- Email: [email protected]
The coming of age of pain expression
Pain 133 (2007) 3–4 www.elsevier.com/locate/pain
Editorial
The coming of age of pain expression The study of facial expressions of pain has historically been of interest to a small group of scientists and clinicians. Although there were isolated reports of the systematic use of facial expression for clinical studies as far back the 1940s (e.g., [2]), contemporary scientific analysis of the nature and properties of pain expression largely began in the 1980s (e.g., [4,8]). The emergence of this area was abetted by the development of the Facial Action Coding System (FACS) [5] which gave investigators interested in pain expression a new, powerful and sophisticated analytic tool. More recent interest in pain expression has been driven by a number of scientific and practical issues. Among these have been concerns about the measurement properties of verbally based tools for assessing pain, including, but not limited to, the fact that some populations (e.g., young children, patients with verbal communication deficits) are deficient in the ability to use language to describe their pain. The existence of an alternative channel of information that may provide an alternative window into pain regulatory systems is one common argument for focusing on the face. Curiosity about the variables that affect this alternative channel and its larger role in social communication [10,14] is another. Nevertheless, despite the availability of sophisticated methodologies, assessing facial expression has been until recently a relatively uncommon approach in pain studies. This is partly because, relative to more common and traditional approaches, such as verbal report, facial expression is inconvenient to measure. Studies are difficult to perform quickly because of the demanding nature of the measurement procedures. In the absence of evidence that they provide added value, it is not clear that they have any particular advantage. Advances in methodology often trigger advances in substantive knowledge, as the imaging revolution has so clearly demonstrated in the neurosciences. Yet a methodology can only be transformative if it has the ability to identify and clarify phenomena not readily addressed by other methods. The paper by Kunz et al. [7] is an excellent example of the ‘‘coming of age’’ of this field; demonstrating certain fundamental properties of pain expres-
sion while also showing how the use of facial measurement brings added scientific value. Their paper builds on previous studies that have reported dementia to be accompanied by increased facial activity in response to pain. Participants were controls or patients with dementia who were exposed to experimental pain induced by five levels of focal pressure stimulation. Careful measurement of the participants’ pain expression, using FACS, showed (1) a ‘‘dose-dependent’’ increase in facial actions that have been associated in the literature with pain that was (2) distinct from changes in facial actions that have not been associated with pain and (3) enhanced among patients with dementia. The authors also report that verbal reports (1) did not differentiate the pain of dementia patients from that of controls and (2) were invalid among significant proportions of patients with dementia. The study was well designed, rigorous, methodically conducted and analyzed. Its findings provide strong support for the conclusion that there is a distinct facial sign, consisting of actions of corrugator, orbicularis oculi and levator muscles [9] and that the process underlying this expression responds specifically to variations in painful stimulation. More novel are the findings that the intensity of the pain expression was both enhanced and showed a steeper pain–response gradient among the patients with dementia suggesting that dementia affects the system for regulating pain expression. This set of findings speaks to the added value the use of facial measurement brings to studies of basic pain processes. The facial measurement procedure was able to identify a phenomenon that could not be observed using the more conventional verbal measurement. Indeed, had the study been restricted simply to verbal report measures, it would have appeared that there was little, if any, difference in pain–response between patients and controls. As the authors point out, this distinct pattern of facial response to pain might reflect enhanced pain processing among patients with dementia or it might reflect a diminution of affect self-regulatory skills. Each possibility is interesting. Taken together they call for further research that is likely to yield information that can add in direct and specific ways to our understanding
0304-3959/$32.00 Ó 2007 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.pain.2007.10.015
4
Editorial / Pain 133 (2007) 3–4
of pain in the presence of neurological impairment and to the clinical practice of pain assessment. The critical point, however, is that facial measurement methodology has opened the window to these possibilities in a way that other techniques might not have. Recent years have provided several other examples in which the study of facial expression holds promise to add interesting new information in pain science, ranging from neuroimaging studies [1,12] to research on pain-related empathy [6], the communal-coping model of pain [13] and pain assessment [11]. Together with the data from Kunz et al. [7] it would appear that the study of pain expression has truly come of age. Technological developments in the foreseeable future that promise to overcome the laborious nature of pain expression measurement, such as automated assessment [3], are likely to accelerate this process.
References [1] Botvinick M, Jha AP, Bylsma LM, Fabian SA, Solomon PE, Prkachin KM. Viewing facial expressions of pain engages cortical areas involved in the direct experience of pain. Neuroimage 2005;25:312–9. [2] Chapman WP, Jones CM. Variations in cutaneous and visceral pain sensitivity in normal subjects. J Clin Investig 1944;23:81–91. [3] Cohn J, Ekman P. Measuring facial action. In: Harrigan JA, Rosenthal R, Scherer K, editors. The new handbook of methods in nonverbal behavior research. New York: Oxford University Press; 2005. p. 9–64.
[4] Craig KD, Patrick CJ. Facial expression during induced pain. J Personal Soc Psychol 1985;48:1080–91. [5] Ekman P, Friesen WV. Manual for the facial action coding system. Palo Alto, CA: Consulting Psychologists Press; 1978. [6] Goubert L, Craig KD, Vervoort T, Morley S, Sullivan MJL, Williams AC de C, et al. Facing others in pain. The effects of empathy. Pain 2005;118:285–8. [7] Kunz M, Scharmann S, Hemmeter U, Schepelmann K, Lautenbacher S. The facial expression of pain in patients with dementia. Pain 2007;133:221–8. [8] LeResche L. Facial expression in pain: a study of candid photographs. J Nonverbal Behav 1982;7:46–56. [9] Prkachin KM. The consistency of facial expressions of pain: a comparison across modalities. Pain 1992;51:297–306. [10] Prkachin KM, Craig KD. Expressing pain: the communication and interpretation of facial pain signals. J Nonverbal Behav 1994;19:191–205. [11] Prkachin KM, Schultz I, Berkowitz J, Hughes E, Hunt D. Assessing pain behaviour in real time: concurrent validity and examiner sensitivity. Behav Res Therapy 2002;40:595–607. [12] Simon D, Craig KD, Miltner WHR, Rainville P. Brain responses to dynamic facial expressions of pain. Pain 2006;126:309–18. [13] Sullivan MJL, Thibault P, Savard A. The influence of communication goals and physical demands on different dimensions of pain behavior. Pain 2006;125:270–7. [14] Williams AC de C. Facial expression of pain: an evolutionary account. Behav Brain Sci 2002;25:439–88.
Kenneth M. Prkachin* University of Northern British Columbia, Department of Psychology, 3333 University Way, Prince George, BC, Canada V2N 4Z9 E-mail address: [email protected]
*
Tel.: +1 250 960 6633; fax: +1 250 960 5536.
Editorial
The coming of age of pain expression The study of facial expressions of pain has historically been of interest to a small group of scientists and clinicians. Although there were isolated reports of the systematic use of facial expression for clinical studies as far back the 1940s (e.g., [2]), contemporary scientific analysis of the nature and properties of pain expression largely began in the 1980s (e.g., [4,8]). The emergence of this area was abetted by the development of the Facial Action Coding System (FACS) [5] which gave investigators interested in pain expression a new, powerful and sophisticated analytic tool. More recent interest in pain expression has been driven by a number of scientific and practical issues. Among these have been concerns about the measurement properties of verbally based tools for assessing pain, including, but not limited to, the fact that some populations (e.g., young children, patients with verbal communication deficits) are deficient in the ability to use language to describe their pain. The existence of an alternative channel of information that may provide an alternative window into pain regulatory systems is one common argument for focusing on the face. Curiosity about the variables that affect this alternative channel and its larger role in social communication [10,14] is another. Nevertheless, despite the availability of sophisticated methodologies, assessing facial expression has been until recently a relatively uncommon approach in pain studies. This is partly because, relative to more common and traditional approaches, such as verbal report, facial expression is inconvenient to measure. Studies are difficult to perform quickly because of the demanding nature of the measurement procedures. In the absence of evidence that they provide added value, it is not clear that they have any particular advantage. Advances in methodology often trigger advances in substantive knowledge, as the imaging revolution has so clearly demonstrated in the neurosciences. Yet a methodology can only be transformative if it has the ability to identify and clarify phenomena not readily addressed by other methods. The paper by Kunz et al. [7] is an excellent example of the ‘‘coming of age’’ of this field; demonstrating certain fundamental properties of pain expres-
sion while also showing how the use of facial measurement brings added scientific value. Their paper builds on previous studies that have reported dementia to be accompanied by increased facial activity in response to pain. Participants were controls or patients with dementia who were exposed to experimental pain induced by five levels of focal pressure stimulation. Careful measurement of the participants’ pain expression, using FACS, showed (1) a ‘‘dose-dependent’’ increase in facial actions that have been associated in the literature with pain that was (2) distinct from changes in facial actions that have not been associated with pain and (3) enhanced among patients with dementia. The authors also report that verbal reports (1) did not differentiate the pain of dementia patients from that of controls and (2) were invalid among significant proportions of patients with dementia. The study was well designed, rigorous, methodically conducted and analyzed. Its findings provide strong support for the conclusion that there is a distinct facial sign, consisting of actions of corrugator, orbicularis oculi and levator muscles [9] and that the process underlying this expression responds specifically to variations in painful stimulation. More novel are the findings that the intensity of the pain expression was both enhanced and showed a steeper pain–response gradient among the patients with dementia suggesting that dementia affects the system for regulating pain expression. This set of findings speaks to the added value the use of facial measurement brings to studies of basic pain processes. The facial measurement procedure was able to identify a phenomenon that could not be observed using the more conventional verbal measurement. Indeed, had the study been restricted simply to verbal report measures, it would have appeared that there was little, if any, difference in pain–response between patients and controls. As the authors point out, this distinct pattern of facial response to pain might reflect enhanced pain processing among patients with dementia or it might reflect a diminution of affect self-regulatory skills. Each possibility is interesting. Taken together they call for further research that is likely to yield information that can add in direct and specific ways to our understanding
0304-3959/$32.00 Ó 2007 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.pain.2007.10.015
4
Editorial / Pain 133 (2007) 3–4
of pain in the presence of neurological impairment and to the clinical practice of pain assessment. The critical point, however, is that facial measurement methodology has opened the window to these possibilities in a way that other techniques might not have. Recent years have provided several other examples in which the study of facial expression holds promise to add interesting new information in pain science, ranging from neuroimaging studies [1,12] to research on pain-related empathy [6], the communal-coping model of pain [13] and pain assessment [11]. Together with the data from Kunz et al. [7] it would appear that the study of pain expression has truly come of age. Technological developments in the foreseeable future that promise to overcome the laborious nature of pain expression measurement, such as automated assessment [3], are likely to accelerate this process.
References [1] Botvinick M, Jha AP, Bylsma LM, Fabian SA, Solomon PE, Prkachin KM. Viewing facial expressions of pain engages cortical areas involved in the direct experience of pain. Neuroimage 2005;25:312–9. [2] Chapman WP, Jones CM. Variations in cutaneous and visceral pain sensitivity in normal subjects. J Clin Investig 1944;23:81–91. [3] Cohn J, Ekman P. Measuring facial action. In: Harrigan JA, Rosenthal R, Scherer K, editors. The new handbook of methods in nonverbal behavior research. New York: Oxford University Press; 2005. p. 9–64.
[4] Craig KD, Patrick CJ. Facial expression during induced pain. J Personal Soc Psychol 1985;48:1080–91. [5] Ekman P, Friesen WV. Manual for the facial action coding system. Palo Alto, CA: Consulting Psychologists Press; 1978. [6] Goubert L, Craig KD, Vervoort T, Morley S, Sullivan MJL, Williams AC de C, et al. Facing others in pain. The effects of empathy. Pain 2005;118:285–8. [7] Kunz M, Scharmann S, Hemmeter U, Schepelmann K, Lautenbacher S. The facial expression of pain in patients with dementia. Pain 2007;133:221–8. [8] LeResche L. Facial expression in pain: a study of candid photographs. J Nonverbal Behav 1982;7:46–56. [9] Prkachin KM. The consistency of facial expressions of pain: a comparison across modalities. Pain 1992;51:297–306. [10] Prkachin KM, Craig KD. Expressing pain: the communication and interpretation of facial pain signals. J Nonverbal Behav 1994;19:191–205. [11] Prkachin KM, Schultz I, Berkowitz J, Hughes E, Hunt D. Assessing pain behaviour in real time: concurrent validity and examiner sensitivity. Behav Res Therapy 2002;40:595–607. [12] Simon D, Craig KD, Miltner WHR, Rainville P. Brain responses to dynamic facial expressions of pain. Pain 2006;126:309–18. [13] Sullivan MJL, Thibault P, Savard A. The influence of communication goals and physical demands on different dimensions of pain behavior. Pain 2006;125:270–7. [14] Williams AC de C. Facial expression of pain: an evolutionary account. Behav Brain Sci 2002;25:439–88.
Kenneth M. Prkachin* University of Northern British Columbia, Department of Psychology, 3333 University Way, Prince George, BC, Canada V2N 4Z9 E-mail address: [email protected]
*
Tel.: +1 250 960 6633; fax: +1 250 960 5536.