Others' Pain Appraisals Modulate the Anticipation and Experience of Subsequent Pain

Analgesic effects of high-frequency rTMS on pain anticipation and perception

Previous studies suggest that pain perception is greatly shaped by anticipation, with M1 and DLPFC involved in this process. We hypothesized that high-frequency rTMS targeting these regions could alter pain anticipation and thereby reduce pain perception. In a double-blind, sham-controlled study, healthy participants received 10 Hz rTMS to M1, DLPFC, or a sham treatment. Assessments were conducted before, immediately after, and 60 min after stimulation, including laser-evoked potentials, pain ratings, and anticipatory EEG. M1-rTMS immediately reduced laser-evoked P2 amplitude, increased sensorimotor high-frequency α-oscillation power, and accelerated peak alpha frequency in the midfrontal region during pain anticipation. In contrast, DLPFC-rTMS reduced the N2-P2 complex and pain ratings 60 min post-stimulation, an effect associated with prolonged microstate C duration during pain anticipation-a microstate linked to default mode network activity. Thus, M1-rTMS immediately modulates anticipatory α-oscillations and laser-evoked potentials, while DLPFC-rTMS induces delayed analgesic effects partially by modulating default mode network activity.

Expectation generation and its effect on subsequent pain and visual perception

Bayesian accounts of perception, such as predictive processing, suggest that perceptions integrate expectations and sensory experience, and thus assimilate to expected values. Furthermore, more precise expectations should have stronger influences on perception. We tested these hypotheses in a paradigm that manipulates both the mean value and the precision of cues within-person. Forty-five participants observed cues-presented as ratings from 10 previous participants-with varying cue means, variances (precision), and skewness across trials. Participants reported expectations regarding the painfulness of thermal stimuli or the visual contrast of flickering checkerboards. Subsequently, similar cues were each followed by a visual or noxious thermal stimulus. While perceptions assimilated to expected values in both modalities, cues' precision mainly affected visual ratings. Furthermore, behavioral and computational models revealed that expectations were biased towards extreme values in both modalities, and towards low-pain cues specifically. fMRI analysis revealed that the cues affected systems related to higher-level affective and cognitive processes-including assimilation to the cue mean in a neuromarker of endogenous contributions to pain and in the nucleus accumbens, and activity consistent with aversive prediction-error-like encoding in the periaqueductal gray during pain perception-but not systems related to early perceptual processing. Our findings suggest that predictive processing theories should be combined with mechanisms such as selective attention to better fit empirical findings, and that expectation generation and its perceptual effects are mostly modality-specific and operate on higher-level processes rather than early perception.

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.

Intact painful sensation but enhanced non-painful sensation in individuals with autistic traits

Somatosensory abnormalities are commonly recognized as diagnostic criteria in autism spectrum disorder (ASD), and may also exist in individuals with autistic traits. The present research included two studies to explore the painful and non-painful sensation and their cognitive-neurological mechanisms of individuals with autistic traits. Study 1 included 358 participants to assess the relationship between autistic traits and pain/non-pain sensitivities using questionnaires: the Autism Spectrum Quotient (AQ), the Pain Sensitivity Questionnaire, and the Highly Sensitive Person Scale, respectively. Study 1 found that autistic traits were positively correlated with non-pain sensitivity, but not associated with pain sensitivity. Study 2 recruited 1,167 participants whose autistic traits were assessed using the AQ. Subsequently, thirty-three participants who scored within the top 10% and bottom 10% on the AQ were selected into High-AQ and Low-AQ groups, respectively, to explore the cognitive-neural responses of individuals with autistic traits to both painful and non-painful stimuli with event-related potential (ERP) technology. Results of Study 2 showed that the High-AQ group showed higher intensity ratings, more negative emotional reactions, and larger N1 amplitudes than the Low-AQ group to the non-painful stimuli, but no difference of response to the painful stimuli was found between High-AQ and Low-AQ groups. These findings suggest that individuals with autistic traits may experience enhanced non-painful sensation but intact painful sensation.

Learning pain from others: a systematic review and meta-analysis of studies on placebo hypoalgesia and nocebo hyperalgesia induced by observational learning

ABSTRACT

Observing someone experience pain relief or exacerbation after an intervention may induce placebo hypoalgesia or nocebo hyperalgesia. Understanding the factors that contribute to these effects could help in the development of strategies for optimizing treatment of chronic pain conditions. We systematically reviewed and meta-analyzed the literature on placebo hypoalgesia and nocebo hyperalgesia induced by observational learning (OL). A systematic literature search was conducted in the databases PubMed, PsycINFO, Web of Science, ScienceDirect, PsycARTICLES, Scopus, and Academic Search Ultimate. Twenty-one studies were included in the systematic review, 17 of which were suitable for meta-analysis (18 experiments; n = 764 healthy individuals). The primary end point was the standardized mean difference (SMD) for pain following placebo cues associated during OL with low vs high pain. Observational learning had a small-to-medium effect on pain ratings (SMD 0.44; 95% confidence interval [CI] 0.21-0.68; P < 0.01) and a large effect on pain expectancy (SMD 1.11; 95% CI 0.49-2.04; P < 0.01). The type of observation (in-person vs videotaped) modulated the magnitude of placebo hypoalgesia/nocebo hyperalgesia ( P < 0.01), whereas placebo type did not ( P = 0.23). Finally, OL was more effective when observers' empathic concern (but no other empathy-related factors) was higher ( r = 0.14; 95% CI 0.01-0.27; P = 0.03). Overall, the meta-analysis demonstrates that OL can shape placebo hypoalgesia and nocebo hyperalgesia. More research is needed to identify predictors of these effects and to study them in clinical populations. In the future, OL could be an important tool to help maximize placebo hypoalgesia in clinical settings.

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 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.