Impact de la stimulation transcrânienne par courant alternatif sur la prise de conscience dans les rêves

There is a long history of interest in lucid dreaming–the awareness of dreaming while dreaming–from the time of ancient Greece. The understanding of lucid dreaming was initially based on personal observations of certain individuals who had themselves experienced lucid dreams. Discovery of the unconscious, as well as rapid-eye-movement (REM) sleep, greatly contributed to the rise of interest in lucid dreaming, which finally became the object of several empirical studies. The Stanford group is one of the first to have conducted laboratory studies specifically on lucid dreams assessing, among other attributes, the ability of dreamers to signal their lucid dreams with different body movements in real-time. Lucid dreaming is a prevalent phenomenon, comprising many dimensions, ranging from self-awareness to control over dream content. Some authors have also described lucid dreaming as a hybrid mental state, mixing REM dreaming and wakefulness characteristics. Moreover, frequent lucid dreamers display certain psychological characteristics, such as high creativity, an internal locus of control, and increases in several cognitive functions. Lucid dreaming has measurable physiological and neurophysiological correlates. Some authors have speculated about the different ways to induce lucid dreams during sleep. The proposed techniques are many and varied, ranging from behavioral techniques to electrical stimulation techniques. Critically, two studies employing frontal transcranial direct (tDC) (Stumbrys et al., 2013) and alternating (tAC) current stimulation (Voss et al., 2014) during REM sleep, have shown an association between increased self-awareness in dreams and fronto-temporal gamma electroencephalographic activity. However, these studies suffer from several methodological weaknesses. We attempted to replicate these important findings using frontal tAC stimulation during morning, REM-rich naps, real-time signal verification and more appropriate conservative statistical tests. We recruited 33 subjects in a single-blind randomized group study in which tAC stimulation was applied (STIM) or not (SHAM) during the REM sleep of a morning nap. During the STIM condition, we applied frontal 40 Hz tAC stimulation during REM sleep for 2.5 min. Subjects were awakened 3 min after stimulation offset for dream reporting and administration of a scale to assess dream lucidity. Although several episodes of signal-verified dream consciousness were observed, these were equally frequent in SHAM and STIM conditions. Self-ratings of dream content also did not distinguish conditions. Therefore, the findings of the present study do not indicate that frontal gamma stimulation increases dreamed self-awareness as measured by real-time signal-verified lucid dreams and self-ratings of dreams. Several methodological considerations may have played a role in the negative findings, such as recruitment criteria, the eyes-closed practice signal and the indirect effects of tAC stimulation during the phosphene and sensation tests. The latter may have masked a real, albeit weak, tAC stimulation effect. Thus, many subjects were able to signal or report lucid dreams in this study, and this supports the notion that further study of lucid dreaming may lead to fruitful applications. Investigating lucid dreaming could be useful for increasing our knowledge of the physiological substrate of dreams, for clarifying theories of consciousness, and for developing potential clinical tools.

Keyphrases: Transcranial stimulation, Lucid dreams, Rapid eye movement sleep