In anticipation of pain: expectancy modulates corticospinal excitability, autonomic response, and pain perception

Nocebo Effect on Pain-Related Autonomic Responses in a State of Experimentally-Induced Sensitization

BACKGROUND

Enhanced pain-related autonomic responses were reported after experimentally-induced secondary mechanical hyperalgesia (SMH) in healthy individuals as well as in a variety of chronic pain cohorts. Stimulus-induced autonomic responses can also be modulated by positive and negative expectations towards the applied stimulus. This study aimed to investigate the influence of negative expectations on pain-related autonomic responses after experimentally-induced SMH.

METHODS

Forty healthy participants (20 females) were recruited and assigned to a NOCEBO or a NAïVE group. Phasic skin conductance responses (SCR) and tonic background skin conductance level (SCL) were recorded in response to 10 pinprick stimuli applied to both volar forearms. On one arm, all stimuli were applied (EXP-arm) before (PRE) and after (POST) an experimental heat pain model to induce SMH. The other arm served as the control (CTRL-arm). The NOCEBO group was instructed that the stimuli will be 'more intense and painful' in the POST-assessment. The NAïVE group did not receive any instructions. Pain ratings were matched to a numeric rating scale 4 across all assessments to control for subjective pain perception.

RESULTS

Only the combination of induced SMH and negative expectation (i.e., EXP-arm in the NOCEBO group) increased the pinprick-evoked phasic SCRs (p < 0.001) from PRE to POST. Tonic background SCL increased from PRE to POST (p < 0.01) independent of stimulation area (i.e., EXP-arm or CTRL-arm) or group (i.e., NOCEBO or NAïVE).

CONCLUSIONS

These results demonstrate facilitatory effects of top-down modulatory processes (i.e., negative expectations) on pain-related autonomic responses after experimentally-induced SMH.

SIGNIFICANCE

This study showed a facilitatory effect of negative expectation on enhanced pain-related autonomic responses in a state of experimentally-induced sensitisation in healthy participants. Hence, pain-related autonomic responses are shaped by both bottom-up (nociceptive input) and top-down (expectation) modulatory processes. This leads to the clinical implication that increased pain-related autonomic responses reported in individuals with chronic pain might not solely reflect pain hypersensitivities through nociceptive sensitisation, but also exaggerated negative expectation.

Topographically selective motor inhibition under threat of pain

ABSTRACT

Pain-related motor adaptations may be enacted predictively at the mere threat of pain, before pain occurrence. Yet, in humans, the neurophysiological mechanisms underlying motor adaptations in anticipation of pain remain poorly understood. We tracked the evolution of changes in corticospinal excitability (CSE) as healthy adults learned to anticipate the occurrence of lateralized, muscle-specific pain to the upper limb. Using a Pavlovian threat conditioning task, different visual stimuli predicted pain to the right or left forearm (experiment 1) or hand (experiment 2). During stimuli presentation before pain occurrence, single-pulse transcranial magnetic stimulation was applied over the left primary motor cortex to probe CSE and elicit motor evoked potentials from target right forearm and hand muscles. The correlation between participants' trait anxiety and CSE was also assessed. Results showed that threat of pain triggered corticospinal inhibition specifically in the limb where pain was expected. In addition, corticospinal inhibition was modulated relative to the threatened muscle, with threat of pain to the forearm inhibiting the forearm and hand muscles, whereas threat of pain to the hand inhibited the hand muscle only. Finally, stronger corticospinal inhibition correlated with greater trait anxiety. These results advance the mechanistic understanding of pain processes showing that pain-related motor adaptations are enacted at the mere threat of pain, as sets of anticipatory, topographically organized motor changes that are associated with the expected pain and are shaped by individual anxiety levels. Including such anticipatory motor changes into models of pain may lead to new treatments for pain-related disorders.

The downside to choice: instrumental control increases conditioned nocebo hyperalgesia

ABSTRACT

Nocebo hyperalgesia is a pervasive problem in which the treatment context triggers negative expectations that exacerbate pain. Thus, developing ethical strategies to mitigate nocebo hyperalgesia is crucial. Emerging research suggests that choice has the capacity to reduce nocebo side effects, but choice effects on nocebo hyperalgesia have not been explored. This study investigated the impact of choice on conditioned nocebo hyperalgesia using a well-established electrocutaneous pain paradigm where increases in noxious stimulation were surreptitiously paired with the activation of a sham device. In study 1, healthy volunteers (N = 104) were randomised to choice over (nocebo) treatment administration, nocebo administration without choice, or a natural history control group. Nocebo hyperalgesia was greater for those with choice than no choice, suggesting that choice increased rather than diminished nocebo hyperalgesia. Study 2 tested whether providing positive information about the benefits of choice in coping with pain could counteract heightened nocebo hyperalgesia caused by choice. A different sample of healthy adults (N = 137) were randomised to receive nocebo treatment with choice and positive choice information, choice only, or no choice. The positive choice information failed to attenuate the effect of choice on nocebo hyperalgesia. The current results suggest that, rather than decreasing nocebo hyperalgesia, treatment choice may exacerbate pain outcomes when a painful procedure is repeatedly administered. As such, using choice as a strategy to mitigate nocebo outcomes should be treated with caution.

Pain Rating is Worth a Thousand Words: Nocebo Hyperalgesia Induced by Verbal Modeling Prevails Over the Effects of Symbolic Modeling and Verbal Suggestion

This study compares the effectiveness of verbal modeling, symbolic modeling, and verbal suggestion in inducing nocebo hyperalgesia. It is the first study to examine the contribution of stress to observationally induced nocebo hyperalgesia. This study's experimental groups represented various sources of social information: a group of people participating in the study (verbal modeling), a single participant (symbolic modeling), and an experimenter (verbal suggestion). During the experiment, participants received electrocutaneous stimuli at the same intensity, some of which were applied with a nocebo (sham device). Participants in the verbal modeling group were acquainted with pain ratings that had allegedly been provided by other participants. The ratings suggested that other participants experienced more pain in the nocebo trials than in the control trials. In the symbolic modeling group, participants observed a videotaped model experiencing more pain in the nocebo than in the control trials. In the verbal suggestion group, participants received a verbal suggestion of hyperalgesia in the nocebo trials and no suggestion in the control trials. No manipulations were used in the control group. To investigate whether nocebo hyperalgesia is stable over time, an additional extinction phase was conducted. Nocebo hyperalgesia was induced by verbal modeling only and was partially mediated by expectancy. Stress was a significant moderator of the induced effect. Nocebo hyperalgesia was extinguished during the extinction phase. The obtained results provide potential implications for minimizing nocebo hyperalgesia in clinical practice by, for instance, controlling patients' expectancies and stress levels. PERSPECTIVE: The study shows the role of pain-related information derived from other people in shaping negative treatment experiences in the individual. Because information from others has a particular impact on individuals experiencing stress, both this information and the stress level of patients should be monitored in the treatment process.

Practitioner warmth and empathy attenuates the nocebo effect and enhances the placebo effect

Augmented patient-practitioner interactions that enhance therapeutic alliance can increase the placebo effect to sham treatment. Little is known, however, about the effect of these interactions on maladaptive health outcomes (i.e., the nocebo effect). Healthy participants (N = 84) were randomised to a 3-day course of Oxytocin nasal drops (actually, sham treatment) in conjunction with a high-warmth interaction (Oxy-HW: N = 28), a low-warmth interaction (Oxy-LW: N = 28) or to a no treatment control group (NT: N = 28). All participants were informed that the Oxytocin treatment could increase psychological well-being but was associated with several potential side effects. Treatment-related side effects, unwarned symptoms, and psychological well-being were measured at baseline and all post-treatment days. Side effect reporting was increased in the Oxy-LW condition compared to the other groups across all days. Conversely, increased psychological well-being was observed in the Oxy-HW condition, relative to the other conditions, but only on Day 1. Among those receiving treatment, positive and negative expectations, and treatment-related worry, did not vary by interaction-style, while psychological well-being and side effect reporting were inversely associated at the level of the individual. Results have important implications for practice, suggesting poorer quality interactions may not only reduce beneficial health outcomes but also exacerbate those that are maladaptive.

Interpersonal physiological and psychological synchrony predict the social transmission of nocebo hyperalgesia between individuals

Witnessing another's pain can heighten pain in the observer. However, research has focused on the observer's intrapersonal experience. Here, a social transmission-chain explored the spread of socially-acquired nocebo hyperalgesia. Dyads of genuine participants were randomised to 'Generations' (G1-G3). G1-Demonstrators, observed by G2-Observers, experienced high/low thermal pain contingent on supposed activity/inactivity of a sham-treatment. G2 became Demonstrators, witnessed by G3-Observers. They experienced fixed low-temperature stimuli irrespective of sham-treatment 'activity'. G3 then Demonstrated for G4-Observers (a confederate), also experiencing low-temperature stimuli only. Pain ratings, electrodermal activity, and facial action units were measured. G1's treatment-related pain propagated throughout the chain. G2 and G3 participants showed heightened subjective and physiological response to sham-treatment, despite equivalent stimulus temperatures, and G3 never witnessing the initial pain-event. Dyadic interpersonal physiological synchrony (electrodermal activity) and psychological synchrony (Observer's ability to predict the Demonstrator's pain), predicted subsequent socially-acquired pain. Implications relate to the interpersonal spread of maladaptive pain experiences.

Neuroimaging-based evidence for sympathetic correlation between brain activity and peripheral vasomotion during pain anticipation

Anticipation of pain engenders anxiety and fear, potentially shaping pain perception and governing bodily responses such as peripheral vasomotion through the sympathetic nervous system (SNS). Sympathetic innervation of vascular tone during pain perception has been quantified using a peripheral arterial stiffness index; however, its innervation role during pain anticipation remains unclear. This paper reports on a neuroimaging-based study designed to investigate the responsivity and attribution of the index at different levels of anticipatory anxiety and pain perception. The index was measured in a functional magnetic resonance imaging experiment that randomly combined three visual anticipation cues and painful stimuli of two intensities. The peripheral and cerebral responses to pain anticipation and perception were quantified to corroborate bodily responsivity, and their temporal correlation was also assessed to identify the response attribution of the index. Contrasting with the high responsivity across levels of pain sensation, a low responsivity of the index across levels of anticipatory anxiety revealed its specificity across pain experiences. Discrepancies between the effects of perception and anticipation were validated across regions and levels of brain activity, providing a brain basis for peripheral response specificity. The index was also characterized by a 1-s lag in both anticipation and perception of pain, implying top-down innervation of the periphery. Our findings suggest that the SNS responds to pain in an emotion-specific and sensation-unbiased manner, thus enabling an early assessment of individual pain perception using this index. This study integrates peripheral and cerebral hemodynamic responses toward a comprehensive understanding of bodily responses to pain.

Neurophysiological oscillatory markers of hypoalgesia in conditioned pain modulation

Introduction

Conditioned pain modulation (CPM) is an experimental procedure that consists of an ongoing noxious stimulus attenuating the pain perception caused by another noxious stimulus. A combination of the CPM paradigm with concurrent electrophysiological recordings can establish whether an association exists between experimentally modified pain perception and modulations of neural oscillations.

Objectives

We aimed to characterize how CPM modifies pain perception and underlying neural oscillations. We also interrogated whether these perceptual and/or neurophysiological effects are distinct in patients affected by chronic pain.

Methods

We presented noxious electrical stimuli to the right ankle before, during, and after CPM induced by an ice pack placed on the left forearm. Seventeen patients with chronic pain and 17 control participants rated the electrical pain in each experimental condition. We used magnetoencephalography to examine the anatomy-specific effects of CPM on the neural oscillatory responses to the electrical pain.

Results

Regardless of the participant groups, CPM induced a reduction in subjective pain ratings and neural responses (beta-band [15-35 Hz] oscillations in the sensorimotor cortex) to electrical pain.

Conclusion

Our findings of pain-induced beta-band activity may be associated with top-down modulations of pain, as reported in other perceptual modalities. Therefore, the reduced beta-band responses during CPM may indicate changes in top-down pain modulations.

Pain-autonomic measures reveal nociceptive sensitization in complex regional pain syndrome

BACKGROUND

Allodynia and hyperalgesia are common signs in individuals with complex regional pain syndrome (CRPS), mainly attributed to sensitization of the nociceptive system. Appropriate diagnostic tools for the objective assessment of such hypersensitivities are still lacking, which are essential for the development of mechanism-based treatment strategies.

OBJECTIVES

This study investigated the use of pain-autonomic readouts to objectively detect sensitization processes in CRPS.

METHODS

Twenty individuals with chronic CRPS were recruited for the study alongside 16 age- and sex-matched healthy controls (HC). All individuals underwent quantitative sensory testing and neurophysiological assessments. Sympathetic skin responses (SSRs) were recorded in response to 15 pinprick and 15 noxious heat stimuli of the affected (CRPS hand/foot) and a control area (contralateral shoulder/hand).

RESULTS

Individuals with CRPS showed increased mechanical pain sensitivity and increased SSR amplitudes compared with HC in response to pinprick and heat stimulation of the affected (p < 0.001), but not in the control area (p > 0.05). Habituation of pinprick-induced SSRs was reduced in CRPS compared to HC in both the affected (p = 0.018) and slightly in the control area (p = 0.048). Habituation of heat-induced SSR was reduced in CRPS in the affected (p = 0.008), but not the control area (p = 0.053).

CONCLUSIONS

This is the first study demonstrating clinical evidence that pain-related autonomic responses may represent objective tools to quantify sensitization processes along the nociceptive neuraxis in CRPS (e.g. widespread hyperexcitability). Pain-autonomic readouts could help scrutinize mechanisms underlying the development and maintenance of chronic pain in CRPS and provide valuable metrics to detect mechanism-based treatment responses in clinical trials.

SIGNIFICANCE

This study provides clinical evidence that autonomic measures to noxious stimuli can objectively detect sensitization processes along the nociceptive neuraxis in complex regional pain syndrome (CRPS) (e.g. widespread hyperexcitability). Pain-autonomic readouts may represent valuable tools to explore pathophysiological mechanisms in a variety of pain patients and offer novel avenues to help guide mechanism-based therapeutic strategies.