In previous studies, emotion generated by a picture-viewing protocol has been shown to reliably modulate pain and physiological nociceptive reactions. The present study used 7 picture contents (mutilation, attack, death/grieving, neutral, families, sports/adventure, erotica) that ranged in valence (unpleasant to pleasant), as well as in arousal (low to high), to determine how each emotional category regulates pain/nociception. Participants (N = 114) viewed a total of 108 pictures presented in pseudorandom order. During 1/3 of the pictures, noxious electrocutaneous stimuli were delivered to the sural nerve to elicit pain and nociceptive responding. Immediately following each picture, participants rated emotional reactions along the dimensions of emotional valence and arousal. After each noxious stimulus, participants rated their subjective pain sensation and physiological nociceptive reactions (nociceptive flexion reflex, heart rate acceleration, skin conductance response) were recorded. All procedures were IRB approved. As expected, relative to neutral pictures, unpleasant pictures led to greater displeasure and pleasant pictures lead to greater pleasure. Moreover, there was significant variability in reported arousal from unpleasant contents (mutilation >attack > death) and pleasant contents (erotica > adventure > families). The most reliable modulation of pain and nociceptive reactions occurred during the most emotionally intense pictures: greatest facilitation of pain and nociceptive reactions occurred during mutilation pictures and the greatest inhibition occurred during erotic pictures. These results support past research, suggesting that the ECON paradigm is a valid and reliable methodology for studying emotional modulation of pain and nociception. This study extends that work by demonstrating that mutilation and erotica are the categories that elicit the strongest emotional modulation. Implications for future research are discussed. (This research was funded by a health research grant from the Oklahoma Center for the Advancement of Science and Technology.) In previous studies, emotion generated by a picture-viewing protocol has been shown to reliably modulate pain and physiological nociceptive reactions. The present study used 7 picture contents (mutilation, attack, death/grieving, neutral, families, sports/adventure, erotica) that ranged in valence (unpleasant to pleasant), as well as in arousal (low to high), to determine how each emotional category regulates pain/nociception. Participants (N = 114) viewed a total of 108 pictures presented in pseudorandom order. During 1/3 of the pictures, noxious electrocutaneous stimuli were delivered to the sural nerve to elicit pain and nociceptive responding. Immediately following each picture, participants rated emotional reactions along the dimensions of emotional valence and arousal. After each noxious stimulus, participants rated their subjective pain sensation and physiological nociceptive reactions (nociceptive flexion reflex, heart rate acceleration, skin conductance response) were recorded. All procedures were IRB approved. As expected, relative to neutral pictures, unpleasant pictures led to greater displeasure and pleasant pictures lead to greater pleasure. Moreover, there was significant variability in reported arousal from unpleasant contents (mutilation >attack > death) and pleasant contents (erotica > adventure > families). The most reliable modulation of pain and nociceptive reactions occurred during the most emotionally intense pictures: greatest facilitation of pain and nociceptive reactions occurred during mutilation pictures and the greatest inhibition occurred during erotic pictures. These results support past research, suggesting that the ECON paradigm is a valid and reliable methodology for studying emotional modulation of pain and nociception. This study extends that work by demonstrating that mutilation and erotica are the categories that elicit the strongest emotional modulation. Implications for future research are discussed. (This research was funded by a health research grant from the Oklahoma Center for the Advancement of Science and Technology.)

Across 3 independent studies our laboratory has shown that emotional pictures reliably modulate pain and physiological nociceptive reactions (nociceptive flexion reflex [NFR], heart rate [HR] acceleration, skin conductance response [SCR]), a procedure referred to as emotional controls of nociception (ECON). Pain and nociception are inhibited by arousing, pleasant pictures and enhanced by arousing, unpleasant pictures. As a result, we have argued that the ECON methodology is a reliable way to study supraspinal modulation of pain. However, it is unclear whether habituation of pain-related responses confounds this interpretation of emotional modulation, given that multiple noxious stimuli are delivered during picture-viewing. For the present study (N = 114 healthy participants), 108 emotional pictures were presented in 4 blocks of 27 pictures that were balanced for picture valence (9 pleasant, 9 neutral, and 9 unpleasant). During each block, 9 noxious electric stimulations were delivered to elicit pain responses (3 per picture valence). Pain responses were averaged by picture valence and block, then analyzed using 3 (Picture Valence) x 4 (Picture Block) ANOVAs. All procedures were IRB approved. Significant main effects of Picture Valence suggest emotion modulated pain and nociceptive reactions as predicted: pleasant pictures decreased pain/nociception and unpleasant pictures increased pain/nociception. The main effect of Block was only noted for NFR and HR, suggesting significant habituation over time for these measures. However, the Picture Valence x Picture Block interaction was non-significant for all responses. These results suggest habituation is not a significant problem for assessing emotional modulation of pain/nociception, as long as the picture presentation design takes into account NFR and HR response habituation. (This work was supported by a health research grant from the Oklahoma Center for the Advancement of Science and Technology (OCAST).)

Relative to men, women report clinical pain more frequently, with longer duration, and greater severity, as well as higher sensitivity to some forms of experimental pain. Although the mechanisms underlying these sex differences are likely to be manifold, sex differences in emotional modulation of pain may contribute. Indeed, sex differences in the experience and processing of emotion have been observed, and emotional processes are known to modulate pain, such that negative emotions enhance pain and positive emotions inhibit pain. In the present study (N = 114), emotionally-charged pictures of different contents (mutilation, attack scenes, death/grieving, neutral, families, adventure, erotica) were presented, during which electrocutaneous stimuli were delivered to elicit pain and the nociceptive flexion reflex (NFR, a physiological measure of spinal nociception). To assess the influence of emotion on nociceptive processing, pain responses were averaged by picture content and analyzed. Additionally, participants rated their emotional reactions to each picture to determine whether there were sex differences in emotional experience. All procedures were IRB approved. Consistent with previous research, results suggested there were sex differences in subjective emotional reactions to the pictures. Relative to men, women rated pictures of families as more pleasurable and pictures of erotica as less pleasurable. Also, women reported higher subjective pain ratings to the electrocutaneous stimuli than men. However, there were no sex differences in emotional modulation of pain and nociception. In both sexes, mutilation pictures enhanced pain ratings and NFR, and erotic pictures inhibited pain ratings and NFR. These results suggest that sex differences may exist in the subjective experience of emotionally-charged visual stimuli, but this does not influence how emotion modulates nociceptive processes. (This work was supported by a health research grant from the Oklahoma Center for the Advancement of Science and Technology (OCAST).)

Advanced age is associated with increased pain. While a number of mechanisms can play a role in enhanced pain in older adults, the contribution of pain regulatory mechanisms is poorly understood. Our laboratory has developed procedures to reliably test supraspinal modulation of pain by emotional processes, a procedure called emotional controls of nociception (ECON). The procedure involves presenting emotionally-charged pictures (unpleasant, neutral, pleasant) during which noxious electrocutaneous stimuli are delivered to the sural nerve to elicit pain and the nociceptive flexion reflex (NFR, a physiological measure of spinal nociception). This research has shown that unpleasant pictures enhance, whereas pleasant pictures inhibit pain and nociception. In the current study (N = 114; mean age = 35 yrs, range = 18-83), 108 pictures were presented from 7 emotional contents (mutilation, attack scenes, death/grieving, neutral, families, adventure, erotica) to manipulate emotion. After each picture, participants rated their subjective emotional reaction. Noxious stimuli were administered during 1/3 of the pictures and were distributed equally across picture contents. All procedures were IRB approved. Pain responses were averaged by picture content to assess emotional modulation. Tertiles were used to form 3 age groups. Results suggested emotion was manipulated as expected: mutilation, attack, and death/grieving pictures were rated as unpleasant, and erotica, adventure, and family pictures were rated as pleasant across all age groups. However, older participants rated pleasant contents as more pleasurable than younger participants. Despite the age difference in emotional reactions, age did not influence emotional modulation of pain. Regardless of age, mutilation pictures enhanced pain and NFR, whereas erotic pictures inhibited pain and NFR. These findings suggest that age-related changes in pain may not be mediated by differences in this form of supraspinal modulation. (This work was supported by a health research grant from the Oklahoma Center for the Advancement of Science and Technology.)

Recent evidence suggests the relationship between pain catastrophizing and experimental pain may depend on when catastrophizing is assessed. Specifically, catastrophizing measured during or after pain testing better predicts pain outcomes than catastrophizing measured before pain testing. This study assessed pain catastrophizing from subscales (rumination, magnification, helplessness) of the Pain Catastrophizing Scale (PCS) in 30 participants before and after pain testing. Electrodermal stimuli were delivered over the sural nerve to assess nociceptive flexion reflex (NFR) threshold, pain threshold, and pain tolerance. Three ascending-descending series of stimuli were first delivered to assess NFR threshold, followed by a short break, and then the stimuli were increased until pain tolerance was reached (or 40 mA maximum). Following every stimulus, participants rated their subjective reaction on a 0 (no sensation) to 100 (maximum tolerable) scale in which pain was anchored at 50. In the last ascending series, pain threshold was defined as the stimulus intensity that was rated 50, and pain tolerance was the stimulus intensity rated 100. Immediately following pain testing, participants also rated their overall subjective pain using the McGill Pain Questionnaire-short form (MPQ-SF). All procedures were IRB approved. Results suggested PCS subscale means were similar pre- and post-test (ps>.65); however, test-retest correlations were non-significant (rs= -.02 to .07, ps>.71). Moreover, most relationships between PCS subscales and pain outcomes were only significant for catastrophizing assessed post-pain-testing. Post-test rumination, magnification, and helplessness were associated with MPQ-SF ratings, and post-test magnification was associated with pain threshold and tolerance (ps<.05). Surprisingly, pre-test helplessness was positively correlated with NFR threshold and negatively correlated with MPQ-SF affective ratings (ps<.05). These results contribute to the growing literature suggesting the relationships between pain catastrophizing and experimental pain depend on the timing of assessment. This research was supported by an Oklahoma Center for the Advancement of Science and Technology grant. Recent evidence suggests the relationship between pain catastrophizing and experimental pain may depend on when catastrophizing is assessed. Specifically, catastrophizing measured during or after pain testing better predicts pain outcomes than catastrophizing measured before pain testing. This study assessed pain catastrophizing from subscales (rumination, magnification, helplessness) of the Pain Catastrophizing Scale (PCS) in 30 participants before and after pain testing. Electrodermal stimuli were delivered over the sural nerve to assess nociceptive flexion reflex (NFR) threshold, pain threshold, and pain tolerance. Three ascending-descending series of stimuli were first delivered to assess NFR threshold, followed by a short break, and then the stimuli were increased until pain tolerance was reached (or 40 mA maximum). Following every stimulus, participants rated their subjective reaction on a 0 (no sensation) to 100 (maximum tolerable) scale in which pain was anchored at 50. In the last ascending series, pain threshold was defined as the stimulus intensity that was rated 50, and pain tolerance was the stimulus intensity rated 100. Immediately following pain testing, participants also rated their overall subjective pain using the McGill Pain Questionnaire-short form (MPQ-SF). All procedures were IRB approved. Results suggested PCS subscale means were similar pre- and post-test (ps>.65); however, test-retest correlations were non-significant (rs= -.02 to .07, ps>.71). Moreover, most relationships between PCS subscales and pain outcomes were only significant for catastrophizing assessed post-pain-testing. Post-test rumination, magnification, and helplessness were associated with MPQ-SF ratings, and post-test magnification was associated with pain threshold and tolerance (ps<.05). Surprisingly, pre-test helplessness was positively correlated with NFR threshold and negatively correlated with MPQ-SF affective ratings (ps<.05). These results contribute to the growing literature suggesting the relationships between pain catastrophizing and experimental pain depend on the timing of assessment. This research was supported by an Oklahoma Center for the Advancement of Science and Technology grant.

Traditionalism is a personality trait associated with conformity, conventionality, and authoritarian beliefs and attitudes. People who score high in Traditionalism also tend to endorse religion, oppose permissive attitudes, and condemn selfishness. The present study assessed the influence of Traditionalism on electrodermal pain threshold, pain tolerance, nociceptive flexion reflex (NFR) threshold, and subjective pain report. To do so, electrodermal stimuli were delivered over the sural nerve in 30 participants. Following every stimulus, participants rated their subjective reaction on a 0 (no sensation) to 100 (maximum tolerable), with pain threshold defined by a rating of 50. Three ascending-descending series of stimuli were delivered to assess NFR threshold. After a short break, a fourth ascending series was delivered until the participant rated the stimulus as 100 (or until the 40 mA maximum was reached). In the last ascending series, pain threshold was defined as the intensity of the stimulus that was first rated ≥50, and pain tolerance was the intensity of the stimulus rated 100 (or 40 mA if max reached). After the completion of pain testing, participants used the McGill Pain Questionnaire-short form to rate their sensory and affective pain in response to testing, and then filled out the Multidimensional Personality Questionnaire to assess Traditionalism and social desirability. All procedures were approved by the IRB. Results suggest Traditionalism was negatively associated with pain threshold (r=-.58, p=.001) and tolerance (r=-.46, p=.01) and positively associated with MPQ affective pain ratings (r=.42, p=.02); however, only associations with pain threshold and tolerance were significant after controlling for social desirability. These data suggest Traditionalism is associated with increased pain sensitivity, an effect that is not likely due to descending controls because correlations with the NFR were non-significant. This study was supported by the Oklahoma Center for the Advancement of Science and Technology.

Constraint is a personality trait associated with harm avoidance, high moral standards, and level-headedness; and persons who score high on the Control subscale of Constraint are described as reflective, cautious, careful, and planning. This study assessed the influence of Control on behavioral, physiological, and subjective pain outcomes (electrodermal pain threshold & pain tolerance, nociceptive flexion reflex [NFR] threshold, subjective pain report) in 30 participants. Electric stimuli were delivered over the sural nerve, and after each stimulus participants rated their subjective reaction on a 0 (no sensation) to 100 (maximum tolerable) scale, with pain anchored at 50. First, 3 ascending-descending series of stimuli were delivered to assess NFR threshold, a physiological correlate of spinal nociceptive threshold. After a short break, a fourth ascending series was delivered until tolerance was reached (rating = 100 or 40 mA max reached). In the last ascending series, pain threshold was defined as the stimulus that was first rated ≥50. After pain tolerance was reached, participants rated their sensory and affective pain in response to testing on the McGill Pain Questionnaire-short form, and filled out the Multidimensional Personality Questionnaire to assess Control and social desirability. All procedures were IRB approved. Results suggest Control was positively associated with NFR threshold (r=.38, p=.06) and pain tolerance (r=.45, p=.02), and negatively associated with the subjective ratings of stimuli at NFR threshold (r=-.33, p=.08). When social desirability was controlled using partial correlations, these relationships remained, and a positive correlation with pain threshold was observed (r=.38, p=.05). These data suggest greater Control is associated with reduced pain sensitivity, an effect that is not simply due to social desirability. Furthermore, this relationship may stem from descending modulation, because Control was correlated with NFR threshold. This work was supported by the Oklahoma Center for the Advancement of Science and Technology.

Psychophysiological reactions to noxious stimuli have been used to make inferences about pain. Despite this, there have been few attempts to assess the within-subject covariance between psychophysiological reactions and subjective experience using statistical techniques that adequately control for non-independence of within-subject data, but also examine group-level effects. For the present study, nociceptive flexion reflex (NFR) magnitude, blink reflex (BR) magnitude, skin conductance (SC) change, and heart rate (HR) change to electrodermal stimuli were assessed during ascending-descending progressions of stimuli used to determine NFR threshold and pain tolerance in 27 participants. Ratings of each stimuli were made on a 0 (no sensation) to 100 (maximum tolerable) scale. Hierarchical linear modeling was used to model within-subject relationships between psychophysiological reactions and subjective ratings while controlling for within-subject data non-independence. Data were only included in the analyses if the stimulus elicited at minimum "discomfort" (≥25 on the rating scale). Models were initially constructed with each psychophysiological predictor entered separately. These results were used to guide the construction of a multivariate model that entered predictors in a stepwise method (according to variance explained). All procedures were IRB approved. Results suggested NFR, BR, and HR were significant predictors in the separate models (ps≤.002), explaining 32%, 15%, and 8% of the variance in ratings, respectively. However, only NFR and BR were significant predictors in the multivariate model (ps≤.009), and together explained 44% of the variance. These results suggest that spinal (NFR) and supraspinal (BR) reflexes contribute significantly to the prediction of subjective ratings of electrodermal stimuli. Future studies can use these methods to examine whether the intercepts or slopes (relationships) in the multivariate model are altered by individual differences variables (eg, coping, chronic pain, sex). This research was supported by the Oklahoma Center for the Advancement of Science and Technology.

Research suggests conditioned fear modulates pain. However, it is unknown whether any variables moderate this relationship. Preparedness theory predicts that some conditioned stimuli (CS) are more readily associated with an unconditioned stimulus (US) and lead to more rapid development of the conditioned fear response. Indeed, pictures depicting facial expressions of fear are more readily associated with an aversive shock US and lead to greater conditioned responses than happy expressions. Therefore, different types of CSs may moderate the influence of conditioned fear on pain. The present study used a differential fear conditioning procedure to examine the influence of conditioned fear on pain threshold (latency of finger withdrawal to radiant heat). Facial expressions (happy vs. fear) served as the CSs and aversive electric stimulation of the sural nerve as the US. Forty-one participants were randomly assigned to have either a fear or happy expression as the CS+ (stimulus paired with shock). The other facial expression served as the CS− (stimulus unpaired with shock). During the acquisition phase, each CS was presented in pseudorandom order, and the CS+ was always paired with shock. During the extinction phase, shock was no longer presented and pain threshold was tested during each CS. Psychophysiological and self-report measures of emotion were used to verify participants’ reactions to CSs and results suggest that fear was effectively conditioned. However, only those people for whom the fear expression served as the CS+ evidenced any pain modulation (p=.01), with lower pain thresholds (hyperalgesia) during the CS+ relative to the CS−. People for whom a happy expression served as the CS+ did not have a significant difference in pain thresholds during the CS+ versus the CS− (p>.05). In sum, these data suggest that conditioned fear-induced pain modulation is moderated by the type of conditioned stimuli used.

Our laboratory has shown that emotion modulates spinal nociception and pain resulting from unpredictable noxious shocks. However, unpredictable aversive events have been shown to increase negative affect; therefore, it is unclear what effect this may have on our experimental paradigm. To examine this issue, the present study examined the influence of emotion on pain and spinal nociception (nociceptive flexion reflex, NFR) resulting from predictable or unpredictable noxious shocks to the sural nerve. To induce emotion, 24 emotionally-charged pictures (threat, neutral, & erotic) were presented in random order and shocks were delivered during and in between pictures. NFR amplitudes and pain from shocks were recorded. For half of the participants (n=25) shocks were always preceded by a cue (predictable), the others (n=25) received no cue (unpredictable). Manipulation checks verified that emotion was successfully induced by picture-viewing. Erotic pictures increased positive emotion and threat pictures increased negative emotion. Irrespective of predictability, pain was always inhibited by positive emotion and enhanced by negative emotion. However, emotional modulation of spinal nociception was moderated by shock predictability. When shocks were unpredictable, spinal nociception (NFR) was modulated in parallel with pain ratings. However, when shocks were predictable, the NFR was unaffected by emotion – an effect that was not due to complete inhibition of the NFR because the NFR was still observed. However, during predictable shocks the NFR did not covary with emotion. These data replicate our prior work demonstrating that emotion can engage descending modulation of spinal nociception when shocks are unpredictable. Extending that research, this study suggests that emotional modulation of spinal nociception is abolished when the noxious stimulus is unpredictable. Subjective pain is modulated by emotion irrespective of predictability. These data imply that separate mechanisms are responsible for emotional modulation of spinal nociception and evaluative pain, and predictability disengages modulation at spinal levels.

Catastrophizing has been found to correlate with pain report, but not nociceptive flexion reflex (NFR) threshold suggesting catastrophizing does not engage descending modulation of spinal nociception (France et al., 2002, Pain). However, recent evidence suggests that in-vivo assessment of catastrophizing (assessed during or just following rather than before the noxious event) is a better predictor of pain outcomes (Edwards et al., 2005, J Pain). Given that France et al. assessed catastrophizing prior to the noxious event, it is unclear whether in-vivo catastrophizing is associated with spinal nociception. To examine this issue, we combined data from two recent NFR studies conducted by our laboratory. Every participant (N=78) filled out questionnaires assessing depression, self-efficacy for pain, and current mood before noxious stimulation. Then, NFR threshold and pain ratings were assessed by noxious electric stimulation to the sural nerve. NFR threshold was defined as the stimulus intensity that elicited a withdrawal response in the ipsilateral biceps femoris muscle. Pain ratings of threshold-level stimuli were assessed using a numerical rating scale (NRS). Catastrophizing was assessed following the NFR assessment using the Coping Strategies Questionnaire (CSQ). NFR threshold and pain ratings were predicted from catastrophizing scores using hierarchical regression analyses that controlled for gender, self-efficacy, depression, and current mood. Results are consistent with the findings of France et al. suggesting that catastrophizing predicts pain ratings (R square change=.07, p=.02; Beta=.290), but not NFR threshold (R square change=.003, p=.62, Beta=.063). No other predictors were significant in either model (ps>.25). Therefore, in-vivo catastrophizing does not appear to engage descending modulation of spinal nociception.

Prior work suggests that emotion can modulate pain. Consistent with the motivational priming theory (MPT), stimuli that lead to appetitive activation and positive affect inhibit pain; whereas stimuli that lead to defensive activation and negative affect enhance pain. However, research examining this issue has relied on voluntary measures of pain (withdrawal, self-report) that may be susceptible to response bias. To overcome this issue, the nociceptive flexion reflex (NFR), an involuntary, pain-related reflex can be examined. Additionally, using the NFR will determine whether emotion can modulate a spinally-mediated measure of pain--an assertion that lacks direct testing in humans. The present study was designed to examine the effect of experimentally-induced emotion on the nociceptive flexion reflex (NFR) and pain intensity ratings—spinal and supraspinal measures of pain, respectively. To do so, 28 participants viewed images from the International Affective Picture System (IAPS) that varied in emotional valence (unpleasant, neutral, pleasant) and electric stimulations were randomly delivered to the sural nerve during and in between pictures. Biceps femoris EMG resulting from the stimulations was used to quantify the NFR, while visual analog scale (VAS) pain intensity ratings to the stimulations were used to measure subjective pain. Psychophysical and self-report manipulation checks suggested that IAPS stimuli effectively manipulated emotion. Moreover, picture viewing modulated NFR magnitude and pain ratings in a parallel manner. Specifically, unpleasant pictures were associated with larger NFR magnitude and increased pain, whereas pleasant pictures were associated with smaller NFR magnitude and decreased pain. Results are discussed in light of the MPT and the implications for studying pain modulation.