Rhythmic drumming is a common method to induce trance states of consciousness in many cultures around the world. The techniques and drum tempi are highly similar across cultures, and likely developed independently (convergent evolution). In order to study the rhythmic induction of trance, shamanic practitioners with extensive experience using drums to alter consciousness, traveled to the Max Planck Institute in Leipzig. The experiment used simultaneous EEG/fMRI and consisted of a resting state scan and 4 experimental trials: 2 shamanic journeys (trance) with rhythmic drumming, and 2 non-trance trials with slightly arrhythmic drumming). Following each 8 minute trial, participants answered subjective “first person” questions adapted from the Phenomenology of Consciousness Inventory. Every participant reported that he/she entered a trance state in the scanner (this was a relief). We are currently analyzing the data. We plan use EEG power signatures to define trance epochs (corroborated with post-experiment subjective reports of their experiential time-course). For the fMRI data, we will use functional connectivity analyses (eigenvector centrality), and multivariate pattern classification.
