Investigation of visual dream reports after transcranial direct current stimulation (tDCS) during REM sleep

Neuroimaging studies have revealed regional patterns of brain activation/deactivation during REM sleep, with the posterior parietal and frontal cortex implicated as key brain regions involved in dreaming. Using a novel brain stimulation technique (tDCS), this study addressed the ongoing debate over the neuroanatomical origins of dreaming. This study examined the effect of cathodal and anodal tDCS applied simultaneously to the right posterior parietal and frontal cortex (respectively) during REM sleep on dream recall reported on awakening. It was hypothesized that such stimulation would have an inhibitory effect on local posterior parietal cortical circuitry and an excitatory effect on local frontal cortical circuitry, and that such a combination would impair dream recall on awakening from REM sleep. Three conditions (tDCS, low tDCS, blank control) were administered in a counterbalanced order in two separate studies, one employing an interval design whereby tDCS was delivered for a fixed duration, the other adopting a threshold approach with tDCS delivered in an increasing fashion until reaching the participants' arousal threshold. TDCS applied during REM sleep did not result in a significant decrease in the percentage of imagery reports, number of visualisable nouns, or imagery ratings. In sum, it appears that tDCS had no effect on reported dream imagery. However, further research would need to be carried out to determine whether such results reflect the unique properties of this stage of sleep or methodological limitations.