Now You See One Letter, Now You See Meaningless Symbols: Perceptual and Semantic Hypnotic Suggestions Reduce Stroop Errors Through Different Neurocognitive Mechanisms

Non-Invasive Brain Stimulation (NIBS), Hypnosis, and Hypnotizability: Literature Review and Future Directions

Non-Invasive Brain Stimulation (NIBS) stands as an advanced technology embraced by researchers and clinicians to influence thoughts, emotions, and behaviors. The prevalent NIBS methods include transcranial Direct Current Stimulation (tDCS) and Transcranial Magnetic Stimulation (TMS), both proficient in either exciting or depressing neural activities in specific cortical regions. Recently, NIBS has been integrated into hypnosis research with the goal of enhancing hypnotizability. Specifically, the limited existing studies have predominantly focused on the dorsolateral prefrontal cortex (DLPFC) due to its significant role in neutral hypnosis. Overall, these studies suggest the fascinating potential to alter hypnotizability and hypnotic phenomena, although the impact on responsiveness to suggestions remains modest. In contrast to psychological and pharmacological methods, NIBS enables alterations in hypnotic experiences that are independent of operators and noninvasive. This grants researchers the chance to employ a causal approach in investigating the brain-behavior relationship associated with suggestibility. The present paper evaluates existing NIBS studies in this domain, delving into the neurocognitive mechanisms at play and their potential implications for hypnosis research and practice.

EEG Correlates of Suggestion-Induced Stroop Interference Reduction in High-Suggestible Individuals: A Systematic Review and Meta-Analysis

Studies have explored the impact of suggestion on the Stroop effect, aiming to understand how effective suggestion is in modulating this phenomenon. The suggestion effect has been replicated in multiple studies, supporting its robustness, but lacks systematic evaluation. We conducted a systematic review and meta-analysis of relevant English-language studies from PubMed, Web of Science, PsycINFO, Scopus, and ScienceDirect since databases inception until January 2023. Quality of included studies was evaluated using the Joanna Briggs Institute (JBI) appraisal checklist, and potential publication biases were assessed. Subgroup analyses were also performed, and effect sizes were estimated using Hedges' g and analyzed using random effects model. The systematic review was comprised of 19 studies. For the meta-analysis, 14 studies examined the suggestion effect on Stroop interference effect (SIE), while six studies investigated suggestion effects on accuracy. Results have revealed significant overall effects of suggestion on Stroop performance in participants, as evidenced by SIE and accuracy. Subgroup analysis based on types of suggestion demonstrated a significant effect on SIE. Six EEG/ERP studies have also been discussed in the context of the review.

Best Practice Recommendations for Conducting and Reporting Controlled Trials in Clinical Hypnosis Research

There is an abundance of outcomes research for clinical hypnosis showing promising results. Nonetheless, hypnosis is still underutilized in clinical care. For a behavioral intervention to enter mainstream clinical care, efficacy needs to be demonstrated with exceptionally high quality of evidence, and its reporting needs to be complete and sufficiently clear to enable replication and clinical use. The present article provides best practice guidelines formulated by the Task Force for Establishing Efficacy Standards for Clinical Hypnosis for conducting and reporting clinical hypnosis research.The recommendations are presented in two tiers. Tier I recommendations include essential best practices, such as a call for the use of detailed research and intervention manuals, plans for and reporting of participant-education about hypnosis, the use of hypnotizability scales with good psychometric properties, and clear reporting of the hypnotizability measurement. Tier I also includes the sharing of intervention manuals, the reporting of the induction procedure, the labeling of the intervention for participants, and the definition of hypnosis used. Tier II includes preferred recommendations, calling for measurement of adherence to home practice, measurement of hypnotizability using scales with both subjective and behavioral measures of responsiveness, and the involvement of participants from the full hypnotizability spectrum. Tier II also includes the assessment of variables related to proposed mechanisms of action, the reporting of participants prior hypnosis experiences, and the relationship of expectancies and treatment outcomes.This list of recommendations will be useful for researchers, reviewers, and journal editors alike when conducting, reporting, or evaluating studies involving clinical hypnosis.

Time Course of Reactive Brain Activities during a Stroop Color-Word Task: Evidence of Specific Facilitation and Interference Effects

The Stroop test represents a widely used task in basic and clinical research for approaching the cognitive system functioning in humans. However, a clear overview of the neurophysiological signatures associated with the different sub-domains of this task remains controversial. In the present study, we leveraged the EEG technique to explore the modulation of specific post-stimulus ERPs components during the Stroop test. Critically, to better disentangle the contribution of facilitation (i.e., faster color identification times for color-congruent Stroop words) and interference (i.e., longer color identification times for color-incongruent Stroop words) processes prompted by the Stroop test, we delivered congruent and incongruent trials in two separate experimental blocks, each including the respective neutral condition. Thanks to this methodological manipulation, we were able to clearly dissociate the two sub-processes. Electrophysiological results suggest specific markers of brain activity for the facilitation and the interference effects. Indeed, distinctive Stroop-related ERPs (i.e., the P3, the N450, and the LPC) were differently modulated in the two sub-processes. Collectively, we provide evidence of selected brain activities involved in the reactive stage of processing associated with the Stroop effect.

Modulation of attentional bias by hypnotic suggestion: experimental evidence from an emotional Stroop task

Hypnosis is considered a unique tool capable of modulating cognitive processes. The extent to which hypnotic suggestions intervenes is still under debate. This study was designed to provide a new insight into this issue, by focusing on an unintentional emotional process: attentional bias. In Experiment 1, highly suggestible participants performed three sessions of an emotional Stroop task where hypnotic suggestions aiming to increase and decrease emotional reactivity towards emotional stimuli were administered within an intra-individual design. Compared to a baseline condition (without hypnotic suggestion), a significant increase in attentional bias was found when a hypnotic suggestion to increase emotional reactivity was administered. In contrast, the bias was eliminated when a suggestion to decrease emotional reactivity was administered. Experiment 2 investigated the effect of session repetition on attentional bias across three successive experimental sessions without hypnosis, and showed that the emotional Stroop effect did not vary across sessions. Hence, session repetition could not account for part of the modulation of attentional bias in Experiment 1. Taken together, the results suggest that specific hypnotic suggestions can influence elicitation of unintentional emotional processing. The implications are discussed regarding the locus of intervention of hypnotic suggestion in cognitive and emotional processes.

In medio stat virtus: The importance of studying mediums in hypnosis research

Most of the experimental investigations on hypnosis used to compare small samples of individuals with low or high responsiveness to hypnosis by systematically excluding medium responders. The present article underlines the limitations of this methodological approach that may have partially weakened the scientific impact of hypnosis research. In fact, the mediums-neglecting bias might be one of the reasons why some investigations suffer from low replicability and generalizability. Themes such as hypnotizability scales, suggestibility, statistical power, and research design are critically reviewed with the aim of proposing a more rigorous approach that boost up impact and reliability of hypnosis research. In particular, the recruitment of medium hypnotizables and the adoption of a within-instead of a between-subjects design currently seem to be some of the best recommendations for strengthening hypnosis research, as well as to renew the dialogue between clinical and experimental hypnosis.

Transcranial direct current stimulation of the prefrontal cortex reduces cigarette craving in not motivated to quit smokers: A randomized, sham-controlled study

Transcranial direct current stimulation (tDCS) over the dorsolaterateral prefrontal cortex (DLPFC) has been indicated as a promising treatment for several addictions, while its contribution for smoking cessation was less investigated. In particular, the role of motivation to quit and the nicotine dependence level as possible mediators of tDCS effect needs to be deepened. In the present study, we recruited twenty smokers who did not look for a treatment to quit: most of them presented a mild level of nicotine addiction, and they were randomly assigned to active or sham group for receiving bilateral tDCS over the DLPFC. tDCS was provided for five consecutive days with anode over the right hemisphere: in the first and the last day the craving level was evaluated through a specific evoking procedure, and the daily cigarette consumption was recorded. Results showed that the active tDCS decreased by about 50% the cigarette craving, while the number of cigarettes smoked remained unchanged and no differences emerged in the sham group. The present study indicates the tDCS of the DLPFC as a possible treatment for smoking addiction because of its effectiveness in reducing craving. Further, as we recruited smokers with no motivation to quit, and the nicotine dependence level was a moderator of the tDCS effect, we suggest that its efficacy might be even greater in the severe smokers looking for a treatment.

Electrophysiological Evidence of Anticipatory Cognitive Control in the Stroop Task

The Stroop task has been largely used to explore the ability to inhibit the automatic process of reading when reporting the ink color of incongruent color-words. Given the extensive literature regarding the processes involved in task performance, here we aimed at exploring the anticipatory brain activities during the Stroop task using the event-related potential (ERP) method. To accomplish this, eighteen participants performed two different blocks where neutral words were intermixed with congruent and incongruent words, respectively. Results revealed consistent pre-stimulus activity over the frontal, premotor and parietal brain areas. The premotor and the parietal activities were also modulated by the Stroop effect, being more enhanced in the incongruent than in the congruent blocks. Present findings add on the current literature pointing at an unexplored locus of anticipatory cognitive control during task preparation, thus offering a new way to investigate top-down preparatory processes of performance control in the Stroop task.