Neural Correlates of the Shamanic State of Consciousness

This brain imaging (EEG) study (n=37) found that the shamanic practitioners showed significant differences to control participants on an altered states of consciousness scale (OAV) and EEG measures. Their brainwaves resembled that of earlier data on those under the influence of psychedelics but still were identified as unique, often stronger, patterns.

Abstract

“Psychedelics have been recognized as model interventions for studying altered states of consciousness. However, few empirical studies of the shamanic state of consciousness, which is anecdotally similar to the psychedelic state, exist. We investigated the neural correlates of shamanic trance using high-density electroencephalography (EEG) in 24 shamanic practitioners and 24 healthy controls during rest, shamanic drumming, and classical music listening, followed by an assessment of altered states of consciousness. EEG data were used to assess changes in absolute power, connectivity, signal diversity, and criticality, which were correlated with assessment measures. We also compared assessment scores to those of individuals in a previous study under the influence of psychedelics. Shamanic practitioners were significantly different from controls in several domains of altered states of consciousness, with scores comparable to or exceeding that of healthy volunteers under the influence of psychedelics. Practitioners also displayed increased gamma power during drumming that positively correlated with elementary visual alterations. Furthermore, shamanic practitioners had decreased low alpha and increased low beta connectivity during drumming and classical music and decreased neural signal diversity in the gamma band during drumming that inversely correlated with insightfulness. Finally, criticality in practitioners was increased during drumming in the low and high beta and gamma bands, with increases in the low beta band correlating with complex imagery and elementary visual alterations. These findings suggest that psychedelic drug-induced and non-pharmacologic alterations in consciousness have overlapping phenomenal traits but are distinct states of consciousness, as reflected by the unique brain-related changes during shamanic trance compared to previous literature investigating the psychedelic state.“

Authors: Emma R. Huels, Hyoungkyu Kim, UnCheol Lee, Tarik Bel-Bahar, Angelo V. Colmenero, Amanda Nelson, Stefanie Blain-Moraes, George A. Mashour & Richard E. Harris

Notes

The eventual analysis of data was done with that of 18 shamanic practitioners (shamans) and 19 control (age- and sex-matched) participants. The average age was 56 and the shamans were practicing for an average of 20 years were doing about 13 healing sessions done every month.

During the EEG measurement, both groups listened to a drumming recording (25 minutes) from Michael Harner. A one hour version of this can be found here.

The study consisted of listening to the drumming recording, classical music recording, baseline measures (start and end) with eyes open and closed, an Altered States of Consciousness scale (OAV), and cognitive tests that will be discussed in a separate paper.

The shamans were asked to perform healing during the experiment and entered an altered state of consciousness to heal a client (not present at the study site).

The OAV data was also compared to that of 43 studies of participants on a variety of psychedelics (ketamine, psilocybin, and MDMA) that were used to validated the scale (Studerus, Gamma & Vollenweider, 2010)

OAV scores

The shamans scored significantly higher than the other participants on 8 of the 11 domains of the OAV during shamanic healing (drumming recording).

Compared to the psychedelics data, shamans scored higher on 1) complex imagery, 2) experiences of unity, 3) spiritual practice, and 4) insightfulness. See supplemental table 2 for all the correlations.

EEG scores

The shamans had significantly higher scores on gamma power during drumming than the other participants. Gamma waves or power is associated with working memory, attention, and perceptual grouping and is also raised for participants on psychedelics (e.g. DMT; Pallavicini et al., 2021) or meditation.

The shamans also had higher scores (greater connectivity) in the low beta band during drumming, and decreased low alpha connectivity.

Finally, the shamans also had higher low & high beta and gamma criticality as measured using the pair correlation function (PCF).

Discussion

This study was the largest neuroimaging study to date that looked at shamans, in the shamanic state. The differences found were similar to, and sometimes even greater, than those experiencing a high dose of psychedelics. The data suggest that shamans are able to reach a state of higher criticality, which can be likened to being more aware or have a richer conscious experience.

Summary

INTRODUCTION

Recent studies have used altered states of consciousness as model systems to study the neuroscience of consciousness. However, pharmacologic manipulation of ”off-target” brain receptors may introduce confounds by affecting other serotonergic and non-serotonergic receptor sites. Shamanic trance is an altered state of consciousness anecdotally similar to the psychedelic state, which can be achieved by listening to repetitive drumming. Shamanic practitioners endure changes in consciousness similar to individuals under the influence of psychedelic substances.

To date, only two studies have investigated brain activity in shamanic practitioners during shamanic trance. These studies suggest increased hub activity in key regions in default mode and control-related networks, and increased low and high beta activity, as well as an anterior-posterior shift in power.

We investigated the shamanic state of consciousness using high-density electroencephalography (EEG) in experienced shamanic practitioners and naive control participants. We used spectral analysis, connectivity, signal diversity, and criticality to characterize EEG changes during shamanic drumming and compared these self-reported changes in consciousness to the altered state of consciousness induced by psychedelic substances.

Participants

Two separate populations were recruited for this study: 24 experienced shamanic healing practitioners and 24 age- and sex-matched control participants. The participants had no experience with shamanism, meditation, spiritual healing, or spiritual training, and no history of hallucinogen, entheogen, or psychedelic drug use. 18 shamanic practitioners and 19 control participants were included in the analysis. They were excluded if they had a history of depression, anxiety, schizophrenia, or other serious psychological disorders.

Pre-study Procedures

Shamanic practitioners were asked to practice entering a shamanic trance before their study visit, while control participants listened to rhythmic solo drumming without any attempts at entering a shamanic trance.

Study Design

Participants underwent baseline EEG recordings, three experimental blocks, and were asked to rest with their eyes open and closed for 5 min following the last experiment.

Shamanic Healing Experiment

Shamanic practitioners and controls listened to the same pre-recorded drumming at home before the study visit and conducted shamanic healing. Both groups completed an Altered States of Consciousness questionnaire after the drumming period.

Classical Music Experiment

The classical music experiment was meant to function as a negative control for the shamanic drumming experiment and consisted of 15 min of classic music listening. Participants were asked to listen with their eyes closed and fill out the OAV scale following classical music listening.

Qualitative Analysis

The OAV Scale questionnaire data were pooled into 11 domains, and the mean and standard error of the mean were calculated for each domain for each participant.

EEG Acquisition

Participants were fitted with a 129-channel HydroCel Geodesic Sensor Net and EEG data were acquired at 500 – 1,000 Hz sampling rate.

EEG Analysis

Data were collected during eye closure (5 min) and shamanic drumming (25 min). Analyses were performed on the first song period (10 min) of classical music, and absolute power, functional connectivity, neural signal diversity, and criticality were computed for each frequency band.

Spectral Analysis

Spectral power was calculated using the short-time Fourier transform and averaged across all time windows and channels for each state.

Functional Connectivity

Functional connectivity was assessed using the average weighted Phase Lag Index (wPLI), which reduces noise and volume conduction effects. The wPLI was calculated for each frequency band and averaged across time and all channels in each state.

Neural Signal Diversity

Recent studies have sought to characterize changes in signal diversity in psychedelic-induced altered states of consciousness, and we used Lempel-Ziv complexity to compare the neural signal diversity of the psychedelic state and the shamanic state of consciousness.

Criticality

Criticality is a balanced state between order and disorder, and is observed ubiquitously in physical and biological systems. It is associated with various functional benefits, including large information storage, optimal information transmission, and flexible response to external stimuli.

Statistical Analysis

We used Wilcoxon signed-rank tests and Wilcoxon rank-sum tests to compare OAV domain scores between shamanic practitioners and individuals under the influence of psychedelic substances, and used unpaired t-tests to assess differences within each condition.

We conducted Spearman correlations to assess relationships between EEG measures and OAV domain scores in shamanic practitioners during shamanic drumming.

Shamanic Practitioners Enter an Altered State of Consciousness During Drumming

Shamanic practitioners had significantly greater scores in 8 of the 11 OAV domains than control participants during shamanic healing, including complex imagery, experience of unity, spiritual experience, blissful state, disembodiment, insightfulness, elementary visual alterations, and changed meaning of percepts. Shamanic practitioners had increased scores in all domains except elementary visual alterations during shamanic drumming compared to classical music listening, and had increased scores in audio-visual synesthesia during classical music listening compared to drumming.

Given the overlap between the shamanic state of consciousness and the psychedelic experience, we compared OAV domain scores from shamanic practitioners with those of individuals under the influence of psychedelic substances.

Studerus et al. found that shamanic practitioners experienced several domains at or above the level of individuals under the influence of various psychedelics, including complex imagery, experience of unity, spiritual experience, and insightfulness. Shamanic practitioners were similar to MDMA and psilocybin in the domains of blissful state, audio-visual synesthesia, impaired control and cognition, and changed meaning of percepts, and were comparable to ketamine in the domain of anxiety.

Absolute Gamma Power Increases During Drumming in Shamanic Practitioners and Correlates With Elementary Visual Alterations

We assessed differences in gamma power between shamanic practitioners and controls during eyes closed, classical music, and drumming. Shamanic practitioners had significantly greater gamma power during drumming compared to controls.

Shamanic Practitioners Have Altered Functional Connectivity in the Low Alpha and Beta Bands During Drumming

We examined differences in functional connectivity within each state in shamanic practitioners and control participants. Shamanic practitioners had significantly decreased low alpha connectivity and significantly greater connectivity in the low beta band during drumming and music compared to controls.

Lempel-Ziv Complexity in the Gamma Band Decreases During Drumming in Shamanic Practitioners and Correlates With Feelings of Insightfulness

We evaluated differences in EEG signal diversity using Lempel-Ziv complexity (LZc). Shamanic practitioners had decreased LZc in the gamma band during drumming, and LZc was negatively correlated with feelings of insightfulness.

Shamanic Practitioners Experience Increased Criticality in Beta and Gamma Bands During Drumming That Correlates With OAV Domain Scores

We examined differences in criticality using the pair correlation function (PCF) during eyes closed, music, and drumming. We found that shamanic practitioners had greater PCF in the low beta, high beta, and gamma bands.

Summary

In the largest and most comprehensive neuroimaging study of shamanic practitioners to date, we revealed that they were significantly different from controls in a majority of the OAV domains during drumming.

Shamanic practitioners had increased gamma power, increased gamma complexity, decreased low alpha and increased low beta connectivity, as well as increased PCF in the low beta, high beta, and gamma bands during drumming. These changes in brain activity correlate with self-reported changes in experience.

The Shamanic State of Consciousness, Gamma Oscillations, and Other Absorptive States of Consciousness

In the current study, we found increased gamma power during shamanic drumming, which is similar to previous findings that increased gamma power during shamanic trance. Gamma power has been implicated in a variety of cognitive processes, including consciousness, maintenance of visual images within working memory, and visual perception. While other trance states, such as possession trance, are frequently characterized by power changes in the theta, alpha, or beta bands, our findings of increased gamma power are unique.

Shamanic practitioners demonstrated decreased neural signal diversity and increased criticality in the gamma band during drumming when compared to control participants. However, meditative practice was characterized by increased entropy and decreased metastability in the gamma band, which indicates increased metastability and brain network susceptibility.

The comparison of EEG changes during the shamanic state of consciousness and other spiritual or religious practices remains less clear. However, the authors note that the shamanic state of consciousness overlaps more with religious or spiritual practices coupled with mystical experiences.

Shamanic Practitioners Enter an Altered State of Consciousness Similar Yet Distinct From the Psychedelic State

Shamanic practitioners experience elevations in 8 of the 11 OAV domains during drumming, which mirror or exceed domains altered during the psychedelic state.

Shamanic trance was different from the drug response in multiple OAV domains, suggesting that it is a distinct altered state and does not perfectly correlate with the drug experience of any of the three substances examined by Studerus et al. (2010). Although the underlying neurobiology of shamanic trance appears to be distinct from altered states of consciousness induced by psychedelics, the results demonstrate an overlap between self-reported changes in consciousness during shamanic trance and the psychedelic state.

While literature investigating functional connectivity during the psychedelic state using EEG and MEG remains scarce, one study found that changes in the delta band were associated with feelings of insightfulness and spiritual experience.

Previous studies have shown that increases in LZc during the psychedelic state correlate with changes in phenomenal content, yet our study found that decreases in LZc during the shamanic state negatively correlated with feelings of insightfulness. Shamanic trance may be different from the psychedelic state because of the lack of decreased alpha power and the increased activity in the default-mode network (DMN) rather than the characteristic decreases found during the psychedelic state.

The Shamanic State of Consciousness and the Entropic Brain Hypothesis

The entropic brain hypothesis suggests that consciousness arises within a critical zone rather than a critical point, and that normal waking consciousness exists within a band positioned in the middle of this critical zone.

In the current study, we found that shamanic trance increased PCF in beta and gamma bands, which indicates increased criticality and, in turn, increased brain network susceptibility to perturbations and metastability. This suggests that shamanic practice may shift the brain to the upper limit of the critical zone.

METHODOLOGIC STRENGTHS AND WEAKNESSES

This study validated the spectral changes noted in the only previous EEG study of shamanic trance, used computational methods to characterize the shamanic state of consciousness, and investigated the relationship between these measures and changes in consciousness reported by shamanic practitioners.

This study has some limitations, such as not collecting electromyography data to control for movement, and a small sample size. However, trends in EEG and PCF measures were significant, and future studies should aim to include a larger cohort.

The shamanic traditions utilized by the practitioners during normal, non-study trance sessions are detailed in Supplementary Table 3.

This study was limited by the fact that control participants were asked to rest quietly during the shamanic drumming period while shamanic practitioners were asked to enter a shamanic trance. However, we collected data during classical music as a contrast condition to identify brain activity specific to shamanic trance.

Methodological differences may have affected the comparison of OAV domain scores between shamanic practitioners and healthy volunteers under the influence of psychedelics. However, given that we are unsure of the strength or ”dose” of the shamanic trance each practitioner endured, this comparison is somewhat preferable.

Studies have found that the greatest changes in brain activity occur during eye closure, and that shamanic practitioners may have heightened OAV scores due to the inclusion of less intense experiences due to eye-opening.

CONCLUSION

We found that shamanic practitioners entered an altered state of consciousness during drumming, and that these changes in brain activity were correlated with measures of their altered states of consciousness.

ACKNOWLEDGMENTS

We would like to thank Dr. Erich Studerus for his agreement to and helpful suggestions, and Kate Durda and Stephanie Tighe for their insight.