Pavlovian Conditioning of Muscular Responses in Chronic Pain Patients : An Experimental Study

Abstract

Objectives: Muscular tension is assigned an important role in the development, enhancement and maintenance of chronic pain syndromes. It is seen as a psychophysiological correlate of learned fear and avoidance behaviour. While theories like the concept of response stereotypy within the biopsychosocial model of musculoskeletal disorders (Flor et al., 1992) and the theory of myogenic headache with its approach of dysfunctional increased muscle effort (Bischof & Traue, 1983) stress the aspect of respondent learning for the chronification process, multidisciplinary pain therapy focuses on a “muscular unlearning”, although empirical evidence has not as yet satisfactorily proved that respondent learning processes are the meditative variable between muscular tension and chronic pain. Design & methods: An experimental study using a differential Classical conditioning paradigm was undertaken. 18 patients with chronic back pain or tension-type headache, respectively, and 18 healthy controls were examined. A high, aversive tone served as CS+ which was paired with an intra-cutaneous electric pain stimulus (US), while a neutral tone was used as CS-. Simultaneously, integrated surface electromyograms (EMG) were recorded from erector spinae, (lumbar, bilateral), musculus trapezius (bilateral), musculus corrugator supercilii and biceps brachii (bilateral). It was hypothesised that the pain patients would demonstrate an enhanced conditionability and symptom-specific learning. Results: Learning occurred in both patient groups. During the two acquisition phases there were significantly more muscular reactions to the CS+ than CS- in terms of the number of reactions across all muscle sites. As this learning was enhanced to the CS+ and the difference between CS+ and CS- reached significance in four sites (lumbar right, trapezius right, right and left arm), the differential conditioning design was verified. Furthermore, the question of augmented conditionability of the patient groups compared to the healthy controls could be supported. The back pain and tension-type headache patients demonstrated significantly more and stronger conditioned responses to the CS+. This also applied to the unconditioned muscular responses as well as to the symptom-specific sites of the back pain patients. Conclusions: The findings supported the idea of a response stereotypy in the group of back pain patients. The response pattern of the tension-type headache patients, though, questioned the current definition of symptom-specificity of this pain syndrome and approved the inclusion of the lower back muscles in future studies. This study has clinical relevance in that the findings support the approach of “muscular unlearning” in multidisciplinary pain therapy.