Investigating the transfer of physical stimuli to the dreamed body: A comparative study of muscular, vestibular, and haptic stimulation on dream incorporation.

The relationship between the dreamed body and the physical body remains an open question in sleep and dream research. This study examined whether somatosensory stimulation applied during REM sleep modulates the corresponding dream content under controlled conditions. Using a within-subject design, we compared three stimulation modalities-electrical muscular, galvanic vestibular, and haptic vibration-each paired with a modality-specific sham stimulation. Twenty-four participants completed one adaptation night followed by three consecutive experimental nights in the sleep laboratory. Dream reports were collected following rapid eye movement sleep awakenings after stimulation or sham periods, yielding a total of 120 reports. Dream incorporation of bodily sensations and actions was observed across all conditions; however, generalized linear mixed-effects analyses revealed no statistically significant differences between stimulation and sham conditions for any modality. No evidence for reliable modality-specific dream incorporation was observed under rigorous sham-controlled conditions. Rather than demonstrating robust stimulation-specific effects, these findings suggest that contextual and expectancy-related influences substantially contribute to bodily dream content under laboratory conditions while highlighting methodological challenges in dream incorporation research. By combining multiple somatosensory stimulation modalities with rigorous sham-controlled procedures, the present study provides a methodological benchmark for future investigations of dream incorporation and dream engineering.