Predictability modulates the anticipation and perception of pain in both self and others

The effect of unpredictability on the perception of pain: a systematic review and meta-analysis

ABSTRACT

Despite being widely assumed, the worsening impact of unpredictability on pain perception remains unclear because of conflicting empirical evidence, and a lack of systematic integration of past research findings. To fill this gap, we conducted a systematic review and meta-analysis focusing on the effect of unpredictability on pain perception. We also conducted meta-regression analyses to examine the moderating effect of several moderators associated with pain and unpredictability: stimulus duration, calibrated stimulus pain intensity, pain intensity expectation, controllability, anticipation delay, state and trait negative affectivity, sex/gender and age of the participants, type of unpredictability (intensity, onset, duration, location), and method of pain induction (thermal, electrical, mechanical pressure, mechanical distention). We included 73 experimental studies with adult volunteers manipulating the (un)predictability of painful stimuli and measuring perceived pain intensity and pain unpleasantness in predictable and unpredictable contexts. Because there are insufficient studies with patients, we focused on healthy volunteers. Our results did not reveal any effect of unpredictability on pain perception. However, several significant moderators were found, ie, targeted stimulus pain intensity, expected pain intensity, and state negative affectivity. Trait negative affectivity and uncontrollability showed no significant effect, presumably because of the low number of included studies. Thus, further investigation is necessary to clearly determine their role in unpredictable pain perception.

Expectations underlie the effects of unpredictable pain: a behavioral and electroencephalogram study

ABSTRACT

Previous studies on the potential effects of unpredictability on pain perception and its neural correlates yielded divergent results. This study examined whether this may be explained by differences in acquired expectations. We presented 41 healthy volunteers with laser heat stimuli of different intensities. The stimuli were preceded either by predictable low, medium, or high cues or by unpredictable low-medium, medium-high, or low-high cues. We recorded self-reports of pain intensity and unpleasantness and laser-evoked potentials (LEPs). Furthermore, we investigated whether dynamic expectations that evolved throughout the experiment based on past trials were better predictors of pain ratings than fixed (nonevolving) expectations. Our results replicate previous findings that unpredictable pain is higher than predictable pain for low-intensity stimuli but lower for high-intensity stimuli. Moreover, we observed higher ratings for the medium-high unpredictable condition than the medium-low unpredictable condition, in line with an effect of expectation. We found significant interactions (N1, N2) for the LEP components between intensity and unpredictability. However, the few significant differences in LEP peak amplitudes between cue conditions did not survive correction for multiple testing. In line with predictive coding perspectives, pain ratings were best predicted by dynamic expectations. Surprisingly, expectations of reduced precision (increased variance) were associated with lower pain ratings. Our findings provide strong evidence that (dynamic) expectations contribute to the opposing effects of unpredictability on pain perception; therefore, we highlight the importance of controlling for them in pain unpredictability manipulations. We also suggest to conceptualize pain expectations more often as dynamic constructs incorporating previous 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.

The temporal effect of uncertain context on the perceptual processing of painful and non-painful stimulation

Uncertainty has been demonstrated to influence the perception of noxious stimuli, but little is known about the effects of prolonged uncertain contexts on the perception of painful and non-painful stimuli. To address this knowledge gap, the present study utilized a cue-based NPU-threat task, where uncertain and certain trials were separated into distinct blocks. The objective was to investigate the impact of uncertain contexts on the temporal dynamics of electroencephalogram (EEG) activity during the processing of painful and non-painful stimuli. The results revealed that the influence of uncertain contexts on neural responses extends beyond painful trials and is also evident in non-painful trials. In uncertain contexts, it has been observed that painful stimuli elicit larger P2 amplitudes and late beta band (13-30 Hz) event-related desynchronization (ERD) around 500-700 ms. However, in certain contexts, painful stimuli evoke stronger late gamma band (50-70 Hz) event-related synchronization (ERS) around 600-700 ms. For non-painful trials, in uncertain contexts, significantly higher amplitudes of the late positive potential (LPP) component and delta-theta band (2-7 Hz) ERS were observed compared to certain non-painful stimuli. These findings demonstrate that uncertain contexts exert a significant impact on the processing of both painful and non-painful stimuli, and this influence is mediated by distinct neural mechanisms.

Group environment modulates how third parties assess unfairly shared losses and unfairly shared gains: neural signatures from ERPs and EEG oscillations

INTRODUCTION

Through its long-term evolution and development, human society has gradually formed stable and effective norms to maintain normal social production and social activities. Altruistic punishment is indispensable in maintaining social norms. Altruistic punishment includes second-party and third-party punishment, and third-party punishment refers to punishing violators by unbiased bystanders who have not suffered damage to their interests. Cooperation is an important form of human social interaction. Third parties play an essential role in maintaining social cooperation. Third parties' behaviors in maintaining cooperative norms may be related to their social environment.

METHOD

We used the prisoner's dilemma (PD) game and distinguished between the gain and loss contexts of the economy to explore how the group environment modulates the cognitive neural mechanisms and psychological processing of the third-party punishment decision. Twenty-six college students (Mage = 19.88 ± 1.58) participated in the experiment; data from four participants were excluded from analyses of the EEG data due to large artifacts.

RESULTS

The behavioral results show that the degree of punishment from the third party in a loss context was greater than in a gain context. ERP analysis results show that the third party applied a lower P300 in the loss context. The loss context induced a greater N100 than the gain context in the individual environment. At the same time, alpha-band power activated by the individual environment was greater than that activated by the group environment under the gain context.

CONCLUSION

These results suggest that a third party maintaining the norms of social cooperation in different contexts will adjust punishment decisions according to the environment, and this process is mainly dominated by the negative emotions caused by environment.

The influence of aggressive exercise on responses to self-perceived and others' pain

Previous studies have reported relationships between exercise and pain. However, little is known about how aggressive exercise modulates individuals' responses to their own and others' pain. This present study addresses this question by conducting 2 studies employing event-related potential (ERP). Study 1 included 38 participants whose self-perceived pain was assessed after intervention with aggressive or nonaggressive exercises. Study 2 recruited 36 participants whose responses to others' pain were assessed after intervention with aggressive or nonaggressive exercise. Study 1's results showed that P2 amplitudes were smaller, reaction times were longer, and participants' judgments were less accurate in response to self-perceived pain stimuli, especially to high-pain stimuli, after intervention with aggressive exercise compared to nonaggressive exercise. Results of study 2 showed that both P3 and LPP amplitudes to others' pain were larger after intervention with aggressive exercise than with nonaggressive exercise. These results suggest that aggressive exercise decreases individuals' self-perceived pain and increases their empathic responses to others' pain.

Testosterone administration enhances the expectation and perception of painful and non-painful somatosensory stimuli

The influence of testosterone on pain perception remains inconsistent in the literature. This randomized, placebo-controlled, double-blind, crossover study investigated the effect of testosterone administration on perception and expectation of electrocutaneous stimulus. Thirty healthy male participants received a single dose of testosterone in one session and a placebo in the other session. For each session, they completed a pain-rating task in which a predictability cue was inserted before a painful or non-painful electocutaneous stimulus delivery, while neural activity was simultaneously recorded by a 64-channel electroencephalographic (EEG) system. Expected and perceived pain ratings, as well as event-related potentials (ERPs) to electocutaneous stimuli and prestimulus EEG oscillatory activities while expecting upcoming electocutaneous stimuli were comprehensively compared between testosterone and placebo sessions. Compared with the placebo session, participants in the testosterone session reported greater pain rating and exhibited greater amplitude of N1 component on ERPs when perceiving both painful and non-painful electrocutaneous stimuli. Mediation analysis revealed that testosterone enhanced the pain-intensity ratings via the N1 response to the electrocutaneous stimulus. Upon viewing the predictability cues after testosterone administration, expected pain intensity increased and spontaneous low-frequency α-oscillation power in the frontal region decreased. These results provide evidence that testosterone enhanced perception and expectation of somatosensory events, and that this was a general effect rather than pain-specific. A plausible explanation for these findings is that testosterone acts to increase vigilance and sustained attention levels, as evidenced by the decreased α-oscillation power. Thus, our findings support a causal role for testosterone in heightening the biological salience of incoming somatosensory information.

Transcranial random noise stimulation over the left dorsolateral prefrontal cortex attenuates pain expectation and perception

OBJECTIVE

The dorsolateral prefrontal cortex (DLPFC) has been increasingly used as a neuromodulatory target in pain management. Transcranial random noise stimulation (tRNS) was shown to effectively elevate cortical excitability. Hence, this study aimed to characterize how tRNS over the left DLPFC affects pain expectation and perception, as well as the efficacy of conditioned-pain modulation (CPM) that reflects the function of the endogenous pain-inhibitory pathway.

METHODS

Using a randomized, double-blinded, and sham-controlled design, healthy participants were randomly recruited to receive tRNS with a direct current offset or sham stimulation. Their expectations and perceptions of painful electrocutaneous stimuli, as well as CPM efficacy were assessed before, immediately after, and 30 min after tRNS.

RESULTS

Compared with sham stimulation, perceived-pain ratings to the painful stimuli, and expected-pain ratings before painful stimuli, attenuated immediately after tRNS, whereas this analgesic effect was ineffective 30 min after tRNS. Importantly, the immediate analgesia induced by tRNS could be accounted for by tRNS effect on attenuating expected-pain ratings before certain painful stimuli. However, CPM efficacy was not significantly affected by tRNS.

CONCLUSIONS

These results demonstrate analgesia immediately after applying tRNS over the left DLPFC.

SIGNIFICANCE

This study provides evidence for analgesia of DLPFC-tRNS on an experimental pain model.

Pain, from perception to action: A computational perspective

Pain is driven by sensation and emotion, and in turn, it motivates decisions and actions. To fully appreciate the multidimensional nature of pain, we formulate the study of pain within a closed-loop framework of sensory-motor prediction. In this closed-loop cycle, prediction plays an important role, as the interaction between prediction and actual sensory experience shapes pain perception and subsequently, action. In this Perspective, we describe the roles of two prominent computational theories-Bayesian inference and reinforcement learning-in modeling adaptive pain behaviors. We show that prediction serves as a common theme between these two theories, and that each of these theories can explain unique aspects of the pain perception-action cycle. We discuss how these computational theories and models can improve our mechanistic understandings of pain-centered processes such as anticipation, attention, placebo hypoalgesia, and pain chronification.

Single-dose testosterone administration modulates instant empathic responses to others' pain: An EEG study

Whether or not testosterone can impair empathy remains unclear in the literature. Given that empathic responses to others' emotional experiences depend strongly upon top-down controlled mechanisms of attention, here we investigated whether the effects of testosterone administration on pain empathy could be modulated by manipulating attention. We used a double-blind, placebo-controlled within-participant design, in which either testosterone or placebo was administrated in separate sessions. Images depicting painful or nonpainful scenes were presented to induce instant empathic responses. Experiment 1 adopted the pain-judgment and hands-counting tasks to direct attention toward painful or nonpainful aspect of the images, respectively. Experiment 2 employed the pain-rating task to estimate affective and cognitive aspects of pain empathy. When discriminating nonpainful aspects of the images in the hands-counting task, accuracies were lower and empathic late positive potential responses were greater in testosterone sessions than in placebo sessions. This suggested that testosterone enhanced empathic responses to task-irrelevant pain-related features, which interfered with task performance. When providing empathic ratings to the images in the pain-rating task, empathic event-related potentials in the early stage were only observed in the testosterone session. This suggested that testosterone facilitated automatic affective reactivity to others' pain when elaborately processing empathic stimuli. Nevertheless, when discriminating painful aspects of the images in the pain-judgment task, we did not observe any significant differences between the two sessions. These results demonstrated that testosterone effects on enhancing brain reactivity to empathic stimuli were dependent upon task demands deploying attention allocation. The enhancement likely arose from the altered brain state (e.g., increased vigilance and arousal levels) after testosterone administration, as evidenced by the reduced amplitude of spontaneous α-oscillation recorded before the onset of the images. It expands our understanding of the neurobiological mechanisms that affect empathy, and highlights the role of testosterone.

Does feedback based on FES-evoked nociceptive withdrawal reflex condition event-related desynchronization? An exploratory study with brain-computer interfaces

Introduction.Event-related desynchronization (ERD) is used in brain-computer interfaces (BCI) to detect the user's motor intention (MI) and convert it into a command for an actuator to provide sensory feedback or mobility, for example by means of functional electrical stimulation (FES). Recent studies have proposed to evoke the nociceptive withdrawal reflex (NWR) using FES, in order to evoke synergistic movements of the lower limb and to facilitate the gait rehabilitation of stroke patients. The use of NWR to provide sensorimotor feedback in ERD-based BCI is novel; thererfore, the conditioning effect that nociceptive stimuli might have on MI is still unknown.Objetive.To assess the ERD produced during the MI after FES-evoked NWR, in order to evaluate if nociceptive stimuli condition subsequent ERDs.Methods. Data from 528 electroencephalography trials of 8 healthy volunteers were recorded and analyzed. Volunteers used an ERD-based BCI, which provided two types of feedback: intrisic by the FES-evoked NWR and extrinsic by virtual reality. The electromyogram of the tibialis anterior muscle was also recorded. The main outcome variables were the normalized root mean square of the evoked electromyogram (RMS_norm), the average electroencephalogram amplitude at the ERD frequency during MI (A¯MI) and the percentage decrease ofA¯MIrelative to rest (ERD%) at the first MI subsequent to the activation of the BCI.Results.No evidence of changes of theRMS_normon both theA¯MI(p = 0.663) and theERD%(p = 0.252) of the subsequent MI was detected. A main effect of the type of feedback was found in the subsequentA¯MI(p < 0.001), with intrinsic feedback resulting in a largerA¯MI.Conclusions.No evidence of ERD conditioning was observed using BCI feedback based on FES-evoked NWR .Significance.FES-evoked NWR could constitute a potential feedback modality in an ERD-based BCI to facilitate motor recovery of stroke people.

Analgesia induced by anodal tDCS and high-frequency tRNS over the motor cortex: Immediate and sustained effects on pain perception

BACKGROUND

Many studies have shown effects of anodal transcranial direct current stimulation (a-tDCS) and high-frequency transcranial random noise stimulation (tRNS) on elevating cortical excitability. Moreover, tRNS with a direct current (DC)-offset is more likely to lead to increases in cortical excitability than solely tRNS. While a-tDCS over primary motor cortex (M1) has been shown to attenuate pain perception, tRNS + DC-offset may prove as an effective means for pain relief.

OBJECTIVE

This study aimed to examine effects of a-tDCS and high-frequency tRNS + DC-offset over M1 on pain expectation and perception, and assess whether these effects could be influenced by the certainty of pain expectation.

METHODS

Using a double-blinded and sham-controlled design, 150 healthy participants were recruited to receive a single-session a-tDCS, high-frequency tRNS + DC-offset, or sham stimulation over M1. The expectation and perception of electrical stimulation in certain and uncertain contexts were assessed at baseline, immediately after, and 30 min after stimulation.

RESULTS

Compared with sham stimulation, a-tDCS induced immediate analgesic effects that were greater when the stimulation outcome was expected with uncertainty; tRNS induced immediate and sustained analgesic effects that were mediated by decreasing pain expectation. Nevertheless, we found no strong evidence for tRNS being more effective for attenuating pain than a-tDCS.

CONCLUSIONS

The analgesic effects of a-tDCS and tRNS showed different temporal courses, which could be related to the more sustained effectiveness of high-frequency tRNS + DC-offset in elevating cortical excitability. Moreover, expectations of pain intensity should be taken into consideration to maximize the benefits of neuromodulation.

Suffer together, bond together: Brain-to-brain synchronization and mutual affective empathy when sharing painful experiences

Previous behavioral studies have shown that sharing painful experiences can strengthen social bonds and promote mutual prosociality, yet the neural mechanisms underlying this phenomenon remain unclear. We hypothesized that sharing a painful experience induces brain-to-brain synchronization and mutual empathy for each other's pain between pain-takers and pain-observers, which then leads to enhanced social bonding. To test this hypothesis, we adopted an electroencephalographic (EEG) hyper-scanning technique to assess neuronal and behavioral activity during a Pain-Sharing task in which high- or low-intensity pain stimulation was randomly delivered to one participant of a dyad on different experimental trials. Single-brain analysis showed that sensorimotor α-oscillation power was suppressed more when expecting high-intensity pain than when expecting low-intensity pain similarly for self-directed or partner-directed pain. Dual-brain analysis revealed that expecting high-intensity pain induced greater brain-to-brain synchronization of sensorimotor α-oscillation phases between pain-takers and pain-observers than did expecting low-intensity pain. Mediation analysis further revealed that brain-to-brain synchronization of sensorimotor α-oscillations mediated the effects of pain-stimulation intensity on mutual affective sharing for partner-directed pain. This mutual affective empathy during the task predicted the social bonding, as indexed by prosocial inclinations measured after the task. These results support the hypothesis that sharing a painful experience triggers emotional resonance between pairs of individuals through brain-to-brain synchronization of neuronal α-oscillations recorded over the sensorimotor cortex, and this emotional resonance further strengthens social bonds and motivates prosocial behavior within pairs of individuals.

The linkage between first-hand pain sensitivity and empathy for others' pain: Attention matters

Many studies suggested shared psychological and neural representations for first-hand physical pain and empathy for others' pain, both of which depend strongly upon top-down controlled mechanisms such as attention. This study aimed to assess the interindividual variation in first-hand physical pain and empathy for pain, and whether their relationship is dependent upon attention. We recruited participants exhibiting high and low sensitivity to first-hand pain (HPS and LPS), and adopted pain empathy paradigms involving attention directed toward or withdrawn from pain of another. Relative to the LPS group, participants in the HPS group estimated greater pain intensity experienced by others, felt greater unpleasantness when viewing others in pain, and exhibited greater sensitivity in discriminating others' pain. Electroencephalographic data showed that when attention was directed toward others' pain, only participants in the HPS group exhibited significant pain empathic effects on the N1 component of event-related potentials and on the α-oscillation response. These empathic neural responses mediated the linkage between first-hand pain sensitivity and empathic behavioral responses. Nevertheless, empathic responses were comparable between two groups when attention was withdrawn from others' pain. These results demonstrate a shared sensitivity to first-hand pain and empathy for pain provided that attention is directed toward pain.

Stimulus predictability moderates the withdrawal strategy in response to repetitive noxious stimulation in humans

Innate defensive behaviors such as reflexes are found across all species, constituting preprogrammed responses to external threats that are not anticipated. Previous studies indicated that the excitability of the reflex arcs like spinal nociceptive withdrawal reflex (NWR) pathways in humans are modulated by several cognitive factors. This study assesses how the predictability of a threat affects the biomechanical pattern of the withdrawal response, showing that distal and proximal muscles are differentially modulated by descending control.

Pain and social decision-making: New insights from the social framing effect

This paper focuses on the social function of painful experience as revealed by recent studies on social decision-making. Observing others suffering from physical pain evokes empathic reactions that can lead to prosocial behavior (e.g., helping others at a cost to oneself), which might be regarded as the social value of pain derived from evolution. Feelings of guilt may also be elicited when one takes responsibility for another’s pain. These social emotions play a significant role in various cognitive processes and may affect behavioral preferences. In addition, the influence of others’ pain on decision-making is highly sensitive to social context. Combining neuroimaging techniques with a novel decision paradigm, we found that when asking participants to trade-off personal benefits against providing help to other people, verbally describing the causal relationship between their decision and other people’s pain (i.e., framing) significantly changed participants’ preferences. This social framing effect was associated with neural activation in the temporoparietal junction (TPJ), which is a brain area that is important in social cognition and in social emotions. Further, transcranial direct current stimulation (tDCS) on this region successfully modulated the magnitude of the social framing effect. These findings add to the knowledge about the role of perception of others’ pain in our social life.