Direct Verbal Suggestibility as a Predictor of Placebo Hypoalgesia Responsiveness

Assessing expectancy and suggestibility in a trial of escitalopram v. psilocybin for depression

BACKGROUND

To investigate the association between pre-trial expectancy, suggestibility, and response to treatment in a trial of escitalopram and investigational drug, COMP360, psilocybin, in the treatment of major depressive disorder (ClinicalTrials.gov registration: NCT03429075).

METHODS

We used data (n = 55) from our recent double-blind, parallel-group, randomized head-to-head comparison trial of escitalopram and investigational drug, COMP360, psilocybin. Mixed linear models were used to investigate the association between pre-treatment efficacy-related expectations, as well as baseline trait suggestibility and absorption, and therapeutic response to both escitalopram and COMP360 psilocybin.

RESULTS

Patients had significantly higher expectancy for psilocybin relative to escitalopram; however, expectancy for escitalopram was associated with improved therapeutic outcomes to escitalopram, expectancy for psilocybin was not predictive of response to psilocybin. Separately, we found that pre-treatment trait suggestibility was associated with therapeutic response in the psilocybin arm, but not in the escitalopram arm.

CONCLUSIONS

Overall, our results suggest that psychedelic therapy may be less vulnerable to expectancy biases than previously suspected. The relationship between baseline trait suggestibility and response to psilocybin therapy implies that highly suggestible individuals may be primed for response to this treatment.

Italian adaptation of the Multidimensional Iowa Suggestibility Scale (MISS)

Background

Suggestibility is a personality trait that reflects a general tendency to accept messages. The Multidimensional Iowa Suggestibility Scale (MISS) is a self-report scale developed to measure the degree of individuals' perceptions of their suggestibility. This study aimed to adapt the MISS in an Italian sample.

Methods

We conducted two studies. In the first study, 345 subjects (270 females (78%), mean age = 36.21 years ± 14.06 SD) completed the translated Italian version of the MISS, composed of five subscales (consumer suggestibility; persuadability; sensation contagion; physiological reactivity; peer conformity). We investigated the structural validity of the scale through confirmatory factor analysis (CFA) testing four measurement models (unidimensional, four-factor, hierarchical four factors, and bifactor) and explored reliability in terms of internal consistency through the McDonald's omega. In the second study, we cross-validated the MISS on a new independent sample. We enrolled 277 participants (196 females (71%), mean age 30.56, SD = 12.58) who underwent the new version of the scale. We performed factor analyses to test structural validity and compared four measurement models. Then, we investigated reliability and conducted a latent variable analysis to explore divergent validity.

Results

The CFA in the first study revealed a bifactor solution of the MISS. This structure was interpretable and provided an adequate fit for the data. The final version of the scale was reduced to forty-six items with globally good indices of adaptation. The scale also demonstrated acceptable reliability in terms of internal consistency through the McDonald's Hierarchical Omega. In the second study, we found that the bifactor structure was confirmed. Factor loadings inspection revealed that there was no justification to report only the separate scores for the subscales. We also found that the scale showed good internal consistency, but mixed evidence for divergent validity.

Conclusions

In the end, the Italian version of the MISS demonstrated good psychometric properties which will be discussed in detail below.

The Role of Phenomenological Control in Experience

To varying degrees, people have the capacity to alter their subjective experience such that it misrepresents reality in ways consistent with their goals and such that the misrepresentation can be sustained over at least minutes despite clear contrary evidence. In other words, people have a capacity for phenomenological control. People can use this capacity to fulfill requirements of social situations or personal needs. One such prominent situation is hypnosis. Another situation that psychologists often place people in is the psychological experiment, in which it is often clear to subjects what experiences are desired. Situations in life may also call for certain experiences, for example, encountering a spiritual world according to one’s religious beliefs. These experiences can be constructed so that they seem to confirm the beliefs of all the people involved.

Comparative effects of hypnotic suggestion and imagery instruction on bodily awareness

Bodily awareness is informed by both sensory data and prior knowledge. Although misleading sensory signals have been repeatedly shown to affect bodily awareness, only scant attention has been given to the influence of cognitive variables. Hypnotic suggestion has recently been shown to impact visuospatial and sensorimotor representations of body-part size although the mechanisms subserving this effect are yet to be identified. Mental imagery might play a causal or facilitative role in this effect, as it has been shown to influence body awareness in previous studies. Nonetheless, current views ascribe only an epiphenomenal role to imagery in the implementation of hypnotic suggestions. This study compared the effects of hypnotic suggestion and imagery instruction for influencing the visuospatial and sensorimotor aspects of body-size representation. Both experimental manipulations produced significant increases (elongation) in both representations compared to baseline, although the effects were larger in the hypnotic suggestion condition. The effects of both manipulations were highly correlated across participants, suggesting overlapping mechanisms. Self-reports suggested that the use of voluntary imagery did not significantly contribute to the efficacy of either manipulation. Rather, top-down effects on body representations seem to be partly driven by response expectancies, spontaneous imagery, and hypnotic suggestibility in both conditions. These results are in line with current theories of suggestion and raise fundamental questions regarding the mechanisms driving the influence of cognition on body representations.

Absorption and dissociation mediate the relationship between direct verbal suggestibility and impulsivity/compulsivity

Direct verbal suggestibility refers to the capacity for an individual to experience perceptual, motor, affective and cognitive changes in response to verbal suggestions. Suggestibility is characterized by pronounced, yet reliable, inter-individual differences. Previous research and theoretical considerations suggest that greater impulsivity and compulsivity is associated to higher suggestibility, but the characteristics and mediating factors of this association are poorly understood. Using established psychometric measures in an online sample, we found positive correlations between the domain comprising impulsivity, compulsivity and behavioural activation, and the domain of suggestibility, dissociation and absorption. We also observed that dissociation and absorption mediated the link between suggestibility and impulsivity, and between suggestibility and behavioural activation, respectively. These results confirm the positive link between suggestibility and the impulsivity/compulsivity domain and shed new light on the characterisation of traits associated with suggestibility.