Inducing unusual bodily sensations and out-of-body experiences across the wake-sleep cycle: a high-density EEG and neurophenomenology study

Unusual bodily experiences (UBEs) are illusory perceptions involving the body and its surroundings, such as body distortions and out-of-body experiences. This study examines UBEs in a controlled sleep laboratory using meditation and light stimulation to facilitate their occurrence. A total of N=35 healthy participants underwent high-density EEG with additional EMG, EOG, and ECG recordings. Participants signalled UBEs by performing left-right-left-right eye movements, providing an objective marker for analysis. Interviews adapted from the micro-phenomenological technique were conducted to capture detailed subjective reports and to guide subsequent sleep and EEG analyses. Of the 35 participants, N=20 reported a total of n=36 UBEs, occurring primarily during meditation (wakefulness) but also during sleep arousals, rapid eye-movement (REM) sleep and non-REM sleep. Spectral EEG analyses and generalized linear mixed models were used to investigate the neural dynamics of these experiences, suggesting that UBEs emerge during intermediate states of consciousness combining EEG features of both wakefulness and sleep. Specifically, exploratory EEG analyses showed that UBEs across sleep and wakefulness were associated with a wake-like EEG reactivation marked by increased high-frequency activity (beta and gamma) and decreased low-frequency activity (delta and theta), with a particularly pronounced effect around temporal regions. Collectively, these results provide novel insights into the electrophysiological mechanisms underlying UBEs and contribute to a deeper understanding of self-consciousness and body perception across sleep and wakefulness.