Anxiety sensitivity, cognitive biases, and the experience of pain

Anxiety Sensitivity, Cognitive Biases, and the Experience of Pain Edmund Keogh and Mary Cochrane Abstract: It is becoming increasingly apparent that the tendency to be fearful of anxiety-related sensations, known as anxiety sensitivity, is closely associated with pain experiences. The aim of the current study was to determine the mechanisms by which such a relationship exists. Selective attentional and interpretative biases for negative material were compared as potential mediators of the anxiety sensitivity–pain relationship. With the cold pressor task, the current study found that high anxiety sensitivity participants exhibited a greater interpretative bias and reported more negative pain experiences than those low in anxiety sensitivity. A negative interpretative bias was also related to higher affective pain experiences. Most important, however, was that the tendency to misinterpret innocuous bodily sensations related to panic was found to mediate the association between anxiety sensitivity and affective pain experiences. These findings not only confirm that anxiety sensitivity plays an important role in the perception of experimental pain but also identify a potential cognitive mechanism by which this relationship exists. © 2002 by the American Pain Society Key words: Pain, anxiety sensitivity, cold pressor, cognitive bias, panic.

A

nxiety sensitivity has recently emerged as an important vulnerability factor in the experience of pain.1,7 Anxiety sensitivity is defined as a trait tendency to be fearful of anxiety-related sensations and is characterized by a belief that such sensations are signs of danger, eg, a rapidly beating heart is interpreted as a sign of an impending heart attack.49,53 Although research indicates that anxiety sensitivity may underpin a wide range of conditions including panic disorder,16,54 hypochondriasis,40 asthma,11 and posttraumatic stress disorder,6 evidence also suggests that anxiety sensitivity is intrinsically related to the experience of pain. For example, anxiety sensitivity has been implicated in a wide range of pain-related disorders, including musculoskeletal pain, recurring headaches, and gastrointestinal disorder.3,8,39,47 Furthermore, anxiety sensitivity has been found to exacerbate the fear of pain,5 lead to the adoption of negative coping strategies,9 and has been implicated in psychopathologic responses to painful events.6 More recently, Muris et al38 have shown anxiety sensitivity to be important in the pain experiences of adolescents, indicating the growing breadth of investigation into this relationship. Perhaps the most convincing evidence that anxiety sensitivity acts as a vulnerability factor to negative pain experiences comes from studies that use experimental pain induction techniques on healthy participants. Such Received October 29, 2001; Revised December 27, 2001; Accepted December 27, 2001 From the Department of Psychology, Goldsmiths College, University of London, UK. Address reprint requests to Edmund Keogh, Department of Psychology, Goldsmiths College, University of London, New Cross, London, SE14 6NW, United Kingdom. E-mail: [email protected] © 2002 by the American Pain Society 1526-5900/2002 $35.00/0 doi:10.1054/jpai.2002.125182

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experimental studies offer a means of disentangling anxiety sensitivity from the experience of pain, which is difficult to achieve with clinical groups.2,26,29 Keogh and Birkby26 found that women with high anxiety sensitivity reported higher sensory pain scores to cold pressor pain when compared to those with low anxiety sensitivity. In a follow-up study, Keogh and Mansoor29 found that participants with high anxiety sensitivity reported higher levels of sensory and affective pain. Taken together, these 2 studies not only suggest that anxiety sensitivity is closely related to negative pain experiences but also indicate that anxiety sensitivity may predispose otherwise healthy individuals toward more negative responses to painful events. Although a link has now been established between anxiety sensitivity and pain, what is not so clear is the reason why such a relationship exits. One potential mechanism that may mediate the anxiety sensitivity– pain relationship is an information processing system that is biased in favor of negative material. We shall now outline the rationale for this belief. It is now widely accepted that negative emotions, such as anxiety and depression, are characterized by negative processing biases.23,33,56,57 The general pattern seems to be that anxiety is associated with a negative attentional and interpretative bias, whereas depression is associated with a negative memory bias. It is also believed that not only are clinical mood states maintained by such biased cognitive processing, but that there exists similar biases in nonclinical groups, which may reflect a latent vulnerability toward negative emotions. Given that pain patients often report high levels of both anxiety and depression, it is likely that they will also exhibit cognitive processing biases. If so, then it is possible that such biases in otherwise healthy individuals may reflect a greater proneness toward extreme negative responses to pain.

The Journal of Pain, Vol 3, No 4 (August), 2002: pp 320-329

ORIGINAL REPORT/Keogh and Cochrane Evidence that pain patients exhibit such cognitive biases, and that they are dependent on emotional state, is now coming to light.19,42,55 However, although there is good evidence to suggest that such biases play a role in pain perception, the relatively general nature of such research means that specific predictions cannot easily be made. Most research has investigated specific memory biases45,60 and found that pain patients selectively recall more negative information, especially if depressed.22,44 Selective attentional biases, which are defined as an increased tendency to direct attentional processes toward the location of negative material, have been investigated to a lesser extent.4,17 Pearce and Morley41 found that compared to healthy control subjects, pain patients displayed increased Stroop interference (ie, distraction) for pain-related words but not for general negative words. Asmundson et al4 found that pain patients with a low fear of anxiety sensations selectively avoided the location of pain stimuli, whereas those high in such fears did not. More recently, Keogh et al28 found that otherwise healthy individuals with a high fear of pain exhibited a selective attentional bias toward pain-related information, whereas those classified as low fearful exhibited avoidance. Interestingly, evidence exists that anxiety sensitivity is also associated with an attentional bias.27,52 Keogh et al27 found that healthy participants with high anxiety sensitivity exhibited a selective attentional bias toward the location of physically threatening material compared to low anxious control subjects, who exhibited cognitive avoidance of such material. This suggests that anxietyrelated attentional biases may reflect a cognitive vulnerability factor toward negative responses to pain among those with a fear of pain-related sensations (although see McNally et al34). Alongside attentional biases, interpretative biases have also been associated with both pain and anxiety sensitivity. Interpretative biases are characterized by the tendency to misinterpret ambiguous events and sensations in a negative manner. The typical procedure is to present words that have ambiguous meanings (eg, the word growth) or when heard aloud have alternative spellings (eg, dye/die) and record how they have been interpreted. As predicted, pain patients make more negative interpretations when compared to non-pain control subjects.21,43,46 As with attentional biases, anxiety sensitivity has also been associated with a tendency to make more negative interpretations of ambiguous stimuli.24,34,50 With the Body Sensations Interpretation Questionnaire (BSIQ; Clark et al, 1997), Keogh and Dillon (unpublished information) found that participants with high anxiety sensitivity ranked negative interpretations of ambiguous scenarios as more likely to come to mind and rated such negative explanations as more believable. This suggests that anxiety sensitivity–related interpretative biases may also reflect a cognitive vulnerability to respond negatively to pain. Taken together, one reason why anxiety sensitivity could be associated with greater negative responses to pain could be due to an increased tendency to orient

321 attentional resources toward pain-related stimuli, as well as to misinterpret innocuous bodily sensations as threatening. However, no known study has directly examined this relationship. The aim of the current study was, therefore, to determine whether cognitive biases mediate the relationship between the anxiety sensitivity and pain experiences.10 As previously mentioned, there are problems disassociating pain from anxiety sensitivity in long-term patients.2,29 Healthy participants who reported no current pain were, therefore, recruited for the current study. Furthermore, because anxiety is typically associated with an attentional and interpretative bias, these 2 paradigms were compared in the current study. Finally, given the relatively exploratory nature of the current study, there are multiple possible combinations of cognitive and bias pain that could prove important. Therefore, only general predictions were made. Specifically, those with high anxiety sensitivity would experience greater cold pressor pain and exhibit a greater cognitive bias in favor of negative material than participants with low anxiety sensitivity; negative cognitive bias would be associated with increased cold pressor pain experiences; and negative cognitive bias would mediate the relationship between anxiety sensitivity and pain experiences.

Material and Methods Design A between-groups design was used. The betweengroups factor was anxiety sensitivity (high versus medium versus low), and the dependent variables consisted of various measures of pain experience (pain tolerance, pain threshold, and self-report measures of pain) and cognitive bias (interpretative bias, attentional bias).

Participants One hundred students were recruited from Goldsmiths College, University of London. There were 81 women and 19 men between 18 and 48 years of age (mean, 24.46 years; standard deviation, 7.04). Age was not recorded for 2 participants. Anxiety sensitivity group was determined from the upper and lower quartile scores of the sampled group on the Anxiety Sensitivity Index (ASI49). Those who scored on or below 8 were classified as low in anxiety sensitivity (mean, 5.95), those who scored above 22 were classified as high in anxiety sensitivity (mean, 30.27), and the remaining as medium anxiety sensitivity (mean, 15.12). These cutoffs are broadly consistent with previous studies that have investigated anxiety sensitivity and pain perception.26,29

Pain Induction Technique Following previous studies,26,29 the cold pressor task was selected as the experimental pain induction technique. Participants were required to place their nondominant hand in an ice-cold water bath for up to 2 minutes. Participants were instructed to concentrate on the cold pain sensations and the emotions it provoked.

322 The cold pressor task allows the measurement of pain threshold, which is the point of just noticeable pain, and pain tolerance, which is the point at which individuals can no longer tolerate pain and as a result withdraw from the noxious stimulus. Following Cioffi and Holloway,13 a measure of recovery from pain was taken from the point at which participants reported the cessation of pain after the cold pressor task. The cold pressor task has previously been found to possess excellent reliability and validity.20,58

Attention Dot-Probe Task The selective attention task used in the current study was a modified version of the visual dot-probe task reported by Keogh et al.27 The main difference was the type of stimuli used. In the current study, stimuli material consisted of 2 word-pair categories: sensory pain-related and affective pain-related. Additional types of emotional stimuli, such as social threat or positive words, were not included in the task because no attentional bias effects toward such stimuli in individuals with high fear of pain were reported by Keogh et al.28 An initial pool of sensory and affective pain-related words were generated from the McGill Pain Questionnaire (MPQ36) and from existing pain-related stimuli generated by Clark et al.15 The pain words were then supplemented with 160 categorized neutral words (household items). All words were then presented to 10 independent judges who rated them on three 7-point scales as to how much they were related to pain (not related to extremely related), the emotionality of the word (neutral to emotional), and the valence of the word (very negative to very positive). On the basis of the mean ratings, 2 sets of 12 pain-related words were generated: 12 associated with the sensory experience of pain (eg, throbbing, shooting) and 12 associated with the affective experience of pain (eg, grueling, tiring). The word groups did not differ significantly with regard to pain, emotionality, or valence ratings (P ⬎ .05). Each pain word was then matched with a neutral word for word frequency by using the word norms and length of Carroll et al.12 Two sets of 12 neutral/neutral word pairs, also matched for length and frequency, were included as filler items (a complete list of words used is presented in Appendix 1). In the dot-probe task, participants were initially presented with a fixation cross in the center of a computer screen for 500 milliseconds. Two words were presented, one above and one below this fixation point. After an additional 500 milliseconds, both words were removed, and in the location of one of the words a small dot appeared. Participants were required to indicate via a key press whether the dot appeared in the upper or lower location. Unknown to participants, on critical trials 1 of the 2 words is emotional and 1 relatively neutral. It is assumed that if attention is directed toward the emotional word, then participants should be faster at responding to this dot when it appears in the location of the emotional word than in the location of the neutral word.

Pain and Cognitive Bias For each word group, there were 4 different presentation conditions. Both the emotional word and the following dot-probe could be presented to either the upper or lower location and was randomly controlled by the computer. Within a word-pair group, these 4 possible presentation conditions occurred an equal number of times. The experiment consisted of 192 trials (96 critical trials and 96 filler trials), in which each emotional word pair (sensory pain/neutral and affective pain/neutral) and each neutral/neutral word pair were repeated 4 times. As soon as a response had been made or after 3000 milliseconds, the dot was erased. After 500 milliseconds the next trial began. For the analysis, reaction times below 200 milliseconds and above 1000 milliseconds were removed as outliers. To help clarify the nature of attentional bias, the same procedure reported by Keogh et al27,28 was followed. An index was calculated by taking the average reaction time for trials in which the probe appeared in the same location as the emotional word away from trials in which it appeared in a different location. Thus a positive score indicates a selective attentional bias toward the location of the emotional word (ie, vigilance), whereas a negative score indicates a bias away from such material (ie, avoidance).

Body Sensations Interpretation Questionnaire (BSIQ) The BSIQ14 consists of 27 ambiguous scenarios that are divided into 4 subscales. These subscales are (1) panicrelated bodily sensations, eg, you notice your heart is beating quickly and pounding; (2) social events, eg, you go into a shop and the assistant ignores you; (3) external events, eg, a member of your family is late arriving home; and (4) other bodily symptoms that are not crucial to panic disorder, eg, you have developed a small spot on the back of your hand. For each scenario, participants are required to generate a possible explanation why such a situation has occurred. Three possible explanations for each scenario are then presented, of which 1 is negative and the remaining 2 neutral. For example, for the scenario “you notice your heart is beating quickly and pounding,” the 3 possible explanations are (1) because you have been physically active (neutral), (2) because there is something wrong with your heart (negative), and (3) because you are feeling excited (neutral). Participants rank each explanation in the order that they would come to mind. A score of 3, 2, or 1 is given depending on whether the negative explanation is ranked first, second, or third. A mean ranking score is then calculated for each of the 4 subscales. For each scenario, participants also rate the extent to which they would believe each of the 3 preset explanations to be true if they were experiencing that particular situation. A mean negative belief rating and a mean neutral belief rating are then calculated (note that there are 2 neutral items per question). The neutral rating scores are not reported in the current analysis because of

ORIGINAL REPORT/Keogh and Cochrane lack of relevance to the aims of the current study (see also Clark et al14). Following the procedures of Clark et al, we analyzed the ranking/rating data.

Self-Report Pain Measure The main self–report pain measures used were based on the short-form McGill Pain Questionnaire (SF-MPQ37). The original SF-MPQ contains a set of 11 sensory pain descriptors (ie, throbbing, shooting, stabbing, sharp, cramping, gnawing, hot-burning, aching, heavy, tender, splitting) and 4 affective pain descriptors (ie, tiring-exhausting, sickening, fearful, punishing-cruel), which are given a score between 0 (none) and 3 (severe). Recent confirmatory factor analysis has shown that the two-factor solution best represents the data in a group of low back pain patients.59 However, for the purposes of the present study, the affective component of the questionnaire was modified by the addition of affective pain words drawn from the MPQ. The words used in the revised affective pain scale were tiring, exhausting, sickening, fearful, punishing, cruel, wretched, blinding, grueling, suffocating, and terrifying. These additional words were included because the authors considered that the SF-MPQ might not contain sufficient items to describe the emotional aspects of pain.26 Therefore, inclusion of additional items would facilitate equal comparisons between the self-reported sensory and affective aspects of pain. Reliability analysis showed a Chronbach’s alpha of .84 for the new affective scale, which indicates that it has excellent internal reliability. Finally, when the analyses conducted in the current study were repeated with the original 4-item version of the affective pain scale, a similar pattern of results was found.

Anxiety Sensitivity Index The Anxiety Sensitivity Index (ASI49) is a 16-item questionnaire that assesses the individual’s fear of anxietyrelated sensations and consists of items relating to physical, social, and cognitive concerns. Participants are asked to indicate on a 5-point scale (scored 0 to 4) how much they generally agree with statements such as “It scares me when I become short of breath” and “It scares me when I am nauseous.” The total ASI score was used in the current study.

Fear of Pain The Fear of Pain Questionnaire (FPQ35) measures fear of 3 types of pain: minor pain (eg, a paper cut on the finger), severe pain (eg, breaking one’s neck), and medical pain (eg, receiving an injection). An overall fear of pain score can also be obtained by summating the scores on these subscales. This scale was included because of the potential overlap between anxiety sensitivity and the fear of pain, in addition to previous findings that the fear of pain is related to an attentional bias.28

Depression Anxiety Stress Scale The short form Depression Anxiety Stress Scale (DASS31) was used to determine whether any effects of

323 anxiety sensitivity were associated with levels of state depression. The DASS was chosen because it does not appear to be constrained by problems of overlap between items pertaining to anxiety and depression observed in older scales.30 The DASS measures levels of depression (DASS-D), anxiety (DASS-A), and stress (DASS-S) experienced by the individual during the past week.

Mill Hill Vocabulary Scale Set B of the Mill Hill Vocabulary Scale (MHVS48) was included to control for the possibility that performance on the dot-probe task was related to the verbal comprehension abilities of the individual. The MHVS consists of 33 multiple-choice items and requires the individual to match a target word with 1 of 6 provided words with regard to their similarity in meaning.

Procedure Participants were initially screened to ensure that they did not currently suffer from pain, had no history of cardiovascular disease or diabetes, and were not currently on any medication. No participant reported any of the above. All participants were then required to sign an ethics committee derived consent form indicating that they were aware of the pain manipulation to be used and that they agreed to participate. The experimental procedure was approved by Goldsmiths College Human Ethical Committee and conformed to the ethical guidelines for pain research in humans as recommended by the International Association for the Study of Pain.25 Participants initially completed the BSIQ, the DASS, FPQ, MHVS, and the ASI. Analysis of variance showed that although no significant differences exist between anxiety sensitivity on age or MHVS scores, group differences were found on the depression, stress, and anxiety scales of the DASS and on the FPQ scale (Table 1). As expected, those with high anxiety sensitivity reported higher state mood levels and a greater fear of pain than those with low anxiety sensitivity. This point is returned to in the results. Participants were then run on either the dot-probe task or the cold pressor task. To control for carryover effects, half the participants were randomly run in the cold pressor pain task first, and the remaining participants were run in the cognitive bias tasks first. Task order was entered as a covariate but did not alter the general pattern of results, indicating that it was not a problem in this study. Task order is, therefore, not reported any further. For the cold pressor task and to provide a baseline, participants placed their nondominant arm in a warm water bath (37°C) for 2 minutes before transferring the hand into an ice-water bath maintained at a temperature of 1°C to 2°C. While the hand was immersed in the ice-water, participants indicated at what point they first began to feel pain (ie, pain threshold) and at what point they could no longer tolerate it (ie, pain tolerance). Unknown to participants, an upper time limit of 2 minutes was used at which point they were asked to remove their hand from the cold tank58 and then asked to sit quietly

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Pain and Cognitive Bias

Table 1. Means and Standard Deviations (in Parentheses) for Questionnaire Measures by Anxiety Sensitivity Group (High vs Medium vs Low)

ASI DASS—Depression DASS—Anxiety DASS—Stress FPQ MHVS Age Number per cell

LOW AS

MEDIUM AS

HIGH AS

5.95 (2.44) 2.00 (2.27) .55 (1.10) 3.50 (2.60) 64.82 (21.79) 18.14 (5.14) 24.76 (7.01) 22

15.11 (4.19) 3.71 (4.09) 1.77 (1.87) 5.16 (3.47) 78.73 (16.56) 15.55 (5.04) 24.98 (7.11) 56

30.27 (7.00) 6.14 (5.40) 5.27 (4.31) 9.09 (4.58) 87.18 (18.15) 16.58 (4.63) 22.76 (6.96) 22

F

VALUES

130.13‡ 4.31* 19.67‡ 11.11‡ 6.23† 2.18 1.97

Abbreviation: AS, anxiety sensitivity group. *P ⬍ .05. †P ⬍ .01. ‡P ⬍ .001, significant difference between groups.

and report when the pain subsided. The SF-MPQ was then completed. For the dot-probe task, participants sat in front of a computer and completed the selective attentional task. Before the experimental trials, participants received 10 practice trials, consisting of 10 pairs of neutral/neutral word pairs (which were not included in the main trials). The duration of the whole experiment was approximately 1 hour, by which time the effect of the pain manipulation had dissipated. Participants were fully debriefed on conclusion of the task.

Results Anxiety Sensitivity and the Experience of Pain Pain experience scores are shown in Table 2. Multivariate analysis of variance (MANOVA) with Wilks criterion was conducted on the pain indexes (threshold, tolerance, recovery, sensory pain, and affective pain), with anxiety sensitivity group (high versus medium versus low) serving as the between-groups factor. The combined pain measures were significantly related to anxiety sensitivity group (F10,184) ⫽ 2.58, Wilks lambda ⫽ .77, P ⬍ .005). To determine the effect of anxiety sensitivity on the pain measures, univariate F tests were examined. Following the recommendations of Tabachnick and Fidell (1996), an adjustment for inflated Type I error was used,

and the critical alpha level set at .05/5 tests ⫽ .01. Univariate F tests showed significant effects for pain threshold (F2,96 ⫽ 5.22, P ⬍ .01), sensory (F2,96 ⫽ 5.00, P ⬍ .01), and affective pain (F2,96 ⫽ 6.74, P ⬍ .005). Simple effects analyses (P ⬍ .05) showed that those with high anxiety sensitivity reported lower pain thresholds and higher sensory and affective pain levels than those with low anxiety sensitivity. Furthermore, those with low and medium anxiety differed in terms of pain threshold and sensory pain, whereas those with medium and high anxiety differed on affective pain scores. It is possible that the anxiety-related effects reported above could have been due to variations in mood. Therefore, a series of correlations were conducted between the pain indexes and the questionnaire measures. Anxiety sensitivity was significantly related to pain threshold (r ⫽ ⫺.21, P ⬍ .05) and SF-MPQ affective pain scores (r ⫽ .26, P ⬍ .01). Similar significant correlations were found with the FPQ (threshold: r ⫽ ⫺.25, P ⬍ .05; affective pain: r ⫽ .21, P ⬍ .05). No significant associations were found between DASS and any of the pain measures, indicating that any effects found with pain are not likely to be due to depression. Finally, partial correlations showed a significant correlation between anxiety sensitivity and affective pain, even when controlling for fear of pain scores (partial r ⫽ .20, P ⬍ .05). These analyses confirm that anxiety sensitivity is associated with a greater susceptibility toward negative pain experiences.

Means and Standard Deviations (in Parentheses) for Pain Measures by Anxiety Sensitivity Group (High vs Medium vs Low)

Table 2.

Threshold (sec) Tolerance (sec) Recovery (sec) SF-MPQ: Sensory SF-MPQ: Affective Abbreviation: AS, anxiety sensitivity group.

LOW AS

MEDIUM AS

HIGH AS

13.05 (9.88) 47.14 (35.08) 81.59 (39.88) 9.45 (4.84) 3.95 (4.28)

8.75 (5.34) 34.50 (33.07) 78.79 (64.67) 12.70 (4.94) 6.15 (5.14)

7.18 (3.46) 24.73 (20.01) 62.18 (27.20) 13.77 (4.47) 9.68 (6.30)

ORIGINAL REPORT/Keogh and Cochrane

325

Table 3. Means and Standard Deviations (in Parentheses) for Cognitive Bias Scores by Anxiety Sensitivity Group (High vs Medium vs Low) LOW AS BSIQ: ranking scale Panic Social External Other BSIQ: rating scale Panic Social External Other Dot-probe bias index Sensory Affective

MEDIUM AS

HIGH AS

1.06 (.12) 1.26 (.40) 1.13 (.21) 1.15 (.21)

1.12 (.19) 1.47 (.47) 1.25 (.32) 1.15 (.24)

1.32 (.49) 1.66 (.46) 1.42 (.38) 1.33 (.34)

8.36 (7.30) 16.50 (11.57) 12.32 (7.17) 9.27 (6.42)

12.07 (8.45) 21.27 (10.95) 15.25 (7.89) 11.78 (7.36)

17.41 (7.63) 29.00 (8.86) 20.09 (7.16) 16.82 (7.13)

⫺2.30 (19.76) 1.32 (18.33)

.16 (24.04) ⫺2.94 (22.49)

8.36 (35.19) .50 (24.07)

Abbreviation: AS, anxiety sensitivity group.

Cognitive Bias The cognitive bias scores were collated and can be found in Table 3. The attentional dot-probe indexes were analyzed by using a mixed groups ANOVA, with anxiety sensitivity group as the between-groups factor (high versus medium versus low) and index valance (sensory versus affective) as the within-groups factor. No significant effects were found. Furthermore, no significant effects involving anxiety sensitivity were found when the analysis was repeated with the raw reaction time data. The interpretative bias data were analyzed with MANOVA. The first analysis, which was conducted on the 4 BSIQ ranking scores, showed a significant overall effect of anxiety sensitivity (F8,178 ⫽ 2.63, Wilks lambda ⫽ .80, P ⬍ .01). Univariate F tests showed that anxiety sensitivity groups differed on all 4 scales (panic, F2,92 ⫽ 6.02, P ⬍ .005; social, F2,92 ⫽ 4.91, P ⬍ .01; external, F2,92 ⫽ 4.91, P ⬍ .01; other, F2,92 ⫽ 5.34, P ⬍ .01). However, follow-up simple effects tests showed significant differences between the high and low anxiety sensitivity groups for the panic, social, and external events scales (P ⬍ .01) but not for the other sensations scale. Furthermore, the high and medium anxiety sensitivity groups differed on the panic and other sensations scales (P ⬍ .01). Analysis of the rating scales showed a similar pattern of effects. A significant overall effect of anxiety sensitivity was found (F8,186 ⫽ 2.26, Wilks lambda ⫽ .83, P ⬍ .05). Univariate F tests showed that anxiety sensitivity groups differed on all 4 scales (panic, F2,92 ⫽ 7.09, P ⬍ .005; social, F2,92 ⫽ 7.77, P ⬍ .005; external, F2,92 ⫽ 5.98, P ⬍ .005; other, F2,92 ⫽ 6.58, P ⬍ .005). Simple effects analyses showed significant differences between the high and low anxiety sensitivity groups (P ⬍ .005) and between the high and medium groups (P ⬍ .05) for all 4 scales. Correlational analyses were also conducted between the pain indexes and cognitive bias measures. Somewhat surprisingly, the affective attentional bias index was related to sensory pain scores (r ⫽ .20, P ⬍ .05). This analysis also showed that SF-MPQ affective pain reports were

related to the tendency to report ambiguous events as negative, the strongest association being with panic-related sensations (panic ranking: r ⫽ .24, P ⬍ .05; panic rating: r ⫽ .29, P ⬍ .01; external rating: r ⫽ .17, P ⬍ .05; other sensations rating: r ⫽ .23, P ⬍ .05). To confirm that affective pain was most strongly related to ambiguous panic-related sensations, a stepwise regression was conducted on affective pain scores, entering the 4 BSIQ ratings as predictors. Only panic ratings was a significant predictor of affective pain (R2 ⫽ .09; F1,97 ⫽ 9.88, P ⬍ .005). Thus, those high in anxiety sensitivity are also more susceptible to negative interpretative bias but not necessarily toward a negative attentional bias.

Testing for Mediator Effects The analyses reported above confirmed that anxiety sensitivity was related to both a negative interpretative bias and higher affective pain experiences. What is not clear, however, is whether a negative interpretative bias mediates the relationship between anxiety sensitivity and affective pain.10 An investigation was, therefore, conducted to determine whether the tendency to misinterpret ambiguous stimuli related to panic mediates the link between anxiety sensitivity and affective pain perception. (Although anxiety sensitivity and fear of pain scales were both significantly associated with pain experiences, when these anxiety measures were entered into a stepwise regression to predict panic-related interpretation ratings, only anxiety sensitivity was a significant predictor. Fear of pain was not, therefore, considered in the mediator analysis. In addition, although it was possible that we could have had 20⫹ combinations of mediator and pain, the number is greatly reduced by the fact that many of these possible relationships do not meet the requirement of Baron and Kenny10 for meditation. If a nonsignificant relationship between a cognitive bias and pain is found, then this fails to meet the requirements for mediation.) To determine mediation we adopted the regression

326 Table 4.

Pain and Cognitive Bias

Testing the Mediating Effect of Interpretative Bias on the Anxiety Sensitivity–Affective Pain Relationship

STEP

PREDICTOR

DEPENDENT

1 2 3⫹4

ASI ASI BSIQ Panic rating ASI

SF-MPQ Affective BSIQ-Panic rating SF-MPQ Affective SF-MPQ Affective

STANDARD .26† .46‡ .21* .17

BETA

R2

F

.07 .21 .11

7.29† 25.59‡ 5.66†

*P ⫽ .052. †

P ⬍ .01.

‡

P ⬍ .01.

procedure recommended by Baron and Kenny.10 The first step in determining mediation is to ensure that the predictor variable (anxiety sensitivity) is related to the dependent variable (affective pain score). Regression analysis indicated this relationship does exist, supporting the first requirement for mediation (Table 4). The second step is to see whether the predictor variable is related to the mediating variable (interpretative bias). Again, regression analysis indicates this is the case, meeting the second step. The final requirement is to demonstrate that the mediating variable (interpretative bias) is related to the dependent variable (affective pain score) when both the predictor variable (anxiety sensitivity) and the mediating variables are entered. If interpretative bias mediates the relationship between anxiety sensitivity and affective pain experiences, then when the bias score is entered into regression, anxiety sensitivity should no longer be a significant predictor, ie, anxiety sensitivity will not add to the prediction of affective pain perception once interpretative bias has been included. As can be seen from Table 4, anxiety sensitivity no longer significantly explains variance associated with affective pain perception, suggesting “complete mediation.”10 Because 3 of the 4 BSIQ rating scales were related to pain, it is also possible that a general interpretative bias, rather than a specific panic-related bias, mediates the relationship between anxiety sensitivity and pain. The data were, therefore, reanalyzed to see whether mediation is more general than originally thought. When these 3 bias ratings were combined and tested for mediation, the bias score was not significant at the final step. This suggests that a general interpretative bias does not have a mediating role.

Discussion The results of the current study confirm that anxiety sensitivity is associated with increased susceptibility to negative pain experiences. Specifically, anxiety sensitivity was related to affective as well as sensory pain experiences, which is broadly consistent with previous studies. For example, Keogh and Mansoor29 also reported similar group differences in sensory and affective pain, whereas Keogh and Birkby26 only found differences for sensory pain. Keogh and Mansoor suggested that the reason why Keogh and Birkby did not find group differences for affective pain was due to the lower cutoff point used to

classify participants as high in anxiety sensitivity. The current study also used a higher cutoff than Keogh and Birkby, indicating that anxiety sensitivity may indeed be associated with higher affective as well as sensory pain experiences, but only among those with extremely high ASI scores. Interestingly, the current study also found that high levels of anxiety sensitivity were related to a lower pain threshold. This is the first time that anxiety sensitivity has been related to both behavioral and self-report indicators of pain experiences. Unfortunately, the lack of consistency between studies regarding anxiety sensitivity and pain threshold means that further clarification is required before any definite conclusions can be made. Although it seems that anxiety sensitivity is a vulnerability factor in negative responses to pain, the principal aim of the current study was to go beyond the anxiety sensitivity–pain link and isolate the potential mechanisms that may mediate this relationship. Drawing on research that demonstrates that both chronic pain and anxiety sensitivity are associated with negative information processing biases, it was predicted that cognitive biases act as just such a mechanism. As predicted, a selective cognitive bias for negative material was found to mediate the anxiety sensitivity–pain relationship. Specifically, the tendency to negatively interpret ambiguous bodily sensations related to panic was found to mediate the association between anxiety sensitivity and emotional responses to cold pressor pain. This finding suggests 1 reason why those with high anxiety sensitivity are likely to report more pain. Even though a cognitive bias was found to mediate the anxiety sensitivity–pain relationship, the effect was dependent on the type of pain measure used. Negative interpretative bias was related to affective pain responses but was not associated with any of the other pain measures taken. This suggests that it is the emotional component of pain that negative interpretative biases are most likely to affect. Therefore, assessment of the efficacy of pain interventions that target the way in which patients interpret their world should include indexes of emotional pain experiences. An additional aim of the current study was to compare 2 different types of cognitive bias: an interpretative and an attentional bias. Although both types of bias have been found in both pain patients and those with high anxiety sensitivity, an interpretative bias but not an at-

ORIGINAL REPORT/Keogh and Cochrane tentional bias was found to be a significant mediator of the anxiety sensitivity–pain relationship. In fact, the only effect found for the attentional bias index was a small but significant correlation between affective pain bias and sensory pain reports. This general lack of significant association with attentional biases is surprising given that previous research implicates both the fear of pain and anxiety sensitivity with increased vigilance toward threat-related material.27,28 However, others have also reported difficulty in finding evidence for attentional biases with the visual dot-probe paradigm (Roelofs et al, personal communication, 2001). Perhaps the best conclusion that can be made is that attentional biases may not be consistently related to pain responses. The finding that negative interpretative biases are related to pain experiences is consistent with current models of anxiety sensitivity and panic disorder. Anxiety sensitivity is believed to be so closely related to panic disorder that it is an important vulnerability factor in the development of this clinical condition.16,54 Indeed, studies show that high levels of anxiety sensitivity are good predictors of panic even among individuals who have never experienced a panic attack.18,32 Furthermore, Schmidt and Cook51 found that anxiety sensitivity moderates the experience of cold pressor pain in patients with panic disorder. Although it may be tempting to conclude that anxiety sensitivity acts as a vulnerability factor that predisposes even healthy individuals toward negative responses to pain, further research is required replicating the effect. Interestingly, the current study also took a measure of the fear of pain, which is also believed to be related to negative pain experiences and cognitive biases.28 However, when controlling for fear of pain, anxiety sensitivity was still related to affective pain scores. Interestingly, Asmundson and Taylor9 found that in a group of 259 patients with chronic pain, anxiety sensitivity exacerbated the fear of pain, which in turn was found to lead to avoidance behaviors, ie, negative coping strategy. This suggests that anxiety sensitivity may mediate both the perception of pain and the way in which pain is dealt with. Although the results of the current study are promising, caution is required before drawing any definite conclusions. One of the main limitations was the low number of men. Although this sex ratio reflects the distribution of male and female psychology students at Goldsmiths College, the low number of men meant that we could not include gender in the analysis. Given that important differences have been found between men and women in the effect anxiety sensitivity has on pain,26 it is possible that different cognitive mechanisms may underpin such gender differences. An additional issue related to the high number of women in the current study is the possible role of the menstrual cycle in moderating pain-related effects. Unfortunately, we did not take a measure of menstrual cycle phase, and so such possibilities are speculative at present. Future research is planned to investigate the role of anxiety sensitivity and cognitive biases in understanding gender differences in pain perception.

327 A second limitation with the current study is that the strength of the relationship between anxiety sensitivity and the pain indexes is relatively small. This may mean that although the above effects are interesting, there may not be a large enough effect size for it to be clinically relevant. However, the fact that this relationship was found in nonclinical groups may mean that the effect size is greater in chronic pain patients. A third limitation is that those who reported greater emotional responses to cold pressor pain could simply have been responding to the pain in a more anxious manner. Because no measure of state anxiety was taken, this issue is unclear at present. Finally, it should be noted that it is also unclear why the negative interpretative bias was related to affective pain and not sensory pain responses. This is particularly puzzling when one considers the strong evidence that pain catastrophizing is strongly related with pain severity. Even so, although the above concerns are important, they do not detract from the fact that evidence was found for complete mediation.10 Further research should clearly follow up this interesting finding. Even though there are limitations with the current research, we believe that they have potential importance for our understanding of the cognitive and emotional factors in chronic pain. Pain patients are not only found to report higher levels of anxiety and depression, but it is also believed that such mood states are important predictors of disability and other health-related outcomes. Given that cognitive biases are thought to maintain mood disorders such as anxiety and depression,23,56,57 it would be interesting to determine what role these biases have in predicting health-related outcomes in chronic pain patients. If the current results are replicable in clinical groups, then this may have implications for pain management. For example, if the reason for extreme emotional responses to pain is because cognitive biases make patients more sensitive toward pain-related sensations, then pain interventions may wish to target such biases, in much the same way as they have been in the treatment of emotional disorders such as anxiety and depression.56,57 If anxiety sensitivity were targeted in such interventions, then it would seem necessary to concentrate on the tendency to catastrophically misinterpret innocuous bodily sensations (eg, maybe through exposure in vivo) and the effect they have on emotional responses to pain. Unfortunately, because we are unaware of any such study, such implications are speculative at present. Further research is planned to investigate the link between anxiety sensitivity and pain in more detail. For example, the current study took measures of interpretative and attentional biases. However, evidence also exists that pain patients possess a negative memory bias. It would be interesting to determine whether negative memory biases have a mediating effect on the type of pain experienced, especially among those who are depressed.41 Further research is also planned to use other methods of determining interpretative bias that do not require the participant to endorse statements, such as

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the use of homophones or homographs.46 It would also be interesting to determine whether the anxiety sensitivity–pain relationship exists when using a different pain induction method to the cold pressor task. Research is currently underway examining the role of anxiety sensitivity on the perception of other types of pain, such as electrical and thermal pain.

In conclusion, the results of the current study add to a growing body of evidence that cognitive and emotional factors are not separate, independent entities but instead are intrinsically linked in the experience and perception of pain. Further research is needed to determine whether interventions that target biased cognitive processes reduce the negative impact and experience of pain.

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Words Used in Attentional Dot-Probe Study

SENSORY/NEUTRAL

AFFECTIVE/NEUTRAL

NEUTRAL/NEUTRAL

NEUTRAL/NEUTRAL

Aching/storage Crushing/bookcase Cutting/mirror Hurting/laundry Pounding/polished Pressing/container Scalding/cupboard Sharp/chair Shooting/candles Smarting/resident Throbbing/wallpaper Tugging/ironing

Blinding/banister Cruel/stair Discomforting/microwave Distressing/mantelpiece Dragging/wardrobe Exhausting/bedspread Fatiguing/decorated Frightful/saucepan Gruelling/corkscrew Punishing/sideboard Tiring/boiler Wretched/teaspoon

Beaker/dusted Curtain/insurance Doorbell/basement Doorknob/brushing Flannel/speakers Interior/blanket Ironing/cutlery Painted/newspaper Radiator/ornament Soap/lamp Sponge/whisk Vacuum/address

Armchairs/housework Bathing/cleaner Dining/towels Kettle/cellar Landing/pillow Magazines/household Plug/bath Radio/cloth Roofing/drawers Shampoo/bedroom Tidy/mugs Tiles/tapes