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. 2014 Mar;155(3):635-42.
doi: 10.1016/j.pain.2013.12.024. Epub 2013 Dec 18.

Pain Relief by Touch: A Quantitative Approach

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Free PMC article

Pain Relief by Touch: A Quantitative Approach

Flavia Mancini et al. Pain. .
Free PMC article

Abstract

Pain relief by touch has been studied for decades in pain neuroscience. Human perceptual studies revealed analgesic effects of segmental tactile stimulation, as compared to extrasegmental touch. However, the spatial organisation of touch-pain interactions within a single human dermatome has not been investigated yet. In 2 experiments we tested whether, how, and where within a dermatome touch modulates the perception of laser-evoked pain. We measured pain perception using intensity ratings, qualitative descriptors, and signal detection measures of sensitivity and response bias. Touch concurrent with laser pulses produced a significant analgesia, and reduced the sensitivity in detecting the energy of laser stimulation, implying a functional loss of information within the ascending Aδ pathway. Touch also produced a bias to judge laser stimuli as less painful. This bias decreased linearly when the distance between the laser and tactile stimuli increased. Thus, our study provides evidence for a spatial organisation of intrasegmental touch-pain interactions.

Keywords: Analgesia; Pain; Relief; Signal detection theory; Space; Touch.

Figures

Fig. 1
Fig. 1
Selection of experimental laser energies. The pinprick detection threshold was determined for each subject, and the “medium” energy level was set as +0.1 J above this level. The energy of the “high” stimulus was then adjusted in 2 ways: 1) Increasing steps of +0.1 J, until the accuracy of discriminating between the 2 levels was >60%; 2) decreasing steps of −0.1 J, until the accuracy of discriminating between the 2 levels was <95%.
Fig. 2
Fig. 2
(a) Experimental conditions. In Experiment 1, laser pulses were given to the volar skin of the left forearm (“Laser” condition). In the “Laser + Touch” condition, 2 von Frey hair filaments accompanied the laser pulse, 1 cm either side. (b) Trial structure. All stimuli were delivered in the centre of a 3-second burst of white noise. Laser pulse duration was 4 ms. In “Laser + Touch” trials, tactile stimulation was applied for 1.5 seconds bracketing the laser pulse.
Fig. 3
Fig. 3
Experiment 1: signal detection results. Group average (± SE) sensitivity (a) and response bias (b) measures for each modality of stimulation; n = 8.
Fig. 4
Fig. 4
Experiment 1: (a) probability of detection, (b) reaction time, (c) rating of subjective pain intensity. Group average (± SE) values for each modality of stimulation (Laser, Laser + Touch) and laser energy (medium, high). (d) Quality of sensation. The mean proportion of agreement with each descriptor is plotted in each condition. Only trials in which the laser stimulus was detected are included; n = 8.
Fig. 5
Fig. 5
Experiment 2: (a) sensitivity and (b) response bias results. Group average (±SE) sensitivity (d’) and criterion (C) scores were plotted by the experimental condition (Laser, Laser + Touch: 1, 5, 9 cm either side of the laser pulse); n = 14.

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