Abstract Psychedelic drugs are emerging as potentially efficacious tools for treating psychiatric conditions and probing the neural basis of consciousness. Although drug administration context is widely believed to shape psychedelic effects, it remains unclear whether it can independently generate placebo and nocebo effects resembling psychedelic experiences and side effects. In a pre-registered experiment, 78 non-clinical participants inhaled inert medical air under placebo and control conditions while completing a time perception task and a resting-state period. In the placebo condition, the gas was presented as nitrous oxide, whereas in the control, it was correctly identified. Placebo administration increased altered states of consciousness, ego dissolution, dissociation, and side effects, but did not significantly impact time perception. Predictive modelling indicated that placebo-induced psychedelic effects were predicted by trait responsiveness to verbal suggestion and absorption. These findings demonstrate that context alone can induce psychedelic effects, with implications for its causal role in psychedelic action.

Abstract Background Placebo responding involves the reduction of symptoms in response to contextual features of an intervention (e.g., verbal suggestions), yet it is characterized by pronounced heterogeneity. Although verbal suggestions are widely recognised as a hallmark method for inducing placebo responses, an open question is whether variability in placebo responding can be partly attributed to individual differences in trait responsiveness to verbal suggestions (REVS). We conducted a pre-registered meta-analysis (PROSPERO registration number CRD420250654692) to quantitatively synthesize available research on the association between trait REVS and placebo responding. Methods PsycInfo, PubMed, MEDLINE, and Embase were searched up to June 2026 for original clinical or experimental studies involving both the assessment of REVS and symptom measures (self-report, behavioural, and/or physiological) in response to an inactive intervention (placebo). Results Of 1,512 search results, 24 articles presenting 66 correlations between REVS and placebo responding were analysed ( N = 1,137). A multi-level meta-analysis revealed a significant, albeit weak, positive correlation between REVS and placebo responses, r = 0.18 [95% CI: 0.13, 0.24], such that individuals with higher REVS reported greater symptom relief in response to the placebo. Meta-regression analyses did not identify any significant moderators of the correlation between REVS and placebo responding and sensitivity analyses based on Bayesian subgroup estimates indicated that the aggregate correlation was stable across methodological quality indicators and study features. Conclusion These findings suggest that individual differences in REVS may partly explain variability in symptom reduction in response to placebos, with implications for the sources of variance in placebo effects in experimental and applied contexts.

Abstract Background Dissociative experiences encompass a variety of discontinuities in awareness and perception that are elevated in the dissociative disorders and associated with extensive comorbid symptomatology. Accumulating evidence points to developmental trauma and trait responsiveness to verbal suggestions (REVS) as factors that confer risk for severe dissociative symptoms, but they have typically been studied in isolation. This study integrated these measures using prediction modelling to better understand their predictive value for the risk of dissociative psychopathology. Method 1,104 non-clinical participants completed measures of trauma, dissociation and trait REVS. The predictive model was developed using elastic net logistic regression, internally validated with 10-fold cross-validation, and assessed using receiver operating characteristic (ROC) curve and area under the ROC (AUROC). Variables entered into the model were components of REVS, trauma, age, and their interactions. Results A dissociative psychopathology at-risk group (7%) was characterised by younger age, greater trauma and elevated REVS, particularly involuntariness during cognitive-perceptual suggestions. The prediction model retained nine of ten predictors, with an AUROC of .77 [95% CI: .73, .82], reflecting good discrimination with moderate sensitivity (78%) but modest specificity (67%). Conclusions These findings reinforce trauma and trait REVS as risk factors for dissociative psychopathology and demonstrate that they can be integrated in a model that can identify at-risk individuals. Further validation and extension of the model is necessary to improve the identification of individuals at risk for severe dissociative symptomatology and the diagnosis of dissociative disorders with implications for outcome trajectories.

Nocebo effects are a heterogenous phenomenon in which contextual cues trigger or exacerbate symptoms independently of active interventions. Suggestion, conditioning, and social observation are widely recognised as hallmark methods for inducing nocebo effects, but the extent to which nocebo effects are differentially influenced by suggestion type (e.g., direct or indirect suggestion) and mode of administration (e.g., verbal, textual, visual, etc.) across symptom domains remains unknown. We conducted a pre-registered meta-analysis (PROSPERO registration number CRD42023402097) to quantitatively synthesize available research on the factors that moderate effects in controlled nocebo experiments. Of 8,469 search results, 105 experiments comprising 5,017 participants and 391 effect sizes were analyzed. A multi-level meta-analysis revealed an overall moderate effect size for nocebo effects, g=0.50, [0.39, 0.62]. The magnitude of symptom expectancy effects was a significant moderator of nocebo effects. Verbal suggestion and social observation yielded moderate and comparable nocebo effects whereas technological devices, sham stimulation, and conditioning were independently associated with the induction of large nocebo effects. Greater specificity in the reporting of nocebo induction methods is required to elucidate the efficacy of different types of suggestions in inducing nocebo effects.

One of the ongoing controversies in interval timing concerns whether human time perception relies on multiple distinct mechanisms. This debate centres around whether subsecond and suprasecond timing may be attributed to a single semi-uniform mechanism or separate and interacting mechanisms. Whereas past studies offer valuable insights, this study overcomes previous limitations by adopting multiple convergent statistical approaches in a design with strong statistical power. We conducted two online experiments involving participants reproducing temporal intervals ranging from 400 to 2400ms (Experiment 1; N=302) and 1000 to 2000ms (Experiment 2; N=302). We contrasted the application of exploratory factor analysis and structural equation modelling to differentiate distinct latent structures underlying duration reproduction patterns. Additionally, we compared the model outcomes with results from changepoint analysis models fitted to individual participants' data. In both experiments, these analyses yielded evidence for a two-factor model comprising a general timing factor spanning the full interval range and a second factor capturing the regression to the mean of presented stimulus intervals (central tendency bias). We observed a low proportion of detected changepoints, further supporting the limited evidence for a discontinuity between the distinct underlying mechanisms, while also finding that the changepoint detection was predicted by factor scores. These results highlight the role of central tendency effects in investigating changepoints and the continuity of timing systems. Our work contributes to integrating factor analytic and computational modelling approaches in the study of time perception and has implications for the measurement and interpretation of interval timing performance in a range of contexts.

Depersonalization-derealization disorder (DDD) frequently includes a sense of bodily detachment such as being unable to feel one's body, with a lack of awareness of bodily sensations. This suggests that body-focused interventions may be efficacious in addressing depersonalization-derealization (DD) symptoms. We developed two dance/movement tasks with an aim to reduce DD symptoms either through dance exercise by raising the salience of bodily signals (DE task) or by training body awareness through paying attention to bodily signals (BA task). Individuals with DDD (n = 18) and non-clinical controls (n = 14) performed both tasks individually in a crossover design. Assessments included DD symptom severity, interoception, mindfulness, proprioceptive accuracy, interval timing, and body vigilance, before, during and after the tasks. At baseline, DDD participants exhibited significantly higher temporal precision but significantly lower interoceptive awareness, mindfulness and visual proprioceptive accuracy compared to controls. No significant group differences were found for interoceptive accuracy or sensibility. Both dance tasks reduced the severity of DD symptoms, overall and anomalous bodily experiences, in the DDD group. Within-subject correlations in the DDD group showed that a decrease in symptoms were associated with task-specific (BA) elevations in mindfulness. Objective measures of task performance corroborated physiological task differences, with the DE task involving a higher average heart rate and more body movements than the BA task. These results provide further support for individual, structured dance/ movement as an efficacious tool to reduce symptoms in DDD by promoting mindful engagement with the body, and highlight the possibility and importance of tailoring dance-based interventions to specific symptoms and disorders.

Background:Dissociative states, characterized by discontinuities in awareness and perception, occur in a diverse array of psychiatric disorders and contexts. These states have been experimentally modeled in the laboratory through various induction methods, but relatively little is known about the efficacy and comparability of different experimental methods. Methods:In this meta-analysis, we quantified dissociative states, as indexed by a standardized instrument (Clinician-Administered Dissociative States Scale), at baseline in varied diagnostic categories and in response to different experimental induction methods (psychological techniques and pharmacological agents) in both clinical and nonclinical samples. Primary outcomes were state dissociation effect sizes (Hedges' g) (PROSPERO registration: CRD42022384886). A total of 2214 articles were screened, which yielded 123 eligible articles and 155 effect sizes comprising 6692 individuals. Results:High levels of baseline state dissociation were observed in multiple diagnostic categories relative to controls, with the largest effects found in the dissociative and complex subtypes of posttraumatic stress disorder (PTSD-DC). In controlled experiments, induced state dissociation was most pronounced in response to mirror gazing and multiple pharmacological agents, with effects in ketamine and cannabis exceeding baseline state dissociation in PTSD-DC. The effect sizes were characterized by pronounced heterogeneity but were not reliably associated with methodological features of the original studies. Conclusions:Elevated state dissociation is present in multiple diagnostic categories, and comparable or higher levels can be reliably induced in controlled experiments using psychological techniques and pharmacological agents. These results demonstrate the efficacy of several methods for experimentally modeling dissociation and have implications for measuring adverse events and predicting outcomes in clinical interventions that involve pharmacological agents.

BACKGROUND:Nocebo responding involves the experience of adverse health outcomes in response to contextual cues. These deleterious responses impact numerous features of mental and physical health but are characterized by pronounced heterogeneity. Suggestion is widely recognized as a contributing factor to nocebo responding but the moderating role of trait responsiveness to verbal suggestions (suggestibility) in nocebo responding remains poorly understood. OBJECTIVE:We conducted a pre-registered meta-analysis (PROSPERO registration number CRD42023425605) to quantitatively synthesize available research on the relationship between suggestibility and nocebo responding. METHODS:Four electronic databases were searched for original studies involving both the assessment of suggestibility and symptom reports in response to an inactive stimulus. RESULTS:Of 7729 search results, 10 articles presenting 13 correlations between suggestibility and nocebo responding were analysed. A random-effects meta-analysis revealed a significant, albeit weak, positive correlation, r = .21 [95% CI: .04, .37], between suggestibility and nocebo responses, such that more highly suggestible individuals displayed larger responses. Sensitivity and meta-regression analyses demonstrated that studies of higher methodological quality, including those that maintained experimenter blinding, exhibited stronger effect sizes. CONCLUSION:These results corroborate proposals that trait responsiveness to verbal suggestions confers greater response to nocebos and warrants renewed attention to the role of suggestibility in symptom induction and perception.

The field of hypnosis has intrigued clinicians and researchers alike for more than 200 years. Below, a review of hypnosis is presented from historical, theoretical, experimental, and clinical perspectives in order to provide those readers less aware of the field with a broad foundation. The literature reveals that while theoretically driven experimental research has led to groundbreaking clinical applications, there remains much to be done regarding dissemination of efficacious interventions and our understanding of underlying mechanisms responsible for observed effects. The goal is to inspire readers to pursue innovative work to improve our understanding of hypnosis and the quality of life of patients through clinical application. Along the way, we highlight empirical findings and selective writings of Dr. Steven Jay Lynn who was a tireless champion of hypnosis and psychotherapy.

Optional stopping refers to the practice of repeatedly performing a statistical analysis on a dataset as new data are collected until a pre-specified decision criterion is reached. This procedure is often adopted because of its effectiveness in optimizing data collection. Discussions of optional stopping to date have primarily centred around statistical issues, with relatively little consideration of any methodological implications of this procedure. Building on recent work drawing attention to methodological biases arising from the use of optional stopping, we highlight experimenter awareness of the current evidence state during data collection (experimenter evidence unmasking) as a salient methodological confound of optional stopping. We argue that experimenter evidence unmasking has the potential to influence an experimenter to implicitly or explicitly modify their behaviour in ways that can reduce the internal validity of an experiment. We conclude by offering recommendations for circumventing this confound and for the transparent reporting of experimenter evidence masking procedures.

Trait responsiveness to verbal suggestions (suggestibility) is relevant to a diverse array of clinical and experimental psychological phenomena. An unresolved question is whether different forms of suggestibility, such as direct verbal suggestibility and indirect (interrogative and sensory) suggestibility, comprise a uniform, superordinate trait or distinct abilities with overlapping characteristics. We conducted a pre-registered meta-analysis in accordance with MOOSE and PRISMA guidelines to quantify associations between diverse measures of suggestibility. Fifty-five eligible suggestibility scale correlation pairs from 18 studies were subjected to random effects meta-analyses and meta-regression analyses. The analyses revealed a scale congruency effect such that direct-direct (k=37) and indirect-indirect (k=5) suggestibility scale pairs were characterized by strong correlations, whereas incongruent scale pairs (direct-indirect; k=13) exhibited near-zero correlations. These results corroborate proposals that direct and interrogative suggestibility scales measure discrete suggestion effects, and trait responsiveness to suggestion does not comprise a uniform set of abilities.

Most empirical studies and theoretical models in research on suggestion and hypnosis presuppose that highly suggestible individuals comprise a uniform population. This assumption contrasts with consistent evidence for heterogeneity in this group, yet these findings have not been systematically integrated or evaluated against competing models of heterogeneity. In this article, I first outline the characteristics of heterogeneity among highly suggestible individuals, highlight methodological considerations, and review the assumptions of different models of heterogeneity. Next, I consider evidence for heterogeneity spanning responsiveness to hypnotic inductions and suggestions, strategy use during response to suggestion, developmental trajectories, cognitive-perceptual profiles, and symptomatology. I identify key limitations in this research area, highlight convergent findings within and across these domains, assess the explanatory scope of different models, and propose priorities for future research on heterogeneity. Elucidating the characteristics and latent structure of heterogeneity among highly suggestible individuals is essential for advancing our understanding of the neurocognitive substrates of suggestion.

Background: Dissociative disorders (DDs) are a group of mental health conditions characterised by disconnection from thoughts, feelings, memories, or sense of identity. It is believed that DDs, particularly dissociative identity disorder (DID) result from severe and chronic childhood trauma. Guidance from the International Society for the Study of Trauma & Dissociation (ISSTD) recommends trauma-informed phase-oriented treatment (PoT) to treat DDs. To date, there has been no systematic evaluation of treatment effectiveness of PoT in DDs.Objective: This review aimed to systematically assess published studies and evaluate the evidence and effectiveness of PoT for DDs relative to other treatments.Method: The search included four databases from 1980-2025 and reference lists of core papers. Studies were included if (1) participants have a primary diagnosis of DID or other specified dissociative disorder (OSDD), (2) it examined PoT and/or other treatments in these populations, and (3) it used at least one outcome measure pre- and post-treatment. Study quality was assessed using the Effective Public Health Practice Project (EPHPP) tool.Results: 6088 articles were screened and 19 articles met the inclusion criteria. All treatment types were associated with improvements in symptoms of dissociation, general mental health symptoms, psychopathology, and general functioning. When compared to one another, each treatment type has its strengths depending on the outcome of interest.Conclusions: This review demonstrates an emerging evidence base for using psychological interventions to treat DDs. High-powered controlled trials are needed to build upon these results to inform clinical practice.

Most mind wandering (MW) paradigms use self-reports following task performance, but the extent to which these reports are confounded by performance cues is unknown. In two experiments, we examined whether self-reports and confidence therein are influenced by performance indicators during visual metronome response tasks. In Experiment 1, we found that sham feedback modulated reports independently of behavioural performance with participants more likely to report MW after incorrect than correct sham feedback. In Experiment 2, we replicated this pattern using a more implicit manipulation of perceived performance, a surreptitious delay in the onset of response targets. Participants were more likely to report MW after delay than control trials. In both experiments, confidence in on-task reports was lower when the corresponding indicator (falsely) implied poor performance. These findings suggest that MW reports and experiential state confidence are partly confounded by performance monitoring and have implications for a variety of experience sampling methodologies.

The resurgence of interest in psychedelics has led to their widespread, and often uncritical, promotion within both popular media and scientific communities. This heightened enthusiasm complicates assessments of the neurocognitive effects of psychedelics as well as their efficacy as adjuncts to psychotherapy. A key challenge for this nascent field involves understanding how suggestion effects can both act as a confound in experimental research on psychedelics but also improve outcomes in therapeutic interventions. By critically examining how these effects operate within psychedelic experiences, we aim to draw greater attention to the role of suggestion effects as both a source of bias but also as a tool that can be leveraged to maximize therapeutic benefits. We argue for more careful consideration of the role of suggestion effects in response to psychedelics.

Functional neurological disorder (FND) is a common and disabling condition at the intersection of neurology and psychiatry. Despite remarkable progress over recent decades, the mechanisms of FND are still poorly understood and there are limited diagnostic tools and effective treatments. One potentially promising treatment modality for FND is virtual reality (VR), which has been increasingly applied to a broad range of conditions, including neuropsychiatric disorders. FND has unique features, many of which suggest the particular relevance for, and potential efficacy of, VR in both better understanding and managing the disorder. In this review, we describe how VR might be leveraged in the treatment and diagnosis of FND (with a primary focus on motor FND and persistent perceptual-postural dizziness given their prominence in the literature), as well as the elucidation of neurocognitive mechanisms and symptom phenomenology. First, we review what has been published to date on the applications of VR in FND and related neuropsychiatric disorders. We then discuss the hypothesised mechanism(s) underlying FND, focusing on the features that are most relevant to VR applications. Finally, we discuss the potential of VR in (1) advancing mechanistic understanding, focusing specifically on sense of agency, attention and suggestibility, (2) overcoming diagnostic challenges and (3) developing novel treatment modalities. This review aims to develop a theoretical foundation and research agenda for the use of VR in FND that might be applicable or adaptable to other related disorders.

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.

The fairness of decisions made at various stages of the publication process is an important topic in meta-research. Here, based on an analysis of data on the gender of authors, editors and reviewers for 23,876 initial submissions and 7,192 full submissions to the journal eLife, we report on five stages of the publication process. We find that the board of reviewing editors (BRE) is men-dominant (69%) and that authors disproportionately suggest male editors when making an initial submission. We do not find evidence for gender bias when Senior Editors consult Reviewing Editors about initial submissions, but women Reviewing Editors are less engaged in discussions about these submissions than expected by their proportion. We find evidence of gender homophily when Senior Editors assign full submissions to Reviewing Editors (i.e., men are more likely to assign full submissions to other men (77% compared to the base assignment rate to men RE of 70%), and likewise for women (41% compared to women RE base assignment rate of 30%))). This tendency was stronger in more gender-balanced scientific disciplines. However, we do not find evidence for gender bias when authors appeal decisions made by editors to reject submissions. Together, our findings confirm that gender disparities exist along the editorial process and suggest that merely increasing the proportion of women might not be sufficient to eliminate this bias. Measures accounting for women's circumstances and needs (e.g., delaying discussions until all RE are engaged) and raising editorial awareness to women's needs may be essential to increasing gender equity and enhancing academic publication.

Dissociation is a phenomenon characterised by a disconnection or detachment from one’s thoughts, identity, consciousness, or surroundings, and can manifest in various psychiatric disorders. Existing measures of dissociation vary considerably in quality and psychometric properties. A comprehensive systematic review of these measures is lacking. This review aimed to assess the psychometric properties and methodological quality of existing dissociation measures. MEDLINE, Embase, and PsycINFO were searched in May 2023 using comprehensive search terms for ‘dissociation’ combined with terms for ‘measurement’ and ‘psychometric properties’. The review was registered with PROSPERO (CRD42023423485) and followed PRISMA and COSMIN guidelines. We assessed content validity, structural validity, cross-cultural validity, and different indices of reliability comprising 1) reliability (test-retest, inter-rater, intra-rater), 2) internal consistency, and 3) measurement error. Of 7564 studies, 164 were eligible, revealing 42 measures of dissociation (90% trait dissociation, 10% state dissociation) and their 12 adapted versions. None of the measures met all COSMIN criteria for good psychometric properties and high methodological quality. Overall, methodological quality was rated as follows: ‘doubtful’ for content validity, ‘adequate’ for measurement error and cross-cultural validity, and ‘very good’ for structural validity and internal consistency. Most included studies did not assess the reliability of investigated measures. The Dissociative Experiences Scale (DES), adolescent DES, Peritraumatic Dissociative Experiences Questionnaire, Somatoform Dissociation Questionnaire-20, and Cambridge Depersonalisation Scale demonstrated strong evidence for measuring general, child/adolescent, trauma-related (state) or somatoform dissociation, and depersonalisation, respectively. Future research should refine or develop dissociation measures following COSMIN guidelines to ensure robust methodology and psychometric properties.

Timing behaviour and the perception of time are fundamental to cognitive and emotional processes in humans. In non-human model organisms, the neuromodulator dopamine has been associated with variations in timing behaviour, but the connection between variations in dopamine levels and the human experience of time has not been directly assessed. Here, we report how dopamine levels in human striatum, measured with sub-second temporal resolution during awake deep brain stimulation surgery, relate to participants' perceptual judgements of time intervals. Fast, phasic, dopaminergic signals were associated with underestimation of temporal intervals, whereas slower, tonic, decreases in dopamine were associated with poorer temporal precision. Our findings suggest a delicate and complex role for the dynamics and tone of dopaminergic signals in the conscious experience of time in humans.