Dissociation in hypnosis and frontal executive function

Brain Functional Correlates of Resting Hypnosis and Hypnotizability: A Review

This comprehensive review delves into the cognitive neuroscience of hypnosis and variations in hypnotizability by examining research employing functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and electroencephalography (EEG) methods. Key focus areas include functional brain imaging correlations in hypnosis, EEG band oscillations as indicators of hypnotic states, alterations in EEG functional connectivity during hypnosis and wakefulness, drawing critical conclusions, and suggesting future research directions. The reviewed functional connectivity findings support the notion that disruptions in the available integration between different components of the executive control network during hypnosis may correspond to altered subjective appraisals of the agency during the hypnotic response, as per dissociated and cold control theories of hypnosis. A promising exploration avenue involves investigating how frontal lobes' neurochemical and aperiodic components of the EEG activity at waking-rest are linked to individual differences in hypnotizability. Future studies investigating the effects of hypnosis on brain function should prioritize examining distinctive activation patterns across various neural networks.

Boosting the hypnotic experience. Inhibition of the dorsolateral prefrontal cortex alters hypnotizability and sense of agency. A randomized, double-blind and sham-controlled tDCS study

Hypnotizability refers to the individual responsiveness to hypnosis, and literature shows that the greater the hypnotizability, the more effective the hypnotic suggestions. So far, few studies attempted to enhance hypnotizability, and only two adopted brain stimulation with magnetic pulses. In the present study, we aimed to boost hypnotizability through transcranial direct current stimulation (tDCS). To this aim, bilateral tDCS was applied over the dorsolateral prefrontal cortex (DLPFC) with the target electrode providing negative current (cathodal stimulation) over the left hemisphere. Twenty-nine subjects participated in the study and they were randomly assigned to the sham or the active group in a double-blind design. The hypnotic experience was assessed before and after the stimulation through a phenomenological measure of consciousness (the PCI-HAP). The main findings revealed that a single tDCS session enhanced the hypnotic depth by 11% and reduced the volitional control by 30%, while no differences emerged in the sham group. This is the first study adopting the electrical neurostimulation to produce an alteration of hypnotizability and sense of agency, and confirmed the key-role of the DLPFC and executive control in the hypnotic phenomena. If confirmed, these findings could have relevant implications as enhanced hypnotizability could be translated into better outcomes for many hypnotic interventions.

Association between Anterior Cingulate Neurochemical Concentration and Individual Differences in Hypnotizability

Hypnosis is the oldest form of Western psychotherapy and a powerful evidence-based treatment for numerous disorders. Hypnotizability is variable between individuals; however, it is a stable trait throughout adulthood, suggesting that neurophysiological factors may underlie hypnotic responsiveness. One brain region of particular interest in functional neuroimaging studies of hypnotizability is the anterior cingulate cortex (ACC). Here, we examined the relationships between the neurochemicals, GABA, and glutamate, in the ACC and hypnotizability in healthy individuals. Participants underwent a magnetic resonance imaging (MRI) session, whereby T1-weighted anatomical and MEGA-PRESS spectroscopy scans were acquired. Voxel placement over the ACC was guided by a quantitative meta-analysis of functional neuroimaging studies of hypnosis. Hypnotizability was assessed using the Hypnotic Induction Profile (HIP), and self-report questionnaires to assess absorption (TAS), dissociation (DES), and negative affect were completed. ACC GABA concentration was positively associated with HIP scores such that the higher the GABA concentration, the more hypnotizable an individual. An exploratory analysis of questionnaire subscales revealed a negative relationship between glutamate and the absorption and imaginative involvement subscale of the DES. These results provide a putative neurobiological basis for individual differences in hypnotizability and can inform our understanding of treatment response to this growing psychotherapeutic tool.

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.

Neurocognition under hypnosis: findings from recent functional neuroimaging studies

Functional neuroimaging studies show that hypnosis affects attention by modulating anterior cingulate cortex activation and uncoupling conflict monitoring and cognitive control function. Considering functional changes in the activation of the occipital and temporal cortices, precuneus, and other extrastriate visual areas, which account for hypnosis-induced altered reality perception, the role of mental imagery areas appears to be central under hypnosis. This is further stressed by the fact that motor commands are processed differently in the normal conscious state, deviating toward the precuneus and extrastriate visual areas. Functional neuroimaging also shows that posthypnotic suggestions alter cognitive processes. Further research should investigate the effects of hypnosis on other executive functions and personality measures.

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.

Motor inhibition in hysterical conversion paralysis

Brain mechanisms underlying hysterical conversion symptoms are still poorly known. Recent hypotheses suggested that activation of motor pathways might be suppressed by inhibitory signals based on particular emotional situations. To assess motor and inhibitory brain circuits during conversion paralysis, we designed a go-nogo task while a patient underwent functional magnetic resonance imaging (fMRI). Preparatory activation arose in right motor cortex despite left paralysis, indicating preserved motor intentions, but with concomitant increases in vmPFC regions that normally mediate motivational and affective processing. Failure to execute movement on go trials with the affected left hand was associated with activations in precuneus and ventrolateral frontal gyrus. However, right frontal areas normally subserving inhibition were activated by nogo trials for the right (normal) hand, but not during go trials for the left hand (affected by conversion paralysis). By contrast, a group of healthy controls who were asked to feign paralysis showed similar activation on nogo trials and left-go trials with simulated weakness, suggesting that distinct inhibitory mechanisms are implicated in simulation and conversion paralysis. In the patient, right motor cortex also showed enhanced functional connectivity with the posterior cingulate cortex, precuneus, and vmPFC. These results suggest that conversion symptoms do not act through cognitive inhibitory circuits, but involve selective activations in midline brain regions associated with self-related representations and emotion regulation.

Heart-rate control during pain and suggestions of analgesia without deliberate induction of hypnosis

Heart rate and heart-rate variability (HRV) were studied through a set of different methods in high (highs) and low hypnotizable subjects (lows) not receiving any deliberate hypnotic induction in basal conditions (simple relaxation) and during nociceptive-pressor stimulation with and without suggestions of analgesia. ANOVA did not reveal any difference between highs and lows for heart rate and for the HRV indexes extracted from the series of the interbeat intervals (RR) of the ECG in the frequency (spectral analysis) and time domain (standard deviation, Poincare plot) in both basal and stimulation conditions. Factors possibly accounting for the results and likely responsible for an underestimation of group differences are discussed.

Effects of vestibular and neck proprioceptive stimulation on posture as a function of hypnotizability

Previous studies on the role of hypnotizability in postural control indicate that the body sway of subjects with high or low hypnotizability to hypnosis is differentially modulated by eye closure. The aim of this study was to investigate whether hypnotizability also modulates the postural response to electrical vestibular stimulation and to head rotation in nonhypnotized individuals. The center of pressure (CoP) displacements were monitored in highs and lows standing on a stabilometric platform with closed eyes during basal conditions and electrical vestibular stimulation in 3 different positions of the head. Results showed that the CoP stimulus-locked displacements as well as the CoP mean position, area, and mean velocity were similar in highs and lows, but only in lows did the head position modulate the mean velocity. This finding might reflect a difference in sensory-motor integration between the 2 groups.

Expect the unexpected: ability, attitude, and responsiveness to hypnosis

Participants' expectancies and hypnotic performance throughout the course of a standardized, individually administered hypnotic protocol were analyzed with a structural equation model that integrated underlying ability, expectancy, and hypnotic response. The model examined expectancies and ability as simultaneous predictors of hypnotic responses as well as hypnotic responses as an influence on subsequent expectancies. Results of the proposed model, which fit very well, supported each of the 4 major hypothesized effects: Expectancies showed significant stability across the course of the hypnosis protocol; expectancies influenced subsequent hypnotic responses, controlling for latent ability; hypnotic responses, in turn, affected subsequent expectancies; and a latent trait underlay hypnotic responses, controlling for expectancies. Although expectancies had a significant effect on hypnotic responsiveness, there was an abundance of variance in hypnotic performance unexplained by the direct or indirect influence of expectation and compatible with the presence of an underlying cognitive ability.

Learning in trance: functional brain imaging studies and neuropsychology

This study examined the fundamental question, whether verbal memory processing in hypnosis and in the waking state is mediated by a common neural system or by distinct cortical areas. Seven right-handed volunteers (25.4 years, sd 3.1) with high-hypnotic susceptibility scores were PET-scanned while encoding/retrieving word associations either in hypnosis or in the waking state. Word-pairs were visually presented and highly imaginable, but not semantically related (e.g. monkey-street). The presentation of pseudo-words served as a reference condition. An emission scan was recorded after each intravenous administration of O-15 water. Encoding under hypnosis was associated with more pronounced bilateral activations in the occipital cortex and the prefrontal areas as compared to learning in the waking state. During memory retrieval of word-pairs which had been previously learned under hypnosis, activations were found in the occipital lobe and the cerebellum. Under both experimental conditions precuneus and prefrontal cortex showed a consistent bilateral activation which was most distinct when the learning had taken place under hypnosis. In order to further analyze the effect of hypnosis on imagery-mediated learning, we administered sets of high-imagery word-pairs and sets of abstract words. In the first experimental condition word-pair associations were presented visually. In the second condition it was found that highly hypnotisable persons recalled significantly more high-imagery words under hypnosis as compared to low-hypnotisables both in the visual and auditory modality. Furthermore, high-imagery words were also better recalled by the highly hypnotisable subjects during the non-hypnotic condition. The memory effect was consistently present under both, immediate and delayed recall conditions. Taken together, the findings advance our understanding of the neural representation that underlies hypnosis and the neuropsychological correlates of hypnotic susceptibility.

Suggestions of altered balance: Possible equivalence of imagery and perception

Hypnotic suggestions describing an altered perception induce congruent changes in the subject's experience and behavior. However, it is not known whether an implicit suggestion, only indirectly referring to an altered perception, induces a behavioral response corresponding to that of the real situation. In this study, an implicit suggestion of backward falling (IMP) was given to high hypnotizable participants not exposed (W-Highs) and exposed (H-Highs) to a hypnotic induction and a group of low hypnotizable individuals (W-Lows). Their posture was evaluated through an elite system. The results after the IMP were compared with those after an explicit suggestion of backward falling (EXP). In both W-Highs and H-Highs, the IMP elicited the backward body sway expected in the corresponding real situation, whereas no response was found in W-Lows. The results are discussed in terms of a possible equivalence of imagery and perception or of a lack of the motor inhibition normally associated with motor imagery.

Hypnotic trait and specific phobia: EEG and autonomic output during phobic stimulation

In a previous study we showed that healthy highly hypnotizable subjects, during the suggestion of a moderately unpleasant situation administered in awake conditions, exhibited a sympathetic response greatly attenuated with respect to non-hypnotizable individuals. This was interpreted as a natural protection of hypnotizable subjects against the cardiovascular effects of cognitive stress. Aim of the present study was to investigate whether the hypnotic trait is able to modulate the autonomic and cerebral activities also in specific phobic awake hypnotizable (Highs) and non-hypnotizable (Lows) subjects. Electroencephalogram, electrooculogram, electromiogram of corrugator muscle, electrocardiogram, respirogram and tonic electrodermal activity were recorded during a guided mental imagery of an animal phobic object. Phobic stimulation induced in both groups the rise of heart and respiratory frequency and the lowering of skin resistance. These changes are less pronounced in Highs than in Lows and are sustained by a different modulation of the sympatho-vagal balance. During phobic stimulation both groups exhibited a similar significant increase of EEG gamma relative power. At variance, significant stimulation-related decrements of alpha1, theta1 and theta2 activities were found only in Highs that exhibited similar changes during the control and phobic stimulation. Results suggest that hypnotizability is able to modulate cerebral and autonomic responses also in specific phobic subjects. However, the presence of a specific phobia attenuates the effectiveness of hypnotizability as a protective factor against possible stress-related cardiac illness.

Perception and modulation of pain in waking and hypnosis: functional significance of phase-ordered gamma oscillations

Somatosensory event-related phase-ordered gamma oscillations (40-Hz) to electric painful standard stimuli under an odd-ball paradigm were analyzed in 13 high, 13 medium, and 12 low hypnotizable subjects during waking, hypnosis, and post-hypnosis conditions. During these conditions, subjects received a suggestion of Focused Analgesia to produce an obstructive hallucination of stimulus perception; a No-Analgesia treatment served as a control. After hypnosis, a post-hypnotic suggestion was given to draw waking subjects into a deep hypnosis with opened eyes. High hypnotizables, compared to medium and low ones, experienced significant pain and distress reductions for Focused Analgesia during hypnosis and, to a greater extent, during post-hypnosis condition. Correlational analysis of EEG sweeps of each individual revealed brief intervals of phase ordering of gamma patterns, preceding and following stimulus onset, lasting approximately six periods. High and medium hypnotizable subjects showed significant reductions in phase-ordered gamma patterns for Focused Analgesia during hypnosis and post-hypnosis conditions; this effect was found, however, more pronounced in high hypnotizable subjects. Phase-ordered gamma scores over central scalp site predicted subject pain ratings across Waking-Pain and Waking-Analgesia conditions, while phase-ordered gamma scores over frontal scalp site predicted pain ratings during post-hypnosis analgesia condition. During waking conditions, this relationship was present in high, low and medium hypnotizable subjects and was independent of stimulus intensity measures. This relationship was unchanged by hypnosis induction in the low hypnotizable subjects, but not present in the high and medium ones during hypnosis, suggesting that hypnosis interferes with phase-ordered gamma and pain relationship.

Kinematic strategies for lowering of upper limbs during suggestions of heaviness: a real-simulator design

The aim of the experiment was to study possible differences between the kinematic strategies for the "involuntary" arm lowering of hypnotized highly susceptible subjects (H-Highs) and for the voluntary movement of non-hypnotizable simulators (Sims) during suggestions of arm heaviness (Part I). In addition, a comparison between awake susceptible subjects (W-Highs) and H-Highs was carried out to clarify the specific role of the hypnotic state and hypnotizability (Part II). Subjects' absorption and attentional/imagery capabilities were evaluated through neuropsychological tests. Their arm movements were monitored three-dimensionally at hand, wrist and elbow level through a Polhemus Fastrack system. A final interview collected self-reports concerning the perception of movement involuntariness. Neuropsychological tests showed better "absorption" and imagery capabilities in Highs. In the interview, H-Highs perceived a higher involvement in the task and greater involuntariness and difficulties in contrasting the arm lowering than the Sims. Kinematic analysis showed significant differences between H-Highs and Sims for arm displacements along the vertical axis and on the horizontal plane. In fact, the former lowered the left arm earlier and to a greater degree than the right arm; on the horizontal plane, a forearm flexion was observed for H-Highs on the right side. On comparing W-Highs and H-Highs, hypnosis appeared to magnify the waking motor strategies, but also to induce specific changes, mainly concerning the horizontal plane. These results cannot be interpreted on the basis of "role playing" and socio-cognitive factors. They are believed to be due to a balance between the effectiveness of the frontal executive control towards the selection of behaviors and movement automaticity, which is in line with the neo-dissociation theory of hypnosis.

Does hypnotizability modulate the stress-related endothelial dysfunction?

Previous studies suggest that hypnotizability represents a protective factor against the cardiac effects of cognitive stress and that hypnosis prevents vascular stress-induced modifications in highly hypnotizable individuals. The aim of the experiment was to investigate whether a similar effect at vascular level is present in awake subjects with a high (Highs) and a low (Lows) hypnotic susceptibility. Thus, brachial artery post-ischaemic flow-mediated vascular dilation (FMD) was evaluated non-invasively by ultrasound methodology during cognitive stress (mental computation) in Highs and Lows. Results showed that Highs, similarly to that previously observed in hypnotized Highs and in contrast with Lows, did not exhibit any stress-related endothelial dysfunction (FMD decrement). Thus, hypnotizability should be considered a protective factor against vascular disease.

Autonomic and EEG correlates of emotional imagery in subjects with different hypnotic susceptibility

The autonomic and EEG correlates of the response to a cognitive unpleasant stimulation (US) verbally administered to awake hypnotizable and non hypnotizable subjects were studied. They were compared with the values obtained during a resting condition immediately preceding the stimulus and with those produced by a cognitive neutral stimulation (NS), also administered after a basal resting period. Results showed hypnotic trait effects on skin resistance, heart and respiratory rate as well as on EEG theta, alpha, beta and gamma relative power changes. The autonomic and EEG patterns observed indicated different strategies in the task execution for hypnotizable and non hypnotizable subjects and a discrepancy between the autonomic and EEG changes associated to the US in susceptible subjects. Results support dissociation theories of hypnosis and suggest for hypnotizable persons an active mechanism of protection against cardiac hazard.

Pain perception, hypnosis and 40 Hz oscillations

A number of brain regions are associated with the subjective experience of pain. This study adds to our understanding of the neural mechanisms involved in pain by considering the relation between cortical oscillations in response to pain, with and without hypnosis and hypnotic analgesia, and the subjective experience of pain. Thirty-three subjects' neural responses (EEG) were measured during the 40-540 ms period following phasic electrical stimulations to the right hand, under control and hypnosis conditions. Resultant FFT amplitudes for frequencies ranging from 8 to 100 Hz were computed. These were grouped into 7 scalp topographies, and for each frequency, relations between these topographies and pain ratings, performance and stimulus intensity measures were assessed. Gamma activity (32-100 Hz) over prefrontal scalp sites predicted subject pain ratings in the control condition (r=0.50, P=0.004), and no other frequency/topography combination did. This relation was present in both high and low hypnotisable subjects and was independent of performance and stimulus intensity measures. This relation was unchanged by hypnosis in the low hypnotisable subjects but was not present in the highs during hypnosis, suggesting that hypnosis interferes with this pain/gamma relation. This study provides evidence for the role of gamma oscillations in the subjective experience of pain. Further, it is in keeping with the view that hypnosis involves the dissociation of prefrontal cortex from other neural functions.

Frontal lobe contributions to hypnotic susceptibility: a neuropsychological screening of executive functioning

Current theory on the cognitive mechanisms of hypnotic experience suggests that hypnosis is mediated by a dissociation between contention-scheduling mechanisms and a supervisory attention system. This theory is based on neuropsychological research with frontal lobe dysfunction patients, who show performance deficits similar in executive functioning to hypnotized individuals. To test an extension of this theory, high hypnotically susceptible (n = 9) and low hypnotically susceptible (n = 7) participants were given four tests of executive functioning. In a baseline condition, high susceptible individuals performed significantly better on one of the four tests (the Wisconsin Card Sorting Test). The role of increased cognitive flexibility in hypnotic susceptibility is considered as a possible component of the dissociated control model of hypnosis.

Somatosensory event-related potential and autonomic activity to varying pain reduction cognitive strategies in hypnosis

OBJECTIVES

The issues of differential effects among cognitive strategies during hypnosis in the control of human pain are under active debate. This study, which employs measures of pain perception, electrocortical and autonomic responses, was aimed at determining these pain-related modulations.

METHODS

Somatosensory event-related potentials (SERPs) to noxious stimuli under an odd-ball paradigm were recorded at the frontal, temporal and parietal regions in 10 high, 9 mid, and 10 low hypnotizable right-handed young women, at waking baseline, varying cognitive strategies (deep relaxation, dissociative imagery, focused analgesia) in hypnosis and placebo conditions. The phasic heart rate (HR) and skin conductance response were also recorded. The analysis was focused on the frequent standard trials of the odd-ball SERPs. Repeated measures analysis of variance was conducted to examine the experimental effects.

RESULTS

Focused analgesia induced the largest reduction in pain rating, more in the high than low hypnotizable subjects. In high hypnotizable subjects, the N2 amplitude was greater over frontal and temporal scalp sites than over parietal and central sites, whereas in moderately and low hypnotizable subjects, N2 was greater over temporal sites than over frontal, parietal, and central sites. These subjects also displayed a larger N2 peak over temporal sites during focused analgesia than in the other conditions. The P3 amplitude was smaller under deep relaxation, dissociative imagery and focused analgesia in the high hypnotizable subjects. For these subjects, the smallest P3 peaks were obtained for dissociated imagery and focused analgesia over frontal and temporal sites. In contrast, for the P3 peak, low hypnotizable subjects failed to show significant condition effects. In all of the subjects, the skin conductance and HR were smaller during hypnotic suggestions than in the waking state.

CONCLUSIONS

The effect of pain modulation is limited to high hypnotizable subjects rather than low hypnotizable ones. Higher frontal-temporal N2 and smaller posterior parietal P3 may indicate active inhibitory processes during cognitive strategies in hypnotic analgesia. These inhibitory processes also regulate the autonomic activities in pain perception.

In search of a deep psychobiology of hypnosis: visionary hypotheses for a new millennium

This search for the deep psychobiological foundations of hypnosis begins with a review of some of the paradoxes of historical hypnosis and the impasse of current theory. It is proposed that further progress requires a deeper investigation of how psychosocial cues can modulate the mechanisms of healing at the CNS, autonomic, neuroendocrine and cellular-genetic levels. The dynamics of hypnotic communication and healing from the cognitive-behavior level to the cellular-genetic are outlined in four stages: (1) Information transduction between the experiences of consciousness and the limbic-hypothalamic-pituitary system; (2) The psychosomatic network of messenger molecules and their receptors; (3) The immediate early gene protein cascade; and (4) State dependent memory, learning and behavior. Neuroscience research is outlined for its contributions to a mathematical model of how a psychobiological approach to the therapeutic applications of hypnosis and the placebo response could facilitate neurogenesis in the human hippocampus and healing at the cellular-genetic-protein level throughout the body. A series of ten hypotheses is proposed as a guide for theory and research in therapeutic hypnosis utilizing DNA chip technology in the new millennium.

Hypnosis and conversion hysteria: a unifying model

There are many similarities between the symptoms of conversion hysteria and phenomena produced in hypnotic contexts. This paper reviews some of those similarities and considers more general features associated with both hypnotic phenomena and conversion hysteria symptoms such as lack of concern, perceived involuntariness, the display of ''implicit knowledge'' and their apparently compliant nature. Neurophysiological and brain-imaging studies of hypnotically produced effects and conversion symptoms are described, which implicate frontal cortical structures in moderating the respective changes elsewhere in the brain, particularly in cingulate cortex. A recurrent theme is the apparent paradox which exists between, on the one hand, the subjective reality and involuntariness of both hypnotic phenomena and the symptoms of conversion hysteria and, on the other, the fact that objectively they appear to be role-congruent enactments responsive to the manipulation of motivational factors, expectancy, and social influence. A model of consciousness and self-awareness is presented which attempts to resolve that paradox whilst describing similar mechanisms underlying hypnotic phenomena and conversion hysteria symptoms. The model develops the idea of a central executive structure, similar to the notion of a supervisory attentional system, acting outside self-awareness but at a late stage of information processing which can be directly influenced from both internal and external sources to produce the relevant phenomena. The paper ends by proposing that as conversion disorder, pain disorder, and the dissociation disorders appear to be linked by a common mechanism they should be classified together under the heading of auto-suggestive disorder.