Cognitive modulation of psychophysical, respiratory and autonomic responses to cold pressor test

Impact of hypnosis on psychophysiological measures: A scoping literature review

Exploring psychophysiological changes during hypnosis can help to better understand the nature and extent of the hypnotic phenomenon by characterizing its influence on the autonomic nervous system (ANS), in addition to its central brain effects. Hypnosis is thought to induce a relaxation response, yet studies using objective psychophysiological measures alongside hypnosis protocols show various results. We review this literature and clarify the effects of hypnosis on psychophysiological indices of ANS activity and more specifically of the stress/relaxation response, such as heart rate variability and electrodermal activity. Studies reporting psychophysical measures during hypnosis were identified by a series of Pubmed searches. Data was extracted with an interest for the influence of hypnotizability and effects of specific suggestions or tasks on the findings. We found 49 studies comprising 1315 participants, 45 concerning healthy volunteers and only 4 on patients. Sixteen compared high vs. low hypnotizable people; 30 measured heart rate, 18 measured heart rate variability, 25 electrodermal activity, and 23 respiratory signals as well as other physiological parameters. Globally, results converge to show reductions in sympathetic responses and/or increases in parasympathetic tone under hypnosis. Several methodological limitations are underscored, such as older studies (N = 16) using manual analyses, small sample sizes (<30, N = 31), as well as uncontrolled multiple comparisons. Nevertheless, we confirm that hypnosis leads to a physiological relaxation response and highlight promising avenues for this research. Suggestions are made for guiding future work in this field.

A new framework for modeling the bidirectional interplay between brain oscillations and cardiac sympathovagal activity

The study of functional brain-heart interplay (BHI) aims to describe the dynamical interactions between central and peripheral autonomic nervous systems. Here, we introduce the Sympathovagal Synthetic Data Generation Model, which constitutes a new computational framework for the assessment of functional BHI. The model estimates the bidirectional interplay with novel quantifiers of cardiac sympathovagal activity gathered from Laguerre expansions of RR series (from the ECG), as an alternative to the classical spectral analysis. The main features of the model are time-varying coupling coefficients linking Electroencephalography (EEG) oscillations and cardiac sympathetic or parasympathetic activity, for either ascending or descending direction of the information flow. In this proof-of-concept study, functional BHI is quantified in the direction from-heart-to-brain, on data from 16 human volunteers undergoing a cold-pressor test. Results show that thermal stress induces heart-to-brain functional interplay originating from sympathetic and parasympathetic activities and sustaining EEG oscillations mainly in the δ and γ bands. The proposed computational framework could provide a viable tool for the functional assessment of the causal interplay between cortical and cardiac sympathovagal dynamics.

Functional assessment of bidirectional cortical and peripheral neural control on heartbeat dynamics: a brain-heart study on thermal stress

The study of functional brain-heart interplay (BHI) from non-invasive recordings has gained much interest in recent years. Previous endeavors aimed at understanding how the two dynamical systems exchange information, providing novel holistic biomarkers and important insights on essential cognitive aspects and neural system functioning. However, the interplay between cardiac sympathovagal and cortical oscillations still has much room for further investigation. In this study, we introduce a new computational framework for a functional BHI assessment, namely the Sympatho-Vagal Synthetic Data Generation Model, combining cortical (electroencephalography, EEG) and peripheral (cardiac sympathovagal) neural dynamics. The causal, bidirectional neural control on heartbeat dynamics was quantified on data gathered from 26 human volunteers undergoing a cold-pressor test. Results show that thermal stress induces heart-to-brain functional interplay sustained by EEG oscillations in the delta and gamma bands, primarily originating from sympathetic activity, whereas brain-to-heart interplay originates over central brain regions through sympathovagal control. The proposed methodology provides a viable computational tool for the functional assessment of the causal interplay between cortical and cardiac neural control.

Concurrent TMS-EEG to Reveal the Neuroplastic Changes in the Prefrontal and Insular Cortices in the Analgesic Effects of DLPFC-rTMS

The dorsolateral prefrontal cortex (DLPFC) is an important target for repetitive transcranial magnetic stimulation (rTMS) to reduce pain. However, the analgesic efficacy of DLPFC-rTMS needs to be optimized, in which the mechanisms of action remain unclear. Concurrent TMS and electroencephalogram (TMS-EEG) is able to evaluate neuroplastic changes beyond the motor cortex. Using TMS-EEG, this study was designed to investigate the local and distributed neuroplastic changes associated with DLPFC analgesia. Thirty-four healthy adults received DLPFC or sham stimulation in a randomized, crossover design. In each session, participants underwent cold pain and TMS-EEG assessment both before and after 10-Hz rTMS. We provide novel findings that DLPFC analgesia is associated with a smaller N120 amplitude in the contralateral prefrontal cortex as well as with a larger N120 peak in the ipsilateral insular cortex. Furthermore, there was a strong negative correlation between N120 changes of these two regions whereby the amplitude changes of this dyad were associated with increased pain threshold. In addition, DLPFC stimulation enhanced coherence between the prefrontal and somatosensory cortices oscillating in the gamma frequency. Overall, our data present novel evidence on local and distributed neuroplastic changes associated with DLPFC analgesia.

Hypnotizability-Related Effects of Pain Expectation on the Later Modulation of Cortical Connectivity

This study examined hypnotizability-related modulation of the cortical network following expected and nonexpected nociceptive stimulation. The electroencephalogram (EEG) was recorded in 9 high (highs) and 8 low (lows) hypnotizable participants receiving nociceptive stimulation with (W1) and without (noW) a visual warning preceding the stimulation by 1 second. W1 and noW were compared to baseline conditions to assess the presence of any later effect and between each other to assess the effects of expectation. The studied EEG variables measured local and global features of the cortical connectivity. With respect to lows, highs exhibited scarce differences between experimental conditions. The hypnotizability-related differences in the later processing of nociceptive information could be relevant to the development of pain-related individual traits. Present findings suggest a lower impact of nociceptive stimulation in highs than in lows.

HYPNOTIZABILITY-RELATED FAAH C385A POLYMORPHISM: POSSIBLE ENDOCANNABINOID CONTRIBUTION TO SUGGESTION-INDUCED ANALGESIA

Fatty acid amide hydrolase (FAAH) degrades the endogenous endocannabinoid (eCB) anandamide and might be involved in the response to suggestions of analgesia in subjects with high hypnotizability scores (highs). Since the A allele of the FAAH C385A polymorphism (rs324420) is associated with lower FAAH activity, it was studied in 21 highs, 66 low hypnotizable individuals (lows), and 172 individuals not selected for hypnotizability (controls) representing the general population. No significant difference was observed among groups, but the A allele frequency showed a significant trend to increase from lows to controls and from controls to highs. Since eCB small differences can be amplified by eCB interactions with other neurotransmitters, a contribution of the FAAH polymorphism to the highs' analgesia should not be excluded.

Neuropsychological functions of verbal recall and psychomotor speed significantly affect pain tolerance

Background

Effects from cognitive performance on pain tolerance have been documented, however, sample sizes are small and confounders often overlooked. We aimed to establish that performance on neuropsychological tests was associated with pain tolerance, controlling for salient confounders.

Methods

This was a cross‐sectional study nested within the Tromsø‐6 survey. Neuropsychological test performance and the cold pressor test were investigated in 4,623 participants. Due to significant interaction with age, participants were divided into three age groups (<60, ≥60 to <70 and ≥70 years). Cox proportional hazard models assessed the relationship between neuropsychological tests and cold pressure pain tolerance, using hand‐withdrawal as event. The fully adjusted models controlled for sex, education, BMI, smoking status, exercise, systolic blood pressure, sleep problems and mental distress.

Results

In the adjusted models, participants aged ≥70 years showed a decreased hazard of hand withdrawal of 18% (HR 0.82, 95% CI (0.73, 0.92) per standard deviation on immediate verbal recall, and a decreased hazard of 23% (HR 0.77, 95% CI (0.65, 0.08) per standard deviation on psychomotor speed. Participants aged ≥60 to <70 years had a significant decreased hazard of 11% (HR 0.89, 95% CI (0.80, 0.98) per standard deviation on immediate word recall. In participants aged <60 years, there was a decreased hazard of 14% (HR 0.86 95% CI: 0.76, 0.98), per standard deviation on psychomotor speed.

Conclusion

Better performance on neuropsychological tests increased pain tolerance on the cold pressor test. These exposure effects were present in all age groups.

Significance

This paper describes substantial associations between cognitive functioning and cold pressor tolerance in 4,623 participants. Reduced psychomotor speed and poor verbal recall gave greater odds for hand‐withdrawal on the cold pressor task. The associations were stronger in older participants, indicating an interaction with age.

Quantitative Sensory Testing (QST) Estimation of Regional Cutaneous Thermal Sensitivity During Waking State, Neutral Hypnosis, and Temperature Specific Suggestions

This study aimed to determine the effects of neutral hypnosis and hypnotic temperature suggestions in thermal and pain thresholds compared to resting state. Sixteen healthy medium or high hypnotizable volunteers were enrolled. Hypnotizability was assessed with the Hypnotic Induction Profile (HIP); QST was checked in resting state, in neutral hypnosis, after suggestions of heat and cold, and after deinduction. A significant increase in heat threshold was recorded during hypnosis with both cold and heat suggestions compared to neutral hypnosis. HIP induction score showed a linear correlation with changes of temperature thresholds after heat and cold suggestions. Thermal suggestions may result in a significant increase of heat perception thresholds with respect to neutral hypnosis. HIP score is related to thermal threshold changes. QST is a valuable and manageable tool to measure temperature threshold change during hypnosis.

HYPNOTIZABILITY AND PAIN MODULATION: A Body-Mind Perspective

The study investigated whether the cardiac activity and cognitive-emotional traits sustained by the behavioral inhibition/activation system (BIS/BAS) may contribute to hypnotizability-related pain modulation. Nociceptive stimulation (cold-pressor test) was administered to healthy participants with high (highs) and low (lows) hypnotizability in the presence and absence of suggestions for analgesia. Results showed that heart rate increased abruptly at the beginning of nociceptive stimulation in all participants. Then, only in highs heart rate decreased for the entire duration of hand immersion. During stimulation with suggestions of analgesia, pain threshold negatively correlated with heart rate. BIS/BAS activity partially accounted for the observed hypnotizability-related differences in the relation between cardiac interoception and pain experience.

Polymorphism of Opioid Receptors μ1 in Highly Hypnotizable Subjects

The possible cooperation between hypnotizability-related and placebo mechanisms in pain modulation has not been consistently assessed. Here, we investigate possible genetic bases for such cooperation. The OPRM1 gene, which encodes the μ1 opioid receptor-the primary site of action for endogenous and exogenous opioids-is polymorphic in the general population for the missense mutation Asn40Asp (A118G, rs1799971). The minor allele 118G results in decreased levels of OPRM1 mRNA and protein. As a consequence, G carriers are less responsive to opioids. The aim of the study was to investigate whether hypnotizability is associated with the presence of the OPRM1 polymorphism. Forty-three high and 60 low hypnotizable individuals, as well as 162 controls, were genotyped for the A118G polymorphism of OPRM1. The frequency of the G allele was significantly higher in highs compared to both lows and controls. Findings suggest that an inefficient opioid system may be a distinctive characteristic of highs and that hypnotic assessment may predict lower responsiveness to opioids.

Pain modulation as a function of hypnotizability: Diffuse noxious inhibitory control induced by cold pressor test vs explicit suggestions of analgesia

The aim of the present study was to compare the effects of explicit suggestions of analgesia and of the activation of the Diffuse Noxious Inhibitory Control (DNIC) by cold pressor test on pain perception and heart rate in healthy participants with high (highs, N=18), low (lows, N=18) and intermediate scores of hypnotizability (mediums, N=15) out of hypnosis. Pain reports and the stimulus-locked heart rate changes induced by electrical nociceptive stimulation of the left hand were studied in the absence of concomitant stimuli (Control), during suggestions of analgesia (SUGG, glove analgesia) and during cold pressor test used as a conditioning stimulus to the right hand (DNIC, water temperature=10-12°C) in the REAL session. Participants were submitted also to a SHAM session in which the DNIC water temperature was 30°C and the suggestions for analgesia were substituted with weather forecast information. Both suggestions and DNIC reduced pain significantly in all subjects; however, the percentage of reduction was significantly larger in highs (pain intensity=55% of the control condition) than in mediums (70%) and lows (80%) independently of the REAL/SHAM session and of the specific pain manipulation. Heart rate was not modulated consistently with pain experience. Findings indicate that both suggestions and DNIC influence pain experience as a function of hypnotizability and suggest that both sensory and cognitive mechanisms co-operate in DNIC induced analgesia.

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.

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.

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).