Lucid dreaming: A new pathway for learning "We are asleep. Our life is a dream. But we wake up, sometimes, just enough to know that we are dreaming." By Quirine Tordoir 0569097 Supervisor Ysbrand van der Werf Co-assessor Winni Hofman LITERATURE THESIS for the degree of MASTER OF SCIENCE in Brain and Cognitive Sciences, University of Amsterdam Track: Cognitive Neuroscience 30th of January, 2015 Word count: 8332 Q.M. Tordoir Lucid dreaming: A new pathway for learning 1. Introduction A normal healthy person sleeps approximately 8 hours a day, meaning that throughout our lives we sleep for about 30% of the time. Of those 8 hours, we spend around 1,5 hours in Rapid Eye Movement (REM) sleep (Hobson, 2009), a stage of sleep in which most of our dreams occur. Hence you could say that we spend roughly 6% of our lives dreaming. That is a fairly large amount of time and for centuries people have been fascinated by the meaning and purpose of dreaming. Several studies have investigated the purpose of sleep and dreaming (Hobson, Pace- schott, & Stickgold, 2000; Nir & Tononi, 2010; Peigneux et al., 2003; Walker & Stickgold, 2006) while others have explored the possibilities of using the time spent sleeping for learning purposes (Antony, Gobel, O’Hare, Reber, & Paller, 2012; Arzi et al., 2012; Rasch, Büchel, Gais, & Born, 2007; Rudoy, Voss, Westerberg, & Paller, 2009). Mostly these studies were done by exposing participants to external stimuli, such as sounds (Antony et al., 2012; Rudoy et al., 2009) or odours (Arzi et al., 2012; Rasch et al., 2007) to test whether they were able to learn from these stimuli during the different stages of sleep. However, even though these studies revealed that the brain is certainly capable of processing sensory information during sleep and that sensory information during sleep can enhance memory traces (Antony et al., 2012) or even create new memory (Arzi et al., 2012), findings have been inconsistent and have not yet resulted in a successful method for active learning. In this review a different and potentially useful way to look at the possibility of learning during sleep will be discussed, not by using external input but by using internal processes; by so called lucid dreaming. A dream is called lucid when the dreamer becomes aware of the fact that he/she is dreaming, making it possible to influence the content and control the script of the dream (LaBerge, Nagel, Dement, & Zarcone, 1981). Moreover, lucid dreamers can be aware of information from waking life and even appear to be able to carry out prearranged tasks within their dream (Erlacher, Schädlich, Stumbrys, & Schredl, 2014; Erlacher & Schredl, 2008; LaBerge et al., 1981). This gives rise to an exciting possibility of using lucid dreaming as a new method for rehearsal. It has been shown that mental rehearsal improves performance and increases learning (Feltz & Landers, 1983; Driskell, Copper & Moran, 1994). Thus, if it is possible to rehearse something that was learned in waking life within a dream, it could possibly even improve performance in waking life. Imagine learning a new piece on the piano and practicing it over night? Rehearsing those Spanish words that you learn before you went to bed? Moreover, by using a lucid dream to practice a skill, you could practice things that are usually difficult or dangerous to practice in real life, e.g. speaking in public, driving a car, difficult conversations, confronting a problem, parachute jumping. 2 Q.M. Tordoir Lucid dreaming: A new pathway for learning The suggestion of using lucid dreaming as a field of practice is not new but has been around for decades (LaBerge et al., 1981; LaBerge & Rheingold, 1990; Tholey, 1983). A comparison has been made with mental rehearsal, suggesting that lucid dream rehearsal might be a very strong form of mental rehearsal (Erlacher, 2005). Yet research on this subject has been limited. This thesis will provide a literature review, investigating the current state of affairs of scientific research on lucid dream rehearsal. Initially it will provide an understanding of the current neuroscientific knowledge behind lucid dreaming, starting off with some background information on dreaming in general. The different stages of sleep, their connection to dreaming and several explanations on why we dream from a neurophysiological and phenomenological/ psychological point of view will be discussed. This will be followed by a section defining the phenomenon of lucid dreaming and its neural correlates. Then a comparison will be made between mental rehearsal and lucid dream rehearsal, possible implications of lucid dreaming will be discussed and an explanation will be given on the lack of experimental studies on the field of lucid dreaming. In sum, this thesis will provide an integrated view on dream functioning and neurophysiology for understanding the current state of affair of the investigation of lucid dream rehearsal as a possible method for learning. 3 Q.M. Tordoir Lucid dreaming: A new pathway for learning 2. Dreaming In the Oxford Dictionary the definition of a dream is “A series of thoughts, images, and sensations occurring in a person’s mind during sleep; A state of mind in which someone is or seems to be unaware of their immediate surroundings”. A dream is defined as a state of mind during sleep in which a person can experience envisioned images, sounds and emotions (Nir & Tononi, 2010). They are usually very visual and vivid, and range from very normal and realistic to bizarre and surreal. They are experienced as extremely sensory and outside of control of the dreamer. Sometimes dreams have such a strong effect on emotions that they terrify or scare the dreamer: these dreams are knows as nightmares. Stages of sleep During sleep, the brain goes through different stages of activity which can be roughly divided into two types: Rapid Eye Movement (REM) and Non Rapid Eye Movement (NREM). Dreaming is mostly related to REM sleep (Dement & Kleitman, 1957), although there have also been reports of dreams during NREM sleep (Manni, 2005). A normal night of sleep is built up in sleep cycles of approximately 90-100 minutes long and within each cycle a person will alternate between periods of NREM and REM sleep (Walker & Stickgold, 2006). NREM sleep can be divided in 3 stages, namely N1, N2 and N3 with each stage having its own specific electroencephalographic (EEG) characteristics (Nir & Tononi, 2010). A cycle usually starts in stage N1, passing through all the NREM stages and ending in REM. Stage N1 is considered light sleep; muscle activity slows down, eyes move slowly and people are easily woken up in this stage. Brain oscillations seem to slow down and transitions start to occur from alpha (8–13 Hz) waves to theta (4–8 Hz) waves. When entering the second stage N2, the eyes stop moving and EEG brain waves slow down even more. Sleep stage N2 EEG is characterized by complete transition to theta waves combined with K-complexes (occasional large electrical sharp waves) and sleep spindles (short bursts of increased frequency oscillatory waves). The last stage N3 is also known as deep- or slow-wave sleep (SWS) due to the prevalence of low frequency delta (<4Hz) oscillations with high amplitude. By this stage it becomes very difficult to wake people up and they are usually disorientated when doing so. The time spent in deep sleep N3 is highest during the first half of the night with short periods of REM. As the night progresses, light sleep stages of NREM predominate and periods of REM sleep increase (see figure 1) (Stickgold, Hobson, Fosse, & Fosse, 2001). REM sleep stage got its name from the involuntary rapid saccadic eye movement that clearly differentiates this stage from other sleep stages (Dement & Kleitman, 1957; Hobson, Stickgold, & Pace-schott, 1998; Nir & Tononi, 2010). During this stage EEG activity shows brain activity similar to that of the waking brain but with inhibition of muscle tone, preventing the dreamer from acting out his/her dreams (Hobson et al., 2000; Muzur, Pace-schott, & 4 Q.M. Tordoir Lucid dreaming: A new pathway for learning Hobson, 2002). Alpha waves and higher frequency waves predominate in the EEG activity of REM sleep. When woken up in this stage, people are most likely to report long vivid and bizarre dreams. The manifestation of sleep stages and wakefulness seem highly influenced by neuromodulatory control of the pontine brainstem (Hobson et al., 1998). Reciprocal interconnections between aminergic inhibitory neurons and cholinergic excitatory neuron determine onset of the different sleep stages. Activation of aminergic cells, such as serotonin and norepinephrine, is high during waking, decreases during NREM and becomes very low in REM sleep. The reverse is true for the cholinergic cells, such as acetylcholine, showing highest activity during REM sleep. Shifts between stages happen when the activity of aminergic and cholinergic switch dominance in activity, with respectively wakefulness and REM sleep arising at the peaks and with NREM sleep being the transition between the two stages (Hobson et al., 1998; Stickgold et al., 2001). Figure 1: from Stickgold et al. (2001). A schematic overview of sleep cycles during a normal night of sleep of 8 hours of sleep. Cycles go through stages of REM, NREM and SWS with SWS prevailing in the first half of the night, and REM sleep during the second half. When comparing the activity of acetylcholine to the onset of REM sleep, it shows a clear interaction; REM sleep arises at peak activity of acetylcholine. When do we dream? Although dream reports appear to be more abundant in REM sleep, there has been evidence that also during NREM sleep it is possible to dream (Manni, 2005). However, these dreams seem to be shorter, fragmentary, thought-like, less vivid and less memorable than those occurring during REM sleep (Hobson, 2009).