Hypnotizability-related integration of perception and action

Hypnosis-induced modulation of corticospinal excitability during motor imagery

Hypnosis can be considered an altered state of consciousness in which individuals produce movements under suggestion without apparent voluntary control. Despite its application in contexts implying motor control, evidence for the neurophysiological mechanisms underlying hypnosis is scarce. Inter-individual differences in hypnotic susceptibility suggest that sensorimotor strategies may manifest in a hypnotic state. We tested by means of transcranial magnetic stimulation applied over the primary motor cortex whether motor system activation during a motor imagery task differs in the awake and in the hypnotic state. To capture individual differences, 30 healthy volunteers were classified as high or low hypnotizable (Highs and Lows) according to ad-hoc validated scales measuring hypnotic susceptibility and personality questionnaires. Corticospinal activation during motor imagery in the hypnotic state was greater in the Highs than the Lows. Intrinsic motivation in task performance and level of persuasion modulated corticospinal activation in the Highs. Corticospinal system activation under hypnosis may have practical implications that merit research in areas where hypnosis can be applied to improve motor performance, such as loss of motor abilities and sports.

Hypnotic susceptibility and affective states in bipolar I and II disorders

BACKGROUND

Highly hypnotizable individuals have impaired executive function, elevated motor impulsivity and increased emotional sensitivity, which are sometimes found in bipolar disorder patients. It is then reasonable to assume that certain aspects of hypnotic susceptibility differ with the types of bipolar disorder.

METHODS

The Stanford Hypnotic Susceptibility Scale: Form C (SHSS:C) test, the Mood Disorder Questionnaire (MDQ), the Hypomanic Checklist-32 (HCL-32) and the Plutchick-van Praag Depression Inventory (PVP) were applied to 62 patients with bipolar I disorder, 33 bipolar II disorder, and 120 healthy volunteers.

RESULTS

The passing rate of the SHSS:C 'Moving hands apart' item was higher in bipolar I patients than in controls, whereas for 'Mosquito hallucination' the rate was lower. Bipolar I and II patients scored significantly higher on MDQ, HCL-32 and PVP scales than controls. The passing rates of 'Mosquito hallucination' in controls, 'Arm rigidity' in bipolar I, and 'Age regression' in bipolar II predicted the respective MDQ scores.

CONCLUSION

In contrast to cognitive suggestions, bipolar I patients followed motor suggestions more often under hypnosis. Furthermore, both bipolar disorder patients and healthy volunteers demonstrated associations between mania levels and certain hypnotic susceptibility features. Our study aids in better understanding the altered conscious states in bipolar disorders, and encourages the use of related psychotherapy for these patients.

Hypnotizability and Performance on a Prism Adaptation Test

The susceptibility to hypnosis, which can be measured by scales, is not merely a cognitive trait. In fact, it is associated with a number of physiological correlates in the ordinary state of consciousness and in the absence of suggestions. The hypnotizability-related differences observed in sensorimotor integration suggested a major role of the cerebellum in the peculiar performance of healthy subjects with high scores of hypnotic susceptibility (highs). In order to provide behavioral evidence of this hypothesis, we submitted 20 highs and 21 low hypnotizable participants (lows) to the classical cerebellar Prism Adaptation Test (PAT). We found that the highs' performance was significantly less accurate and more variable than the lows' one, even though the two groups shared the same characteristics of adaptation to prismatic lenses. Although further studies are required to interpret these findings, they could account for earlier reports of hypnotizability-related differences in postural control and blink rate, as they indicate that hypnotizability influences the cerebellar control of sensorimotor integration.

Asymmetric Tactile Foot Stimulation: How Postural Studies May Suggest New Views of Hypnotizability

Earlier studies have shown hypnotizability-related postural effects of visual suppression and of leg and neck proprioceptive alteration. This study completes this investigation by demonstrating the postural effects of asymmetric tactile foot stimulation in standing participants with different hypnotizability scores. During this stimulation, body sway changed in medium-to-high more than in low-to-medium hypnotizable participants. Findings support the view that high hypnotizability is associated with higher vulnerability of posture to sensory alteration; together with earlier results, they suggest a role of the cerebellum in the observed hypnotizability-related differences and prompt investigation of cerebral structures and factors potentially responsible for both the cognitive and physiological aspects of hypnotizability.

Pain perception and EEG dynamics: does hypnotizability account for the efficacy of the suggestions of analgesia?

We report novel findings concerning the role of hypnotizability, suggestions of analgesia and the activity of the Behavioral Inhibition/Activation System (BIS/BAS) in the modulation of the subjective experience of pain and of the associated EEG dynamics. The EEG of high (highs) and low hypnotizable participants (lows) who completed the BIS/BAS questionnaire was recorded during basal conditions, tonic nociceptive stimulation without (PAIN) and with suggestions for analgesia (AN). Participants scored the perceived pain intensity at the end of PAIN and AN. The EEG midline dynamics was characterized by indices indicating the signal predictability (Determinism) and complexity (Entropy) obtained through the Recurrence Quantification Analysis. The reduced pain intensity reported by highs during AN was partially accounted for by the activity of the Behavioral Activation System. The decreased midline cortical Determinism observed during nociceptive stimulation in both groups independently of suggestions remained significantly reduced only in lows after controlling for the activity of the Behavioral Activation System. Finally, controlling for the activity of the Behavioral Inhibition System abolished stimulation, suggestions and hypnotizability-related differences. Results indicate that the BIS/BAS activity may be more important than hypnotizability itself in pain modulation and in the associated EEG dynamics.

Hypnosis and imaging of the living human brain

Over more than two decades, studies using imaging techniques of the living human brain have begun to explore the neural correlates of hypnosis. The collective findings provide a gripping, albeit preliminary, account of the underlying neurobiological mechanisms involved in hypnotic phenomena. While substantial advances lend support to different hypotheses pertaining to hypnotic modulation of attention, control, and monitoring processes, the complex interactions among the many mediating variables largely hinder our ability to isolate robust commonalities across studies. The present account presents a critical integrative synthesis of neuroimaging studies targeting hypnosis as a function of suggestion. Specifically, hypnotic induction without task-specific suggestion is examined, as well as suggestions concerning sensation and perception, memory, and ideomotor response. The importance of carefully designed experiments is highlighted to better tease apart the neural correlates that subserve hypnotic phenomena. Moreover, converging findings intimate that hypnotic suggestions seem to induce specific neural patterns. These observations propose that suggestions may have the ability to target focal brain networks. Drawing on evidence spanning several technological modalities, neuroimaging studies of hypnosis pave the road to a more scientific understanding of a dramatic, yet largely evasive, domain of human behavior.

Hypnotic relaxation results in elevated thresholds of sensory detection but not of pain detection

Background

Many studies show an effectiveness of hypnotic analgesia. It has been discussed whether the analgesic effect is mainly caused by the relaxation that is concomitant to hypnosis. This study was designed to evaluate the effects of hypnotic relaxation suggestion on different somatosensory detection and pain thresholds.

Methods

Quantitative sensory testing (QST) measurements were performed before and during hypnosis in twenty-three healthy subjects on the dorsum of the right hand. Paired t-test was used to compare threshold changes. The influence of hypnotic susceptibility was evaluated by calculating correlation coefficients for threshold changes and hypnotic susceptibility (Harvard group scale).

Results

During hypnosis significantly changed somatosensory thresholds (reduced function) were observed for the following sensory detection thresholds: Cold Detection Threshold (CDT), Warm Detection Threshold (WDT), Thermal Sensory Limen (TSL) and Mechanical Detection Threshold (MDT). The only unchanged sensory detection threshold was Vibration Detection Threshold (VDT). No significant changes were observed for the determined pain detection thresholds (Cold Pain Thresholds, Heat Pain Thresholds, Mechanical Pain Sensitivity, Dynamic Mechanical Allodynia, Wind-up Ratio and Pressure Pain Threshold). No correlation of hypnotic susceptibility and threshold changes were detected.

Conclusion

Hypnotic relaxation without a specific analgesic suggestion results in thermal and mechanical detection, but not pain threshold changes. We thus conclude that a relaxation suggestion has no genuine effect on sensory pain thresholds.

Trial Registration

ClinicalTrials.gov, Identifier: NCT02261155 (9^th October 2014).

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.

Stabilizing posture through imagery

Abstract In the general population, suppression of vision modulates body sway by increasing the center of pressure (CoP) velocity, while a light fingertip touch reduces the area of the CoP displacement in blindfolded subjects. This study assessed whether imagined fixation and fingertip touch differentially stabilize posture in subjects with high (highs) and low (lows) hypnotizability. Visual and tactile imageries were ineffective in lows. In highs, the effects of visual imagery could not be evaluated because the real information was ineffective; real tactile stimulation was effective only on velocity, but the imagery effects could not be definitely assessed owing to low effect size. The highs' larger variability could account for this and represents the most important finding.

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-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.

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

Hypnotizability is associated with peculiar characteristics of sensorimotor integration, imaginal abilities, and preferences in the sensory modality of imagery. The visual recognition of haptically explored objects involves an interaction among these processes and is a proper tool to investigate their possible hypnotizability-related modulation. Sixteen high hypnotizables and 16 lows participated in the study. Higher frequencies of correct recognition (RF) were observed in highs. RF improved across both groups. As an effect of learning, shorter recognition times were found in males among highs and in females among lows. The findings are consistent with the literature suggesting that hypnotizability levels may be associated with specific modes of sensory integration and/or imagery.

Hypnotizability-related effects of vestibular impairment on posture and locomotion

Body sway and locomotion are differentially modulated in high (highs) and low (lows) hypnotizable subjects undergoing alteration of visual and neck/leg proprioceptive inputs. The study's aim was to investigate whether partial impairment of vestibular information due to backward head extension affects postural (Study 1) and locomotor behavior (Study 2) differentially in highs and lows. Results showed that, at variance with the visual and proprioceptive modalities, vestibular inactivation did not induce major differences between the 2 groups, with the exception of improvement in walking straight across consecutive trials, which was observed only in highs. The article presents an overview of the structures and mechanisms possibly involved in the observed hypnotizability-related differences in motor control and suggests that hypnotic susceptibility might be a relevant factor in neuro-rehabilitative treatments because it accounts for part of the variability in the sensorimotor self.

Hypnotizability and sensorimotor integration: an Italian Space Agency project

In highly hypnotizable individuals (highs), postural control is more independent of sensory information than in low hypnotizable subjects (lows). The aim of the study was to find out whether locomotion is also less affected in highs than in lows by visual suppression and changes in the neck proprioceptive input. Eighteen highs and 20 lows were asked to walk straight ahead, blindfolded, in basal conditions (face forward), during real and imagined right/left head rotation and mental computation. Highs detected deviations from the straight trajectory better than lows. Their walking direction was more straight during basal conditions and less influenced than the lows' one by mental computation and real/imagined rotation of the head. The results confirm highs' lower dependence on sensory inputs, although this cannot be definitely attributed to a better internal representation of space or to higher behavioral automaticity.

Modulation of the postural effects of cognitive load by hypnotizability

Aim of the experiment was to study whether cognitive load affects postural control more in low (Lows) than in highly hypnotizable (Highs) subjects due to the latter's greater attentional abilities. Standing Highs and Lows underwent an experimental session (closed eyes) consisting of a basal condition and of mental computation in an easy (stable support) and a difficult (unstable support) postural condition. Variability [standard deviation (SD)] and complexity [sample entropy (SampEn)] of the movement of the centre of pressure (CoP), its mean velocity (Velocity), the area swept by the CoP (Area) and the ratio between the CoP trajectory length and area [length for surface (LFS)] were measured. Few hypnotizability-related differences were detected (reduction in the Highs' SD and increases in the Lows' LFS in the difficult postural condition). Thus, the hypnotizability-related postural differences observed in previous studies during sensory alteration could not be accounted mainly by attentional abilities.