Spatial and temporal summation of sensory and affective dimensions of deep somatic pain.

There is considerable evidence in support of differential information processing of the sensory-discriminative and motivational-affective meanings of pain. The purpose of this work was to examine whether temporal (acute, tonic, persistent) and spatial (local, regional, widespread) aspects of deep somatic pain influence the sensory and affective dimensions of pain. Acute pain consisted of a short bout of pain, lasting about 100 s. Tonic pain was the 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 randomization of the application sequence. Comparing the response of experimental subjects to a group of matched cases with persistent masticatory myalgia alone or in combination with widespread musculoskeletal pain, we examine whether the experimental state is different from the matched clinical condition, and whether there is a difference between the condition being restricted 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 tonic/unilateral face pain (P = 0.055, borderline s.), and so was the normalized affective score (P = 0.009, s.). When comparing tonic/unilateral versus tonic/bilateral face pain, the affective scores increased with increased pain involvement (P = 0.009, s.) while the sensory sores were unaffected by the additional pain induced in the contralateral masseter muscle (P = 0.357, n.s). Notably, sensory and affective scores for tonic/bilateral and persistent/bilateral face pain were not statistically different (sensory: P = 0.169, n.s.; affective: P = 0.643, n.s). On the other hand, when contrasting persistent/bilateral face pain with persistent/ widespread musculoskeletal pain, both scores were significantly different (sensory: P < 0.001, s.; affective: P = 0.041, s.). Time in and spread of pain influenced the perceptual correlates of pain to a significant degree. The major increase in the sensory dimension occurred from 'no pain' to 'acute pain'. Affective scores showed the most significant increases from acute to tonic pain, particularly with greater spatial involvement. The significant increases in sensory scores observed when contrasting persistent facial pain alone and in combination with widespread musculoskeletal pain was attributed to the broader body experience. Because the perceptual correlates of tonic and matched persistent (chronic) pain states were similar, we concluded that it does not require months for the development of the sensory and affective meaning of persistent pain as assumed.