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.

Influences of hypnotic suggestibility, contextual factors, and EEG alpha on placebo analgesia.

We tested the role of hypnotic suggestibility, involuntariness, pain expectation, and subjective hypnotic depth in the prediction of placebo analgesia (PA) responsiveness. We also tested the link of lower and upper alpha sub-band (i.e., 'alpha1' and 'alpha2') power changes with tonic PA responding during waking and hypnosis conditions. Following an initial PA manipulation condition, we recorded EEG activity during waking and hypnosis under two treatments: (1) painful stimulation (Pain); (2) painful stimulation after application of a PA cream. Alpha1 and alpha2 power were derived using the individual alpha frequency method. We found that (1) PA in both waking and hypnosis conditions significantly reduced relative pain perception; (2) during waking, all the above mentioned contextual measures were associated with pain reduction, while involuntariness alone was associated with pain reduction within hypnosis. Enhanced alpha2 power at the left-parietal lead was solely associated with pain reduction in waking, but not in hypnosis condition. Using multiple regression and mediation analyses we found that: (i) during waking, the enhancement of relative left-parietal alpha2 power, directly influenced the enhancement in pain reduction, and, indirectly, through the mediating positive effect of involuntariness; (j) during hypnosis, the enhancement of left-temporoparietal alpha2 power, through the mediation of involuntariness, influenced pain reduction. Current findings obtained during waking suggest that enhanced alpha2 power may serve as a direct-objective measure of the subjective reduction of tonic pain in response to PA treatment. Overall, our findings suggest that placebo analgesia during waking and hypnosis involves different processes of top-down regulation.

Effects of Prehypnotic Instructions on Hypnotizability and Relationships Between Hypnotizability, Absorption, and Empathy.

Although hypnotizability exhibits high across-time and across-test consistencies, it is not clear (a) how different preambles to a hypnotic procedure (metasuggestions) influence responsiveness to suggestions and the strength of the association between two hypnotizability scales and (b) how hypnotizability relates to absorption and empathy. In Experiment 1, nonclinical participants (N = 152 women) were administered the Modified Tellegen Absorption Scale (MODTAS), Interpersonal Reactivity Index (IRI), Hypnotic Induction Profile (HIP), and Stanford Hypnotic Susceptibility Scale, Form C (SHSS:C). In Experiment 2, nonclinical participants (N = 188; 105 women and 83 men) were administered the MODTAS, IRI, and Harvard Group Scale of Hypnotic Susceptibility, Form A (HGSHS:A). The induction scores of the HIP (HIP-IND) and the SHSS:C scores showed a significantly stronger correlation when the HIP was introduced to the participants after hypnosis metasuggestion (HIP-H-IND) than after imagination metasuggestion (HIP-I-IND). Metasuggestion was a moderator of the association between HIP-IND and SHSS:C scores. Participants with low and medium, but not with high, hypnotizability levels on the SHSS:C showed significantly higher scores on the HIP-I-IND than on the HIP-H-IND. The strong correlations between the SHSS:C, HIP-H-IND, and HIP eye-roll (HIP-ER) scores indicate that both the HIP-H-IND and HIP-ER are robust measures of hypnotizability. Absorption and empathy were not significantly associated with hypnotizability. Women were more hypnotizable than men, as assessed by the HGSHS:A. The clinical relevance of metasuggestions, intended to increase responsiveness to suggestions, is discussed as a strategy to improve treatment outcomes.

Psychopathy traits and reinforcement sensitivity theory: Prepulse inhibition and ERP responses.

This study examined the associations between Reinforcement Sensitivity Theory (RST-PQ, Corr & Cooper, 2016) and psychopathy traits (LSRPS, Levenson et al., 1995) in university students. The aim was to identify psychopathy and RST traits associated with prepulse inhibition (PPI) of acoustic startle and ERP responses by using two prepulse-stimulus intensities (70 and 85 dB) combined with a 105 dB startle pulse (200 ms prepulse-plus-pulse interval). The higher intensity prepulse produced a larger PPI, although both prepulse stimuli reliably activated the startle system. Higher Primary Psychopathy was associated with a higher Defensive-Fight trait and both measures were associated with larger PPI. A principal components factor analysis disclosed an N1-startle factor that was a significant predictor of both reward reactivity and Goal-Drive Persistence scores. Results appear in line with Newman's response modulation hypothesis emphasizing the engagement of attention and recognition of stimulus salience, which may be disrupted in psychopathy.

New directions in hypnosis research: strategies for advancing the cognitive and clinical neuroscience of hypnosis.

This article summarizes key advances in hypnosis research during the past two decades, including (i) clinical research supporting the efficacy of hypnosis for managing a number of clinical symptoms and conditions, (ii) research supporting the role of various divisions in the anterior cingulate and prefrontal cortices in hypnotic responding, and (iii) an emerging finding that high hypnotic suggestibility is associated with atypical brain connectivity profiles. Key recommendations for a research agenda for the next decade include the recommendations that (i) laboratory hypnosis researchers should strongly consider how they assess hypnotic suggestibility in their studies, (ii) inclusion of study participants who score in the middle range of hypnotic suggestibility, and (iii) use of expanding research designs that more clearly delineate the roles of inductions and specific suggestions. Finally, we make two specific suggestions for helping to move the field forward including (i) the use of data sharing and (ii) redirecting resources away from contrasting state and nonstate positions toward studying (a) the efficacy of hypnotic treatments for clinical conditions influenced by central nervous system processes and (b) the neurophysiological underpinnings of hypnotic phenomena. As we learn more about the neurophysiological mechanisms underlying hypnosis and suggestion, we will strengthen our knowledge of both basic brain functions and a host of different psychological functions.

Hypnotizability and Placebo Analgesia in Waking and Hypnosis as Modulators of Auditory Startle Responses in Healthy Women: An ERP Study.

We evaluated the influence of hypnotizability, pain expectation, placebo analgesia in waking and hypnosis on tonic pain relief. We also investigated how placebo analgesia affects somatic responses (eye blink) and N100 and P200 waves of event-related potentials (ERPs) elicited by auditory startle probes. Although expectation plays an important role in placebo and hypnotic analgesia, the neural mechanisms underlying these treatments are still poorly understood. We used the cold cup test (CCT) to induce tonic pain in 53 healthy women. Placebo analgesia was initially produced by manipulation, in which the intensity of pain induced by the CCT was surreptitiously reduced after the administration of a sham analgesic cream. Participants were then tested in waking and hypnosis under three treatments: (1) resting (Baseline); (2) CCT-alone (Pain); and (3) CCT plus placebo cream for pain relief (Placebo). For each painful treatment, we assessed pain and distress ratings, eye blink responses, N100 and P200 amplitudes. We used LORETA analysis of N100 and P200 waves, as elicited by auditory startle, to identify cortical regions sensitive to pain reduction through placebo and hypnotic analgesia. Higher pain expectation was associated with higher pain reductions. In highly hypnotizable participants placebo treatment produced significant reductions of pain and distress perception in both waking and hypnosis condition. P200 wave, during placebo analgesia, was larger in the frontal left hemisphere while placebo analgesia, during hypnosis, involved the activity of the left hemisphere including the occipital region. These findings demonstrate that hypnosis and placebo analgesia are different processes of top-down regulation. Pain reduction was associated with larger EMG startle amplitudes, N100 and P200 responses, and enhanced activity within the frontal, parietal, and anterior and posterior cingulate gyres. LORETA results showed that placebo analgesia modulated pain-responsive areas known to reflect the ongoing pain experience.

BIS/BAS sensitivity and emotional modulation in a prepulse-inhibition paradigm: A brain potential study.

We investigated whether prepulse inhibition (PPI) is sensitive to emotion modulation vis-à-vis individual differences in the sensitivity of the behavioral inhibition system (BIS) and behavioral activation system (BAS). Participants (n=50) performed a PPI task while recording the eyeblink reflex and auditory evoked potentials (i.e., N100 and P200). The results showed an increase in PPI from positive to negative stimuli at parietal sites, for both the N100 and P200. The N100 wave of the auditory evoked potential was sensitive to emotional valence high in arousal, whereas the P200 wave was sensitive to emotional valence low in arousal. Importantly, individual differences in BAS sensitivity, but not BIS sensitivity, influenced the emotional modulation of the startle response and PPI. This influence was most evident for the N100. Our findings are consistent with previous reports showing that PPI is sensitive to emotion modulation. The current results extent previous findings by highlighting the importance of the combined influence of valence and arousal. The findings indicate that state and trait emotions bias selective encoding of affective stimuli thereby priming behavioral output.

Pain modulation in waking and hypnosis in women: event-related potentials and sources of cortical activity.

Using a strict subject selection procedure, we tested in High and Low Hypnotizable subjects (HHs and LHs) whether treatments of hypoalgesia and hyperalgesia, as compared to a relaxation-control, differentially affected subjective pain ratings and somatosensory event-related potentials (SERPs) during painful electric stimulation. Treatments were administered in waking and hypnosis conditions. LHs showed little differentiation in pain and distress ratings between hypoalgesia and hyperalgesia treatments, whereas HHs showed a greater spread in the instructed direction. HHs had larger prefrontal N140 and P200 waves of the SERPs during hypnotic hyperalgesia as compared to relaxation-control treatment. Importantly, HHs showed significant smaller frontocentral N140 and frontotemporal P200 waves during hypnotic hypoalgesia. LHs did not show significant differences for these SERP waves among treatments in both waking and hypnosis conditions. Source localization (sLORETA) method revealed significant activations of the bilateral primary somatosensory (BA3), middle frontal gyrus (BA6) and anterior cingulate cortices (BA24). Activity of these contralateral regions significantly correlated with subjective numerical pain scores for control treatment in waking condition. Moreover, multivariate regression analyses distinguished the contralateral BA3 as the only region reflecting a stable pattern of pain coding changes across all treatments in waking and hypnosis conditions. More direct testing showed that hypnosis reduced the strength of the association of pain modulation and brain activity changes at BA3. sLORETA in HHs revealed, for the N140 wave, that during hypnotic hyperalgesia, there was an increased activity within medial, supramarginal and superior frontal gyri, and cingulated gyrus (BA32), while for the P200 wave, activity was increased in the superior (BA22), middle (BA37), inferior temporal (BA19) gyri and superior parietal lobule (BA7). Hypnotic hypoalgesia in HHs, for N140 wave, showed reduced activity within medial and superior frontal gyri (BA9,8), paraippocampal gyrus (BA34), and postcentral gyrus (BA1), while for the P200, activity was reduced within middle and superior frontal gyri (BA9 and BA10), anterior cingulate (BA33), cuneus (BA19) and sub-lobar insula (BA13). These findings demonstrate that hypnotic suggestions can exert a top-down modulatory effect on attention/preconscious brain processes involved in pain perception.

Preferred EEG brain states at stimulus onset in a fixed interstimulus interval equiprobable auditory Go/NoGo task: a definitive study.

This study examined the occurrence of preferred EEG phase states at stimulus onset in an equiprobable auditory Go/NoGo task with a fixed interstimulus interval, and their effects on the resultant event-related potentials (ERPs). We used a sliding short-time FFT decomposition of the EEG at Cz for each trial to assess prestimulus EEG activity in the delta, theta, alpha and beta bands. We determined the phase of each 2 Hz narrow-band contributing to these four broad bands at 125 ms before each stimulus onset, and for the first time, avoided contamination from poststimulus EEG activity. This phase value was extrapolated 125 ms to obtain the phase at stimulus onset, combined into the broad-band phase, and used to sort trials into four phase groups for each of the four broad bands. For each band, ERPs were derived for each phase from the raw EEG activity at 19 sites. Data sets from each band were separately decomposed using temporal Principal Components Analyses with unrestricted VARIMAX rotation to extract N1-1, PN, P2, P3, SW and LP components. Each component was analysed as a function of EEG phase at stimulus onset in the context of a simple conceptualisation of orthogonal phase effects (cortical negativity vs. positivity, negative driving vs. positive driving, waxing vs. waning). The predicted non-random occurrence of phase-defined brain states was confirmed. The preferred states of negativity, negative driving, and waxing were each associated with more efficient stimulus processing, as reflected in amplitude differences of the components. The present results confirm the existence of preferred brain states and their impact on the efficiency of brain dynamics in perceptual and cognitive processing.

Hypnotizability, hypnosis and prepulse inhibition of the startle reflex in healthy women: an ERP analysis.

A working model of the neurophysiology of hypnosis suggests that highly hypnotizable individuals (HHs) have more effective frontal attentional systems implementing control, monitoring performance, and inhibiting unwanted stimuli from conscious awareness, than low hypnotizable individuals (LHs). Recent studies, using prepulse inhibition (PPI) of the auditory startle reflex (ASR), suggest that HHs, in the waking condition, may show reduced sensory gating although they may selectively attend and disattend different stimuli. Using a within subject design and a strict subject selection procedure, in waking and hypnosis conditions we tested whether HHs compared to LHs showed a significantly lower inhibition of the ASR and startle-related brain activity in both time and intracerebral source localization domains. HHs, as compared to LH participants, exhibited (a) longer latency of the eyeblink startle reflex, (b) reduced N100 responses to startle stimuli, and (c) higher PPI of eyeblink startle and of the P200 and P300 waves. Hypnosis yielded smaller N100 waves to startle stimuli and greater PPI of this component than in the waking condition. sLORETA analysis revealed that, for the N100 (107 msec) elicited during startle trials, HHs had a smaller activation in the left parietal lobe (BA2/40) than LHs. Auditory pulses of pulse-with prepulse trials in HHs yielded less activity of the P300 (280 msec) wave than LHs, in the cingulate and posterior cingulate gyrus (BA23/31). The present results, on the whole, are in the opposite direction to PPI findings on hypnotizability previously reported in the literature. These results provide support to the neuropsychophysiological model that HHs have more effective sensory integration and gating (or filtering) of irrelevant stimuli than LHs.

Effects of personality trait emotionality on acoustic startle response and prepulse inhibition including N100 and P200 event-related potential.

OBJECTIVES: To examine the association of personality trait-emotionality (behavioural inhibition system, BIS; behavioural activation system, BAS; anxiety and fear) and measures of auditory startle response (ASR) and prepulse inhibition (PPI) in a non-clinical sample. METHODS: Forty-seven women were tested for ASR and prepulse inhibition of the eyeblink component of the startle reflex as measured by electromyographic (EMG) responses of the left orbicularis oculi muscle and N100 and P200 components of the event-related potential (ERP) using sLORETA (standardized low resolution brain electromagnetic tomography). Startling stimuli (115 dB, 40 ms) were presented alone (pulse-alone) or were preceded by discrete (20 ms) prepulse stimuli (85 dB) at three prepulse-to-pulse intervals (30, 60 and 120 ms) over a steady background noise (70 dB). Measures of trait emotionality were assessed using a comprehensive battery of theoretically motivated personality scales. RESULTS: Consistent with previous reports, PPI (defined as percentage reduction in the amplitude of the ASR) increased as the prepulse-to-pulse interval increased. PPI measures were insensitive to individual differences in personality traits, while measures of ASR to pulse-alone stimuli disclosed significant effects. Higher BAS was associated with reduced N100 and P200 amplitudes to the pulse-alone stimulus, and with reduced current density for the N100 in the parietal lobe (BA40 and BA31). This effect indicated a smaller sensitivity or a higher avoidance level of these individuals for negative-startle stimuli. Higher trait anxiety was associated with larger ASR, suggesting an enhanced sensitivity to intense stimuli and a hasty style of reaction in anxious individuals. Lower self-report fear was associated with larger P200 amplitude, and enhanced current density in the medial and superior frontal gyrus (BA6). This effect indicates that prefrontal cortex may play an important role in inhibiting fear responses. CONCLUSIONS: Our findings are in good accordance with existing brain imaging studies and underline that ERP source localization is a useful alternative for identifying startle-relevant cortical regions. SIGNIFICANCE: The present observations extend previous startle findings observed in clinical samples to normal personality individuals. These results imply that hypotheses derived from clinical data may hold important implications for understanding human emotion and motivation, especially in relation to fear and anxiety.

Hypnotizability-related EEG alpha and theta activities during visual and somesthetic imageries.

Hypnotizability is a cognitive multidimensional trait that involves peculiar imagery characteristics. Subjects with high- (Highs) and low (Lows)-susceptibilities to hypnosis have shown different levels of skill at visual and somesthetic-guided imageries performed during upright stance. The aim of this experiment is to study the modulation of the EEG alpha and theta band amplitude during guided visual and somesthetic imageries in Highs and Lows, as these rhythms are responsive to the cognitive activities involved in mental imagery. Our results show that, at variance with standing subjects, subjects in both groups in a semi-reclined position report higher vividness and lower effort for visual than for somesthetic imagery. EEG patterns however are different between the two groups. Highs exhibit a more widespread alpha desynchronization and slightly different EEG patterns during visual and somesthetic imageries, while Lows show segregated alpha- and theta-desynchronization, without any difference between the tasks. Our results indicate that different, hypnotizability-related cognitive strategies, that are revealed by differences in EEG modulation, are responsible for the similar subjective experience associated with visual and somesthetic imageries in Highs and Lows. In addition, in both groups higher order mental representation of different sensory modalities might be subserved by a unique integrated neural network.

Focused analgesia in waking and hypnosis: effects on pain, memory, and somatosensory event-related potentials.

Somatosensory event-related potentials (SERPs) to painful electric standard stimuli under an odd-ball paradigm were analyzed in 12 high hypnotizable (HH), 12 medium hypnotizable (MH), and 12 low hypnotizable (LH) subjects during waking, hypnosis, and a cued eyes-open posthypnotic condition. In each of these conditions subjects were suggested to produce an obstructive imagery of stimulus perception as a treatment for pain reduction. A No-Analgesia treatment served as a control in waking and hypnosis conditions. The subjects were required to count the number of delivered target stimuli. HH subjects experienced significant pain and distress reductions during posthypnotic analgesia as compared to hypnotic analgesia and between these two analgesic conditions as compared to the two control conditions. Outside of hypnosis, these subjects remembered less pain and distress levels than they reported during hypnotic and posthypnotic analgesia treatments. In contrast, for waking-analgesia treatment, HH subjects remembered similar pain and distress levels to those they reported concurrently with the stimulation. HH subjects, during hypnotic and posthypnotic analgesia treatments, detected a smaller number of target stimuli and displayed a significant amplitude reduction of the midline frontal and central N140 and P200 SERP components. No significant SERP differences were observed for these subjects between treatments in waking condition and between hypnotic and posthypnotic analgesic treatments. For the MH and LH subjects no significant N140 and P200 amplitude changes were observed among analgesic conditions as compared to control conditions. These amplitude findings are seen as indicating that hypnotic analgesia can affect earlier and later stages of stimulus processing.

Pain perception, obstructive imagery and phase-ordered gamma oscillations.

The neural mechanisms underlying pain perception and anti-nociceptive effects of mental imagery are not well understood. Using a measure of phase-ordered beta and gamma EEG oscillations in response to painful electric stimulation, we recently found that somatosensory event-related phase-ordered gamma oscillations (38-42 Hz), elicited by the onset of painful stimuli over Cz scalp site, were linearly related to pain perception. In the present study, 38 subjects were engaged in a painful stimulus detection task using an oddball paradigm. This task was performed under a condition in which subjects were required simply to count the number of target stimuli (pain condition) and under another condition in which subjects were required to produce an obstructive mental imagery of painful stimulus perception (obstructive imagery). Only EEG responses to standard stimuli were analyzed in this study. Correlation analysis of sweeps for each individual revealed brief intervals of phase ordering of EEG patterns in the beta and gamma bands. The frequencies of interest were the beta1 (26-30 Hz), beta2 (30-34 Hz), gamma1 (34-38 Hz), gamma2 (38-42 Hz) and gamma3 (42-46 Hz) bands. Obstructive imagery treatment, compared to pain condition, significantly reduced pain perception. This reduction was paralleled by significant decreases of evoked phase-ordered gamma2 and gamma3 patterns over Cz scalp site. Phase-ordered oscillations at Cz scalp site, for both gamma2 and gamma3 bands, significantly predicted pain ratings during pain condition. Phase-ordered oscillation scores, obtained for these gamma bands over parietal and frontal scalp sites, resulted the best predictor of pain ratings during obstructive imagery. This study provides evidence for the role of gamma oscillations in the subjective experience of pain. Further, it has provided support for the view that pain reduction during obstructive mental imagery is the product of an inhibitory process involving frontal and parietal cortical regions.

Pain-reduction strategies in hypnotic context and hypnosis: ERPs and SCRs during a secondary auditory task.

Pain-rating scores were obtained from 10 high, 10 medium, and 10 low hypnotizable subjects who were holding a painful cold bottle in their left hands and were exposed to pain reduction treatments while they were performing a secondary oddball task. All subjects received suggestions of dissociative imagery and focused analgesia as cognitive strategies for pain reduction. The following measures were obtained for tone targets of the auditory oddball task: (a) reaction time; (b) P300 peak amplitude of the event-related potentials; (c) skin conductance levels and skin conductance responses. Focused analgesia produced the most pain reduction in high, but not medium or low, hypnotizable subjects who showed shorter reaction times, higher central and parietal P300 peaks, and higher skin conductance responses. These findings were discussed vis-a-vis the dissociated-control model assuming that capacity demands of hypnotic suggestion are low.

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.

Temporal aspects of hypnotic processes.

The authors examine the cortical processes underlying the process of hypnosis, especially as related to the temporal appearance of specific waveforms in relation to pain. Nonhypnotic pain research suggests that in terms of temporal processing early EEG components are more sensory in nature, and later components are of a more emotional or evaluative nature. In the present work, the authors report that the influence of hypnosis is less on the EEG components associated with the initial sensory experience itself and more on the later components that carry with them rich cognitive/emotional information. The research reviewed in this paper clearly suggests an inhibitory process for the high susceptible individuals associated with the hypnotic analgesia.

Preferred EEG brain states at stimulus onset in a fixed interstimulus interval auditory oddball task, and their effects on ERP components.

Previous work has indicated the importance of ongoing EEG activity in the elicitation of the event-related potential (ERP), supporting the conceptualisation of the ERP in terms of amplification and attenuation of component frequencies in the EEG. We investigated the importance of the phase of narrow-band EEG activity in generating N1 and P2 components in the auditory ERP. An auditory oddball paradigm requiring a button-press response to targets, with fixed interstimulus interval (ISI) and 15% target probability, was utilised. The continuous EEG at Cz was recorded from 16 subjects as the raw data set. Offline digital filtering was used to separate the EEG into 13 narrow bands from 1 to 13 Hz. For each band, the phase at the onset of each non-target stimulus was determined. These were used to sub-average the unfiltered data stream at each of four phases for each of 13 frequencies for each subject. Phase effects were examined in terms of two orthogonal dimensions of electrical brain activity: Cortical negativity and negative driving. Stimulus onset varied as a function of these dimensions in a non-random fashion across frequency, indicating the preferential occurrence of particular phases, interpretable as preferred brain states. Large differential effects were also apparent in N1 and P2 amplitudes. These data indicate important aspects of brain dynamics, suggesting that in a fixed-ISI paradigm the component frequencies of the EEG are dynamically adjusted in order to provide particular brain states at stimulus occurrence to facilitate the brain's processing of the stimulus.

The contribution of suggestibility and expectation to placebo analgesia phenomenon in an experimental setting.

This study reports how placebo analgesia was produced by conditioning whereby the intensity of electric stimulation was surreptitiously reduced in order to examine the contribution of psychological factors of suggestibility and expectancy on placebo analgesia. This strategy was used in order to manipulate expectancy for pain reduction. The magnitudes of the placebo effects were estimated after a manipulation procedure and during experimental trials in which stimulus intensities were reset to original baseline levels. Individual differences in suggestibility, verbal expectancy for drug efficacy and manipulation procedure for pain reduction were tested as possible mediators of placebo analgesia. The following dependent variables were measured: (a) subjective expectancy for drug efficacy in pain relief, (b) expected pain intensity and unpleasantness, (c) concurrent pain intensity and unpleasantness and (d) remembered pain intensity and unpleasantness. Statistically significant placebo effects on sensory and affective measures of pain were obtained independently of the extent of the surreptitious lowering of stimulus strength during manipulation trials. The pairing of placebo administration with painful stimulation was sufficient to produce a generalized placebo analgesic effect. However, verbal expectancy for drug efficacy and individual differences in suggestibility were found to contribute significantly to the magnitude of placebo analgesia. The highest placebo effect was shown by the most pronounced reductions in pain ratings in highly suggestible subjects who received suggestions presumed to elicit high expectancy for drug efficacy. The results also demonstrated that placebo effects established on remembered pain were at least twice as great as those obtained on concurrent placebo effects. This was mainly because baseline pain was remembered as being much more intense than it really was. Moreover, remembered placebo effects, like the concurrent placebo effects, were highly correlated with expected pain scores obtained just after manipulation trials. These results indicate that multiple factors contribute to the placebo effect, including suggestibility, expectancy and conditioning, and that the judgement of placebo analgesia is critically determined by whether pain relief is assessed concurrently or after treatment.

Pain perception, somatosensory event-related potentials and skin conductance responses to painful stimuli in high, mid, and low hypnotizable subjects: effects of differential pain reduction strategies.

In this study, pain perception, somatosensory event-related potential (SERP) and skin conductance response (SCR) changes during hypnotic suggestions of Deep Relaxation, Dissociated Imagery, Focused Analgesia, and Placebo, compared with a Waking baseline condition, were investigated. SERPs were recorded from frontal, temporal, central, and parietal scalp sites. Ten high, 9 mid, and 10 low hypnotizable right-handed women participated in the experiment. The following measures were obtained: (1) pain and distress tolerance ratings; (2) sensory and pain thresholds to biphasic electrical stimulation delivered to the right wrist; (3) reaction time and number of omitted responses; (4) N2 (280+/-11 ms) and P3 (405+/-19 ms) peak amplitudes of SERPs to target stimuli delivered using an odd-ball paradigm; (5) number of evoked SCRs and SCR amplitudes as a function of stimulus repetition. Results showed, high, mid and low hypnotizables exhibited significant reductions of reported pain and distress ratings during conditions of Deep Relaxation/Suggestion of Analgesia, Dissociated Imagery and Focused Analgesia. High hypnotizable subjects displayed significant reductions in pain and distress levels compared to mid and low hypnotizables during Dissociated Imagery, Focused Analgesia and, to a lesser degree, during Deep Relaxation. Placebo condition did not display significant differences among hypnotizability groups. High hypnotizables, compared to mid and low hypnotizables, also showed significant increases in sensory and pain thresholds during Dissociated Imagery and Focused Analgesia. High, mid, and low groups showed significant reductions in P3 peak amplitudes across all hypnosis conditions and, to a lesser degree, during Placebo. The temporal cortical region was the most sensitive in differentiating SERP responses among hypnotizability groups. On this recording area the subjects highly susceptible to hypnosis displayed significantly smaller P3 and greater N2 peaks during Focused Analgesia than did the other hypnotizable groups. In this condition highly susceptible subjects also reported the highest number of omitted responses and the shortest Reaction Times. These subjects also showed faster habituation of SCRs when compared with mid and low hypnotizables. During Dissociated Imagery and Focused Analgesia, highly hypnotizable subjects also disclosed a smaller total number of evoked SCRs than did mid and low hypnotizable subjects. The results are discussed considering possible common and different mechanisms to account for the effects of different hypnotic suggestions.