent years a number of empirical studies have been carried out that expanded our knowledge about induction techniques and new prospective methods emerged (e.g., Noreika, Windt, Lenggenhager, & Karim, 2010). Another issue is that a considerable number of techniques included in these systems were based on personal or anecdotal accounts and lacked any empirical validation. The overlap between different categories is also a problem of these systems: Some induction methods, e.g. Tholey’s combined technique, encompass both lucid awareness training and intention, or an intentional technique might result in an internal cue during a dream that will lead to the attainment of lucidity.

Therefore, in this paper we aim to present an empirically based classification of lucid dream induction techniques together with an extensive systematic review of published empirical evidence on lucid dream induction. Considering difficulties defining the exact boundaries between different groups of induction techniques, we defined the following broad categories:

  • (1)

    cognitive techniques – encompass all cognitive activities (lucid awareness training, intention, suggestion, hypnagogic techniques, etc.) that are carried out to increase the likelihood of achieving lucidity in a dream state;

  • (2)

    external stimulation – includes all types of stimuli (acoustic, light, electric, vibration, vestibular, brain stimulation, etc.) presented during REM sleep that can trigger dream lucidity;

  • (3)

    miscellaneous techniques – cover all other diverse induction methods that are not covered by the two categories above (e.g. intake of specific substances).

We hope that such an empirically-based classification will benefit not only lucid dreaming-interested scientists, providing them most promising directions for future research and most effective means to facilitate lucid dreaming both in a sleep laboratory or home environment, but also a broader audience, including therapists, artists, athletes, nightmare sufferers and others who may want to purse lucid dreams for their professional or personal reasons.

Section snippets

Identification of studies

A comprehensive literature search was carried out to identify relevant studies, including both electronic bibliographic databases and (lucid) dreaming specific resources. The following electronic databases were searched: MEDLINE, PsycINFO, PsycArticles, Academic Search Premier, IngentaConnect, ScienceDirect, Scopus, Web of Science, ProQuest Dissertations & Theses Database and PSYNDEX. Specific resources included scientific journals dedicated to (lucid) dream research (such as Lucidity Letter,

Literature search and excluded studies

Initial literature search and its replication brought equivalent results: Only one additional citation was retrieved and 11 sources were no longer available on ProQuest database. In total, literature search in electronic databases yielded 131 initial references. A first examination of titles and abstracts led to the following: 83 citations were rejected as not relevant, i.e. they were not dealing with lucid dream induction. Further nine citations were rejected according to our

Discussion

Thirty-five studies that explored over a dozen various techniques for lucid dream induction were examined in this review. Three classes of methods were employed by researchers to facilitate lucid dream induction: Cognitive techniques, external stimulation and drug application. Cognitive techniques are based on the continuity hypothesis of dreaming, which states that dreams reflect waking-life experiences (Schredl & Hofmann, 2003), and aim to increase the likelihood of lucid dreams by training

Future directions

We hope that the present review will serve as a new starting point in the lucid dream science, inviting researchers to further explore the most promising directions for induction research and to employ the most effect techniques for general lucid dream research and practical applications. The following ideas, we believe, are worth to tackle and pursue further.

The techniques that showed to be the most effective, such as Tholey’s combined technique or MILD, should be tested further and the

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