Underpredicting pain: an experimental investigation into the benefits and risks

The role of pain expectancy and its confidence in placebo hypoalgesia and nocebo hyperalgesia

ABSTRACT

Placebo hypoalgesia and nocebo hyperalgesia, which exemplify the impact of expectations on pain, have recently been conceptualised as Bayesian inferential processes, yet empirical evidence remains limited. Here, we explore whether these phenomena can be unified within the same Bayesian framework by testing the predictive role of expectations and their level of precision (ie, expectation confidence) on pain, with both predictors measured at the metacognitive level. Sixty healthy volunteers underwent a pain test (ie, 8 noxious electrical stimuli) before (Baseline) and after (T0, T1, T2) receiving a sham treatment associated with hypoalgesic (placebo), hyperalgesic (nocebo), or neutral (control) verbal suggestions, depending on group allocation. Trial-by-trial expectations, their precision, and perceived pain were measured. Skin conductance response (SCR) was also recorded as an autonomic response marker. Bayesian linear mixed models analyses revealed that, for both placebo and nocebo, pain was predicted by expectations alone and by their interaction with expectations precision. In addition, the discrepancy between expected and perceived pain was predicted by expectation precision, with greater alignment between expected and perceived pain when precision was higher. This suggests that both placebo and nocebo responses are well described from a Bayesian perspective. A main effect of time for SCR was observed, suggesting habituation to painful stimuli. Our data provide evidence indicating that both placebo hypoalgesia and nocebo hyperalgesia can be unified within the same Bayesian framework in which not only expectations but also their level of precision, both measured at the metacognitive level, are key determinants of the pain inferential process.

How the magnitude and precision of pain predictions shape pain experiences

BACKGROUND

In Bayesian models including predictive processing, the magnitude and precision of pain expectancies are key determinants of perception. However, relatively few studies have directly tested whether this holds for pain, and results so far have been inconclusive. Here, we investigated expectancy effects on pain experiences and associated affective responses.

METHODS

In two studies, healthy participants (n = 30 in each) received painful electrical stimuli preceded by explicit pain predictions. In study 1, the magnitude of pain predictions and administered pain intensities were varied. In study 2, the magnitude and precision of pain predictions were varied, while administered pain intensity was kept constant. Experienced pain intensity was the primary outcome in both studies.

RESULTS

Pain experiences assimilated towards both under- and overpredictions of pain. In study 1, however, effects were small, if present at all, for non-painful stimuli and effects were not necessarily larger with predictions of greater magnitude. In study 2, assimilation of pain experiences appeared regardless of precision level, while no significant effects on EMG eyeblink startle responses were observed. Moreover, under- and overpredictions caused disappointment and relief, respectively, with greater disappointment upon precise than imprecise predictions.

CONCLUSIONS

The influence of pain predictions on pain might be more complex than assumed in simple instantiations of current theoretical frameworks, with no systematically stronger assimilation of pain experiences to larger and more precise predictions. Since overpredictions are associated with relief, but underpredictions with disappointment, these findings underline the importance of providing correct predictions when preparing for upcoming painful procedures.

SIGNIFICANCE STATEMENT

Our work supports, challenges, and extends the application of Bayesian and predictive processing frameworks to the influence of pain predictions on pain. Under- and overpredictions of pain yielded assimilation of pain experiences, but assimilation was not systematically stronger with larger prediction errors or greater precision. Moreover, under- and overpredictions resulted in disappointment and relief, respectively. This research signifies the importance of establishing accurate predictions of pain in clinical practice.

Nocebo hyperalgesia and other expectancy-related factors in daily fibromyalgia pain: Combining experimental and electronic diary methods

OBJECTIVE

Expectancies are known to shape pain experiences, but it remains unclear how different types of expectancies contribute to daily pain fluctuations in fibromyalgia. This combined experimental and diary study aims to provide insights into how experimentally-derived nocebo hyperalgesia and other, diary-derived, expectancy-related factors are associated with each other and with daily pain in fibromyalgia.

METHODS

Forty-one female patients with fibromyalgia first participated in a lab procedure measuring nocebo hyperalgesia magnitude, then filled out an electronic diary 3 times a day over 3 weeks regarding the expectancy-related factors of pain expectancy, anxiety, optimism, and pain-catastrophizing thoughts, and current pain intensity.

RESULTS

Our results indicate that experimentally-induced nocebo hyperalgesia was not significantly related to diary-assessed expectancy-related factors and did not predict daily fibromyalgia pain. Higher levels of the self-reported expectancy-related factors pain expectancy and pain catastrophizing, but not anxiety and optimism, predicted moment-to-moment pain increases in fibromyalgia, after controlling for current pain, moment-of-day and all other expectancy-related factors.

CONCLUSION

Our exploratory research findings indicate that self-reported expectancy-related factors, particularly pain expectancy and pain catastrophizing, are potentially more relevant for predicting daily pain experience than experimentally-induced nocebo hyperalgesia. Further translation of nocebo hyperalgesia is needed from experimental to Ecological Momentary Assessment research. Our findings imply that targeting the decrease in pain expectancy and catastrophizing thoughts e.g., via Cognitive Behavioral Therapy, have potential for improving daily pain levels in fibromyalgia.

How should uncertainty about upcoming painful procedures be communicated? An experimental study into highly uncertain pain predictions

OBJECTIVE

Uncertainty is unavoidable in the context of painful medical procedures. It is important to investigate the impact of different ways of communicating uncertainty on upcoming pain.

METHODS

In our exploratory study, healthy participants (n = 30) were repeatedly presented with three highly uncertain pain predictions communicated by a hypothetical doctor. A direct statement of high uncertainty ("I don't know") was compared to more indirect predictions (social prediction: "It varies widely among people"; range prediction: "… not painful at all to very highly painful"), followed by individually calibrated electrical stimuli of non-, moderately, or very highly painful intensity.

RESULTS

The direct expression of uncertainty led to the most intense pain sensation (for moderately painful stimuli only), lowest and most certain pain expectations, lowest trust in the hypothetical doctor, and lowest feeling of being well-informed, especially as compared to the social prediction. No differential effects on anxiety were observed.

CONCLUSIONS

Expressing high uncertainty indirectly, with reference to the common experiences of others, may be beneficial for optimizing pain experiences and enhancing patients' trust in a medical professional.

PRACTICE IMPLICATIONS

Our findings inform on how high uncertainty about upcoming pain may impact patient and health outcomes, pointing to some advantages of indirect communication.

Suggestion Timing Moderates the Effects of Prior Pain Experiences on Pain Perception

Two common elements in patient care are reoccurring painful events (eg, blood draws) and verbal suggestions from others for lessened pain. Research shows that verbal suggestions for lower pain can decrease subsequent pain perception from novel noxious stimuli, but it is less clear how these suggestions and prior painful experiences combine to influence the perception of a reoccurring painful event. The presented experiment tested the hypothesis that the order of these 2 factors influence pain perception for a reoccurring painful event. All participants (702 healthy college-student volunteers, 58% women, 85.5% White) experienced a novel painful event on one arm, then again on their other arm (now a familiar pain event). Participants who received the suggestion that they can tolerate more pain on the second arm relative to the first from the outset, before the initial pain event, perceived relatively less pain during the repeated event as compared to participants who received the same suggestion after the first painful event or no-suggestion (control). Given many pain events within medical contexts are, or become, familiar to patients, further researching the timing at which patients receive verbal suggestions for lower pain can inform practices to optimize the therapeutic, pain-reducing potential of such suggestions. PERSPECTIVE: Providing suggestions that a familiar pain event (ie, the second of 2) will be less painful than a prior event can reduce perceived pain for the familiar event depending on when it is presented. These findings can inform practices to optimize the therapeutic potential of verbal suggestions for reduced pain.

The Optimal Learning Cocktail for Placebo Analgesia: A Randomized Controlled Trial Comparing Individual and Combined Techniques

This study investigated for the first time the effects of individual and combined application of 3 learning techniques (verbal suggestions, classical conditioning, and observational learning) on placebo analgesia and extinction. Healthy participants (N = 206) were assigned to 8 different groups in which they were taught through either a verbal suggestion, a conditioning paradigm, a video observing someone, or any combination thereof that a placebo device (inactive transcutaneous electric nerve stimulation [TENS]) was capable of alleviating heat pain, whereas one group did not (control). Placebo analgesia was quantified as the within-group difference in experienced pain when the placebo device was (sham) 'activated' or 'inactivated' during equal pain stimuli, and compared between groups. Placebo analgesia was induced in groups with 2 or 3 learning techniques. Significantly stronger placebo analgesia was induced in the combination of all 3 learning techniques as compared to the individual learning techniques or control condition, underlining the additional contribution of 3 combined techniques. Extinction did not differ between groups. Furthermore, pain expectancies, but not state anxiety or trust, mediated placebo analgesia. Our findings emphasize the added value of combining 3 learning techniques to optimally shape expectancies that lead to placebo analgesia, which can be used in experimental and clinical settings. PERSPECTIVE: This unique experimental study compared the individual versus combined effects of 3 important ways of learning (verbal suggestions, classical conditioning, and observational learning) on expectation-based pain relief. The findings indicate that placebo effects occurring in clinical practice could be optimally strengthened if healthcare providers apply these techniques in combination.

Placebo effects on cutaneous pain and itch: a systematic review and meta-analysis of experimental results and methodology

ABSTRACT

Placebo effects, positive treatment outcomes that go beyond treatment processes, can alter sensations through learning mechanisms. Understanding how methodological factors contribute to the magnitude of placebo effects will help define the mechanisms by which these effects occur. We conducted a systematic review and meta-analysis of experimental placebo studies in cutaneous pain and itch in healthy samples, focused on how differences in methodology contribute to the resulting placebo effect magnitude. We conducted meta-analyses by learning mechanism and sensation, namely, for classical conditioning with verbal suggestion, verbal suggestion alone, and observational learning, separately for pain and itch. We conducted subgroup analyses and meta-regression on the type of sensory stimuli, placebo treatment, number of acquisition and evocation trials, differences in calibrated intensities for placebo and control stimuli during acquisition, age, and sex. We replicated findings showing that a combination of classical conditioning with verbal suggestion induced larger placebo effects on pain ( k = 68, g = 0 . 59) than verbal suggestion alone ( k = 39, g = 0.38) and found a smaller effect for itch with verbal suggestion alone ( k = 7, g = 0.14). Using sham electrodes as placebo treatments corresponded with larger placebo effects on pain than when topical gels were used. Other methodological and demographic factors did not significantly affect placebo magnitudes. Placebo effects on pain and itch reliably occur in experimental settings with varied methods, and conditioning with verbal suggestion produced the strongest effects. Although methods may shape the placebo effect to some extent, these effects appear robust overall, and their underlying learning mechanisms may be harnessed for applications outside the laboratory.

Counterconditioning as Treatment to Reduce Nocebo Effects in Persistent Physical Symptoms: Treatment Protocol and Study Design

Persistent physical symptoms have a high prevalence and a large impact for patients and society. To date, treatment effects for these symptoms are often limited. Nocebo effects (i.e., negative outcomes that are not attributable to active treatment components) have a substantial influence on treatment success and can be established via learning through classical conditioning. Therefore, interventions aimed at reducing nocebo effects by means of counterconditioning, in which an alternative association (inhibiting the previous association) is learned, could be a promising method for improving physical symptoms. In experimental studies, counterconditioning has been shown promising in reducing experimentally-induced nocebo effects on pain and itch. Application of counterconditioning procedures to reduce nocebo effects on clinical symptoms has yet to be researched. This paper provides a protocol of a 6-week counterconditioning intervention aimed at reducing nocebo effects and clinical pain in patients with fibromyalgia. A study in patients with fibromyalgia is proposed to examine the feasibility and potential effectiveness of this counterconditioning intervention as a novel treatment method for reducing nocebo effects and generalization to clinical pain symptoms. Results can help design an optimized treatment protocol for reducing nocebo effects, based on the experiences of participants and the first indications of treatment efficacy.

How expectancy violations facilitate learning to cope with pain - An experimental approach

BACKGROUND

Expectations of painful sensations constitute a core feature of chronic pain. An important clinical question is whether such expectations are revised when disconfirming experiences are made (e.g., less pain than expected). This study examined how people adjust their pain expectations when the experience of decreasing pain is expected vs. unexpected.

METHODS

In a novel randomized between-subjects design, a subclinical sample of people who frequently experience pain was provided with painful thermal stimulations. Unbeknownst to participants, the temperature applied was decreased from trial to trial. Based on the experimental instructions provided, this experience of decreasing pain was expected in one condition (expectation-confirmation; n = 34), whereas it was unexpected in another (expectation-disconfirmation; n = 39).

RESULTS

Perceived pain intensity was lower in the expectation-confirmation condition than in the expectation-disconfirmation condition (p = .014, η_p² = 0.083). The expectation-confirmation condition also showed a greater adjustment of their pain expectations than the expectation-disconfirmation condition (p = .046, η_p² = 0.047). Across groups, large expectation violations (i.e., less pain than expected) were associated with increases in pain tolerance and the ability to cope with pain at a one-week follow-up.

CONCLUSIONS

In terms of assimilation, perceived pain intensity was shaped in the direction of pain expectations. The greater adjustment of expectations in the expectation-confirming condition is consistent with a confirmation bias in pain perception. Though participants who experienced large discrepancies between expected and experienced pain were hesitant to adjust their pain expectations immediately, expectation violations increased their ability to cope with pain one week later, suggesting some beneficial longer-term effects of expectation violations.

Beyond Pain Scales: A Critical Phenomenology of the Expression of Pain

In this paper, we discuss the qualitative dimension of painful experiences by exploring the role of imagination and metaphorical association in the conceptualization and expression of pain. We employ an engaged critical-phenomenological approach to offer original analysis influenced by the perspectives of people in pain. The paper is organized into three parts. Part 1 reviews literature on the expression of pain, its communication, and its reception-attending in particular to the emphasis on verbalizing pain in healthcare contexts. We here discuss benefits and limitations of standard methods aimed at facilitating the meaningful expression of pain (such as "pain scales") from the perspectives of patients and practitioners, respectively. We suggest that these methods might be importantly complemented by facilitating creative expression of painful lived experiences with respect to personal lifeworlds. Part 2 deals with the role of imagination and metaphorical association in making sense of pain. We explore how imagination is a cognitive and affective mode of experiencing the world which plays a crucial role in determining how pain is experienced, as well as helping to make sense of pain figuratively in relation to the lifeworld. In Part 3, we draw from principles of engaged phenomenology to foreground case studies in which projects have been able facilitate the intersubjective expression of pain. These examples demonstrate the value of attending to the contours of painful lifeworlds in their specificity, affording both agency and accessibility in their communication, while remaining mindful of the complex power relations which govern perceived legitimacy and testimony relating to the transformation of pain. The overall paper aims to contribute to literature on qualitative pain research on both theoretical and practical levels. By exploring the expression of pain through phenomenology, we aim to enrich current debate on the qualitative experience of pain. We also seek to critically highlight the socio-political dimensions which frame painful experiences, their expression, their lived significance, and their treatment.

The association of affective state with the assimilation of daily pain expectancy and pain experience

ABSTRACT

Expectancies for pain and pain relief are central to experimental models of placebo analgesia and nocebo hyperalgesia, and are a promising target for clinical intervention in patients with chronic pain. Affective states may play an important role in modulating the degree to which expectancies influence pain, broadening the opportunities for intervention targets. However, findings to date have been mixed and mostly limited to laboratory designs. Few studies have examined the interplay of naturally occurring affective states, pain expectancies, and pain experiences in the course of daily life with chronic pain. In the present study, patients with temporomandibular disorder reported their daily pain expectancies and affective states each morning, and their daily pain experience each evening, over a two-week period. Multilevel modeling analyses revealed the association of morning pain expectancies with subsequent pain experiences was moderated by morning positive affective state (B=.04, SE=.02, t=2.00, p=.046), such that the congruent assimilation of a low pain expectancy with a low pain experience was starkest when morning positive affect was higher than usual. Relatedly, higher morning positive affect predicted greater odds of experiencing a match between pain expectancies and pain experience when the expectation was for low, but not high, pain levels (OR: 1.19, CI: 1.01-1.41, p=.03). Negative affect, in contrast, did not significantly influence the assimilation of high pain expectancies with high pain experiences. These findings extend prior experimental studies by showing that the association of daily pain expectancies with pain experience varies as a function of affective state.

The Importance of Patient Expectations: A Mixed-Methods Study of U.S. Psychiatrists

Objective: To examine how psychiatrists think about and modulate non-specific factors (e.g., hope, expectations) in clinical practice. Methods: U.S. psychiatrists were recruited for two studies assessing attitudes and behaviors related to non-specific factors. Study 1 entailed remote qualitative focus groups (k = 7) with n = 26 participants (36.0% female). Study 2 was a quantitative survey with n = 346 respondents (34.0% female) designed to assess the generalizability of focus group findings. Results: Four themes were identified in Study 1 that were used to inform the survey (Study 2): (1) Expectations (2) Hope, (3) Placebo Effect, and (4) Aesthetic Features. Nearly all surveyed psychiatrists (92.2%) considered patient expectations at least "most of the time" when interacting with a patient. Focus groups revealed that psychiatrists often attempt to balance optimism and realism to improve outcomes. A majority of survey respondents believed office design and physician attire could at least somewhat influence expectations (72.5 and 77.3%, respectively) and even outcomes (51.5 and 58.7%, respectively). Focus group psychiatrists described how physical features may be used as therapeutic tools. Conclusions: Psychiatrists are highly mindful of patient expectations. Although there is variability in the perceived importance of expectations, hope, the placebo effect, and aesthetic features, many utilize these factors in clinical practice.