Spatial and temporal summation of sensory and affective dimensions of deepsomatic pain

There is considerable evidence in support of differential information proce ssing of the sensory-discriminative and motivational-affective meanings of pain. The purpose of this work was to examine whether temporal (acute, toni c, persistent) and spatial (local, regional, widespread) aspects of deep so matic pain influence the sensory and affective dimensions of pain. Acute pa in consisted of a short bout of pain, lasting about 100 s. Tonic pain was t he experience of experimentally maintained pain for 18 min. Both acute and tonic pain were induced by infusion of an algesic or control substance into muscle with the subject blinded with respect to the type of infusion and r andomization of the application sequence. Comparing the response of experim ental subjects to a group of matched cases with persistent masticatory myal gia alone or in combination with widespread musculoskeletal pain, we examin e whether the experimental state is different from the matched clinical con dition, and whether there is a difference between the condition being restr icted to the face or not. The McGill pain questionnaire was used to assess the sensory and affective correlates of pain. The normalized sensory score for acute/unilateral face pain was different from that established for toni c/unilateral face pain (P = 0.055, borderline s.), and so was the normalize d affective score (P = 0.009, s.), When comparing tonic/unilateral versus t onic/bilateral face pain, the affective scores increased with increased pai n involvement (P = 0.009, s.) while the sensory sores were unaffected by th e additional pain induced in the contralateral masseter muscle (P = 0.357, n.s). Notably, sensory and affective scores for tonic/bilateral and persist ent/bilateral face pain were not statistically different (sensory: P = 0.16 9, n.s.; affective: P = 0.643, n.s). On the other hand, when contrasting pe rsistent/bilateral face pain with persistent/widespread musculoskeletal pai n, both scores were significantly different (sensory: P < 0.001, s.; affect ive: P = 0.041, s.). Time in and spread of pain influenced the perceptual c orrelates of pain to a significant degree. The major increase in the sensor y dimension occurred from 'no pain' to 'acute pain'. Affective scores showe d the most significant increases from acute to tonic pain, particularly wit h greater spatial involvement. The significant increases in sensory scores observed when contrasting persistent facial pain alone and in combination w ith widespread musculoskeletal pain was attributed to the broader body expe rience. Because the perceptual correlates of tonic and matched persistent ( chronic) pain states were similar, we concluded that it does not require mo nths for the development of the sensory and affective meaning of persistent pain as assumed. (C) 1999 International Association for the Study of Pain. Published by Elsevier Science B.V.