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Conditioned Pain Modulation (CPM) Effects Captured in Facial Expressions

Authors Kunz M, Bunk SF, Karmann AJ, Bär KJ, Lautenbacher S

Received 4 January 2021

Accepted for publication 26 February 2021

Published 23 March 2021 Volume 2021:14 Pages 793—803


Checked for plagiarism Yes

Review by Single anonymous peer review

Peer reviewer comments 3

Editor who approved publication: Dr Jonathan Greenberg

Miriam Kunz,1 Stefanie F Bunk,2 Anna J Karmann,3 Karl-Jürgen Bär,4 Stefan Lautenbacher3

1Department of Medical Psychology and Sociology, University of Augsburg, Augsburg, Germany; 2Department of General Practice and Elderly Care Medicine, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands; 3Physiological Psychology, Otto-Friedrich University Bamberg, Bamberg, Germany; 4Department of Psychosomatic Medicine and Psychotherapy, University Hospital, Jena, Germany

Correspondence: Miriam Kunz
Department of Medical Psychology and Sociology, University of Augsburg, Augsburg, Germany
Tel +49 821 598-3720
Fax +49 821 598-5116
Email [email protected]

Purpose: Conditioned pain modulation (CPM) is most often assessed using self-report of pain. However, self-report of pain is not always available (eg in individuals with cognitive impairment) and is susceptible to report bias. In comparison, the facial expression of pain is more reflex-like and represents one of the most sensitive and specific non-verbal signals of pain. The aim of the present study was to investigate whether the facial expression of pain is sensitive enough to capture endogenous pain inhibition as elicited during CPM paradigms.
Patients and Methods: In total, 26 female participants took part in this study. Facial and verbal responses to phasic heat pain were assessed once while participants immersed their hand in a hot water bath and once without additional stimulation. Facial responses were analyzed using the Facial Action Coding System (FACS). Verbal responses were assessed using a Numerical Rating Scale (NRS).
Results: Pain-relevant facial responses as well as pain ratings to phasic heat pain were significantly reduced when participants simultaneously immersed their hand in a hot water bath compared to baseline. Thus, CPM effects could be demonstrated both on subjective as well as on facial responses. Moreover, CPM-induced changes in pain-relevant facial responses and in NRS ratings were significantly correlated.
Conclusion: The present study shows that facial expressions of pain are sensitive enough to capture CPM effects. Given the proven clinical usefulness of assessing CPM, the parallel assessment of verbal and facial CPM effects might be a promising approach with wider scope of applications. Further research in other demographic healthy participant and clinical cohorts is warranted.

Keywords: pain, CPM, conditioned pain modulation, facial expression, FACS

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