Visual identification of haptically explored objects in high and low hypnotizable subjects

Hypnotizability influences the cortical representation of visually and kinaesthetically imagined head position

The study investigates the cortical representation of the visual and kinesthetic image of a rotated position of the head in highly (highs) and low hypnotizable individuals (lows) of both gender. Participants were invited to imagine maintaining their head rotated toward one side by seeing their chin aligned with their right shoulder (V, visual imagery), and in a different condition, by feeling tension in their neck muscles (K, kinaesthetic imagery). Vividness of imagery and cognitive effort were reported after each task. Alpha and beta band absolute power was studied. Highs reported higher vividness than lows only for the kinaesthetic modality of imagery. The cortical desyncronization observed during visual and kinaesthetic imagery were different in high females (HM), low females (LF), high males (HM) and low males (LM). In fact, only HF and LM exhibited significant power changes during the kinaesthetic task, whereas visual imagery was associated with cortical desynchronization in all subgroups except HM. The study supports earlier findings of an advantage of highs in kinesthetic imagery, shows an intriguing interaction of hypnotizability and gender, and indicates topographical difference in the four subgroups of participants suggesting differences in underlying generators.

Cross-evidence for hypnotic susceptibility through nonlinear measures on EEGs of non-hypnotized subjects

Assessment of hypnotic susceptibility is usually obtained through the application of psychological instruments. A satisfying classification obtained through quantitative measures is still missing, although it would be very useful for both diagnostic and clinical purposes. Aiming at investigating the relationship between the cortical brain activity and the hypnotic susceptibility level, we propose the combined use of two methodologies - Recurrence Quantification Analysis and Detrended Fluctuation Analysis - both inherited from nonlinear dynamics. Indicators obtained through the application of these techniques to EEG signals of individuals in their ordinary state of consciousness allowed us to obtain a clear discrimination between subjects with high and low susceptibility to hypnosis. Finally a neural network approach was used to perform classification analysis.

Structural and functional cerebral correlates of hypnotic suggestibility

Little is known about the neural bases of hypnotic suggestibility, a cognitive trait referring to the tendency to respond to hypnotic suggestions. In the present magnetic resonance imaging study, we performed regression analyses to assess hypnotic suggestibility-related differences in local gray matter volume, using voxel-based morphometry, and in waking resting state functional connectivity of 10 resting state networks, in 37 healthy women. Hypnotic suggestibility was positively correlated with gray matter volume in portions of the left superior and medial frontal gyri, roughly overlapping with the supplementary and pre-supplementary motor area, and negatively correlated with gray matter volume in the left superior temporal gyrus and insula. In the functional connectivity analysis, hypnotic suggestibility was positively correlated with functional connectivity between medial posterior areas, including bilateral posterior cingulate cortex and precuneus, and both the lateral visual network and the left fronto-parietal network; a positive correlation was also found with functional connectivity between the executive-control network and a right postcentral/parietal area. In contrast, hypnotic suggestibility was negatively correlated with functional connectivity between the right fronto-parietal network and the right lateral thalamus. These findings demonstrate for the first time a correlation between hypnotic suggestibility, the structural features of specific cortical regions, and the functional connectivity during the normal resting state of brain structures involved in imagery and self-monitoring activity.

Watching neutral and threatening movies: subjective experience and autonomic responses in subjects with different hypnotizability levels

Subjects with high hypnotizability scores (Highs) have been considered more prone to experience negative affect and more vulnerable to its autonomic effects with respect to low hypnotizable individuals (Lows). The aim of the study was to analyze the subjective experience, tonic skin conductance (SC), respiratory frequency (RF), heart rate (HR) and heart rate variability (HRV) of healthy Highs and Lows during a long-lasting, emotionally neutral task (Session R, 46 subjects) and a moderately threatening one (Session T, 35 subjects). At the end of the relaxing Session R, all participants reported an increased relaxation. At the end of the threatening Session T, only 20 subjects reported a decreased relaxation (effective T: eT subsample). Highs and Lows of this subsample reported a similarly reduced relaxation and showed a similarly increased skin conductance. HR and HRV did not differ between the two sessions and between Highs and Lows. Among the subjects not reporting decreased relaxation at the end of Session T (ineffective T: iT subsample, n=15), relaxation was deeper and associated with lower skin conductance in Highs, although HR and HRV did not differ between Highs and Lows. All together, the results do not support the hypothesis of higher proneness of Highs to experience negative affect and to exhibit the autonomic correlates of negative emotion.

Hypnotizability-related differences in written language

The study analyzed the writing products of subjects with high (highs) and low (lows) hypnotizability. The participants were asked to write short texts in response to highly imaginative scenarios in standard conditions. The texts were processed through computerized and manual methods. The results showed that the highs' texts were more sophisticated due to a higher number of abstract nouns, more intense and imaginative due to a larger number of similes, metaphors, and onomatopoeias, and less detailed due to a higher nouns-to-adjectives ratio. The differences in the use of abstract nouns and highly imageable expressions are discussed in relation to the preeminent left-hemisphere activity of highs during wakefulness and to a possibly different involvement of the precuneus, which is involved in hypnotic phenomena.

Hypnotizability-dependent accuracy in the reproduction of haptically explored paths

The study assessed differences between highly (Highs) and low hypnotizable (Lows) subjects in the blindfolded reproduction of paths connected at acute or obtuse angles. Reproduction attempts were made after path exploration performed by one finger, with or without concomitant cognitive activities (mental computation or imagery of exploring an angle larger than the explored one). The variables analyzed were: subjective experience (scores of the exploring effort, reproduction difficulty, perceived accuracy of reproduction, attention to mental computation and efficacy of imagery), exploration time, relative error in reproduction (under or overestimation) and the percentage of "successful" trials (absolute error <10°). The results showed that the subjective experience of exploration/reproduction and the exploration times are similar in Highs and Lows and that all subjects underestimate the explored angles and reproduce the acute angle more accurately than the obtuse one. Exploration of the acute angle concomitant with imagery of a larger one reduced its underestimation in both groups. Highs exhibited a larger number of successful trials after exploration of the obtuse angle, while Lows (males) decreased their relative error in the reproduction of the acute angle. In conclusion, in the more demanding condition of reproducing an obtuse angle, the Highs' reproduction was more accurate and more independent of cognitive load than that of the Lows.

Can imagery become reality?

Previous studies showed that highly hypnotizable persons imagining a specific sensory context behave according to the corresponding real stimulation and perceive their behaviour as involuntary. The aim of the study was to confirm the hypothesis of a translation of sensory imagery into real perception and, thus, of a true involuntary response. We studied the imagery-induced modulation of the vestibulospinal (VS) reflex earlier component in highly (Highs) and low hypnotizable subjects (Lows), as it is not affected by voluntary control, its amplitude depends on the stimulus intensity, and the plane of body sway depends on the position of the head with respect to the trunk. Results showed that the effects of the "obstructive" imagery of anaesthesia are different from those elicited by the "constructive" imagery of head rotation. Indeed, both Highs and Lows having their face forward and reporting high vividness of imagery experienced anaesthesia and reduced their VS reflex amplitude in the frontal plane, while only Highs changed the plane of body sway according to the imagined head rotation that is from the frontal to the sagittal one. These effects cannot be voluntary and should be attributed to translation of sensory imagery into the corresponding real perception.