Neural Correlates of the Shamanic State of Consciousness

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.

Keywords: EEG; Trance; altered states of consciousness; consciousness; shamanism.

Figure 1

Study design. (A) Example timelines of a typical study day based on a given experiment block. Each individual was randomized to the order they underwent cognitive testing, shamanic drumming, and classical music listening. Eyes open and eyes closed resting periods occurred at the beginning and end of the experimental day. The Altered States of Consciousness Questionnaire, known as the OAV scale, was administered following classical music and shamanic drumming. (B) All participants underwent high-density electroencephalogram (EEG) recordings during drumming, classical music, and periods of eye-opening and closure. Following preprocessing, EEG signals were used to compute subsequent measures within each frequency band, including the power spectrum, functional connectivity measured by weighted Phase Lag Index, signal diversity measured by Lempel-Ziv complexity (image referenced from Leemburg and Bassetti, 2018), and criticality measured by the pair correlation function.

Figure 2

Shamanic practitioners enter an altered state of consciousness during shamanic drumming. (A) Shamanic Practitioners (SP, purple, n = 18) were significantly different from control participants (CC, green, n = 19) during drumming in 8 of the 11 OAV domains. Each point represents the mean of all SP or CC for the percent of the theoretical scale maximum for that domain. Error bars represent the standard error of the mean. (B) SP did not differ from CC during classical music listening on any of the domains. (C) We replotted the OAV mean and standard error for healthy controls taking psilocybin (green, n = 327), ketamine (blue, n = 162), or MDMA (orange, n = 102) from Studerus et al. (2010) and compared these scores to those acquired from SP. Overall, SP had increased scores in several domains compared to all three drug conditions, as well as similar scores in the remaining domains compared to various drug conditions.

Figure 3

Gamma power is greater in shamanic practitioners during the drumming and correlates with elementary visual alterations. (A) Power spectrogram comparing the difference in power across frequencies (1–45 Hz) between shamanic practitioners (SP; n = 18) and control participants (CC; n = 19) during eyes closed, classical music, and drumming periods. Warmer colors represent greater power in SP and cooler colors indicate more power in CC. The dotted line represents the gamma frequency band (30–45 Hz), which was significantly different between groups during shamanic drumming. (B) Box plots representing the mean absolute power of SP (purple) or CC (green) during eyes closed, drumming, and music. Whiskers represent the lower (25%) and upper (75%) quartiles and the center band of each box represents the median for the group. SP had significantly greater gamma power during the drumming period compared to CC. Significance is indicated by the key in the lower righthand corner of the figure. (C) We correlated absolute gamma power with each of the eight ASC domain scores that were significantly different between groups during drumming in Figure 2A; revealing a positive correlation between absolute gamma power and the degree of elementary visual alterations.

Figure 4

Shamanic practitioners have increased low beta and decreased low alpha connectivity during drumming and classical music. (A) Differences in functional connectivity, measured by weighted Phase Lag Index (wPLI), between shamanic practitioners (SP; n = 18) and control participants (CC; n = 19). Warmer colors represent greater connectivity in SP while cooler colors indicate greater connectivity in CC. The dotted lines represent the low alpha (8–10 Hz) and low beta (13–20 Hz) frequency bands, which were significantly different between groups. (B1,B2) Box plots illustrating the average wPLI in the low alpha (B1) or low beta (B2) frequency bands in SP (purple) and CC (green) during eyes closed, drumming, and music. Whiskers represent the lower (25%) and upper (75%) quartiles and the center band of each box represents the median for the group. SP experienced statistically significant decreases in wPLI in the low alpha band during classical music and drumming compared to CC (B1), as well as statistically significant increases in the low beta band (B2). Significance is indicated by the key in the lower righthand corner of the figure.

Figure 5

Shamanic practitioners have decreased neural signal diversity in the gamma band during drumming which is negatively correlated with feelings of insightfulness. (A) Comparison of the Lempel-Ziv complexity (LZc), a surrogate measure of neural signal diversity, across frequencies in shamanic practitioners (SP; n = 18) and controls (CC; n = 19). Warmer colors represent greater LZc in SP while cooler colors indicate greater LZc in CC. The dotted lines represent the gamma band (30–45 Hz), which was significantly different between groups. (B) Box plots comparing the average LZc in the gamma band for SP (purple) and CC (green) during eyes closed, classical music, and drumming. Whiskers represent the lower (25%) and upper (75%) quartiles and the center band of each box represents the median for the group. SP experienced statistically significant decreases in LZc in the gamma band compared to CC. Significance is indicated by the key in the lower righthand corner of the figure. (C) Correlations between LZc in the gamma band and ASC domain scores revealed a negative correlation between gamma LZc and feelings of insightfulness.

Figure 6

Shamanic practitioners have increased criticality in beta and gamma bands during drumming, with low beta increases correlating with complex imagery and elementary visual alterations. (A) Comparison of criticality, measured using a pair correlation function (PCF), across different frequencies between shamanic practitioners (SP; n = 18) and control participants (CC; n = 19). Warmer colors indicate greater PCF in SP while cooler colors represent increased PCF in CC. Dotted lines represent the low (13–20 Hz) and high (20–30 Hz) beta and gamma (30–45 Hz) bands, which were significantly different between SP and controls. (B1–B3) Box plots illustrating the average PCF value for the low (B1) and high (B2) beta and gamma (B3) bands in SP (purple) and CC (green) during eyes closed, classical music, and drumming. Whiskers represent the lower (25%) and upper (75%) quartiles and the center band of each box represents the median for the group. SP had greater PCF in the low and high beta (B1,B2) and gamma (B3) bands during drumming compared to CC, with increases extending to the classic music condition in high beta (B2) and gamma (B3) bands and the eyes closed condition in the gamma band (B3). Significance is indicated by the key in the lower righthand corner. (C1,C2) Spearman correlations revealed a positive correlation between PCF in the low beta band and both complex imagery (C1) and elementary visual alterations (C2).