Hypnotic induction modulates both state and dynamics EEG measures during an imagination task
Poster No:
979
Submission Type:
Abstract Submission
Authors:
Ruxandra Tivadar1, Nina Rimorini1, Geoffroy Solelhac1, Chantal Berna1
Institutions:
1Centre Hospitalier Universitaire Lausanne (CHUV), Lausanne, Switzerland
First Author:
Co-Author(s):
Introduction:
Measures of neural information content have been shown to successfully quantify human awareness and consciousness levels (Carhart-Harris et al., 2014; Lau et al., 2022). Here, we viewed the EEG signal as a complex system and described characteristics of its state and dynamics (Khanna et al., 2015). We investigated whether measures of signal complexity (i.e. dynamics) can discriminate between neural activity during an imagination task following or not a hypnotic induction. Complexity has been shown to fluctuate with states of consciousness (Aamodt et al., 2021; Alnes et al., 2023; Schartner et al., 2015; Schartner et al., 2017), administration of psychedelic substances (Schartner et al., 2017), or tasks (Cnudde et al., 2023). Given evidence of variation of microstate characteristics with behavioural states (Lehmann et al., 2010), neuropsychiatric disorders (Pirondini et al., 2020) and interventions (Khanna et al., 2015), we also studied whether such changes were illustrated in topographical measures (i.e. the state) of brain activity, Finally, we correlated these measures. We hypothesized an increase in brain complexity during hypnosis, as compared to outside of hypnosis, given evidence that high entropy states might be rich in phenomenological experience (Carhart-Harris, 2018; Tagliazucchi et al., 2014). In addition, imagery during hypnosis is often experienced as being enhanced (Crawford et al., 1983), more intense and hallucinatory (Kunzendorf, 1986), and subjects reportedly shift to more holistic, imagery-oriented strategies during hypnosis (Crawford et al., 1983). We also expected changes in the duration of microstates during hypnosis, as transitions in functional brain states are thought to be mirrored in modulations in microstate characteristics (Lehmann et al., 2009).
Methods:
We recorded 3 minutes of continuous 128-channel EEG in 4 volunteers (3 female, 1 male) while participants engaged in free imagination of a safe place outside of hypnosis and following a hypnotic induction.
We focused our exploratory EEG analysis on global, reference-independent measures. We explored global broadband Lempel-Ziv complexity (LZc) over all 128 channels and over the full (1-40Hz) EEG signal as in (Alnes et al., 2023). LZc is a measure of signal diversity, or how regular a signal is across time. We also explored topographical microstates, which are defined as short periods of quasi-stable distributions of electrical potentials (Lehmann et al., 2009), in the attempt to characterise the brain response during an imagination task in the Hypnosis and the No Hypnosis conditions.
We focused our exploratory EEG analysis on global, reference-independent measures. We explored global broadband Lempel-Ziv complexity (LZc) over all 128 channels and over the full (1-40Hz) EEG signal as in (Alnes et al., 2023). LZc is a measure of signal diversity, or how regular a signal is across time. We also explored topographical microstates, which are defined as short periods of quasi-stable distributions of electrical potentials (Lehmann et al., 2009), in the attempt to characterise the brain response during an imagination task in the Hypnosis and the No Hypnosis conditions.
Results:
LZc. LZc was generally higher in Hypnosis (µ = 0.25) as compared to the No Hypnosis (µ = 0.22) condition (n.s., Figure 1).
Microstates. Our screeplot indicated an elbow after 5 microstates. These 5 microstates explained 65% of the total variance across the EEG recordings in both conditions. The duration of each of the microstates was extracted, and plots suggest differences between the Hypnosis and No Hypnosis condition (not significant, n.s.). The duration of the 5th microstate showed a moderate (r = 0.53, n.s.) correlation with LZc overall.
Microstates. Our screeplot indicated an elbow after 5 microstates. These 5 microstates explained 65% of the total variance across the EEG recordings in both conditions. The duration of each of the microstates was extracted, and plots suggest differences between the Hypnosis and No Hypnosis condition (not significant, n.s.). The duration of the 5th microstate showed a moderate (r = 0.53, n.s.) correlation with LZc overall.
·Complexity measures and microstate analysis for 4 subjects
Conclusions:
Our results indicate trend-level changes in both complexity measures and microstate duration. Decreases in complexity were found during visualization as compared to a mind wandering task, indicating more focused attention (Walter & Hinterberger, 2022). On the contrary, increases in complexity measures during mind wandering are thought to reflect greater processing flexibility across functional configurations (Cnudde et al., 2023). These measures have the potential to inform us about the cortical mechanisms by which a hypnotic induction might induce changes in cognitive processing. With data collection ongoing until a target sample of N=50 is reached, these preliminary results will be strengthened and expanded upon.
Higher Cognitive Functions:
Imagery 1
Perception, Attention and Motor Behavior:
Consciousness and Awareness 2
Keywords:
Electroencephaolography (EEG)
Sleep
Other - Hypnosis, Complexity, Microstates
1|2Indicates the priority used for review
Provide references using author date format
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