Pain additivity, diffuse noxious inhibitory controls, and attention: A functional measurement analysis

Abstract

This study utilized the methodology of Functional Measurement theory to investigate the additivity of painful and non-painful thermally induced experiences at one body site with those produced by brief noxious and innocuous electrical stimuli at another. Forty healthy young subjects were tested, using a Peltier thermode to induce tonic pain and an electrocutaneous stimulator for presenting phasic pain, under conditions of either full attention or visual/cognitive distraction (counting numerous light signals) in order to evaluate whether the summed effects are attributable to refocused attention. Six levels of intensity were combined in a factorial design for both tonic and phasic pain. Subjects indicated the overall strength of their dual perception on a visual analog scale. Stimuli showed complex patterns of interaction. Two stimuli were generally rated as greater than one, but the summation was far from additive and greatly influenced by the intensity of the stronger stimulus, suggesting inhibitory action. In general, tonic heat pain strongly affected the perception of phasic electrocutaneous pain whereas the reverse was only partly true. Distraction had a very small effect, suggesting that the "pain inhibits pain" phenomenon attributable to diffuse noxious inhibitory controls (DNIC) is not due to attentional processes. Our data also relate to issues regarding spatial summation across dermatomes and to adaptation level effects in pain, in which a strong painful experience serves as an anchor or comparison point by which others are judged. The psychophysical findings provide a perceptual foundation for clinical phenomena in which patients face with comorbid pain disorders.

Role of endogenous pain modulation in chronic pain mechanisms and treatment

“…Lautenbacher et al 45 have reached similar conclusions based on a computational model of CPM. Another pertinent issue is the interrelations of CPM and expectation, suggestion, and placebo.…”

Diffuse noxious inhibitory controls and nerve injury

“…34 Conditioned pain modulation paradigms can be used to assess the efficacy of the DNIC system as a surrogate measure of descending inhibition and are diminished in many patients with chronic pain who are suffering from conditions including osteoarthritis, fibromyalgia, and diabetic neuropathy. 1,19,36 Meanwhile, a weak CPM is predictive of those initially pain-free patients who are more likely to develop postsurgical persistent pain. 35 Animals who received sham surgery had an identical DNIC to control unoperated animals.…”

Perception and suppression of thermally induced pain: A fMRI study

“…However, only thermal stimulation by thermode (Apkarian et al 2001;Lautenbacher et al 2007;Peyron et al 1999;Talbot et al 1991;Tracey et al 2002;Valet et al 2004) or laser (Bornhö vd et al 2002;Frot and Mauguiere 2003) can produce isolated true c-fibre activation (Brodal 2004). Therefore, stationary thermal stimulation is generally considered the best experimental surrogate for natural c-fibre excitation (Disbrow et al 1998).…”