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Memory for pain: Relation between past and present pain intensity
375
Pain, 23 (1985) 375-379 Elsevier
PA1 00812
Memory for Pain: Relation between Past and Present Pain Intensity Eric Eich *,I, John L. Reeves **, Bernadette Jaeger ** and Steven B. Graff-Radford ** * Department
of Psychology, University of British Columbia, Vancouver, B.C. V6T I Y7 (Canada), and ** Department of Anesthesiology, University of California, LAS Angeles, CA 90024 (U.S.A.) (Received
24 April 1985, accepted
13 June 1985)
Memory for the intensity of past physical pain depends critically on the intensity of present pain. When their present pain intensity was high, patients with chronic headaches of myofascial origin rated their maximum, usual, and minimum levels of prior pain as being more severe than their hourly pain diaries indicated. When their present pain intensity was low, the same patients remembered all 3 levels of prior pain as being less severe than they actually had been. The results show that pain produces systematic distortions of memory similar to those associated with alterations of affect or mood, and suggest a resolution to a conspicuous conflict in the current pain literature.
Introduction Memory for pain plays a prominent role in medical practice [3-71. In addition to providing patients with an incentive for seeking professional aid and advice, retrospective reports of pain influence both the diagnosis and the treatment they receive. Furthermore, clinicians routinely rely on changes in past and present pain complaints to evaluate the effects of therapy. For these reasons, it is important to ask: what factors affect the accuracy of remembered pain?
’ To whom reprint
0304-3959/85/$03.30
requests
and correspondence
should be sent.
0 1985 Elsevier Science Publishers
B.V. (Biomedical
Division)
276
One such factor may be the intensity at which pain is present when memory for prior pain is assessed. Recent research in the area’of affect and cognition suggests that emotions exert strong assimilative effects on memory [1.2]. For instance. whereas happy subjects retrieve memories of pleasant personal experiences more rapidly than those of unpleasant experiences, sad subjects retrieve sad memories faster than happy ones [12]. Similarly, autobiographical events retrieved in response to affectively neutral cues, such as the words vtuter and chuir. are rated as more pleasant by happy than by sad individuals [g]. Since affect is an integral component of pain behavior and experience [9.10]. it is possible that pain mav produce assimilative effects on memory that parallel those engendered by emotions. An intriguing implication of this line of thought is that prior pain may be remembered as being more severe than it actually had been when the intensity of present pain is high. but as less severe when present pain intensity is low. The purpose of the present study was to investigate this implication.
Methods To examine the effects of present pain intensity on memory for prior pain. we reviewed the clinical records of 57 patients with histories of chronic headaches of muscular/skeletal origin [13]. These records related to the patients’ participation in a pain management program sponsored by the UCLA Department of Anesthesiology. Participation involved a preliminary physical/psychological evaluation and a variable number of treatment sessions, scheduled at approximately weekly intervals. Three tasks were performed at the start of every treatment session. First, pain diaries which the patients had been instructed to maintain since their last visit were collected. Included in these diaries were hourly ratings of pain intensity made on a O-10 numerical scale, where 0 meant ‘no pain’ and 10 meant ‘the most intense pain imaginable.’ Second, the patients were asked to rate the intensity of pain they were experiencing at that moment. Patients rated their present pain intensity by placing a slash mark through a visual analogue scale (111: a 10 cm line labeled ‘no pain’ at one end and ‘the most intense pain imaginable’ at the other. Third, the patients were asked to recall the maximum, usual, and minimum levels of pain they had experienced since their last visit. Patients indicated their recall by placing 3 slash marks through a visual analogue scale identical to the one just described. By employing physically different but conceptually related measures of diary versus recalled pain (viz.. ratings on a O-10 numerical vs. a 10 cm visual analogue scale), we endeavored to make the patients’ memory task one of remembering the experience of prior pain, rather than one of remembering a specific rating of that experience [see ref. 51. Of the 57 patients whose records were reviewed, 25 were selected for detailed analysis. These were patients who had returned a virtually complete pain diary at the start of both (a) the session in which they had registered their highest rating of present pain intensity, and (b) the session in which they had registered their lowest such rating. This selection strategy had the advantage of producing a sharp separation between high and low levels of present pain intensity without imposing any
arbitrary criteria or artificial cutoffs on the patients’ present pain ratings. Diaries that accompanied the patients’ highest and lowest ratings of present pain intensity spanned means of 6.9 and 6.8 days, respectively. The average diary contained 17.0 hourly ratings of pain intensity per day, and was 96% complete with respect to the total number of days it was intended to cover. The selected 25 patients averaged 41.2 years of age (S = 13.4) and 8.8 years of persistent myofascial pain (S = 9.3); all but three of the patients were women. The patients’ highest ratings of present pain intensity ranged from 0.8 to 9.3, and averaged 5.9 (s = 2.3); their lowest ratings of present pain intensity ranged from 0.0 to 2.4, and averaged 0.8 (S = 0.9). The majority of the patients registered their highest rating within the first half of the pain management program (which involved an average of 10.5 treatment sessions), and their lowest rating within the second half; this pattern provides a welcome sign of improvement in the patients’ pain condition over the course of therapy.
Results Data of chief concern, in the form of average actual (diary defined) and recalled ratings of maximum, usual, and minimum levels of prior pain intensity, are displayed in Fig. 1 as a function of present pain intensity. A 2 x 3 x 2 (present pain X prior pain X rating type) repeated-measures analysis of variance of the rating data (transformed into logarithms in order to reduce the heterogeneity of related variances) revealed significant simple effects of both present and prior pain intensity
PRESENT
PRIOR
PAIN
PAIN
INTENSITY
INTENSITY
Fig. 1. Mean actual (diary defined) and recalled ratings of maximum, usual, and minimum levels of prior pain intensity as a function of present pain intensity. For each patient, the actual rating of usual pain intensity was determined by dividing the sum of all hourly ratings of pain intensity recorded in the patient’s pain diary by the total number of hours rated.
378
(F (1/w = 20.86, mse = 0.68, P -c 0.01and F (2/48) = 192.83, mse = 0.05, p -C 0.01, respectively), as well as a reliable interaction’of present pain with rating type (F (l/24) = 9.50, mse = 0.13, P < 0.01). (No other effects, simple or interactive in nature. approached statistical significance; Ps > 0.10.) As is apparent in the figure. the patients recalled their maximum, usual. and minimum levels of prior pain as being more severe than they actually had been when the intensity of their present pain was high, but as less severe when their present pain intensity was low. The tendency of patients to overestimate or underestimate the severity of their past pain, depending on their present pain state. was also observed when differences between actual and recalled pain ratings were analyzed non-parametrically. For purposes of this analysis, we counted the number of times in which the patients either overestimated or underestimated any of their 3 levels of prior pain by at least 1 .O point. Whereas most of the errors of overestimation (19/25. or 76%) occurred under conditions of high present-pain intensity. the majority of the errors of underestimation (1X/24, or 75%) occurred under conditions of low present-pain intensity (x’ (1) = 12.75. P -c0.01). Earlier it was observed that most patients registered their highest rating of present pain intensity in the first half of the treatment program, and their lowest such rating in the second half. In light of this observation. it is possible that the pattern of data depicted in Fig. 1 is attributable to the beneficial effects of therapy or to an increase in learning proficiency. To check this possibility, we reanalyzed the log-transformed rating data in the context of a 2 x 3 x 2 X 2 mixed analysis of variance design, the factors being present pain, prior pain, rating type, and treatment half (i.e.. whether a particular rating of present pain - either the highest or the lowest ever recorded for a particular patient - had been registered in the first vs. the second half of that patient’s program). Mirroring the results reported above. the reanalysis yielded a marginally significant effect of present pain intensity (F (l/46) = 3.62. 1?1.~e= 1.00. P -c0.07). a highly significant effect of prior pain intensity (F (2/92) = 207.58. mse = 0.04, P -c 0.01) and a reliable interaction between present pain and rating type ( F (l/46) = 5.50, nose = 0.07. P < 0.05). Importantly. neither the simple effect of treatment half, nor any interactions involving this effect. were significant (Ps> 0.10). Viewed as a whole. these results indicate that present pain intensity produces systematic distortions of memory for prior pain intensity. and that the magnitude of these distortions is independent of whatever changes in treatment outcome or learning competence may occur over the course of therapy.
Discussion
Present pain intensity appears to exert an assimilative effect on memory for prior pain intensity, such that ratings of the latter are attracted to or displaced toward ratings of the former. This conclusion seems to suit our data quite well. and it may also apply to the conflicting results obtained by others. In a recent study by Hunter et al. [3], patients experiencing acute head pain rated the intensity of their discomfort on a 5-point scale, and were asked to recall these ratings 1 or 5 days later. On
379
the average, patients underestimated their original intensity ratings by 6% at the l-day test and by 11% at the 5-day test; neither of these differences were statistically significant. In a subsequent study by Linton and Melin [7], patients with chronic back or joint pain rated the intensity of their pain on a loo-point scale before beginning a physical rehabilitation program, and attempted to recall these ratings 3-11 weeks later, upon termination of treatment. On the average, these patients overestimated their original ratings by 19% - a reliable (P < 0.01) margin. The conflict between the outcomes of these two studies may be more apparent than real. Whereas the patients in Hunter’s study performed recall in a pain-free state, those in Linton’s study perceived little or no change in their pain condition between the beginning of treatment, when original intensity ratings were taken, and its end, when memory for these ratings was tested. In light of the data depicted in Fig. 1, we suggest that this difference in level of present pain intensity - rather than, or in addition to, differences in the manner in which pain intensity was measured, the nature of the pains investigated, or the length of the retention intervals examined - may be primarily responsible for the observed disparity in experimental outcomes. We also suggest that although Hunter’s results appear to conflict with those reported by Linton, both sets of results are compatible with the conclusion that present pain intensity has an assimilative influence on memory for prior pain intensity. Whether this conclusion can be expanded to encompass dimensions of pain other than intensity (e.g., affective as opposed to sensory components of pain [9,10]), and forms of cognitive functioning other than memory (e.g., selective attention to or distorted perception of pain-related material [1,2]), are clinically and theoretically interesting issues that await detailed analysis.
Acknowledgements Preparation of this article was aided by grants to the first author from the (Canadian) Natural Sciences and Engineering Research Council (U0298) and the (American) National Institute of General Medical Sciences (GM32037). We thank J.M. Eich, S.J. Rachman, P.M. Smith, A.M. Treisman and L.M. Ward for providing valuable comments and suggestions, and E. Maslow, K. Pape and D. Sharpe for assisting in data collection and analysis.
References 1 Bower, C&H., Mood and memory, Amer. Psychol., 36 (1981) 129-148. 2 Bower, G.H. and Cohen, P.R., Emotionaf influences in memory and thinking: data and theory. In: MS. Clark and S.T. Fiske (Eds.). Affect and Cognition, Lawrence Erlbaum Associates, Hillsdale, NJ. 1982, pp. 291-331. 3 Hunter, M., Philips, C. and Rachman. S.. Memory for pain. Pain, 6 (1979) 35-46. 4 Kent, G., Memory of dental pain, Pain, 21 (1985) 187-194. 5 Kwilosz, D.M., Gracely, R.H. and Torgerson. W.S., Memory for post-surgical dental pain, Pain. Suppl. 2 (1984) S426.
6 Linton. S.J. and Gotestam. K.G.. A clinical comparison of two pain scales: correlation, remembering chronic pain. and a measure of compliance, Pain, 17 (1983) S7765. 7 Lmton. S.J. and Melin. L.. The accuracy of remembering chronic pain. Pain, 13 (1982) 2X1 2X5. R Madigan. R.J. and Bollenhach. A.K.. Effects of induced mood on retrieval of personal episodic and semantic memories, Psycho]. Rep.. 50 (1982) 1477157. 9 Melzack, R. and Torgerson. W.S.. On the language of pain. Anesthesiology. 34 (1971) SO-59 IO Melzack. R. and Wall. P.D.. The Challenge of Pain, Penguin, Harmondsworth. 19X2. 1 I Scott, J. and Huskisson. EC‘., Graphic representation of pain, Pain, 2 (1976) 175. 1X4. 12 ‘Teasdale. J.D. and Fogarty. F.J.. Differenttal effects of induced mood on retrieval of pleasant and unpleasant events from episodic memory. J. ahnorm. P\ychol., 88 (1979) 24X-257. 13 Travell. J.G. and Simons, D.G., Myofascial Pain and Dysfunction: the Trigger Point Manual. Williams and Wilkins. Baltimore. MD. 19X3.
Pain, 23 (1985) 375-379 Elsevier
PA1 00812
Memory for Pain: Relation between Past and Present Pain Intensity Eric Eich *,I, John L. Reeves **, Bernadette Jaeger ** and Steven B. Graff-Radford ** * Department
of Psychology, University of British Columbia, Vancouver, B.C. V6T I Y7 (Canada), and ** Department of Anesthesiology, University of California, LAS Angeles, CA 90024 (U.S.A.) (Received
24 April 1985, accepted
13 June 1985)
Memory for the intensity of past physical pain depends critically on the intensity of present pain. When their present pain intensity was high, patients with chronic headaches of myofascial origin rated their maximum, usual, and minimum levels of prior pain as being more severe than their hourly pain diaries indicated. When their present pain intensity was low, the same patients remembered all 3 levels of prior pain as being less severe than they actually had been. The results show that pain produces systematic distortions of memory similar to those associated with alterations of affect or mood, and suggest a resolution to a conspicuous conflict in the current pain literature.
Introduction Memory for pain plays a prominent role in medical practice [3-71. In addition to providing patients with an incentive for seeking professional aid and advice, retrospective reports of pain influence both the diagnosis and the treatment they receive. Furthermore, clinicians routinely rely on changes in past and present pain complaints to evaluate the effects of therapy. For these reasons, it is important to ask: what factors affect the accuracy of remembered pain?
’ To whom reprint
0304-3959/85/$03.30
requests
and correspondence
should be sent.
0 1985 Elsevier Science Publishers
B.V. (Biomedical
Division)
276
One such factor may be the intensity at which pain is present when memory for prior pain is assessed. Recent research in the area’of affect and cognition suggests that emotions exert strong assimilative effects on memory [1.2]. For instance. whereas happy subjects retrieve memories of pleasant personal experiences more rapidly than those of unpleasant experiences, sad subjects retrieve sad memories faster than happy ones [12]. Similarly, autobiographical events retrieved in response to affectively neutral cues, such as the words vtuter and chuir. are rated as more pleasant by happy than by sad individuals [g]. Since affect is an integral component of pain behavior and experience [9.10]. it is possible that pain mav produce assimilative effects on memory that parallel those engendered by emotions. An intriguing implication of this line of thought is that prior pain may be remembered as being more severe than it actually had been when the intensity of present pain is high. but as less severe when present pain intensity is low. The purpose of the present study was to investigate this implication.
Methods To examine the effects of present pain intensity on memory for prior pain. we reviewed the clinical records of 57 patients with histories of chronic headaches of muscular/skeletal origin [13]. These records related to the patients’ participation in a pain management program sponsored by the UCLA Department of Anesthesiology. Participation involved a preliminary physical/psychological evaluation and a variable number of treatment sessions, scheduled at approximately weekly intervals. Three tasks were performed at the start of every treatment session. First, pain diaries which the patients had been instructed to maintain since their last visit were collected. Included in these diaries were hourly ratings of pain intensity made on a O-10 numerical scale, where 0 meant ‘no pain’ and 10 meant ‘the most intense pain imaginable.’ Second, the patients were asked to rate the intensity of pain they were experiencing at that moment. Patients rated their present pain intensity by placing a slash mark through a visual analogue scale (111: a 10 cm line labeled ‘no pain’ at one end and ‘the most intense pain imaginable’ at the other. Third, the patients were asked to recall the maximum, usual, and minimum levels of pain they had experienced since their last visit. Patients indicated their recall by placing 3 slash marks through a visual analogue scale identical to the one just described. By employing physically different but conceptually related measures of diary versus recalled pain (viz.. ratings on a O-10 numerical vs. a 10 cm visual analogue scale), we endeavored to make the patients’ memory task one of remembering the experience of prior pain, rather than one of remembering a specific rating of that experience [see ref. 51. Of the 57 patients whose records were reviewed, 25 were selected for detailed analysis. These were patients who had returned a virtually complete pain diary at the start of both (a) the session in which they had registered their highest rating of present pain intensity, and (b) the session in which they had registered their lowest such rating. This selection strategy had the advantage of producing a sharp separation between high and low levels of present pain intensity without imposing any
arbitrary criteria or artificial cutoffs on the patients’ present pain ratings. Diaries that accompanied the patients’ highest and lowest ratings of present pain intensity spanned means of 6.9 and 6.8 days, respectively. The average diary contained 17.0 hourly ratings of pain intensity per day, and was 96% complete with respect to the total number of days it was intended to cover. The selected 25 patients averaged 41.2 years of age (S = 13.4) and 8.8 years of persistent myofascial pain (S = 9.3); all but three of the patients were women. The patients’ highest ratings of present pain intensity ranged from 0.8 to 9.3, and averaged 5.9 (s = 2.3); their lowest ratings of present pain intensity ranged from 0.0 to 2.4, and averaged 0.8 (S = 0.9). The majority of the patients registered their highest rating within the first half of the pain management program (which involved an average of 10.5 treatment sessions), and their lowest rating within the second half; this pattern provides a welcome sign of improvement in the patients’ pain condition over the course of therapy.
Results Data of chief concern, in the form of average actual (diary defined) and recalled ratings of maximum, usual, and minimum levels of prior pain intensity, are displayed in Fig. 1 as a function of present pain intensity. A 2 x 3 x 2 (present pain X prior pain X rating type) repeated-measures analysis of variance of the rating data (transformed into logarithms in order to reduce the heterogeneity of related variances) revealed significant simple effects of both present and prior pain intensity
PRESENT
PRIOR
PAIN
PAIN
INTENSITY
INTENSITY
Fig. 1. Mean actual (diary defined) and recalled ratings of maximum, usual, and minimum levels of prior pain intensity as a function of present pain intensity. For each patient, the actual rating of usual pain intensity was determined by dividing the sum of all hourly ratings of pain intensity recorded in the patient’s pain diary by the total number of hours rated.
378
(F (1/w = 20.86, mse = 0.68, P -c 0.01and F (2/48) = 192.83, mse = 0.05, p -C 0.01, respectively), as well as a reliable interaction’of present pain with rating type (F (l/24) = 9.50, mse = 0.13, P < 0.01). (No other effects, simple or interactive in nature. approached statistical significance; Ps > 0.10.) As is apparent in the figure. the patients recalled their maximum, usual. and minimum levels of prior pain as being more severe than they actually had been when the intensity of their present pain was high, but as less severe when their present pain intensity was low. The tendency of patients to overestimate or underestimate the severity of their past pain, depending on their present pain state. was also observed when differences between actual and recalled pain ratings were analyzed non-parametrically. For purposes of this analysis, we counted the number of times in which the patients either overestimated or underestimated any of their 3 levels of prior pain by at least 1 .O point. Whereas most of the errors of overestimation (19/25. or 76%) occurred under conditions of high present-pain intensity. the majority of the errors of underestimation (1X/24, or 75%) occurred under conditions of low present-pain intensity (x’ (1) = 12.75. P -c0.01). Earlier it was observed that most patients registered their highest rating of present pain intensity in the first half of the treatment program, and their lowest such rating in the second half. In light of this observation. it is possible that the pattern of data depicted in Fig. 1 is attributable to the beneficial effects of therapy or to an increase in learning proficiency. To check this possibility, we reanalyzed the log-transformed rating data in the context of a 2 x 3 x 2 X 2 mixed analysis of variance design, the factors being present pain, prior pain, rating type, and treatment half (i.e.. whether a particular rating of present pain - either the highest or the lowest ever recorded for a particular patient - had been registered in the first vs. the second half of that patient’s program). Mirroring the results reported above. the reanalysis yielded a marginally significant effect of present pain intensity (F (l/46) = 3.62. 1?1.~e= 1.00. P -c0.07). a highly significant effect of prior pain intensity (F (2/92) = 207.58. mse = 0.04, P -c 0.01) and a reliable interaction between present pain and rating type ( F (l/46) = 5.50, nose = 0.07. P < 0.05). Importantly. neither the simple effect of treatment half, nor any interactions involving this effect. were significant (Ps> 0.10). Viewed as a whole. these results indicate that present pain intensity produces systematic distortions of memory for prior pain intensity. and that the magnitude of these distortions is independent of whatever changes in treatment outcome or learning competence may occur over the course of therapy.
Discussion
Present pain intensity appears to exert an assimilative effect on memory for prior pain intensity, such that ratings of the latter are attracted to or displaced toward ratings of the former. This conclusion seems to suit our data quite well. and it may also apply to the conflicting results obtained by others. In a recent study by Hunter et al. [3], patients experiencing acute head pain rated the intensity of their discomfort on a 5-point scale, and were asked to recall these ratings 1 or 5 days later. On
379
the average, patients underestimated their original intensity ratings by 6% at the l-day test and by 11% at the 5-day test; neither of these differences were statistically significant. In a subsequent study by Linton and Melin [7], patients with chronic back or joint pain rated the intensity of their pain on a loo-point scale before beginning a physical rehabilitation program, and attempted to recall these ratings 3-11 weeks later, upon termination of treatment. On the average, these patients overestimated their original ratings by 19% - a reliable (P < 0.01) margin. The conflict between the outcomes of these two studies may be more apparent than real. Whereas the patients in Hunter’s study performed recall in a pain-free state, those in Linton’s study perceived little or no change in their pain condition between the beginning of treatment, when original intensity ratings were taken, and its end, when memory for these ratings was tested. In light of the data depicted in Fig. 1, we suggest that this difference in level of present pain intensity - rather than, or in addition to, differences in the manner in which pain intensity was measured, the nature of the pains investigated, or the length of the retention intervals examined - may be primarily responsible for the observed disparity in experimental outcomes. We also suggest that although Hunter’s results appear to conflict with those reported by Linton, both sets of results are compatible with the conclusion that present pain intensity has an assimilative influence on memory for prior pain intensity. Whether this conclusion can be expanded to encompass dimensions of pain other than intensity (e.g., affective as opposed to sensory components of pain [9,10]), and forms of cognitive functioning other than memory (e.g., selective attention to or distorted perception of pain-related material [1,2]), are clinically and theoretically interesting issues that await detailed analysis.
Acknowledgements Preparation of this article was aided by grants to the first author from the (Canadian) Natural Sciences and Engineering Research Council (U0298) and the (American) National Institute of General Medical Sciences (GM32037). We thank J.M. Eich, S.J. Rachman, P.M. Smith, A.M. Treisman and L.M. Ward for providing valuable comments and suggestions, and E. Maslow, K. Pape and D. Sharpe for assisting in data collection and analysis.
References 1 Bower, C&H., Mood and memory, Amer. Psychol., 36 (1981) 129-148. 2 Bower, G.H. and Cohen, P.R., Emotionaf influences in memory and thinking: data and theory. In: MS. Clark and S.T. Fiske (Eds.). Affect and Cognition, Lawrence Erlbaum Associates, Hillsdale, NJ. 1982, pp. 291-331. 3 Hunter, M., Philips, C. and Rachman. S.. Memory for pain. Pain, 6 (1979) 35-46. 4 Kent, G., Memory of dental pain, Pain, 21 (1985) 187-194. 5 Kwilosz, D.M., Gracely, R.H. and Torgerson. W.S., Memory for post-surgical dental pain, Pain. Suppl. 2 (1984) S426.
6 Linton. S.J. and Gotestam. K.G.. A clinical comparison of two pain scales: correlation, remembering chronic pain. and a measure of compliance, Pain, 17 (1983) S7765. 7 Lmton. S.J. and Melin. L.. The accuracy of remembering chronic pain. Pain, 13 (1982) 2X1 2X5. R Madigan. R.J. and Bollenhach. A.K.. Effects of induced mood on retrieval of personal episodic and semantic memories, Psycho]. Rep.. 50 (1982) 1477157. 9 Melzack, R. and Torgerson. W.S.. On the language of pain. Anesthesiology. 34 (1971) SO-59 IO Melzack. R. and Wall. P.D.. The Challenge of Pain, Penguin, Harmondsworth. 19X2. 1 I Scott, J. and Huskisson. EC‘., Graphic representation of pain, Pain, 2 (1976) 175. 1X4. 12 ‘Teasdale. J.D. and Fogarty. F.J.. Differenttal effects of induced mood on retrieval of pleasant and unpleasant events from episodic memory. J. ahnorm. P\ychol., 88 (1979) 24X-257. 13 Travell. J.G. and Simons, D.G., Myofascial Pain and Dysfunction: the Trigger Point Manual. Williams and Wilkins. Baltimore. MD. 19X3.