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Abstract:
Rhythmic drumming has long been used to alter consciousness and induce states of trance. Rhythm-induced trance is common in shamanism, humanity’s most ancient healing tradition. Despite similar techniques across cultures and powerful phenomenology, little is known about the mechanisms underlying trance. We examined the neural correlates of rhythm-induced trance in experienced shamanic practitioners. In the first study, we used fMRI to examine the neural patterns associated with trance. Shamanic practitioners (n=15) underwent 8 minute brain scans while they listened to rhythmic drumming and entered a trance state (or remained in non-trance in a control condition). In trance, brain networks displayed notable reconfigurations, including increased connectivity in regions associated with internal thought (the default mode’s posterior cingulate cortex) and cognitive control (dorsal anterior cingulate cortex and insula), as well as decreased connectivity within the brainstem and auditory pathway. This network configuration suggests perceptual decoupling and that the repetitive drumming was gated out to maintain an internally oriented stream of consciousness. In a follow-up EEG study, we used a similar design to examine auditory gating and network activity while shamanic practitioners (n=18) experienced rhythm-induced trance and a control state. In response to clicks embedded in the drumming, the N100 and P200 ERP components were decreased during Trance. This indicates decreased sensory encoding and elaborative processing during trance. Together this work suggests that repetitive drumming promotes an internally directed state via perceptual decoupling, and explicates why trance is a common way to promote insight across cultures.
