The induction of synaesthesia with chemical agents: A systematic review

Despite the general consensus that synaesthesia emerges at an early developmental stage and is only rarely acquired during adulthood, the transient induction of synaesthesia with chemical agents has been frequently reported in research on different psychoactive substances. Nevertheless, these effects remain poorly understood and have not been systematically incorporated. Here we review the known published studies in which chemical agents were observed to elicit synaesthesia. Across studies there is consistent evidence that serotonin agonists elicit transient experiences of synaesthesia. Despite convergent results across studies, studies investigating the induction of synaesthesia with chemical agents have numerous methodological limitations and little experimental research has been conducted. Cumulatively, these studies implicate the serotonergic system in synaesthesia and have implications for the neurochemical mechanisms underlying this phenomenon but methodological limitations in this research area preclude making firm conclusions regarding whether chemical agents can induce genuine synaesthesia

Pupillometry tracks errors in interval timing

Peer reviewe

Acquired synaesthesia following 2C-B use

Psychedelic drugs reliably trigger experiences that closely resemble synaesthesia (Luke and Terhune 2013), a condition in which inducer stimuli will reliably and automatically elicit atypical concurrent experiences (Ward 2013). These transient episodes are considered controversial because they do not meet behavioural diagnostic criteria for developmental synaesthesia (Terhune et al. 2016). However, if these behavioural markers are attributable to the consolidation of synaesthetic associations over time (Terhune et al. 2016), they should be observed in cases of acquired synaesthesia. Here we report a case of drug-induced acquired synaesthesia (LW) that meets standard diagnostic criteria for developmental synaesthesia

Primary visual cortex excitability is not atypical in acquired synaesthesia

A wealth of data suggests that psychedelic drugs elicit spontaneous perceptual states that resemble synaesthesia although it is unclear whether these different forms of synaesthesia share overlapping neural mechanisms. Multiple studies have shown that developmental and trained synaesthesia is characterized by selective hyperexcitability in primary visual cortex and it has been proposed that cortical hyperexcitability may contribute to induced and acquired synaesthesia. This study tested the prediction that a case of acquired synaesthesia (LW) would display selectively elevated primary visual cortex excitability, as reflected in lower transcranial magnetic stimulation (TMS) phosphene thresholds, but no difference in motor thresholds, relative to controls. In contrast to this prediction, LW’s phosphene threshold was well within the threshold range of controls. These results suggest that acquired synaesthesia is not characterized by atypical visual cortex excitability

Hypnotherapy for procedural pain, itch, and state anxiety in children with acute burns: A feasibility and acceptability study protocol

Background: Burns and related procedures are painful and distressing for children, exposing them to acute and chronic sequelae that can negatively afect their physiological, psychological, and social functions. Non-pharmacological interventions such as distraction techniques are benefcial adjuncts to pharmacological agents for procedural pain, state anxiety, and itch in children with burns but have limitations (e.g. lack of research on burn-related itch, tailoring, and consensus on optimal treatment). Hypnotherapy is a non-pharmacological intervention that can be tailored for varied settings and populations with evidence of beneft for itch and superior efectiveness in comparison to other non-pharmacological interventions for children’s procedural pain and state anxiety. Thus, children with burns can beneft from hypnotherapy as an adjunct to pharmacological agents. Yet, in paediatric burns, rigorous studies of efectiveness are limited and no studies have been identifed that screen for hypnotic suggestibility, an important predictor of hypnotherapy outcomes. Considering potential barriers to the delivery of hypnotherapy in paediatric burns, the proposed study will examine the feasibility and acceptability of hypnotic suggestibility screening followed by hypnotherapy for procedural pain, state anxiety, and itch in children with acute burns. Methods: An observational mixed-methods feasibility and acceptability study will be conducted over 15 weeks. Eligible children (N = 30) aged 4 to 16 years presenting to a paediatric burns outpatient centre in a metropolitan children’s hospital in Australia with acute burns requiring dressing changes will be included. Eligible parents of children (N = up to 30) and clinicians who perform dressing changes (N = up to 20) will also be included. Child participants screened as having medium to high suggestibility as assessed by behavioural measures will receive hypnotherapy during dressing changes. A process evaluation will target feasibility and acceptability as primary outcomes and implementation (i.e. fdelity in delivery), reach, potential efectiveness, and adoption of evaluation procedures and intervention as secondary outcomes. Discussion: Ethical approval was obtained from the Queensland Children’s Hospital and Health Service ethics committee. Results will be published in peer-reviewed publications and conference proceedings. The fndings will guide the design of future trials on the efectiveness of hypnotherapy and inform the development of child-centred hypnotic interventions in children with burns. Trial registration: Australian New Zealand Clinical Trials Registry ACTRN1262000098895

Suggestibility in functional neurological disorder: a meta-analysis

Objective Responsiveness to direct verbal suggestions (suggestibility) has long been hypothesized to represent a predisposing factor for functional neurological disorder (FND) but previous research has yielded conflicting results. The aim of this study was to quantitatively evaluate whether FND patients display elevated suggestibility relative to controls via meta-analysis. Methods Four electronic databases were searched in November 2019, with the search updated in April 2020, for original studies assessing suggestibility using standardized behavioural scales or suggestive symptom induction protocols in FND (including somatization disorder) patients and controls. The meta-analysis followed Cochrane, PRISMA, and MOOSE guidelines. Data extraction and study quality coding were performed by two independent reviewers. Standardized suggestibility scores and responsiveness to symptom induction protocols were used to calculate standardized mean differences (SMDs) between groups. Results Of 26,643 search results, 19 articles presenting 11 standardized suggestibility datasets (FND: n=316; control: n=360) and 11 symptom suggestibility datasets (FND: n=1285; control: n=1409) were included in random-effects meta-analyses. Meta-analyses revealed that FND patients displayed greater suggestibility than controls on standardized behavioural scales (SMD, 0.48 [95% CI, 0.15, 0.81]) and greater responsiveness to suggestive symptom induction (SMD, 1.39 [95% CI, 0.92, 1.86]). Moderation analyses presented mixed evidence regarding the extent to which effect sizes covaried with methodological differences across studies. No evidence of publication bias was found. Conclusions These results corroborate the hypothesis that FND is characterized by heightened responsiveness to verbal suggestion. Atypical suggestibility may confer risk for FND and be a cognitive marker that can inform diagnosis and treatment of this condition

Hypnotic suggestibility in dissociative and related disorders: A meta-analysis

Elevated responsiveness to verbal suggestions is hypothesized to represent a predisposing factor for dissociative disorders (DDs) and related conditions. However, the magnitude of this effect has not been estimated in these populations nor has the potential moderating influence of methodological limitations on effect size variability across studies. This study assessed whether patients with DDs, trauma- and stressor-related disorders (TSDs), and functional neurological disorder (FND) display elevated hypnotic suggestibility. A systematic literature search identified 20 datasets. A random-effects meta-analysis revealed that patients displayed greater hypnotic suggestibility than controls, Hedges’s g=0.92 [0.66, 1.18]. This effect was observed in all subgroups but was most pronounced in the DDs. Although there was some evidence for publication bias, a bias-corrected estimate of the group effect remained significant, g=0.57 [0.30, 0.85]. Moderation analyses did not yield evidence for a link between effect sizes and methodological limitations. These results demonstrate that DDs and related conditions are characterized by elevated hypnotic suggestibility and have implications for the mechanisms, risk factors, and treatment of dissociative psychopathology

The effectiveness of hypnosis for pain relief: A systematic review and meta-analysis of 85 controlled experimental trials

The current meta-analysis aimed to quantify the effectiveness of hypnosis for reducing pain and identify factors that influence efficacy. Six major databases were systematically searched for trials comparing hypnotic inductions with no- intervention control conditions on pain ratings, threshold and tolerance using experimentally-evoked pain models in healthy participants. Eighty-five eligible studies (primarily crossover trials) were identified, consisting of 3632 participants (hypnosis n=2892, control n=2646). Random effects meta-analysis found analgesic effects of hypnosis for all pain outcomes (g=0.54-0.76, p’s<.001). Efficacy was strongly influenced by hypnotic suggestibility and use of direct analgesic suggestion. Specifically, optimal pain relief was obtained for hypnosis with direct analgesic suggestion administered to high and medium suggestibles, who respectively demonstrated 42% (p<.001) and 29% (p<.001) clinically meaningful reductions in pain. Minimal benefits were found for low suggestibles. These findings suggest that hypnotic intervention can deliver meaningful pain relief for most people and therefore may be an effective and safe alternative to pharmaceutical intervention. High quality clinical data is, however, needed to establish generalisability in chronic pain populations