Cortical power spectrum analysis of hypnotic pain control in surgery

Mechanisms of hypnosis: toward the development of a biopsychosocial model

Evidence supports the efficacy of hypnotic treatments, but there remain many unresolved questions regarding how hypnosis produces its beneficial effects. Most theoretical models focus more or less on biological, psychological, and social factors. This scoping review summarizes the empirical findings regarding the associations between specific factors in each of these domains and response to hypnosis. The findings indicate that (a) no single factor appears primary, (b) different factors may contribute more or less to outcomes in different subsets of individuals or for different conditions, and (c) comprehensive models of hypnosis that incorporate factors from all 3 domains may ultimately prove to be more useful than more restrictive models that focus on just 1 or a very few factors.

Psychophysiological correlates of hypnosis and hypnotic susceptibility

This article reviews and summarizes electroencephalographic (EEG)-based research on physiological and cognitive indicators of hypnotic responding and hypnotic susceptibility, with special attention to the author's programmatic research in this area. Evidence that differences in attention levels may account for hypnotic depth and individual differences in hypnotizability is provided with traditional EEG rhythms, event-related potentials, and 40-Hz EEG activity. The alteration of stimulus perception may be a secondary effect with respect to allocation of attentional resources. In both nonhypnosis and hypnosis conditions, high hypnotizables appeared to show greater task-related EEG hemispheric shifts than did low hypnotizables. Findings concerning cognitive and physiological correlates of hypnotic analgesia are discussed with respect to hemispheric functioning in the apparent control of focused and sustained attention. The conclusion is that although a definitive EEG-based signature for hypnosis and hypnotizability is not yet established, there are a number of promising leads.

Hypnotic control of pain: historical perspectives and future prospects

Hypnotic analgesia has occupied a pivotal place in experimental and clinical hypnosis. It emerged early in the 19th century when effective clinical techniques for pain management had not yet developed, and the relief of pain and suffering had not even become a well-defined social goal. Its acceptance was further complicated by political struggles surrounding the humanitarian transformation of medicine during this era as well as a redefinition of the physician-patient relationship that wrested control from the patient. The initial struggle for professional acceptance was won only when the debate became almost entirely localized within the professional community. Acceptance of hypnosis by professional organizations has been followed by alternating periods of interest and indifference. While the evidence for the powerful effects of suggestion and related variables has often been observed and reported in nonhypnotic contexts, their relationship to hypnotic phenomena has often not been appreciated. Since the mid-20th century, scientific information about hypnotic analgesia has grown substantially and has had significant influence on strategies for acute and chronic pain management. If recent calls for its wider application in pain management are to succeed, it will require additional data from clinical populations and a balanced and scientifically prudent approach by its advocates.

EEG asymmetry and heart rate during experience of hypnotic analgesia in high and low hypnotizables

This study evaluates the effects of hypnotic analgesia and hypnosis on bilateral EEG activity recorded from frontal, central and posterior areas during three painful electrical stimulation conditions: waking, hypnosis/no-analgesia, hypnosis/analgesia. Eight high-hypnotizable and eight low-hypnotizable (right handed) subjects participated in the experiment. The following measures were obtained: pain and distress tolerance ratings; EEG spectral amplitudes for the frequency bands: delta (0.5-3.75 Hz), theta 1 (4-5.75 Hz), theta 2 (6-7.75 Hz), alpha 1 (8-9.75 Hz), alpha 2 (10-12.75 Hz), beta 1 (13-15.75 Hz), beta 2 (16-31.75 Hz), total band (0.5-31.75 Hz), '40-Hz' (36-44 Hz); cardiac interbeat interval (ms); mid-frequency and high-frequency peaks from power spectral analysis of heart period variability. During hypnosis/analgesia, high hypnotizable subjects displayed significant reductions in pain and distress scores compared to hypnosis/no-analgesia and waking conditions. In each experimental condition these subjects displayed significant lower total and beta 1 amplitudes compared to low hypnotizables. High hypnotizables, on central and posterior recording sites, during both hypnosis/analgesia and hypnosis/no-analgesia conditions also showed total and delta EEG amplitude reductions in both hemispheres and a theta 1 amplitude reduction in the left hemisphere. However, for total, delta and beta 1 bands in the hypnosis/analgesia condition the amplitude reduction was more pronounced in the right hemisphere as shown by hemispheric asymmetry in favor of the left hemisphere. Low hypnotizables, on posterior recording sites, displayed a delta amplitude reduction during hypnosis/no-analgesia and hypnosis/analgesia conditions. These subjects also showed, for all recording sites, a reduction in theta 1 amplitude during hypnosis/no-analgesia compared to the waking condition. Lows, however, failed in evidencing amplitude differences between hypnosis/no-analgesia and hypnosis/analgesia conditions. During hypnotic analgesia the hemispheric asymmetry found in high hypnotizables was parallel to a significant reduction in the spectral mid-frequency peak of heart period variability which indicated a decrease in the level of sympathetic activity. In contrast, during hypnosis/no-analgesia the EEG amplitude reduction was not paralleled by a decrease in sympathetic activity.

Hypnotic analgesia reduces R-III nociceptive reflex: further evidence concerning the multifactorial nature of hypnotic analgesia

Mechanisms of hypnotic analgesia were investigated by examining changes in the R-III, a nociceptive spinal reflex, during hypnotic reduction of pain sensation and unpleasantness. The R-III was measured in 15 healthy volunteers who gave VAS-sensory and VAS-affective ratings of an electrical stimulus during conditions of resting wakefulness, suggestions for hypnotic analgesia, and attempted suppression of the reflex during non-hypnotic conditions. The H-reflex was also measured to monitor and control for general changes in alpha-motoneuron excitability. Hypnotic sensory analgesia was related to reduction in the R-III after controlling for changes in the H-reflex (R2 = 0.51, P < 0.003), suggesting that hypnotic sensory analgesia is at least in part mediated by descending antinociceptive mechanisms that exert control at spinal levels in response to hypnotic suggestion. The relationship between hypnotic affective analgesia and reduction in R-III approached significance (R2 = 0.26; P = 0.053). Reduction in R-III was 67% as great and accounted for 51% of the variance in reduction of pain sensation. In turn, reduction in pain sensation was 75% as great and accounted for 77% of the variance in reduction of unpleasantness. The results suggest that 3 general mechanisms may be involved in hypnotic analgesia. The first, implicated by reductions in R-III, is related to spinal cord antinociceptive mechanisms. The second, implicated by reductions in pain sensation over and beyond reductions in R-III, may be related to brain mechanisms that serve to prevent awareness of pain once nociception has reached higher centers, as suggested by Hilgard.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain dynamics and hypnosis: attentional and disattentional processes

This article reviews recent research findings, expanding an evolving neuropsychophysiological model of hypnosis (Crawford, 1989; Crawford & Gruzelier, 1992), that support the view that highly hypnotizable persons (highs) possess stronger attentional filtering abilities than do low hypnotizable persons, and that these differences are reflected in underlying brain dynamics. Behavioral, cognitive, and neurophysiological evidence is reviewed that suggests that highs can both better focus and sustain their attention as well as better ignore irrelevant stimuli in the environment. It is proposed that hypnosis is a state of enhanced attention that activates an interplay between cortical and subcortical brain dynamics during hypnotic phenomena, such as both attentional and disattentional processes, among others, are important in the experiencing of hypnosis and hypnotic phenomena. Findings from studies of electrocortical activity, event-related potentials, and regional cerebral blood flow during waking and hypnosis are presented to suggest that these attentional differences are reflected in underlying neurophysiological differences in the far fronto-limbic attentional system.

Effects of hypnosis on regional cerebral blood flow during ischemic pain with and without suggested hypnotic analgesia

Using 133Xe regional cerebral blood flow (CBF) imaging, two male groups having high and low hypnotic susceptibility were compared in waking and after hypnotic induction, while at rest and while experiencing ischemic pain to both arms under two conditions: attend to pain and suggested analgesia. Differences between low and highly-hypnotizable persons were observed during all hypnosis conditions: only highly-hypnotizable persons showed a significant increase in overall CBF, suggesting that hypnosis requires cognitive effort. As anticipated, ischemic pain produced CBF increases in the somatosensory region. Of major theoretical interest is a highly-significant bilateral CBF activation of the orbito-frontal cortex in the highly-hypnotizable group only during hypnotic analgesia. During hypnotic analgesia, highly-hypnotizable persons showed CBF increase over the somatosensory cortex, while low-hypnotizable persons showed decreases. Research is supportive of a neuropsychophysiological model of hypnosis (Crawford, 1991; Crawford and Gruzelier, 1992) and suggests that hypnotic analgesia involves the supervisory, attentional control system of the far-frontal cortex in a topographically specific inhibitory feedback circuit that cooperates in the regulation of thalamocortical activities.

EEG spectral analysis during hypnotic induction, hypnotic dream and age regression

EEG was recorded monopolarly at frontal (F3, F4), central (C3, C4) and posterior (in the middle of O1-P3-T5 and O2-P4-T6 triangles) derivations during the hypnotic induction of the Stanford Hypnotic Clinical Scale (SHCS) and during performance following suggestions of hypnotic dream and age-regression as expressed in the before-mentioned scale. 10 low-hypnotizable and 9 highly-hypnotizable and right-handed female students participated in one experimental session. Evaluations were Fast-Fourier spectral analyses during the following conditions: waking-rest in eyes-open and eyes-closed condition; early, middle, and late phases of hypnotic induction; rest-hypnosis in eyes closed condition; hypnotic dream and age regression. After spectral analysis of 0 to 44 Hz, the mean spectral amplitude estimates across seven Hz bands (theta 1, 4-6 Hz, theta 2, 6-8 Hz; alpha 1, 8-10 Hz; alpha 2, 10-13 Hz; beta 1, 13-16 Hz; beta 2, 16-20 Hz; beta 3, 20-36 Hz) and the 40-Hz EEG band (36-44 Hz) for each experimental condition were extracted. In eyes-open and -closed conditions in waking and hypnosis highly-hypnotizable subjects produced a greater 40-Hz EEG amplitude than did low hypnotizable subjects at all frontal, central and posterior locations. In the early and middle hypnotic induction highly-hypnotizables displayed a greater amount of beta 3 than did low hypnotizables and this difference was even more pronounced in the left hemisphere. With posterior scalp recordings, during hypnotic dream and age regression, high hypnotizables displayed, as compared with the rest-hypnosis condition, a decrease in alpha 1 and alpha 2 amplitudes. This effect was absent for low hypnotizables. Beta 1, beta 2 and beta 3 amplitudes increased in the left hemisphere during age regression for high hypnotizables; low hypnotizables, in contrast, displayed hemispheric balance across imaginative tasks. High hypnotizables during the hypnotic dream also displayed in the right hemisphere a greater 40-Hz EEG amplitude as compared with the left hemisphere. This difference was even more evident for posterior recording sites. This hemispheric trend was not evidenced for low hypnotizable subjects. Theta power was never a predictor of hypnotic susceptibility, 40-Hz EEG amplitude displayed a very high main effect (p < 0.004) for hypnotizability in hypnotic conditions by displaying a greater 40-Hz EEG amplitude in high hypnotizables with respect to lows.

The effect of experimental muscle pain on the background electrical brain activity

The purpose of this project was to investigate whether specific effects in the background activity of the brain associated with the experience of pain can be depicted by means of quantitative electroencephalography (EEG). Lasting pain was induced by intramuscular infusion of hypertonic saline. The infusion was titrated to maintain pain for a sufficient time to obtain enough data for meaningful analysis. In a first study on 12 subjects, using a single, blind, repeated measures design with randomization of the administration of isotonic (0.9%) and hypertonic (5%) saline, and with subjects unaware of the fact that one substance was isotonic saline, a statistically significant pain response could be attributed to the administration of hypertonic saline. In a second study on 19 subjects, again using a randomized repeated measures design, topographic EEG measures were examined with respect to experimentally induced pain and pain from memory. Prior to each of these experimental stages, baseline recordings were obtained to satisfy the requirement of the crossover design. In addition to the common frequency bands used in EEG, we also obtained data in the frequency range of 35-100 Hz. The short-term variability of the selected EEG measures and their suitability as a sample estimate were assessed by computing the coefficient of variation from all selected epochs of a given subject at baseline. When compared to baseline, spectral analyzed EEG measures during experimental pain demonstrated statistically significant increases in the beta and 35-100 Hz frequency ranges, most notably at the temporal recording sites. There was no statistically significant difference between the EEG measures for (1) experimental pain vs. pain from memory, and (2) the 2 baseline recordings. The great variability in the topographical aspect of the between-subject response was interpreted as being strongly suggestive of the contamination of EEG measures by phenomena attributed to the jaw, facial and scalp musculature. In fact, Pearson correlation coefficients, as high as 0.92, were found between measures in the frequency band of 35-100 Hz and the beta frequency range. The unexplained variance in the heightened beta cortical power density can be attributed to the vigilance scanning of pain processes. Due to the fact that the statistically significant effect of pain on the topographic EEG measures were not different from imagined pain, we concluded that these effects are non-specific for pain.

Hypnosis and lateralized brain functions

Bilateral EEG measures were obtained on 16 high hypnotizable Ss (scores of greater than 8 on the Harvard Group Scale of Hypnotic Susceptibility, Form A, Shor & E. Orne, 1962), while performing hemisphere-specific tasks during hypnosis and a no-hypnosis control condition. Conditions and tasks were presented in counterbalanced order, and Ss served as their own controls. The data call into question the right hemisphere activation interpretation of lateralized brain function during hypnosis; rather, the data suggest a lack of task appropriate activity during hypnosis. The failure to attend to baseline activity measurements and the use of ratios to evaluate interhemispheric lateralization may contribute to potential misinterpretations of data. It is critical that activity changes of the separate hemispheres be taken into account in the interpretative process.

Cortical power spectral analysis of acute pathophysiological pain

In the past decade, advances in quantitative EEG methods, such as the analysis of cortical power spectrum, have proven a useful tool for observing changes in brain activity as a function of physiological and behavioral states. The cortical power spectrum (CPS) is a computer-derived analysis of brain electrical activity using mathematical principles of Fast Fourier Transform function. The total energy output of specific cortical areas can be estimated over time, as a function of EEG spectral frequencies. This report describes the study of CPS in pathophysiological pain patients, using acute dental pain as a model. Seven "walk-in" acute pain patients in an emergency dental clinic were recorded during 10 min of pain, before treatment. Approximately one week later, 10 min recordings during nonpain states were obtained as control. Subjective pain scales and other psychological measures were administered to all subjects before and after recording on each visit. Each 10 min stage of continuous CPS recording consisted of 10 spectra per stage, 6 epochs/spectrum, and 10.24 sec/epoch; each spectrum was stored, averaged, transformed, displayed, printed, and plotted by the Pain Microcomputer System. Results show significant cortical power reduction along all frequency bands (0.5-50 Hz) when pain-states are compared to nonpain states. The magnitude of reduction also appears to correspond to subjective pain report. Analysis for rank order may be inversely related to subjective painfulness, indicating that pain and alpha-desynchronization are closely associated. This study demonstrates that the brain activity of clinical pain patients can be measured. The feasibility of developing a pathophysiological objective pain measuring system is discussed.