Methodological and interpretative issues regarding the Phenomenology of consciousness inventory--hypnotic assessment procedure: a comment on pekala et al. (2010a, 2010b)

An interhemispheric frontoparietal network supports hypnotic states

Understanding the neural substrate of altered conscious states is an important cultural, scientific, and clinical endeavour. Although hypnosis causes strong shifts in conscious perception and cognition, it remains largely unclear how hypnosis affects information processing in cortical networks. Here we manipulated the depth of hypnotic states to study information processing between cortical regions involved in attention and awareness. We used high-density Electroencephalography (EEG) to record resting-state cortical activity from 30 hypnosis experts during two hypnotic states with different depth. Each participant entered a light and a deep hypnotic state as well as two well-matched control states. Bridging top-down and lateralisation models of hypnosis, we found that interhemispheric frontoparietal connectivity distinguished hypnosis and control conditions, while no difference was found between the two hypnotic states. Using a graph-theoretic measure, we revealed that the amount of information passing through individual nodes (measured via betweenness centrality) is reduced during hypnosis relative to control states. Finally, we found that theta power was enhanced during hypnosis. Our result contributes to the current discussion around a role for theta power in bringing about hypnotic states, as well as other altered conscious states. Overall, our findings support the notion that altered top-down control in frontoparietal regions facilitates hypnosis by integrating information between cortical hemispheres.

Gamma power and beta envelope correlation are potential neural predictors of deep hypnosis

Hypnosis is a psychological intervention that is commonly used to enhance the effectiveness of therapeutic suggestions. Despite extensive fascination and study, the neural mechanisms behind hypnosis remain elusive. In the current study, we undertook a systematic exploration of these neural correlates. We first extracted well-studied neurophysiological features from EEG sensors and source-localized data using spectral analysis and two measures of functional connectivity: weighted phase lag index (wPLI) and power envelope correlation (PEC). Next, we developed classification models that predicted self-rated hypnotic experience based on the extracted feature sets. Our findings reveal that gamma power computed on sensor-level data and beta PEC computed between source-localized brain networks are the top predictors of hypnosis depth. Further, a SHapley Additive exPlanations (SHAP) analysis suggested reduced gamma power in the midline frontal area and increased beta PEC between interhemispheric Dorsal Attention Networks (DAN) contribute to the hypnotic experience. These results broaden our understanding of the neural correlates of deep hypnosis, highlighting potential targets for future research. Moreover, this study demonstrates the potential of using predictive models in understanding the neural underpinnings of self-reported hypnotic depth, offering a template for future investigations.

Boosting the hypnotic experience. Inhibition of the dorsolateral prefrontal cortex alters hypnotizability and sense of agency. A randomized, double-blind and sham-controlled tDCS study

Hypnotizability refers to the individual responsiveness to hypnosis, and literature shows that the greater the hypnotizability, the more effective the hypnotic suggestions. So far, few studies attempted to enhance hypnotizability, and only two adopted brain stimulation with magnetic pulses. In the present study, we aimed to boost hypnotizability through transcranial direct current stimulation (tDCS). To this aim, bilateral tDCS was applied over the dorsolateral prefrontal cortex (DLPFC) with the target electrode providing negative current (cathodal stimulation) over the left hemisphere. Twenty-nine subjects participated in the study and they were randomly assigned to the sham or the active group in a double-blind design. The hypnotic experience was assessed before and after the stimulation through a phenomenological measure of consciousness (the PCI-HAP). The main findings revealed that a single tDCS session enhanced the hypnotic depth by 11% and reduced the volitional control by 30%, while no differences emerged in the sham group. This is the first study adopting the electrical neurostimulation to produce an alteration of hypnotizability and sense of agency, and confirmed the key-role of the DLPFC and executive control in the hypnotic phenomena. If confirmed, these findings could have relevant implications as enhanced hypnotizability could be translated into better outcomes for many hypnotic interventions.

A Critical Review of Standardized Measures of Hypnotic Suggestibility

The most well-established finding gleaned from decades of experimental hypnosis research is that individuals display marked variability in responsiveness to hypnotic suggestions. Insofar as this variability impacts both treatment outcome in therapeutic applications of hypnosis as well as responsiveness to suggestions in experimental contexts, it is imperative that clinicians and researchers use robust measures of hypnotic suggestibility. The current paper critically evaluates contemporary measures of hypnotic suggestibility. After reviewing the most widely used measures, we identify multiple properties of these instruments that result in the loss of valuable information, including binary scoring and single-trial sampling, and hinder their utility, such as the inclusion of suboptimal suggestion content. The scales are not well-suited for contemporary research questions and have outlived their usefulness. We conclude by outlining ways in which the measurement of hypnotic suggestibility can be advanced.

THE ROLES OF RESPONSE EXPECTANCIES, BASELINE EXPERIENCES, AND HYPNOTIZABILITY IN SPONTANEOUS HYPNOTIC EXPERIENCES

This study evaluated factors underlying individual differences in spontaneous (unsuggested) experiences during hypnosis. Participants varying in hypnotizability (low, medium, and high) completed a questionnaire about various dimensions of consciousness they would expect to experience at the "deepest level of hypnosis" (expectancy), an eyes-closed resting condition (baseline), and their actual experiences during "neutral hypnosis" (hypnosis). Responses during hypnosis were characterized by higher scores in dimensions related to alterations in conscious experience, affect, and imagery, and lower scores in rationality and agency. Only highs and mediums evinced increases in altered experience and body image. Across conditions, highs reported greater alterations in time experience and lower self-awareness than other groups. Participants overall tended to overestimate the changes they would experience in hypnosis. Baseline and hypnosis correlated in various dimensions, including affect, arousal, and internal dialogue. After controlling for baseline scores and hypnotizability, expectancies correlated with some dimensions having to do with alterations in consciousness. In sum, spontaneous experiences during hypnosis are driven by response expectancies, hypnotizability, and baseline experiences, which show differential effects.

Discrete response patterns in the upper range of hypnotic suggestibility: A latent profile analysis

High hypnotic suggestibility is a heterogeneous condition and there is accumulating evidence that highly suggestible individuals may be comprised of discrete subtypes with dissimilar cognitive and phenomenological profiles. This study applied latent profile analysis to response patterns on a diverse battery of difficult hypnotic suggestions in a sample of individuals in the upper range of hypnotic suggestibility. Comparisons among models indicated that a four-class model was optimal. One class was comprised of very highly suggestible (virtuoso) participants, two classes included highly suggestible participants who were alternately more responsive to inhibitory cognitive suggestions or posthypnotic amnesia suggestions, and the fourth class consisted primarily of medium suggestible participants. These results indicate that there are discrete response profiles in high hypnotic suggestibility. They further provide a number of insights regarding the optimization of hypnotic suggestibility measurement and have implications for the instrumental use of hypnosis for the modeling of different psychological conditions.

A cross-validation of two differing measures of hypnotic depth

Several sets of regression analyses were completed, attempting to predict 2 measures of hypnotic depth: the self-reported hypnotic depth score and hypnoidal state score from variables of the Phenomenology of Consciousness Inventory: Hypnotic Assessment Procedure (PCI-HAP). When attempting to predict self-reported hypnotic depth, an R of .78 with Study 1 participants shrank to an r of .72 with Study 2 participants, suggesting mild shrinkage for this more attributional measure of hypnotic depth. Attempting to predict hypnoidal state (an estimate of trance) using the same procedure, yielded an R of .56, that upon cross-validation shrank to an r of .48. These and other results suggest that, although there is some variance in common, the self-reported hypnotic depth score appears to be tapping a different construct from the hypnoidal state score.

Reply to Wagstaff: "Hypnosis and the relationship between trance, suggestion, expectancy, and depth: some semantic and conceptual issues"

Wagstaff (2010) reviews and comments on two recent papers by Pekala et al. (2010a, 2010b), concluding that "many of the problems relating to the definition and conceptualization of terms associated with hypnosis... may stem from insufficient attention to the role of suggestion and expectancies in producing hypnotic phenomena, and an over-reliance on the role of the procedures and mechanics of the induction process" (p. 47). Although I agree with his semantic and conceptual focus, I believe that a number of these problems are due to not operationally defining terms such as hypnosis, hypnotic state, or trance in a comprehensive phenomenological manner. By using the PCI (Phenomenology of Consciousness Inventory) via retrospective phenomenological assessment, and using a phenomenological state instrument like the PCI-HAP (Phenomenology of Consciousness Inventory - Hypnotic Assessment Procedure) to obtain a state measure of hypnotic responsiveness, a means is available to define and empirically address some of these issues in a way that can significantly further our understanding of the nature of hypnotism. Such an approach might also address Kallio and Revonsuo's (2005) admonition concerning the need to develop "an internally coherent and widely shared theoretical vocabulary" (p. 51) to better understand consciousness, altered states of consciousness, and related phenomena, such as hypnosis/hypnotism.