Electrocortical evidence for preferential processing of dynamic pain expressions compared to other emotional expressions

Better safe than sorry?-On the influence of learned safety on pain perception

The experience of threat was found to result-mostly-in increased pain, however it is still unclear whether the exact opposite, namely the feeling of safety may lead to a reduction of pain. To test this hypothesis, we conducted two between-subject experiments (N = 94; N = 87), investigating whether learned safety relative to a neutral control condition can reduce pain, while threat should lead to increased pain compared to a neutral condition. Therefore, participants first underwent either threat or safety conditioning, before entering an identical test phase, where the previously conditioned threat or safety cue and a newly introduced visual cue were presented simultaneously with heat pain stimuli. Methodological changes were performed in experiment 2 to prevent safety extinction and to facilitate conditioning in the first place: We included additional verbal instructions, increased the maximum length of the ISI and raised CS-US contingency in the threat group from 50% to 75%. In addition to pain ratings and ratings of the visual cues (threat, safety, arousal, valence, and contingency), in both experiments, we collected heart rate and skin conductance. Analysis of the cue ratings during acquisition indicate successful threat and safety induction, however results of the test phase, when also heat pain was administered, demonstrate rapid safety extinction in both experiments. Results suggest rather small modulation of subjective and physiological pain responses following threat or safety cues relative to the neutral condition. However, exploratory analysis revealed reduced pain ratings in later trials of the experiment in the safety group compared to the threat group in both studies, suggesting different temporal dynamics for threat and safety learning and extinction, respectively. Perspective: The present results demonstrate the challenge to maintain safety in the presence of acute pain and suggest more research on the interaction of affective learning mechanism and pain processing.

Neural response and representation: Facial expressions in scenes

Previous studies have shown that the brain generates expectations based on scenes, which affects facial expression recognition. However, although facial expressions are known to interact with perception, the mechanism underlying this interaction remains poorly understood. Here, we used frequency labeling and decoding techniques to reveal the effects of scene-based expectation on the amplitude and representational strength of neural activity. We also reduced the relative reliability between expectation and sensory input by blurring facial expressions to further investigate the effects of this relative reliability on the pattern of neural activation and representation. Participants viewed emotional changes in unblurred or blurred facial expressions, which flickered at a rate of 6 Hz within a scene. We found that facial expressions that were congruent with the emotional significance of the scene elicited a larger steady-state visual evoked potential amplitude than did facial expressions that were incongruent with the emotional significance of a scene, in both unblurred and blurred conditions. We also found that expected facial expression representations were stronger than unexpected representations during the unblurred condition. In the blurred condition, unexpected representations were stronger than expected representations. Taken together, these results suggested that facial expression processing in the visual cortex is modulated by top-down signals. The relative reliability of expectation and sensory input moderated the influence of a scene on facial expression representation. Furthermore, our study showed that neural activation amplitudes did not correspond to representational strength.

How gender affects the decoding of facial expressions of pain

OBJECTIVES

Gender has been suggested to play a critical role in how facial expressions of pain are perceived by others. With the present study we aim to further investigate how gender might impact the decoding of facial expressions of pain, (i) by varying both the gender of the observer as well as the gender of the expressor and (ii) by considering two different aspects of the decoding process, namely intensity decoding and pain recognition.

METHODS

In two online-studies, videos of facial expressions of pain as well as of anger and disgust displayed by male and female avatars were presented to male and female participants. In the first study, valence and arousal ratings were assessed (intensity decoding) and in the second study, participants provided intensity ratings for different affective states, that allowed for assessing intensity decoding as well as pain recognition.

RESULTS

The gender of the avatar significantly affected the intensity decoding of facial expressions of pain, with higher ratings (arousal, valence, pain intensity) for female compared to male avatars. In contrast, the gender of the observer had no significant impact on intensity decoding. With regard to pain recognition (differentiating pain from anger and disgust), neither the gender of the avatar, nor the gender of the observer had any affect.

CONCLUSIONS

Only the gender of the expressor seems to have a substantial impact on the decoding of facial expressions of pain, whereas the gender of the observer seems of less relevance. Reasons for the tendency to see more pain in female faces might be due to psychosocial factors (e.g., gender stereotypes) and require further research.

Neural correlates of the attentional bias towards pain-related faces in fibromyalgia patients: An ERP study using a dot-probe task

BACKGROUND

One of the major cognitive deficits in fibromyalgia has been linked to the hypervigilance phenomenon. It is mainly reflected as a negative bias for allocating attentional resources towards both threatening and pain-related information. Although the interest in its study has recently grown, the neural temporal dynamics of the attentional bias in fibromyalgia still remains an open question.

METHOD

Fifty participants (25 fibromyalgia patients and 25 healthy control subjects) performed a dot-probe task. Two types of facial expressions (pain-related and neutral) were employed as signal stimuli. Then, as a target stimulus, a single dot replaced the location of one of these two faces. Event-related potentials (ERP) in response to facial expressions and target stimulation (i.e., dot) were recorded. Reaction time (RT) and accuracy measures in the experimental task were collected as behavioural outcomes.

RESULTS

Temporal dynamics of brain electrical activity were analysed on two ERP components (P2 and N2a) sensitive to the facial expressions meaning. Pain-related faces elicited higher frontal P2 amplitudes than neutral faces for the whole sample. Interestingly, an interaction effect between group and facial expressions was also found showing that pain-related faces elicited enhanced P2 amplitudes (at fronto-central regions, in this case) compared to neutral faces only when the group of patients was considered. Furthermore, higher P2 amplitudes were observed in response to pain-related faces in patients with fibromyalgia compared to healthy control participants. Additionally, a shorter latency of P2 (at centro-parietal regions) was also detected for pain-related facial expressions compared to neutral faces. Regarding the amplitude of N2a, it was lower for patients as compared to the control group. Non-relevant effects of the target stimulation on the ERPs were found. However, patients with fibromyalgia exhibited slower RT to locate the single dot for incongruent trials as compared to congruent and neutral trials.

CONCLUSIONS

Data suggest the presence of an attentional bias in fibromyalgia that it would be followed by a deficit in the allocation of attentional resources to further process pain-related information. Altogether the current results suggest that attentional biases in fibromyalgia might be explained by automatic attentional mechanisms, which seem to be accompanied by an alteration of more strategic or controlled attentional components.

Effects of Age on Emotion Regulation, Emotional Empathy, and Prosocial Behavior

OBJECTIVES

The degree to which older adults experience emotional empathy and show subsequent prosocial behavior versus experience personal distress in response to another's distress remains unclear.

METHOD

Young (n = 40; 17-29 years) and older (n = 39; 61-82 years) adults watched videos of individuals expressing pain or no pain. Pain mimicry was recorded using facial electromyography. Participants were then asked if they would spend the remaining time helping the experimenter. Self-reported tendency to suppress or reappraise emotion was assessed, as well as trait and state emotional empathy and personal distress.

RESULTS

Pain mimicry was associated with reduced trait suppression in older adults. In both age groups, greater emotional empathy, averaged across video condition, was associated with increased helping. In addition, relative to young adults, older adults reported more personal distress and emotional reactivity in response to the videos but were just as willing to help. They also put more effort into helping.

DISCUSSION

These findings contribute to clarification of mixed previous evidence regarding the experience of emotional empathy in young versus older adulthood. We discuss the importance of considering additional subcomponents of empathy such as emotion regulation, while also accounting for the relevance of the empathy induction to each age group.

The Time Course of Facial Expression Recognition Using Spatial Frequency Information: Comparing Pain and Core Emotions

We are able to recognize others' experience of pain from their facial expressions. However, little is known about what makes the recognition of pain possible and whether it is similar or different from core emotions. This study investigated the mechanisms underpinning the recognition of pain expressions, in terms of spatial frequency (SF) information analysis, and compared pain with 2 core emotions (ie, fear and happiness). Two experiments using a backward masking paradigm were conducted to examine the time course of low- and high-SF information processing, by manipulating the presentation duration of face stimuli and target-mask onset asynchrony. Overall, we found a temporal advantage of low-SF over high-SF information for expression recognition, including pain. This asynchrony between low- and high-SF happened at a very early stage of information extraction, which indicates that the decoding of low-SF expression information is not only faster but possibly occurs before the processing of high-SF information. Interestingly, the recognition of pain was also found to be slower and more difficult than core emotions. It is suggested that more complex decoding process may be involved in the successful recognition of pain from facial expressions, possibly due to the multidimensional nature of pain experiences. PERSPECTIVE: Two studies explore the perceptual and temporal properties of the decoding of pain facial expressions. At very early stages of attention, the recognition of pain was found to be more difficult than fear and happiness. It suggests that pain is a complex expression, and requires additional time to detect and process.

Placebo Manipulations Reverse Pain Potentiation by Unpleasant Affective Stimuli

According to the motivational priming hypothesis, unpleasant stimuli activate the motivational defense system, which in turn promotes congruent affective states such as negative emotions and pain. The question arises to what degree this bottom-up impact of emotions on pain is susceptible to a manipulation of top-down-driven expectations. To this end, we investigated whether verbal instructions implying pain potentiation vs. reduction (placebo or nocebo expectations)-later on confirmed by corresponding experiences (placebo or nocebo conditioning)-might alter behavioral and neurophysiological correlates of pain modulation by unpleasant pictures. We compared two groups, which underwent three experimental phases: first, participants were either instructed that watching unpleasant affective pictures would increase pain (nocebo group) or that watching unpleasant pictures would decrease pain (placebo group) relative to neutral pictures. During the following placebo/nocebo-conditioning phase, pictures were presented together with electrical pain stimuli of different intensities, reinforcing the instructions. In the subsequent test phase, all pictures were presented again combined with identical pain stimuli. Electroencephalogram was recorded in order to analyze neurophysiological responses of pain (somatosensory evoked potential) and picture processing [visually evoked late positive potential (LPP)], in addition to pain ratings. In the test phase, ratings of pain stimuli administered while watching unpleasant relative to neutral pictures were significantly higher in the nocebo group, thus confirming the motivational priming effect for pain perception. In the placebo group, this effect was reversed such that unpleasant compared with neutral pictures led to significantly lower pain ratings. Similarly, somatosensory evoked potentials were decreased during unpleasant compared with neutral pictures, in the placebo group only. LPPs of the placebo group failed to discriminate between unpleasant and neutral pictures, while the LPPs of the nocebo group showed a clear differentiation. We conclude that the placebo manipulation already affected the processing of the emotional stimuli and, in consequence, the processing of the pain stimuli. In summary, the study revealed that the modulation of pain by emotions, albeit a reliable and well-established finding, is further tuned by reinforced expectations-known to induce placebo/nocebo effects-which should be addressed in future research and considered in clinical applications.

How the visual brain detects emotional changes in facial expressions: Evidence from driven and intrinsic brain oscillations

The processing of facial expressions is often studied using static pictorial cues. Recent work, however, suggests that viewing changing expressions more robustly evokes physiological responses. Here, we examined the sensitivity of steady-state visual evoked potentials and intrinsic oscillatory brain activity to transient emotional changes in facial expressions. Twenty-two participants viewed sequences of grayscale faces periodically turned on and off at a rate of 17.5 Hz, to evoke flicker steady-state visual evoked potentials (ssVEPs) in visual cortex. Each sequence began with a neutral face (flickering for 2290 msec), immediately followed by a face from the same actor (also flickering for 2290 msec) with one of four expressions (happy, angry, fearful, or another neutral expression), followed by the initially presented neutral face (flickering for 1140 msec). The amplitude of the ssVEP and the power of intrinsic brain oscillations were analyzed, comparing the four expression-change conditions. We found a transient perturbation (reduction) of the ssVEP that was more pronounced after the neutral-to-angry change compared to the other conditions, at right posterior sensors. Induced alpha-band (8-13 Hz) power was reduced compared to baseline after each change. This reduction showed a central-occipital topography and was strongest in the subtlest and rarest neutral-to-neutral condition. Thus, the ssVEP indexed involvement of face-sensitive cortical areas in decoding affective expressions, whereas mid-occipital alpha power reduction reflected condition frequency rather than expression-specific processing, consistent with the role of alpha power changes in selective attention.

The neuroelectric dynamics of the emotional anticipation of other people's pain

When we observe a dynamic emotional facial expression, we usually automatically anticipate how that expression will develop. Our objective was to study a neurocognitive biomarker of this anticipatory process for facial pain expressions, operationalized as a mismatch effect. For this purpose, we studied the behavioral and neuroelectric (Event-Related Potential, ERP) correlates, of a match or mismatch, between the intensity of an expression of pain anticipated by the participant, and the intensity of a static test expression of pain displayed with the use of a representational momentum paradigm. Here, the paradigm consisted in displaying a dynamic facial pain expression which suddenly disappeared, and participants had to memorize the final intensity of the dynamic expression. We compared ERPs in response to congruent (intensity the same as the one memorized) and incongruent (intensity different from the one memorized) static expression intensities displayed after the dynamic expression. This paradigm allowed us to determine the amplitude and direction of this intensity anticipation by measuring the observer's memory bias. Results behaviorally showed that the anticipation was backward (negative memory bias) for high intensity expressions of pain (participants expected a return to a neutral state) and more forward (memory bias less negative, or even positive) for less intense expressions (participants expected increased intensity). Detecting mismatch (incongruent intensity) led to faster responses than detecting match (congruent intensity). The neuroelectric correlates of this mismatch effect in response to the testing of expression intensity ranged from P100 to LPP (Late Positive Potential). Path analysis and source localization suggested that the medial frontal gyrus was instrumental in mediating the mismatch effect through top-down influence on both the occipital and temporal regions. Moreover, having the facility to detect incongruent expressions, by anticipating emotional state, could be useful for prosocial behavior and the detection of trustworthiness.

The role of spatial frequency information in the decoding of facial expressions of pain: a novel hybrid task

Spatial frequency (SF) information contributes to the recognition of facial expressions, including pain. Low-SF encodes facial configuration and structure and often dominates over high-SF information, which encodes fine details in facial features. This low-SF preference has not been investigated within the context of pain. In this study, we investigated whether perpetual preference differences exist for low-SF and high-SF pain information. A novel hybrid expression paradigm was used in which 2 different expressions, one containing low-SF information and the other high-SF information, were combined in a facial hybrid. Participants are instructed to identify the core expression contained within the hybrid, allowing for the measurement of SF information preference. Three experiments were conducted (46 participants in each) that varied the expressions within the hybrid faces: respectively pain-neutral, pain-fear, and pain-happiness. In order to measure the temporal aspects of image processing, each hybrid image was presented for 33, 67, 150, and 300 ms. As expected, identification of pain and other expressions was dominated by low-SF information across the 3 experiments. The low-SF preference was largest when the presentation of hybrid faces was brief and reduced as the presentation duration increased. A sex difference was also found in experiment 1. For women, the low-SF preference was dampened by high-SF pain information, when viewing low-SF neutral expressions. These results not only confirm the role that SF information has in the recognition of pain in facial expressions but suggests that in some situations, there may be sex differences in how pain is communicated.

Observing dyspnoea in others elicits dyspnoea, negative affect and brain responses

Dyspnoea is usually caused by diagnosable cardiorespiratory mechanisms. However, frequently dyspnoea relates only weakly or not at all to cardiorespiratory functioning, suggesting that additional neuropsychosocial processes contribute to its experience. We tested whether the mere observation of dyspnoea in others constitutes such a process and would elicit dyspnoea, negative affect and increased brain responses in the observer.

In three studies, series of pictures and videos were presented, which either depicted persons suffering from dyspnoea or nondyspnoeic control stimuli. Self-reports of dyspnoea and affective state were obtained in all studies. Additionally, respiratory variables and brain responses during picture viewing (late positive potentials in electroencephalograms) were measured in one study.

In all studies, dyspnoea-related pictures and videos elicited mild-to-moderate dyspnoea and increased negative affect compared to control stimuli. This was paralleled by increased late positive potentials for dyspnoea-related pictures while respiratory variables did not change. Moreover, increased dyspnoea correlated modestly with higher levels of empathy in observers.

The present results demonstrate that observing dyspnoea in others elicits mild-to-moderate dyspnoea, negative affect, and increased brain responses in the absence of respiratory changes. This vicarious dyspnoea has clinical relevance, as it might increase suffering in the family and medical caregivers of dyspnoeic patients.

Face-to-face: Perceived personal relevance amplifies face processing

The human face conveys emotional and social information, but it is not well understood how these two aspects influence face perception. In order to model a group situation, two faces displaying happy, neutral or angry expressions were presented. Importantly, faces were either facing the observer, or they were presented in profile view directed towards, or looking away from each other. In Experiment 1 (n = 64), face pairs were rated regarding perceived relevance, wish-to-interact, and displayed interactivity, as well as valence and arousal. All variables revealed main effects of facial expression (emotional > neutral), face orientation (facing observer > towards > away) and interactions showed that evaluation of emotional faces strongly varies with their orientation. Experiment 2 (n = 33) examined the temporal dynamics of perceptual-attentional processing of these face constellations with event-related potentials. Processing of emotional and neutral faces differed significantly in N170 amplitudes, early posterior negativity (EPN), and sustained positive potentials. Importantly, selective emotional face processing varied as a function of face orientation, indicating early emotion-specific (N170, EPN) and late threat-specific effects (LPP, sustained positivity). Taken together, perceived personal relevance to the observer-conveyed by facial expression and face direction-amplifies emotional face processing within triadic group situations.

Do Interoceptive Sensations Provoke Fearful Responses in Adolescents With Chronic Headache or Chronic Abdominal Pain? A Preliminary Experimental Study

Objective

To determine whether fear can be triggered when experiencing interoceptive sensations locally proximal to the primary pain region.  Two groups of adolescents (11-18 years) with chronic headache ( n  = 20) or chronic abdominal pain (CAP; n  = 20) completed three muscle tensing tasks to induce proximal versus distal sensations: (1) "frown" task (proximal for chronic headache; distal for CAP), (2) "tighten stomach" task (proximal for CAP; distal for chronic headache), and (3) safe comparison task (clench fist). Fear and avoidance were assessed via self-report. Adolescents with CAP reported greater fear and avoidance after the proximal compared with the distal task, while adolescents with chronic headache did not. Both groups reported similar levels of fear and avoidance in the frown and safe comparison task.  Results suggest that the perception of proximal interoceptive sensations appears to activate the fear system in adolescents with CAP. Future research is warranted.

A Screening Mechanism Differentiating True from False Pain during Empathy

Empathizing with another's suffering is important in social interactions. Empathic behavior is selectively elicited from genuine, meaningful pain but not from fake, meaningless scenarios. However, the brain's screening mechanism of false information from meaningful events and the time course for the screening process remains unclear. Using EEG combined with principle components analysis (PCA) techniques, here we compared temporal neurodynamics between the observation of pain and no-pain pictures as well as between true (painful expressions and needle-penetrated arms) and false (needle-penetrated faces with neutral expressions) pain pictures. The results revealed that pain vs. no-pain information is differentiated in the very early ERP components, i.e., the N1/P1 for the face and arm pictures categories and the VPP/N170 for the facial expression category while the mid-latency ERP components, N2 and P3, played key roles in differentiating true from false situations. The complex of N2 and P3 components may serve as a screening mechanism through which observers allocate their attentions to more important or relevant events and screen out false environmental information. This is the first study to describe and provide a time course of the screening process during pain empathy. These findings shed new light on the understanding of empathic processing.

The impact of individuation on the bases of human empathic responding

While there is substantial overlap in the neural systems underlying empathy for people we know as opposed to strangers, social distance has been shown to significantly moderate empathic neural responses towards the negative experiences of others. Intriguingly however, variance in empathic neural responses towards known and unknown targets has not been reflected by behavioral differences as indexed by self-reported empathic ratings. One explanation for this disconnect is that empathic evaluations of known and unknown individuals draw on different bases (e.g. target identity/reactions) within the empathic process. To test this hypothesis, we utilized high density EEG to assess how individuating targets with personal names moderated the link between behavioral pain ratings and attentional processing oriented towards (a) initial target processing and (b) subsequent expressions target discomfort. Consistent with prior findings, no differences in pain ratings between individuated and unindividuated targets was observed. However, individual mean pain rating differences for individuated targets was strongly positively related to attentional processing levels, indexed by the P300, during the initial presentation of those targets, a relationship absent for unindividuated targets. In contrast, pain ratings for unindividuated targets was positively related to levels of attentional processing, indexed by the Late Positive Potential (LPP), during the subsequent discomfort expression stage. Furthermore, the LPP response to individuated target discomfort was positively linked to behavioral measures of emotional expressivity whereas the LPP response to unindividuated target discomfort was positively associated with cognitive appraisal. These findings suggest that individuation can significantly shift the bases of empathic responding.

Emotional mimicry signals pain empathy as evidenced by facial electromyography

Facial mimicry has been suggested to be a behavioral index for emotional empathy. The present study is the first to investigate the link between facial muscle activity and empathy for pain by facial electromyographic (EMG) recording while observers watched videos depicting real-life painful events. Three types of visual stimulus were used: an intact painful scene and arm-only (needle injection) and face only (painful expression) scenes. Enhanced EMG activity of the corrugator supercilii (CS) and zygomaticus major (ZM) muscles was found when observers viewed others in pain, supporting a unique pain expression that is distinct from the expression of basic emotions. In the intact video stimulus condition, CS activity was correlated positively with the empathic concern score and ZM activity, suggesting facial mimicry mediated empathy for pain. Cluster analysis of facial EMG responses revealed markedly different patterns among stimulus types, including response category, ratio, and temporal dynamics, indicating greater ecological validity of the intact scene in eliciting pain empathy as compared with partial scenes. This study is the first to quantitatively describe pain empathy in terms of facial EMG data. It may provide important evidence for facial mimicry as a behavioral indicator of pain empathy.

Effects of context and individual predispositions on hypervigilance to pain-cues: an ERP study

BACKGROUND

Hypervigilance to pain is the automatic prioritization of pain-related compared with other stimuli. The processing of threat information is influenced by negative contexts. Therefore, we intended to explore such context effects on hypervigilance to pain-cues, taking individual differences in self-reported vigilance to pain into consideration.

METHODS

In all, 110 healthy subjects viewed task-irrelevant emotional facial expressions (anger, happy, neutral, and pain) overlaid in half of the trials with a fine grid. The instructed task was to indicate the presence/absence of this grid. A threatening context was established by applying electrical stimuli slightly below pain-threshold. Using scores of Pain Vigilance and Awareness Questionnaire, the sample was divided into high vs low pain vigilant subjects. Reaction times and event-related brain potentials were recorded.

RESULTS

No distinct attentional processing of pain faces (based on the event-related brain potentials) was observed as a function of high levels of self-reported vigilance to pain and contextual threat induction. High pain vigilant subjects showed generally enhanced processing of emotional and neutral faces as indicated by parameters of early (early posterior negativity) and late (late positive complex) processing stages. This enhancement was abolished when electro-stimuli were presented.

CONCLUSION

Contextual threat does not enhance the attentional capture of pain-cues when they are presented concurrently with competing task demands. The study could, however, replicate a generally enhanced attentional processing of emotional cues in high pain vigilant subjects. This underpins that hypervigilance to pain is related to changes in emotional processing.

Mutual influences of pain and emotional face processing

The perception of unpleasant stimuli enhances whereas the perception of pleasant stimuli decreases pain perception. In contrast, the effects of pain on the processing of emotional stimuli are much less known. Especially given the recent interest in facial expressions of pain as a special category of emotional stimuli, a main topic in this research line is the mutual influence of pain and facial expression processing. Therefore, in this mini-review we selectively summarize research on the effects of emotional stimuli on pain, but more extensively turn to the opposite direction namely how pain influences concurrent processing of affective stimuli such as facial expressions. Based on the motivational priming theory one may hypothesize that the perception of pain enhances the processing of unpleasant stimuli and decreases the processing of pleasant stimuli. This review reveals that the literature is only partly consistent with this assumption: pain reduces the processing of pleasant pictures and happy facial expressions, but does not - or only partly - affect processing of unpleasant pictures. However, it was demonstrated that pain selectively enhances the processing of facial expressions if these are pain-related (i.e., facial expressions of pain). Extending a mere affective modulation theory, the latter results suggest pain-specific effects which may be explained by the perception-action model of empathy. Together, these results underscore the important mutual influence of pain and emotional face processing.

Developmental and individual differences in the neural processing of dynamic expressions of pain and anger

We examined the processing of facial expressions of pain and anger in 8-month-old infants and adults by measuring event-related brain potentials (ERPs) and frontal EEG alpha asymmetry. The ERP results revealed that while adults showed a late positive potential (LPP) to emotional expressions that was enhanced to pain expressions, reflecting increased evaluation and emotional arousal to pain expressions, infants showed a negative component (Nc) to emotional expressions that was enhanced to angry expressions, reflecting increased allocation of attention to angry faces. Moreover, infants and adults showed opposite patterns in their frontal asymmetry responses to pain and anger, suggesting developmental differences in the motivational processes engendered by these facial expressions. These findings are discussed in the light of associated individual differences in infant temperament and adult dispositional empathy.

Vigilance for pain-related faces in a primary task paradigm: an ERP study

BACKGROUND

Pain-related stimuli are supposed to be automatically prioritized over other stimuli. This prioritization has often been tested using primary task paradigms in which pain information is irrelevant for completing the explicitly posed task. Task-irrelevant stimuli are only processed if they are very salient, and pain-related stimuli are assumed to be salient enough.

OBJECTIVE

We wanted to further investigate this assumption by assessing event-related brain potentials (ERPs) - a very sensitive method for studying attention and reaction times in response to pictures of people in pain and other emotional faces - using a primary task paradigm. In addition, we assumed that individuals describing themselves as vigilant to pain are especially responsive to pain cues.

METHODS

One hundred pain-free subjects were tested in a primary task paradigm using pictures of facial expressions of pain, anger, happiness, and neutral mood. ERPs were assessed at midline electrodes. Vigilance to pain was assessed by the pain vigilance and awareness questionnaire.

RESULTS

In contrast to previous studies (which have used pain words), effects of facial expressions of pain and other emotions on the ERPs and reaction times were surprisingly weak throughout and did not give evidence for a distinct processing of pain-related stimuli. However, hypervigilant subjects appeared to be strongly and cognitively absorbed by all emotional stimuli.

CONCLUSION

Accordingly, it appears that pain-related stimuli are not always of outstanding salience, but that certain characteristics (eg, type of material, emotional richness) have to be present, for pain-related stimuli to be prioritized over stimuli of other emotional content. Hypervigilance to pain may generally predispose individuals to process emotional stimuli in greater depth.

On the mutual effects of pain and emotion: facial pain expressions enhance pain perception and vice versa are perceived as more arousing when feeling pain

Perception of emotional stimuli alters the perception of pain. Although facial expressions are powerful emotional cues - the expression of pain especially plays a crucial role for the experience and communication of pain - research on their influence on pain perception is scarce. In addition, the opposite effect of pain on the processing of emotion has been elucidated even less. To further scrutinize mutual influences of emotion and pain, 22 participants were administered painful and nonpainful thermal stimuli while watching dynamic facial expressions depicting joy, fear, pain, and a neutral expression. As a control condition of low visual complexity, a central fixation cross was presented. Participants rated the intensity of the thermal stimuli and evaluated valence and arousal of the facial expressions. In addition, facial electromyography was recorded as an index of emotion and pain perception. Results show that faces per se, compared to the low-level control condition, decreased pain, suggesting a general attention modulation of pain by complex (social) stimuli. The facial response to painful stimulation revealed a significant correlation with pain intensity ratings. Most important, painful thermal stimuli increased the arousal of simultaneously presented pain expressions, and in turn, pain expressions resulted in higher pain ratings compared to all other facial expressions. These findings demonstrate that the modulation of pain and emotion is bidirectional with pain faces being mostly prone to having mutual influences, and support the view of interconnections between pain and emotion. Furthermore, the special relevance of pain faces for the processing of pain was demonstrated.