Behavioural and brain responses in cognitive trance: A TMS-EEG case study.

Abstract

https://doi.org/10.1016/j.clinph.2019.11.011 1388-2457/ 2019 The Authors. Published by Elsevier B.V. on behalf of In This is an open access article under the CC BY-NC-ND license (http://creativ Cognitive trance is defined as a volitional, purposeful and selfinduced modified state of consciousness (inherited from shamanic traditional practice), characterized by lucid but narrowed awareness of external surroundings with hyper-focused immersive experience of flow, expanded inner imagery, modified somatosensory processing, and an altered sense of self and time (Flor-Henry et al., 2017). The underlying neurophysiology of this particular state of consciousness remains poorly understood. We here report a case study of a highly trained expert in cognitive trance using transcranial magnetic stimulation combined with electroencephalography (TMS-EEG), aiming to probe trance-induced changes of electrical reactivity of cortical circuits to magnetic field perturbations. The study was approved by the Ethics Committee of the Faculty of Medicine of the University of Liège in Belgium, and the subject gave her written informed consent. The participant (C.S.), a 56 year-old right-handed female, originally trained in Mongolia, has been practicing trance for 17 years and is able to self-induce a trance state without external help. Neuropsychiatric conditions were excluded. TMS-evoked EEG potentials (TEPs) were recorded in eyes-closed conditions during (i) normal resting wakefulness (baseline) and (ii) cognitive trance. Cognitive trance was induced using a standardized protocol (Flor-Henry et al., 2017) employing body movements and vocalizations for about 2 minutes, after which the participant remains in trance without moving throughout the recordings. After each TMS-EEG session, C.S. provided a free recall of her subjective experience and scored her time perception (i.e., subjective duration of the experience, in minutes), level of arousal (i.e., wakefulness), absorption (i.e., become fully involved in the experience), and dissociation (i.e., mental separation from the environment) using 0– 10 VAS scorings (Vanhaudenhuyse et al., 2019). TMS-EEG was performed as previously described (e.g., Bodart et al., 2018), with a TMS compatible 60-channels EEG amplifier and a neuronavigation system (Nexstim Plc, Finland). We targeted one frontal area (premotor cortex) and one parietal area (posterior parietal cortex) on the right hemisphere, using the subject’s T1weighted structural MRI. At least 150 TMS pulses were delivered at randomly jittered frequencies between 0.4 and 0.5 Hz. TEPs were obtained by averaging a minimum of 130 artifact-free trials for each session. We first calculated the Divergence Index (DI) to evaluate differences between resting state and cognitive trance. DI was computed on TEPs filtered between 1 and 45 Hz, as the percentage of samples that significantly differ across all channels and latencies, and compared them to normative test-retest variability (Casarotto et al., 2010). Then, we characterized the differences between rest and trance by means of three local measures calculated across the four channels located under the stimulation coil