Mutual influences of pain and emotional face processing

Vicarious facilitation of facial responses to pain: Does the others' expression need to be painful?

INTRODUCTION

Prior exposure to others' facial expressions of pain can lead to a facilitation of pain responses, including its corresponding response channel, namely facial responses to pain. It has been questioned, however, whether this vicarious pain facilitation occurs only when observing others' pain or whether the observation of other negative expressions can trigger similar facilitation of facial responses to pain. The study aimed to test this, by comparing the impact of viewing others' facial expressions of pain versus another negative expression (sadness) and two control expressions (neutral, happiness) on facial responses to pain.

METHOD

Participants (N = 56; 31 females), watched short video clips of computer-generated facial expressions (pain, sadness, neutral & happiness) before they received painful and non-painful heat stimuli. Facial responses were analysed using the Facial Action Coding System. In addition, subjective and autonomic responses were assessed.

RESULTS

The prior exposure to others' expressions of pain and sadness versus neutral did not lead to significantly increased facial responses to pain. Likewise, subjective and autonomic pain responses were not facilitated. However, viewing others' expressions of happiness, consistently reduced facial as well as subjective and autonomic responses to pain compared to others' negative or neutral expressions. This dampening effect was not observed for non-painful heat.

DISCUSSION

Facial and other pain responses were most strongly affected by prior exposure to others' facial expressions of happiness, which led to a pain-dampening effect. In contrast, the evidence for vicarious facilitation of pain was rather weak in the present study, with no evidence of pain-specificity.

SIGNIFICANCE STATEMENT

Facial responses to pain - along with subjective and autonomic responses - are reduced when observing others' expressions of happiness, demonstrating pain modulation by positive affective social signals, which may also transfer to clinical contexts.

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.

Pain and related suffering reduce attention toward others

BACKGROUND

It has been proposed that the expression of pain-related suffering may lead to an enhanced focus on oneself and reduced attention toward the external world. This study aimed at investigating whether experimentally induced painrelated suffering may lead persons to withdraw into themselves, causing a reduced focus on external stimuli as reflected by impaired performance in a facial recognition task and heightened perception of internal stimuli measured by interoceptive awareness.

METHODS

Thirty-two participants had to recognize different emotional facial expressions (neutral, sad, angry, happy), or neutral geometrical figures under conditions of no pain, low, and high prolonged pain intensities. Interoceptive accuracy was measured using a heartbeat-detection task prior to and following the pain protocol.

RESULTS

Males but not females were slower to recognize facial expressions under the condition of high painful stimulation compared to the condition of no pain. In both, male and female participants, the difficulty in recognizing another person's emotions from a facial expression was directly related to the level of suffering and unpleasantness experienced during pain. Interoceptive accuracy was higher after the pain experiment. However, neither the initial interoceptive accuracy nor the change were significantly related to the pain ratings.

CONCLUSIONS

Our results suggest that long-lasting and intense painful stimuli, which induce suffering, lead to attentional shifts leading to withdrawal from others. These findings contribute to a better understanding of the social dynamics of pain and pain-related suffering.

Far from the eyes, far from the heart: COVID-19 confinement dampened sensitivity to painful facial features

In the last 2 years, governments of many countries imposed heavy social restrictions to contain the spread of the COVID-19 virus, with consequent increase of bad mood, distress, or depression for the people involved. Few studies investigated the impact of these restrictive measures on individual social proficiency, and specifically the processing of emotional facial information, leading to mixed results. The present research aimed at investigating systematically whether, and to which extent, social isolation influences the processing of facial expressions. To this end, we manipulated the social exclusion experimentally through the well-known Cyberball game (within-subject factor), and we exploited the occurrence of the lockdown for the Swiss COVID-19 first wave by recruiting participants before and after being restricted at home (grouping factor). We then tested whether either form of social segregation influenced the processing of pain, disgust, or neutral expressions, across multiple tasks probing access to different components of affective facial responses (state-specific, shared across states). We found that the lockdown (but not game-induced exclusion) affected negatively the processing of pain-specific information, without influencing other components of the affective facial response related to disgust or broad unpleasantness. In addition, participants recruited after the confinement reported lower scores in empathy questionnaires. These results suggest that social isolation affected negatively individual sensitivity to other people's affect and, with specific reference to the processing of facial expressions, the processing of pain-diagnostic information.

Perspective-taking influences attentional deployment towards facial expressions of pain: an eye-tracking study

Empathetic perspective-taking (PT) may be critical in modulating attention and associated responses to another's pain. However, the differential effects of imagining oneself to be in the pain sufferer's situation ("Self-perspective") or imagining the negative impacts on the pain sufferer's experience ("Other-perspective") on attention have not been studied. The effects of observer PT (Self vs Other) and level of facial pain expressiveness (FPE) upon attention to another person's pain was investigated. Fifty-two adults were assigned to 1 of 3 PT conditions; they were instructed to view pairs of pain expressions and neutral faces and either (1) consider their own feelings (Self-perspective), (2) consider the feelings of the person in the picture (Other-perspective), or (3) received no further instructions (Control). Eye movements provided indices of early (probability and duration of first fixation) and later (total gaze duration) attentional deployment. Pain faces were more likely to be fixated upon first. A significant first fixation duration bias towards pain was observed, which increased with increasing levels of FPE, and was higher in the Self-PT than the Control condition. The proportion of total gaze duration on pain faces was higher in both experimental conditions than the Control condition. This effect was moderated by FPE in the Self-PT condition; there was a significant increase from low to high FPE. When observers attend to another's facial display of pain, top-down influences (such as PT) and bottom-up influences (such as sufferer's FPE) interact to control deployment and maintenance of attention.

Does my pain affect your disgust? Cross-modal influence of first-hand aversive experiences in the appraisal of others' facial expressions

BACKGROUND

Embodied models of social cognition argue that others' affective states are processed by re-enacting a sensory-specific representation of the same state in the observer. However, neuroimaging studies suggest that a reliable part of the representation shared between self and others is supramodal and relates to dimensions such as Unpleasantness or arousal, common to qualitatively different experiences. Here we investigated whether representations of first-hand pain and disgust influenced the subsequent evaluation of facial expressions in Modality-specific fashion, or in terms of Unpleasantness or arousal.

METHODS

Thirty volunteers were subjected to thermal painful and olfactory disgusting events, and subsequently were asked to classify computer-generated faces expressing pain (characterized by high Unpleasantness and arousal), disgust (high Unpleasantness and low arousal), surprise (low Unpleasantness and high arousal) and hybrid combinations thereof.

RESULTS

Thermal and olfactory events were associated with comparable Unpleasantness ratings and heart rate (but stronger galvanic response was found for painful temperatures). Furthermore, we found that the appraisal of facial expressions was biased by the prior stimulus, with more frequent pain classifications following thermal stimuli, and more frequent disgust classifications following olfactory stimuli. Critically, this modulation was cross-modal in nature, as each first-hand stimulation influenced in comparable fashion facial traits diagnostic of both pain and disgust, without instead generalizing to features of surprise.

CONCLUSION

Overall, these data support the presence of shared coding between one's aversive experiences and the appraisal of others' facial responses, which is best describable as supramodal representation of the Unpleasantness of the experience.

SIGNIFICANCE

These results extend previous findings about common representational coding between the experience of first-hand and others' pain. In particular, they highlight that reliable part of the information shared is supramodal in nature and relates to a broad dimension of Unpleasantness common also to painless aversive states such as disgust.

Pain aversion and anxiety-like behavior occur at different times during the course of chronic inflammatory pain in rats

Pain is considered a multidimensional conscious experience that includes a sensory component and a negative affective-motivational component. The negative affective-motivational component of pain is different from the sensory component and amplifies the pain experience. Nowadays, a significant number of preclinical research groups have focused their attention on the affective symptoms of pain. In the present study, we investigated the pain aversion and anxiety-like behavior of the complete Freund’s adjuvant (CFA)-induced chronic pain model. CFA rats experienced spontaneous pain during pain-paired conditioning (pain aversion) and spontaneous pain produces an affective response (anxiety-like behavior). Moreover, pain aversion was gradually attenuated, while the anxiety-like behavior increased in 4 weeks. Therefore, although the negative effect (including pain aversion and anxiety) is always associated with hyperalgesia, the manifestations of negative effect may follow different time courses, which may influence the progress of primary disease. The findings illustrate that targeted therapy should focus on a specific aspect in different stages of pain. Our study emphasizes the necessity of using multiple tests to study pain comorbidities.

5-HT in the dorsal raphe nucleus is involved in the effects of 100-Hz electro-acupuncture on the pain-depression dyad in rats

The pain-depression dyad is becoming widespread in the clinic and is attracting increasing attention. A previous study by our group found that 100-Hz electro-acupuncture (EA), but not 2-, 50- and 2/100-Hz EA, was effective against the reserpine-induced pain-depression dyad. This finding is in contrast to the fact that low-frequency EA is commonly used to treat supraspinal-originating diseases. The present study aimed to investigate the mechanism underlying the effects of 100-Hz EA on the pain-depression dyad. Repeated reserpine injection was found to induce allodynia and depressive behaviors in rats. It decreased 5-hydroxytryptamine (5-HT) levels and immunoreactive expressions in the dorsal raphe nucleus (DRN). 100-Hz EA alleviated the pain-depression dyad and upregulated 5-HT in the DRN of reserpine-injected rats. Intracerebroventricular injection of para-chlorophenylalanine, an inhibitor of 5-HT resynthesis, suppressed the upregulation of 5-HT in the DRN by 100-Hz EA and partially counteracted the analgesic and anti-depressive effects of 100-Hz EA. The present study was the first to demonstrate that 5-HT in the DRN is involved in mediating the analgesic and anti-depressive effects of 100-Hz EA on the pain-depression dyad. This finding provided a scientific basis for high-frequency EA as a potential treatment for the pain-depression dyad.

In the face of pain: The choice of visual cues in pain conditioning matters

BACKGROUND

Visual cue conditioning is a valuable experimental paradigm to investigate placebo and nocebo effects in pain. However, little attention has been paid to the cues themselves and potential variability of effects (their quantity and quality) stemming from the choice of stimuli. Yet, this seemingly methodological question has important implications for the interpretation of experimental findings in terms of their significance for clinical practice.

METHODS

We investigated the effect of heat pain conditioning using different types of visual cues (abstract images, faces and pseudo-words) in a group of 22 healthy volunteers. We analysed conditioning effects calculated as the difference in pain ratings to heat stimuli of identical temperature preceded by conditioned high or low pain cues with (1) subliminal and supraliminal presentation; and (2) immediately after conditioning and following extinction. Awareness manipulation and test following indirect, observational extinction allowed us to assess the strength and robustness of the conditioning effects induced with different cue types.

RESULTS

We observed no differences in conditioning effect magnitudes between images, faces and words when all stimuli were presented supraliminally. With subliminal presentation, only face stimuli elicited a significant effect; equally only face cue-induced effect withstood extinction.

CONCLUSIONS

Our findings indicate that face-related associations to pain might be stronger than those elicited with other visual cues, as face cues seem to induce stronger subliminal effects and withstand mild extinction.

SIGNIFICANCE

We compared different types of neutral cues commonly used in conditioning paradigms and found that faces elicited a stronger, more robust nonconscious effect than abstract images or pseudo-words.

On the Origin of Interoception

Over the course of a century, the meaning of interoception has changed from the restrictive to the inclusive. In its inclusive sense, it bears relevance to every individual via its link to emotion, decision making, time-perception, health, pain, and various other areas of life. While the label for the perception of the body state changes over time, the need for an overarching concept remains. Many aspects can make any particular interoceptive sensation unique and distinct from any other interoceptive sensation. This can range from the sense of agency, to the physical cause of a sensation, the ontogenetic origin, the efferent innervation, and afferent pathways of the tissue involved amongst others. In its overarching meaning, interoception primarily is a product of the central nervous system, a construct based on an integration of various sources, not per se including afferent information. This paper proposes a definition of interoception as based on subjective experience, and pleas for the use of specific vocabulary in addressing the many aspects that contribute to it.

Enhance placebo, avoid nocebo: How contextual factors affect physiotherapy outcomes

INTRODUCTION

Placebo and nocebo represent complex and distinct psychoneurobiological phenomena in which behavioural and neurophysiological modifications occur together with the application of a treatment. Despite a better understanding of this topic in the medical field, little is known about their role in physiotherapy.

PURPOSE

The aim of this review is: a) to elucidate the neurobiology behind placebo and nocebo effects, b) to describe the role of the contextual factors as modulators of the clinical outcomes in rehabilitation and c) to provide clinical and research guidelines on their uses.

IMPLICATIONS

The physiotherapist's features, the patient's features, the patient-physiotherapist relationship, the characteristics of the treatment and the overall healthcare setting are all contextual factors influencing clinical outcomes. Since every physiotherapy treatment determines a specific and a contextual effect, physiotherapists should manage the contextual factors as a boosting element of any manual therapy to improve placebo effects and avoid detrimental nocebo effects.

Emotional pictures and sounds: a review of multimodal interactions of emotion cues in multiple domains

In everyday life, multiple sensory channels jointly trigger emotional experiences and one channel may alter processing in another channel. For example, seeing an emotional facial expression and hearing the voice’s emotional tone will jointly create the emotional experience. This example, where auditory and visual input is related to social communication, has gained considerable attention by researchers. However, interactions of visual and auditory emotional information are not limited to social communication but can extend to much broader contexts including human, animal, and environmental cues. In this article, we review current research on audiovisual emotion processing beyond face-voice stimuli to develop a broader perspective on multimodal interactions in emotion processing. We argue that current concepts of multimodality should be extended in considering an ecologically valid variety of stimuli in audiovisual emotion processing. Therefore, we provide an overview of studies in which emotional sounds and interactions with complex pictures of scenes were investigated. In addition to behavioral studies, we focus on neuroimaging, electro- and peripher-physiological findings. Furthermore, we integrate these findings and identify similarities or differences. We conclude with suggestions for future research.