Attachment style and children and young people with chronic dermatological conditions.

BACKGROUND: Dermatological conditions are common in childhood and, in their more severe forms, can cause pain, disability and social marginalisation. Despite attachment being a known factor contributing to psychological and physiological development in childhood and several adult studies showing associations between attachment and dermatology outcomes (Tomas-Aragones, 2018), attachment in young dermatology patients has not been investigated. OBJECTIVES: This study examined if (1) 8-16-year-olds with chronic dermatological conditions were more likely to show attachment insecurity than general population peers; (2) attachment style was linked to psychological functioning; and (3) facial involvement was associated with attachment insecurity. METHOD: One hundred and twenty-two 8-16-year-olds attending a specialist paediatric dermatological service were compared on the Child Attachment Interview (CAI) to general population data. The Strengths and Difficulties Questionnaire (SDQ) was used to measure psychosocial functioning. RESULTS: The dermatology group was significantly more likely to be insecurely attached than their general population peers (χ2 [1] = 4.76, p < .05). The secure group self-reported significantly better psychological functioning on all indices compared with the insecure group (Total Difficulties: F[1,89] = 15.30, p < .001). There were no significant differences between secure and insecure groups on parent-reported psychological measures (Total Difficulties: F[1,94] = 0.67, p = .42). Children with facial involvement were not significantly more likely to be insecurely attached. CONCLUSIONS: Increased risk of attachment insecurity, particularly in the anxious pre-occupied category, as well as an association between attachment and psychosocial functioning resonated with adult studies suggesting that further research about the role of attachment with young dermatology patients is warranted.

The Relationship Between the Ability to Infer Another's Pain and the Expectations Regarding the Appearance of Pain Facial Expressions: Investigation of the Role of Visual Perception.

Although pain is a commonly experienced and observed affective state, it is frequently misinterpreted, which leads to inadequate caregiving. Studies show the ability at estimating pain in others (estimation bias) and detecting its subtle variations (sensitivity) could emerge from independent mechanisms. While estimation bias is modulated by variables such as empathy level, pain catastrophizing tendency, and overexposure to pain, sensitivity remains unimpacted. The present study verifies if these 2 types of inaccuracies are partly explained by perceptual factors. Using reverse correlation, we measured their association with participants' mental representation of pain, or more simply put, with their expectations of what the face of a person in pain should look like. Experiment 1 shows that both parameters are associated with variations in expectations of this expression. More specifically, the estimation bias is linked with expectations characterized by salient changes in the middle face region, whereas sensitivity is associated with salient changes in the eyebrow region. Experiment 2 reveals that bias and sensitivity yield differences in emotional representations. Expectations of individuals with a lower underestimation tendency are qualitatively rated as expressing more pain and sadness, and those of individuals with a higher level of sensitivity as expressing more pain, anger, and disgust. Together, these results provide evidence for a perceptual contribution in pain inferencing that is independent of other psychosocial variables and its link to observers' expectations. PERSPECTIVE: This article reinforces the contribution of perceptual mechanisms in pain assessment. Moreover, strategies aimed to improve the reliability of individuals' expectations regarding the appearance of facial expressions of pain could potentially be developed, and contribute to decrease inaccuracies found in pain assessment and the confusion between pain and other affective states.

Moderate similarity leads to empathic concern, but high similarity can also induce personal distress towards others' pain.

Empathic concern and personal distress are common vicarious emotional responses that arise when witnessing someone else's pain. However, the influence of perceived similarity on these responses remains unclear. In this study, we examined how perceived similarity with an injured target impacts vicarious emotional responses. A total of 87 participants watched a video of an athlete in pain preceded by a clip describing the athlete's trajectory, which indicated either high, moderate, or low similarity to the participants. Emotional self-reports, facial expressions, gaze behavior, and pupil diameter were measured as indicators of the participants' emotional responses. Participants in the moderate- and high-similarity groups exhibited greater empathic concern, as evidenced by their display of more sadness compared with those in the low-similarity group. Furthermore, those in the moderate-similarity group exhibited less avoidance by displaying reduced disgust, indicating lower personal distress compared with those in the low-similarity condition. Nevertheless, the high-similarity group displayed just as much disgust as the low-similarity group. These findings suggest that perceived similarity enhances empathic concern to others' suffering, but that high similarity can also lead to personal distress. Future studies on empathy should explore distinct vicarious states using multimodal measurements to further advance our understanding of these processes.

Familiarity From Facial Appearance Leads to Hypoalgesia.

Social context has been shown to influence pain perception. This study aimed to broaden this literature by investigating whether relevant social stimuli, such as faces with different levels of intrinsic (based on physical resemblance to known individuals) and episodic (acquired through a previous experience) familiarity, may lead to hypoalgesia. We hypothesized that familiarity, whether intrinsic or acquired through experience, would increase pain threshold and decrease pain intensity. Sixty-seven participants underwent pain induction (the cold pressor test) viewing previously seen faces (Episodic Group) or new faces (Non-episodic Group) that differed in the level of intrinsic familiarity (high vs low). Pain threshold was measured in seconds, while pain intensity was measured on a rating scale of 0 to 10. The results did not show an effect of episodic familiarity. However, compared to low, high intrinsic familiar faces had an attenuating effect on pain intensity, even after controlling for pain expectation. These results suggest that physical features conveying a higher feeling of familiarity induce a top-down hypoalgesic modulation, in line with the idea that familiarity may signal safety and that the presence of familiar others reduce perceived threat-related distress. This study provides further evidence on the social modulation of pain and contributes to the literature on first impressions' influence on social behavior. PERSPECTIVE: Consistent with the idea that familiar others signal safety and reduce the sense of threat, facial features conveying familiarity induce a top-down hypoalgesic modulation. This knowledge may contribute to understanding differences in pain perception in experimental and clinical contexts.

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.

Children's experiences of intravenous injection using the draw, write, and tell method: A mixed-methods study.

PURPOSES: This study aimed to explore children's perceptions and experiences of receiving intravenous (IV) injections and the self-reported pain scores and management strategies that can support children while receiving IV injections. DESIGN AND METHODS: This mixed-methods study included 17 children aged 4-11 years who presented to the outpatient clinic of a pediatric hospital and received IV injections. Data were collected using the draw, write, and tell method (DWT) and Facial Pain Rating Scale. Descriptive statistics and content analyses were performed. RESULTS: The children's self-reported mean pain score was 4.82, indicating moderate pain. Many expressions indicated that IV injections were painful or caused tingling or stinging sensations. A vague fear of needles in addition to pain was identified after listening to the children and analyzing their own interpretation of drawings. Three main themes were identified: (1) physical and emotional experiences, (2) parents as my secure base, and (3) comfort and relief strategies. CONCLUSIONS: Children expressed their experiences during IV injections, the alleviation of their pain and fear, and their suggestions for comfort and relief strategies visually, auditorily, and verbally. Parents played an important role in supporting their children and reducing pain, anxiety, and distress related to the IV procedure. PRACTICE IMPLICATIONS: The DWT, as an arts-based and child-centered approach, is a useful and valid method to understand children's experience related to the IV injection. Children experience comfort and relief within a family-centered care context during IV injection. Nurses should promote children's and parents' participation in the development of strategies to reduce the negative effects of IV injections in children.

Children's experiences of stress and coping during hospitalization: A mixed-methods examination.

Children often experience hospitalization as stressful. To better understand children's experiences, this current study involved interviews with and assessments of 17 children who were currently admitted at a U.S. children's hospital. On average, they reported low levels of distress on the Facial Affective Scale (FAS) (M = .34) and moderate levels of anxiety on the Child Drawing: Hospital (M = 107.01). Results revealed themes in children's experiences including stressors in the hospital, such as pain, disruptions to normalcy, and uncertainty. Children also reported factors that contributed to coping, including social support from parents and peers, and distractions from the medical routine such as leaving their hospital room. When children were grouped into clusters based on coping, those who were younger and who had received child life specialist services tended to be coping well. Regardless of understanding of diagnosis, those who demonstrated high levels of stress (distress and anxiety) in assessments tended to be categorized as not coping well. The findings inform interventions to support children's coping during hospitalization.

Pain E-motion Faces Database (PEMF): Pain-related micro-clips for emotion research.

A large number of publications have focused on the study of pain expressions. Despite the growing knowledge, the availability of pain-related face databases is still very scarce compared with other emotional facial expressions. The Pain E-Motion Faces Database (PEMF) is a new open-access database currently consisting of 272 micro-clips of 68 different identities. Each model displays one neutral expression and three pain-related facial expressions: posed, spontaneous-algometer and spontaneous-CO2 laser. Normative ratings of pain intensity, valence and arousal were provided by students of three different European universities. Six independent coders carried out a coding process on the facial stimuli based on the Facial Action Coding System (FACS), in which ratings of intensity of pain, valence and arousal were computed for each type of facial expression. Gender and age effects of models across each type of micro-clip were also analysed. Additionally, participants' ability to discriminate the veracity of pain-related facial expressions (i.e., spontaneous vs posed) was explored. Finally, a series of ANOVAs were carried out to test the presence of other basic emotions and common facial action unit (AU) patterns. The main results revealed that posed facial expressions received higher ratings of pain intensity, more negative valence and higher arousal compared with spontaneous pain-related and neutral faces. No differential effects of model gender were found. Participants were unable to accurately discriminate whether a given pain-related face represented spontaneous or posed pain. PEMF thus constitutes a large open-source and reliable set of dynamic pain expressions useful for designing experimental studies focused on pain processes.

Investigating the relationship between pain indicators and observers' judgements of pain.

BACKGROUND: Due to the inherent subjectivity of pain, it is difficult to make accurate judgements of pain in others. Research has found discrepancies between the ways in which perceived "objective" (e.g., medical evidence of injury) and "subjective" information (e.g., self-report) influence judgements of pain. This study aims to explore which potential cues (depictions of sensory input, brain activation, self-reported pain and facial expressions) participants are most influenced by when evaluating pain in others. METHODS: First, 60 participants (23 women, 36 ± 10 years old) judged who was in more pain between two different pain indicators representing two different patients. These trials revealed which congruent indicator (i.e., two high pain indicators) would most influence participant decisions. Second, participants prescribed quantities of analgesia for one patient's pain based on two different pain indicators. These trials revealed which incongruent indicators (i.e., one high and one low indicator) would most influence participant decisions. RESULTS: As predicted, facial expressions were perceived as subjective and were the least likely, among all pain indicators, to influence observer's judgements of pain. Participants relied upon indicators they perceived as objective. Self-report pain ratings had the greatest influence on participants judgements about how much analgesic cream to prescribe and was perceived as objective by half of the participants. CONCLUSIONS: We found that in situations where incongruent information was presented about an individual's pain, participants relied on pain indicators that they perceived to be objective. The current study provides important insights about biases that people hold when making judgements of pain in others. SIGNIFICANCE: Interpretation and assessment of pain remains one of the largest barriers to pain management and involves complex, idiosyncratic processing. This study provides insights into what information participants view as critical in making attributions of pain when presented with multiple, seemingly incongruent sources of information.

Psychiatric symptoms and pain in maxillofacial injury following motor vehicle accidents: A comparative study.

BACKGROUND/AIM: Post-traumatic stress disorders, depression, and pain are rarely discussed in the literature on maxillofacial injuries, and psychiatric symptoms and pain are not identified and managed in such patients. The aim of this study was to determine the symptoms of post-traumatic stress disorders, depression, and pain in people with maxillofacial injuries following motor vehicle accidents. MATERIAL AND METHODS: In this cross-sectional study, people injured in motor vehicle accidents from March to September 2015 who were referred to a medical educational center in the northern part of Iran for treatment follow-up were sampled. The existing symptoms of post-traumatic stress disorder by PSS, depression by BDI-II, and pain by NRS were assessed. SPSS software version 21 was used for analysis. RESULTS: Maxillofacial injured patients had significant differences in terms of post-traumatic stress disorder (p = .006), depression (p = .001), pain (p = .001), and length of hospital stay (p = .002) than patients without maxillofacial injuries. CONCLUSIONS: Motor vehicle accident victims with maxillofacial injuries suffered significantly more from post-traumatic stress disorders and depression, pain and length of hospital stay than patients with other injuries.

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.

The Effect of Cognitive Strategies and Facial Attractiveness on Empathic Neural Responses.

Empathy is a phenomenon that brings together both emotions and an understanding of another person. Recent studies have disentangled the mechanisms of empathy into emotional and cognitive aspects. Event-related potential (ERP) studies suggest that emotional empathy is related to the modulation of the amplitude of early ERPs, and cognitive empathy is linked to later ERPs. In the current study, we examined the influences of facial attractiveness on empathic response and the effect of cognitive strategies with setting the participants' attention to attractiveness or pain. Participants (N= 19) viewed photos of physically attractive and unattractive men and women receiving painful stimulation. The amplitude of the N2 component measured at the frontal regions was more negative in painful stimulation compared to the non-painful, but only for attractive faces. There were no differences between painful and non-painful stimulation for unattractive faces. The amplitude of the P3 measured at the central-parietal region component was more positive in the painful condition compared to the non-painful one, but only when participants performed a pain judgment task. There were no differences in the attractiveness judgment task. This study showed that the attractiveness of a model and drawing the participants' attention to pain constitute an essential modulator of pain empathy.

Processing of Facial Expressions of Emotions and Pain in Alzheimer's Disease.

BACKGROUND: Alzheimer's disease (AD) is a neurodegenerative pathology that disrupts processing of facial expressions of emotion. The impairment was demonstrated for negative emotions in tasks of matching, discriminating, and labeling facial expressions but no study has included the expression of pain in its protocol. OBJECTIVE: The objective was to study the processing of emotional facial expressions in AD with a particular interest in pain expression. METHODS: Twenty-seven controls, 15 mild AD patients, and 15 moderate AD patients had to perform four emotional tasks: identification of facial expressions, matching pain expressions, discriminating the intensity of pain expressions, and judging pain intensity. RESULTS: Some emotions were less efficiently recognized by AD patients compared to controls (p < 0.001), specifically fear from the mild stage (p < 0.05), pain and disgust from the moderate stage (p < 0.05 and p < 0.001 respectively). The Exploratory Factor Analysis showed that recognition of pain and recognition of other discreet emotions were underpinned by two different latent factors. Performances on pain expression matching task and pain intensity discrimination task did not differ by group. (p = 0.334 and p = 0.787 respectively). Finally, moderate AD patients judged the pain less intensively than the Control group for both, moderate, and severe pain intensity (p < 0.001). CONCLUSION: Our data suggest that AD disrupts the recognition of pain expression along with recognition of fear and disgust. Additionally, AD patients seem to underestimate pain intensity compared to controls. The self-rated pain scales should be adapted to the pain processing deficit of AD patients.

Automated recognition of pain in cats.

Facial expressions in non-human animals are closely linked to their internal affective states, with the majority of empirical work focusing on facial shape changes associated with pain. However, existing tools for facial expression analysis are prone to human subjectivity and bias, and in many cases also require special expertise and training. This paper presents the first comparative study of two different paths towards automatizing pain recognition in facial images of domestic short haired cats (n = 29), captured during ovariohysterectomy at different time points corresponding to varying intensities of pain. One approach is based on convolutional neural networks (ResNet50), while the other-on machine learning models based on geometric landmarks analysis inspired by species specific Facial Action Coding Systems (i.e. catFACS). Both types of approaches reach comparable accuracy of above 72%, indicating their potential usefulness as a basis for automating cat pain detection from images.

Central nervous activity during a dot probe task with facial expressions in fibromyalgia.

Fibromyalgia syndrome (FMS) is a chronic pain condition accompanied by affective symptoms and cognitive impairments. This study investigated central nervous correlates of attentional and emotional processing in FMS. Therefore, event-related potentials were recorded in 26 FMS patients and 26 healthy controls during a dot probe task, which required participants to decide which side of the screen an asterisk was displayed on; the asterisk was immediately preceded by a facial expression (anger, pain, happiness, neutral) on the left or right side. Comorbid depression was also assessed. In patients, N170 amplitude was smaller for anger and pain expressions than for happy expressions, and P2 was greater for pain expressions than for happy expressions. N170 and P2 were unaffected by emotional expressions in controls. LPC was smaller overall in patients than controls. Though reaction times were longer overall in patients than controls, no behavioral effects of emotional stimuli arose in these groups. In contrast, FMS patients with comorbid depression showed less attentional interference due to emotional expressions, and less difficulty disengaging from these stimuli than patients without depression. While the observations concerning N170 suggested facilitated encoding of facial features representing negative rather than positive emotions in FMS and more automatized processing of pain expressions, those for P2 indicated increased attentional resource allocation to pain-related information. Reduced LPC reflects nonspecific deficits in sustained attention in FMS, which is in line with the longer reaction times. Behavioral data suggest lower processing depth of emotional information in patients with comorbid depression.

Facial expressions modulate pain perception in patients with chronic migraine.

AIM: First, we investigated whether the exposure to different visual feedback conditions may modulate pain perception by means of visual induced analgesia in patients with chronic migraine. Second, to comprehend the way emotional face expressions could induce visual analgesia, we evaluated the degree of identification with the four experimental conditions. METHODS: In a 1 × 4 within-subject study design, 38 female chronic migraine patients were exposed to different visual stimuli - positive face, neutral face, negative face, and control (white screen) - during a migraine attack. Visual stimuli were presented 3 times in a randomized order (each condition lasted 40 seconds). Migraine pain ratings and identification scores were assessed immediately after the observation of each visual condition. RESULTS: We observed a significant difference in pain ratings between the positive (median: 30, 95% CI 26.69 to 38.20) and the negative (median: 30, 95% CI 33.09 to 44.13) (z = -4.46, p < 0.0001) facial expressions or the neutral facial expression (median: 30, 95% CI 31.89 to 42.41) (z = 3.41, p < 0.001). Participants identified more with the neutral face condition than with the other conditions. CONCLUSIONS: Observation of a positive emotional face resulted sufficient to modulate pain perception possibly via the mediation of emotion regulation for positive emotions. This study paves the way for the integration of new cognitive behavioural interventions based on the adoption of visual induced analgesia to further control pain perception in chronic migraine patients.

Pain processing in older adults with dementia-related cognitive impairment is associated with frontal neurodegeneration.

Experimental pain research has shown that pain processing seems to be heightened in dementia. It is unclear which neuropathological changes underlie these alterations. This study examined whether differences in pressure pain sensitivity and endogenous pain inhibition (conditioned pain modulation (CPM)) between individuals with a dementia-related cognitive impairment (N=23) and healthy controls (N=35) are linked to dementia-related neurodegeneration. Pain was assessed via self-report ratings and by analyzing the facial expression of pain using the Facial Action Coding System. We found that cognitively impaired individuals show decreased CPM inhibition as assessed by facial responses compared to healthy controls, which was mediated by decreased gray matter volume in the medial orbitofrontal and anterior cingulate cortex in the patient group. This study confirms previous findings of intensified pain processing in dementia when pain is assessed using non-verbal responses. Our findings suggest that a loss of pain inhibitory functioning caused by structural changes in prefrontal areas might be one of the underlying mechanisms responsible for amplified pain responses in individuals with a dementia-related cognitive impairment.

Pain modulation by your partner: An experimental investigation from a social-affective perspective.

BACKGROUND: Social context such as the relationship between a person experiencing pain and a caregiver has been shown to affect the experience of pain, yet, results are not consistent. Possibly, differential effects of interpersonal relationships are modulated by affective states expressed by social partners. Viewing partner pictures in experimental designs is not only associated with lowered perceived pain intensity, but also affects neural responses. However, the role of affective modulation is not clear. The present study aimed to systematically examine the pain modulating effects of stimuli varying in affect and social content including personal relevance using subjective report and psychophysiological measures of facial and autonomic activity. METHODS: Twenty-nine women underwent a tonic heat pain paradigm with simultaneous picture viewing to investigate the influence of their partners' faces with a neutral facial expression compared to strangers' happy, angry and neutral facial expressions on pain intensity and accompanying psychophysiological parameters (facial activity: corrugator muscle activity, autonomic activity: skin conductance level, heart rate). In addition to perceived partner support and relationship characteristics, the contribution of the affective value (valence, arousal) of the partner faces to the observed pain modulation was examined. RESULTS: Partner and happy faces reduced self-reported pain intensity and corrugator activity, the latter being lowest when viewing partner faces as compared to all other picture categories. As corrugator activity is indexing stimulus unpleasantness and a core feature of the facial pain expression, this physiological pattern matches well with the subjective ratings. Neutral objects, neutral and angry faces had no effect on pain self-report, although angry faces were rated as highly negative. Partner faces also led to increased skin conductance, being an index of motivational activation, and heart rate deceleration, possibly reflecting increased sensory intake. Partner-related pain modulation was primarily related to perceived arousal of the partner's picture, i.e., the intensity of the activation of approach motivation, and pain-related catastrophizing. DISCUSSION: Our results are partially consistent with emotional pain control models, especially regarding the modulatory influence of valence. Within the context of socially adaptive behavior, they particularly underline the social signal value of emotion and attachment figures. Clinically, our results imply that just looking at pictures of one's partner when undergoing acute painful procedures can have a robust hypoalgesic effect.

Pain Behaviors and Pharmacological Pain Management Among Newly Admitted Nursing Home Residents.

BACKGROUND: Clinicians may place more weight on vocal complaints of pain than the other pain behaviors when making decisions about pain management. OBJECTIVES: We examined the association between documented pain behaviors and pharmacological pain management among nursing home residents. METHODS: We included 447,684 residents unable to self-report pain, with staff-documented pain behaviors (vocal, nonverbal, facial expressions, protective behaviors) and pharmacological pain management documented on the 2010-2016 Minimum Data Set 3.0. The outcome was no pharmacological pain medications, as needed only (pro re nata [PRN]), as scheduled only, or as scheduled with PRN medications. We estimated adjusted odds ratios and 95% confidence intervals from multinomial logistic models. RESULTS: Relative to residents with vocal complaints only, those with one pain behavior documented (i.e., nonverbal, facial, or protective behavior) were more likely to lack pain medication versus scheduled and PRN medications. Residents with multiple pain behaviors documented were least likely to have no treatment relative to scheduled with PRN medications, PRN only, or scheduled only pain medication regimens. DISCUSSION: The type and number of pain behaviors observed are associated with pharmacological pain management regimen. Improving staff recognition of pain among residents unable to self-report is warranted in nursing homes.

Effect of transportation and social isolation on facial expressions of healthy horses.

Horses have the ability to generate a remarkable repertoire of facial expressions, some of which have been linked to the affective component of pain. This study describes the facial expressions in healthy horses free of pain before and during transportation and social isolation, which are putatively stressful but ordinary management procedures. Transportation was performed in 28 horses by subjecting them to short-term road transport in a horse trailer. A subgroup (n = 10) of these horses was also subjected to short-term social isolation. During all procedures, a body-mounted, remote-controlled heart rate monitor provided continuous heart rate measurements. The horses' heads were video-recorded during the interventions. An exhaustive dataset was generated from the selected video clips of all possible facial action units and action descriptors, time of emergency, duration, and frequency according to the Equine Facial Action Coding System (EquiFACS). Heart rate increased during both interventions (p<0.01), confirming that they caused disruption in sympato-vagal balance. Using the current method for ascribing certain action units (AUs) to specific emotional states in humans and a novel data-driven co-occurrence method, the following facial traits were observed during both interventions: eye white increase (p<0.001), nostril dilator (p<0.001), upper eyelid raiser (p<0.001), inner brow raiser (p = 0.042), tongue show (p<0.001). Increases in 'ear flicker' (p<0.001) and blink frequency (p<0.001) were also seen. These facial actions were used to train a machine-learning classifier to discriminate between the high-arousal interventions and calm horses, which achieved at most 79% accuracy. Most facial features identified correspond well with previous findings on behaviors of stressed horses, for example flared nostrils, repetitive mouth behaviors, increased eye white, tongue show, and ear movements. Several features identified in this study of pain-free horses, such as dilated nostrils, eye white increase, and inner brow raiser, are used as indicators of pain in some face-based pain assessment tools. In order to increase performance parameters in pain assessment tools, the relations between facial expressions of stress and pain should be studied further.