Neural Mechanisms With Respect to Different Paradigms and Relevant Regulatory Factors in Empathy for Pain

Exploring potential neuroimaging biomarkers for the response to non-steroidal anti-inflammatory drugs in episodic migraine

BACKGROUND

Non-steroidal anti-inflammatory drugs (NSAIDs) are considered first-line medications for acute migraine attacks. However, the response exhibits considerable variability among individuals. Thus, this study aimed to explore a machine learning model based on the percentage of amplitude oscillations (PerAF) and gray matter volume (GMV) to predict the response to NSAIDs in migraine treatment.

METHODS

Propensity score matching was adopted to match patients having migraine with response and nonresponse to NSAIDs, ensuring consistency in clinical characteristics and migraine-related features. Multimodal magnetic resonance imaging was employed to extract PerAF and GMV, followed by feature selection using the least absolute shrinkage and selection operator regression and recursive feature elimination algorithms. Multiple predictive models were constructed and the final model with the smallest predictive residuals was chosen. The model performance was evaluated using the area under the receiver operating characteristic (ROCAUC) curve, area under the precision-recall curve (PRAUC), balance accuracy (BACC), sensitivity, F1 score, positive predictive value (PPV), and negative predictive value (NPV). External validation was performed using a public database. Then, correlation analysis was performed between the neuroimaging predictors and clinical features in migraine.

RESULTS

One hundred eighteen patients with migraine (59 responders and 59 non-responders) were enrolled. Six features (PerAF of left insula and left transverse temporal gyrus; and GMV of right superior frontal gyrus, left postcentral gyrus, right postcentral gyrus, and left precuneus) were observed. The random forest model with the lowest predictive residuals was selected and model metrics (ROCAUC, PRAUC, BACC, sensitivity, F1 score, PPV, and NPV) in the training and testing groups were 0.982, 0.983, 0.927, 0.976, 0.930, 0.889, and 0.973; and 0.711, 0.648, 0.639, 0.667,0.649, 0.632, and 0.647, respectively. The model metrics of external validation were 0.631, 0.651, 0.611, 0.808, 0.656, 0.553, and 0.706. Additionally, a significant positive correlation was found between the GMV of the left precuneus and attack time in non-responders.

CONCLUSIONS

Our findings suggest the potential of multimodal neuroimaging features in predicting the efficacy of NSAIDs in migraine treatment and provide novel insights into the neural mechanisms underlying migraine and its optimized treatment strategy.

Can the neural representation of physical pain predict empathy for pain in others?

The question of whether physical pain and vicarious pain have some shared neural substrates is unresolved. Recent research has argued that physical and vicarious pain are represented by dissociable multivariate brain patterns by creating biomarkers for physical pain (Neurologic Pain Signature, NPS) and vicarious pain (Vicarious Pain Signature, VPS), respectively. In the current research, the NPS and two versions of the VPS were applied to three fMRI datasets (one new, two published) relating to vicarious pain which focused on between-subject differences in vicarious pain (Datasets 1 and 3) and within-subject manipulations of perspective taking (Dataset 2). Results show that (i) NPS can distinguish brain responses to images of pain vs no-pain and to a greater extent in vicarious pain responders who report experiencing pain when observing pain and (ii) neither version of the VPS mapped on to individual differences in vicarious pain and the two versions differed in their success in predicting vicarious pain overall. This study suggests that the NPS (created to detect physical pain) is, under some circumstances, sensitive to vicarious pain and there is significant variability in VPS measures (created to detect vicarious pain) to act as generalizable biomarkers of vicarious pain.

Psycho-Neuroendocrinology in the Rehabilitation Field: Focus on the Complex Interplay between Stress and Pain

Chronic stress and chronic pain share neuro-anatomical, endocrinological, and biological features. However, stress prepares the body for challenging situations or mitigates tissue damage, while pain is an unpleasant sensation due to nociceptive receptor stimulation. When pain is chronic, it might lead to an allostatic overload in the body and brain due to the chronic dysregulation of the physiological systems that are normally involved in adapting to environmental challenges. Managing stress and chronic pain (CP) in neurorehabilitation presents a significant challenge for healthcare professionals and researchers, as there is no definitive and effective solution for these issues. Patients suffering from neurological disorders often complain of CP, which significantly reduces their quality of life. The aim of this narrative review is to examine the correlation between stress and pain and their potential negative impact on the rehabilitation process. Moreover, we described the most relevant interventions used to manage stress and pain in the neurological population. In conclusion, this review sheds light on the connection between chronic stress and chronic pain and their impact on the neurorehabilitation pathway. Our results emphasize the need for tailored rehabilitation protocols to effectively manage pain, improve treatment adherence, and ensure comprehensive patient care.

The Empathy for Pain Stimuli System (EPSS): Development and preliminary validation

We present the Empathy for Pain Stimuli System (EPSS): a large-scale database of stimuli for studying people's empathy for pain. The EPSS comprises five sub-databases. First, the Empathy for Limb Pain Picture Database (EPSS-Limb) provides 68 painful and 68 non-painful limb pictures, exhibiting people's limbs in painful and non-painful situations, respectively. Second, the Empathy for Face Pain Picture Database (EPSS-Face) provides 80 painful and 80 non-painful pictures of people's faces being penetrated by a syringe or touched by a Q-tip. Third, the Empathy for Voice Pain Database (EPSS-Voice) provides 30 painful and 30 non-painful voices exhibiting either short vocal cries of pain or neutral interjections. Fourth, the Empathy for Action Pain Video Database (EPSS-Action_Video) provides 239 painful and 239 non-painful videos of whole-body actions. Finally, the Empathy for Action Pain Picture Database (EPSS-Action_Picture) provides 239 painful and 239 non-painful pictures of whole-body actions. To validate the stimuli in the EPSS, participants evaluated the stimuli using four different scales, rating pain intensity, affective valence, arousal, and dominance. The EPSS is available to download for free at https://osf.io/muyah/?view_only=33ecf6c574cc4e2bbbaee775b299c6c1 .

Vicarious facilitation of facial responses to pain

INTRODUCTION

Observing facial expressions of pain has been shown to lead to increased subjective, neural and autonomic pain responses. Surprisingly, these vicarious facilitation effects on its corresponding response channel, namely facial responses to pain have mostly been neglected. We aim to examine whether the prior exposure to facial expressions of pain leads to a facilitation of facial responses to experimental pain; and whether this facilitation is linked to the valence (pain vs. neutral expression) or also linked to specific motor-features of the facial pain expressions (different facial muscle movements).

METHOD

Subjective (intensity and unpleasantness ratings) and facial responses (Facial Action Coding System) of 64 participants (34 female) to painful and non-painful heat stimuli were assessed. Before each heat stimulus, video clips of computer-generated facial expressions (three different pain expressions and a neutral expression) were presented.

RESULTS

The prior exposure to facial expressions of pain led to increased subjective and facial responses to pain. Further, vicarious pain facilitation of facial responses was significantly correlated with facilitation of unpleasantness ratings. We also found evidence that this vicarious facilitation of facial responses was not only linked to the presentation of pain versus neutral expressions but also to specific motor-features of the pain cue (increase in congruent facial muscle movements).

DISCUSSION

Vicarious pain facilitation was found for subjective and facial responses to pain. The results are discussed with reference to the motivational priming hypothesis as well as with reference to motor priming.

SIGNIFICANCE

Our study uncovers evidence that facial pain responses are not only influenced by motivational priming (similar to other types of pain responses), but also by motor-priming. These findings shed light on the complexity - ranging from social, affective and motor mechanisms - underling vicarious facilitation of pain.

Words hurt: common and distinct neural substrates underlying nociceptive and semantic pain

Introduction

Recent studies have shown that processing semantic pain, such as words associated with physical pain, modulates pain perception and enhances activity in regions of the pain matrix. A direct comparison between activations due to noxious stimulation and processing of words conveying physical pain may clarify whether and to what extent the neural substrates of nociceptive pain are shared by semantic pain. Pain is triggered also by experiences of social exclusion, rejection or loss of significant others (the so-called social pain), therefore words expressing social pain may modulate pain perception similarly to what happens with words associated with physical pain. This event-related fMRI study aims to compare the brain activity related to perceiving nociceptive pain and that emerging from processing semantic pain, i.e., words related to either physical or social pain, in order to identify common and distinct neural substrates.

Methods

Thirty-four healthy women underwent two fMRI sessions each. In the Semantic session, participants were presented with positive words, negative pain-unrelated words, physical pain-related words, and social pain-related words. In the Nociceptive session, participants received cutaneous mechanical stimulations that could be either painful or not. During both sessions, participants were asked to rate the unpleasantness of each stimulus. Linguistic stimuli were also rated in terms of valence, arousal, pain relatedness, and pain intensity, immediately after the Semantic session.

Results

In the Nociceptive session, the 'nociceptive stimuli' vs. 'non-nociceptive stimuli' contrast revealed extensive activations in SI, SII, insula, cingulate cortex, thalamus, and dorsolateral prefrontal cortex. In the Semantic session, words associated with social pain, compared to negative pain-unrelated words, showed increased activity in most of the same areas, whereas words associated with physical pain, compared to negative pain-unrelated words, only activated the left supramarginal gyrus and partly the postcentral gyrus.

Discussion

Our results confirm that semantic pain partly shares the neural substrates of nociceptive pain. Specifically, social pain-related words activate a wide network of regions, mostly overlapping with those pertaining to the affective-motivational aspects of nociception, whereas physical pain-related words overlap with a small cluster including regions related to the sensory-discriminative aspects of nociception. However, most regions of overlap are differentially activated in different conditions.

Do Psychological Factors Influence the Elastic Properties of Soft Tissue in Subjects with Fibromyalgia? A Cross-Sectional Observational Study

Nowadays, there is evidence related to the impact that psychological factors have on symptoms, specifically vegetative ones, and on the autonomic nervous system in patients with fibromyalgia (FM). However, there are no studies to correlate the level of association between psychological factors and the elastic properties of tissue in the FM population. Elastic properties of soft tissue reflect age- and disease-related changes in the mechanical functions of soft tissue, and mechanical failure has a profound impact on morbidity and mortality. The study has a cross-sectional observational design with 42 participants recruited from a private clinic and rehabilitation service. The Pain Catastrophizing Scale, Tampa Kinesiophobia Scale and Self-Efficacy Scale were used to assess psychological factors. The elastic properties of the tissue in the characteristic painful points, which patients suffering from FM described, were assessed by strain elastography. A low and significant level of association was found between pain catastrophising scale (PCS) and the non-dominant lateral epicondyle (r = -0.318; p = 0.045). Kinesiophobia was found to be related to the dominant lateral epicondyle (r = 0.403; p = 0.010), the non-dominant knee (r = -0.34; p = 0.027) and the dominant forearm (r = 0.360; p = 0.010). Self-Efficacy showed a low level of association with the non-dominant supraspinatus (r = -0.338; p = 0.033) and the non-dominant medial epicondyle (r = -0.326; p = 0.040). Psychological factors and the elastic properties of tissue seem to be associated in patients suffering from FM. The most profound association between psychological factors and non-dominant parts of the body could be related to neglect and non-use of those parts of the body.

Skin Color and Attractiveness Modulate Empathy for Pain: An Event-Related Potential Study

Although racial in-group bias in empathy for pain has been reported, empathic responses to others’ pain may be influenced by other characteristics besides race. To explore whether skin color and attractiveness modulate empathy for pain, we recorded 24 participants’ reactions to painful faces from racial in-group members with different skin color (fair, wheatish, or dark) and attractiveness (more or less attractive) using event-related potentials (ERPs). Results showed that, for more attractive painful faces, dark skin faces were judged as less painful and elicited smaller N2 amplitudes than fair- and wheatish-skinned faces. However, for less attractive faces, there were no significant differences among the three skin colors. Our findings suggest that empathy for pain toward racial in-group members may be influenced by skin color and attractiveness.

Different priming effects of empathy on neural processing associated with firsthand pain and nonpain perception

The shared-representation model of empathy is still debated. One of the major questions is whether empathy-eliciting stimuli depicting others' pain selectively activate the representations of self-pain. To address this issue, we assessed the priming effects of empathy-eliciting pictures on firsthand pain and nonpain perception, as well as its associated neural processing. In Experiment 1, when compared with nonpainful pictures depicting individuals' body parts with no injury, participants primed by painful pictures showing individuals' body parts with injury reported higher ratings for perceived intensity, unpleasantness, and salience of nociceptive and auditory stimuli, but they only exhibited increased N2 amplitude in response to nociceptive stimuli. In Experiment 2, the results from another group of participants replicated the observations of Experiment 1 and validated the findings in the non-nociceptive somatosensory modality. Importantly, participants' concern ratings for priming pictures predicted their unpleasantness ratings for subsequent nociceptive stimuli, while participants' attention ratings predicted their unpleasantness ratings for subsequent auditory and tactile stimuli. This finding implies that empathy for pain might influence pain and nonpain perception via different psychological mechanisms. In summary, our findings highlight the existence of pain-selective representations in empathy for pain and contribute to a better understanding of the shared-representation model of empathy.

Placebo Analgesia Does Not Reduce Empathy for Naturalistic Depictions of Others' Pain in a Somatosensory Specific Way

The shared representations account postulates that sharing another's pain recruits underlying brain functions also engaged during first-hand pain. Critically, direct causal evidence for this was mainly shown for affective pain processing, while the contribution of somatosensory processes to empathy remains controversial. This controversy may be explained, however, by experimental paradigms that did not direct attention towards a specific body part, or that did not employ naturalistic depictions of others' pain. In this preregistered functional magnetic resonance imaging study, we aimed to test whether causal manipulation of first-hand pain affects empathy for naturalistic depictions of pain in a somatosensory-matched manner. Forty-five participants underwent a placebo analgesia induction in their right hand and observed pictures of other people's right and left hands in pain. We found neither behavioral nor neural evidence for somatosensory-specific modulation of pain empathy. However, exploratory analyses revealed a general effect of the placebo on empathy, and higher brain activity in bilateral anterior insula when viewing others' right hands in pain (i.e., corresponding to one's own placebo hand). These results refine our knowledge regarding the neural mechanisms of pain empathy, and imply that the sharing of somatosensory representations seems to play less of a causal role than the one of affective representations.

Impaired pain empathic abilities among patients with functional dyspepsia

INTRODUCTION

Brain structure or functioning abnormality in regions such as insula and anterior cingulate cortex (ACC) is associated with functional dyspepsia (FD) and pain empathy, but the relationship between FD and pain empathy remains unclear. The aim of this study was to compare the pain empathic abilities of FD patients and healthy controls (HCs) and investigate the association of pain empathy with clinical characteristics and quality of life of FD patients.

METHODS

Pain empathic abilities was measured in 30 FD patients and 30 HCs using a validated pain empathy paradigm. Demographic characteristics, Helicobacter pylori status, duration, dyspeptic symptom score and Nepean Dyspepsia Life Quality Index (NDLQI) were obtained from all patients.

RESULTS

FD patients scored higher than HCs when rating painful pictures, but the accuracy for painful pictures was significantly lower than HCs. Pearson correlation analysis showed significant negative correlation between NDLQI and pain rating scores for painful pictures. When sex, age, educational level, the number of complaints, duration, H. pylori infection and NDLQI were included in multiple linear regression analysis, NDLQI was independently associated with pain ratings.

CONCLUSIONS

FD patients showed abnormally enhanced pain empathic abilities, which may be associated with the severity of symptoms and quality of life.

Postural correlates of painful stimuli exposure: impact of mental simulation processes and pain-level of the stimuli

Previous studies have reported (i) freezing-like posturographic correlates in response to painful as compared to non-painful scenes vision (Lelard et al., Front Hum Neurosci 7:4, 2013) and (ii) an increase of this response during the mental simulation as compared to the passive viewing of the painful scenes (Lelard et al., Front Psychol 8:2012, 2017). The main objective of the present study was to explore the modulation of posturographic correlates of painful scenes vision by the level of depicted pain and the influence of mental simulation on this modulation. Thirty-six participants (36.3 ± 11.4 years old) were included in this study. During the experiment, participants had to stand on a posturographic platform. Three types of static visual stimuli were randomly depicting different pain-level situations: no-pain, low-pain, high-pain. In a first run, participants watched these stimuli passively (passive condition); in a second run, they were asked to "imagine that they were personally experiencing the situations they were about to see" (mental simulation condition). For each picture, subjective ratings were recorded for displeasure and desire to avoid at the end of the posturographic session. Results support an approach-type behavior in response to high-pain stimuli in the passive condition which becomes a withdrawal-type behavior in the mental simulation condition. Moreover, this withdrawal-type behavior is modulated by the level of depicted pain and this modulation does not appear for the subjective data. As a conclusion, these results are in accordance with those of previous studies showing the modulation of posturographic correlates of pain perception by mental simulation and report, for the first time, modulation of this effect by the level of depicted pain. The dichotomy of this modulatory effect between subjective and objective data is discussed as well as the finding of an approach-type behavior towards painful stimuli when passively viewing them becoming a withdrawal-type behavior when mental simulation is applied to the same stimuli.

Transcranial direct current stimulation for empathy: A systematic review and meta-analysis

Transcranial Direct Current Stimulation (tDCS) has been used to modulate empathy, but no studies have meta-analyzed the evidence base for its efficacy. This study aimed to determine the efficacy of tDCS at modulating empathy. We conducted a systematic review and meta-analysis of randomized controlled trials involving anodal or cathodal versus sham tDCS to modulate empathy in healthy adults and clinical populations. Random-effects modelling was applied to pooling overall efficacy estimates using standardized mean differences (Hedge's g) and 95% confidence intervals. Outcome measures for tasks designed to measure empathy were reaction time and accuracy. Anodal tDCS appears to improve lab-based computerized measures of cognitive empathy in healthy adult volunteers. While the evidence provided by this review may be of relevance to individuals with impaired empathic capabilities, the generalizability of our findings is geared towards nonclinical populations given the preponderance of healthy volunteers in our review. Hence, it is not clear if moderate improvements in speed and accuracy on lab-based computerized empathy measures would lead to meaningful clinical improvements. Future studies should consider the use of tDCS to modulate empathy in clinical populations.

Influence of acute pain on valence rating of words

Numerous studies showed the effect of negative affective and pain-related semantic primes enhancing the perceived intensity of successive painful stimuli. It remains unclear whether and how painful primes are able to influence semantic stimuli in a similar way. Therefore, we investigated the effects of noxious primes on the perception of the valence of subsequent semantic stimuli. In two experiments, 48 healthy subjects were asked to give their valence ratings regarding different semantic stimuli (pain-related, negative, positive, and neutral adjectives) after they were primed with noxious electrical stimuli of moderate intensity. Experiment 1 focused on the existence of the effect, experiment 2 focused on the length of the effect. Valence ratings of pain-related, negative, and positive words (not neutral words) became more negative after a painful electrical prime was applied in contrast to no prime. This effect was more pronounced for pain-related words compared to negative, pain-unrelated words. Furthermore, the priming effect continued to affect the valence ratings even some minutes after the painful priming had stopped. So, painful primes are influencing the perception of semantic stimuli as well as semantic primes are influencing the perception of painful stimuli.

Itch processing in the brain

Itch is a sensation defined as the urge to scratch. The central mechanisms of itch are being increasingly studied. These studies are usually based on experimental itch induction methods, which can be classified into the following categories: histamine-induced, induction by other non-histamine chemicals (e.g. cowhage), physically induced (e.g. electrical) and mentally induced (e.g. audio-visual). Because pain has been more extensively studied, some extrapolations to itch can be proposed and verified by experiments. Recent studies suggest that the itch-processing network in the brain could be disrupted in certain diseases. This disruption could be related to the implication of new regions or the exclusion of already engaged brain regions from itch-processing network in the brain.

Changes in Empathy in Patients With Chronic Low Back Pain: A Structural-Functional Magnetic Resonance Imaging Study

Objective: Many pieces of research have focused on pain within individuals, but little attention has been paid to whether pain can change an individual’s empathic ability and affect social relationships. The purpose of this study is to explore how chronic low back pain changes empathy.

Methods: Twenty-four chronic low back pain patients and 22 healthy controls were recruited. We set up an experimental pain-exposed model for each healthy subject. All subjects received a painful-empathic magnetic resonance scan. After the scan, all subjects rated the pain intensity and multiple empathy-related indicators. The clinical assessment scale was the 20-item Basic Empathy Scale in Adults.

Result: The chronic low back pain patients reported lower scores on the total scores of BES-A, the subscale scores of emotional disconnection and cognitive empathy, and the discomfort rating. The fMRI results in the chronic low back pain patients showed that there were multiple abnormal brain pathways centered on the anterior insula. The DTI results in the chronic low back pain patients showed that there were reduced fractional anisotropy values in the corpus callosum, bilateral anterior thalamic radiation (ATR), right posterior thalamic radiation (PTR), right superior longitudinal fasciculus (SLF), and left anterior corona radiate (ACR).

Conclusion: Our study found that patients with chronic low back pain have impaired empathy ability. The abnormal functional connectivity of multiple brain networks, multiple damaged white matter tracts, and the lower behavioral scores in chronic low back pain patients supported our findings.

Differential brain responses for perception of pain during empathic response in binge drinkers compared to non-binge drinkers

•

We measure empathic responses to imagery pain while adopting a ‘self’ vs ‘other’ perspective.

•

Social drinkers who binge drink respond more slowly to imagery pain than those who do not.

•

Binge drinkers show also stronger activation in fusiform body area to imagery pain ‘other’

•

Differences between binge and non-binge drinkers relate to ‘self’ vs. ‘other’ distinction.

Individuals who engage in binge drinking behaviors may show evidence of impaired cognitive function and emotional dysregulation. Impaired empathy, characterized by a reduced ability to understand and respond appropriately to feelings of others, is increasingly recognized for its role in Alcohol Use Disorders (AUD). The present study examined a population of young adult social drinkers to compare individuals who show binge drinking behavior to those who do not on measures of empathic processing and associated neural responses. A secondary aim explored similarities and differences between binge drinkers living in the UK and France. Alcohol drinking history and impulsivity ratings were recorded from seventy-one participants [(37 UK (Binge drinkers N = 19); 34 France (Binge drinkers N = 17)], who then underwent a neuroimaging study. During functional magnetic resonance imaging, participants viewed images of bodily pain (vs. no-pain), while adopting the perspective of self (pain recipient) or other (observer of someone else experiencing pain). Anterior midcingulate cortex (aMCC) and insula activation distinguished pain from no-pain conditions. Binge drinkers showed stronger regional neural activation than non-binge drinkers within a cluster spanning fusiform gyrus and inferior temporal gyrus, encompassing the Fusiform Body Area. Binge drinkers compared to non-binge drinkers also took longer to respond when viewing pictures depicting pain, in particular when adopting the perspective of self. Relationships between changes in brain activation and behavioural responses in pain versus no pain conditions (self or other perspective) indicated that whereas non-binge drinkers engage areas supporting self to other distinction, binge drinkers do not. Our findings suggest that alcohol binge drinking is associated with different empathy-related behavioral and brain responses, consistent with the proposed importance of empathy in the development of AUD.

Functional and anatomical brain connectivity in psoriasis patients and healthy controls: a pilot brain imaging study after exposure to mentally induced itch

BACKGROUND

Despite the prevalence of psoriasis, the processing of itch in psoriasis and its impact on the central nervous system (CNS) remain unclear.

OBJECTIVE

We studied the influence of psoriasis on the CNS using magnetic resonance imaging techniques (fMRI and DTI, respectively) to investigate whether mentally induced itch can modify the functional connectivity or the white matter microstructure of the brain.

METHODS

Fourteen patients with chronic psoriasis and 15 healthy controls were recruited. Itch was mentally induced in subjects by videos showing others scratching themselves.

RESULTS

The observation of functional connectivity during the viewing the video revealed an interconnected network of brain regions that are more strongly coupled in psoriasis patients than in healthy controls. This network links the cerebellum, the thalami, the anteroposterior cingulum, the inferior parietal lobules, the middle temporal poles and the parahippocampal, hippocampal, lingual and supramarginal gyri. We also found connections with the right precuneus and both left insula and superior temporal gyrus. The DTI analysis showed that chronic itch affects the microstructure of white matter, including the anterior thalamic radiations, the superior and inferior longitudinal fasciculi, the corticospinal tracts, the cingulum, the external capsules, the inferior frontal-occipital fasciculi and both minor and major forceps.

CONCLUSION

Our results indicate that there could exist a network which is more interconnected in psoriasis patients. Among two building blocks of this network, the subnetwork encoding the perception and control of itch sensation is more affected than the subnetwork representing mentalizing and empathy. With an approach consisting of measuring microstructural changes at a local level in the brain, we also contradict the findings obtained with global measures which stated that chronic psoriasis cannot alter the anatomy of the brain. This confirms that itchy pathophysiological conditions have similar effects on functional and structural connectivity as those observed in chronic pain.

Differences between empathy for face and body pain: Cognitive and neural responses

Empathy for pain is a hotspot in the field of empathy research because of its specific cognitive and neural mechanism. Currently, studies of empathy for pain can be classified into two categories based on the body regions receiving the painful stimulus, i.e., empathy for face pain and empathy for body pain, which conveys painful information based on individuals’ faces or body parts, respectively. Although the existing evidence revealed differences between these two kinds of pain empathy regarding the underlying cognitive and neural mechanisms, the current studies tend to confuse these findings. Therefore, we summarized the differences between empathy for face and body pain, mainly regarding the behavioral reactivity tendency, brain activations, and electrophysiological (EEG) signals. These differences probably stem from the fact that the human face contains more emotional information, while other body parts contain more perceptual information. Thus, future studies should identify the distinctions between empathy for face and body pain, to explore further how empathy for face pain is affected by the facial information of others and focus on empathy for face pain in individuals with psychopathological disorders. Furthermore, the specific reasons for these distinctions and their underlying neuromechanisms deserve to be further reviewed.

Identification of the cerebral effects of paracetamol in healthy subjects: an fMRI study

Introduction

Paracetamol is commonly used for its antipyretic properties and analgesic effects, but the central mechanism remains elusive. We designed a study in healthy volunteers to detect the central functional working mechanism of paracetamol.

Subjects material and methods

A total of 20 subjects had a baseline functional magnetic resonance imaging (fMRI) before the intake of 1000 mg paracetamol orally; 60 minutes later, a second fMRI was made aiming detection of regional blood flow differences.

Results

A decreased connectivity was observed in the ventral volume of interest (VOI), with the posterior cingulate (with both the left anterior cingulate cortex (ACC) and right ACC: respectively, Ke = 576; t = -6.8894 and Ke = 185; t = -4.8178) and the inferior temporal left (Ke = 103; t = -5.0993); in the combined ventral and dorsal VOIs, the posterior cingulate (with the left ACC; Ke = 149; t = -4.5658) and, both with the right ACC, the inferior temporal left (Ke = 88; t = -3.8456) and the inferior frontal gyrus (Ke = 86; t = -4.3937) had a decrease in connectivity. An increase was seen in other regions, including, among others, the middle frontal and temporal gyri (respectively, Ke = 85; t = 4.4256 and Ke = 85; t = 5.6851), the inferior frontal (with the left ACC: Ke = 165; t = 4.4998) and the superior frontal gyrus (with the right ACC; Ke = 281; t = 4.5992), and the post/precentral gyrus (with the right ACC, respectively, Ke = 102; t = 6.0582 and Ke = 105; t = 4.0776).

Conclusions

On fMRIs in healthy volunteers, the ingestion of paracetamol affects connections with the ACC. This suggests a central effect of paracetamol in cerebral areas known to be associated with pain. Further studies are needed to demonstrate the same effects in acute and chronic pain states.

Central mechanisms of itch: A systematic literature review and meta-analysis

In recent years, studying the central mechanism of itch has gained momentum. However, a proper meta-analysis has not been conducted in this domain. In this study, we tried to respond to this need. A systematic search and a meta-analysis were carried out to estimate the central mechanism of itch. The itch matrix comprises the thalamus and the parietal, secondary somatosensory, insular and cingulate cortices. We have shown that the basal ganglia (BG) play an important role in itch reduction. Finally, we explored itch processing in AD patients and observed that the itch matrix in these patients was different. In conclusion, this is the first meta-analysis on the central mechanisms of itch perception and processing. Our study demonstrated that different modalities of itch induction can produce a common pattern of activity in the brain and provided further insights into understanding the underlying nature of itch central perception.

Gender differences in empathic responses to others' economic payoffs: an event-related potentials study

Although gender differences in empathy have been well established through measuring subjective outcomes, some studies of the neural mechanisms of pain empathy have not found gender differences. This inconsistent evidence may be caused by different research methods or different paradigms. The present study adopted a different approach from the pain empathy paradigm to examine gender differences in empathic responses to others' economic payoffs using event-related potentials. The results showed that the N2 amplitudes in female participants were more negative than those in male participants, indicating a greater female than male susceptibility to facial expressions at the early stage of empathy. The LPP amplitudes for male participants were found to be more positive in the observation condition (involving no self-interest) than in the participation condition (involving self-interest), but there was no significant difference in the LPP amplitudes for the female participants between the two conditions. The results suggest that females' empathic responses are more likely to be elicited automatically by the perception of others' emotional states. In contrast, males' empathic responses are more likely to be mediated by self-interest, which subsequently reduces their empathic responses.

Self-Interest Induces Counter- Empathy at the Late Stage of Empathic Responses to Others' Economic Payoffs

Previous studies have found that individuals exhibit empathic responses when others are treated unfairly. However, there remains a lack of clarity over the extent to which self-interest regulates these empathic responses, and in identifying which component of empathy is more likely to be affected. To investigate these issues, an experiment was designed based on a money distribution task with two conditions [observation condition (OC) vs. participation condition (PC)], and carried out using scalp-recorded event-related potentials (ERPs). Behavioral data showed that the participants' empathic responses were consistent with their coplayers' emotional expressions in the OC, whereas they were inconsistent with the coplayers' expressions in the PC. The electrophysiological data showed that the neural encoding of facial expressions (reflected in the N170) was not affected by self-interest. However, the late stage of empathic responses (LPP) showed a decline when participants' self-interest was involved. Disadvantageous inequality and relatively fair distribution to others elicited a more pronounced feedback-related negativity (FRN) than advantageous inequality distribution in both the OC and PC. As the late stage of empathic responses is also indexed by the LPP amplitude, these results indicate that the participants were more concerned for their own outcomes than for others' benefits when self-interest was involved, which reduced their empathy toward their coplayers at the late stage of empathic responses.

Competitive Intensity Modulates the Pain Empathy Response: An Event-Related Potentials Study

Previous studies have widely reported that competition modulates an individual's ability to empathize with pain experienced by others. What remains to be clarified, however, is how modulations in the intensity of competition might affect this type of empathy. To investigate this, we first used a Eriksen Flanker task to set different competitive intensity context (high competitive intensity, HCI; medium competitive intensity, MCI; low competitive intensity, LCI). Then we used a recognition task as a competitive task, in which we recorded event-related potentials (ERP) while participants viewed static images of body parts in painful and non-painful situations. Participants were informed that both sets of images depicted an opponent that they were required to play against in the recognition task that varied in levels of competitive intensity according to condition (HCI, MCI, and LCI). We observed an early N2 differentiation between pain and no-pain stimuli over the frontal area under MCI and LCI conditions, but this was not detected under HCI condition. Moreover, we observed a pattern of pain and no-pain differentiation for the late LPP over the frontal and centro-parietal regions under HCI, MCI, and LCI condition. As the pain empathy response is indexed by pain and no-pain differentiation, these results indicate a down-regulation of pain empathy response attributable to a high level of competition. With its very early onset, this effect appears to inhibit bottom-up processing of the ability to perceive pain experienced by an opponent. Our results provide neuroscientific evidence for a deficit in early automatic arousal in response to the pain of the opponent under the influence of high competitive intensity.