School of Psychology

Blocking the painful effects of electrical stimulation in inflamed skin

Researchers     Lone Knudsen, Dana Hince

Supervisors      Peter Drummond

Date:                27th July, 2009
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This study aimed to investigate the remote effects of topical capsaicin, an inflammatory agent, applied to the forearm on pain sensitivity in each side of the forehead in 17 healthy volunteers. Pressure-pain thresholds and sharpness sensations were assessed on each side of the forehead before and during 48 hours of capsaicin treatment. Heat was applied to the treated area to rekindle pain at times of assessment. Tests of sensation were also performed in the treated forearm and the contralateral forearm before and after 48 hours of treatment. Hyperalgesia to sharpness, but not pressure-pain, developed in the treated area whereas sensations remained stable in the contralateral forearm. Sharpness ratings decreased bilaterally in the forehead 6 hours after treatment, and an ipsilateral analgesia to pressure-pain developed when the treated area was heated after 48 hours of treatment. No contralateral changes were observed for pressure-pain. Diffuse noxious inhibitory controls and stress-induced analgesia may account for the bilateral decrease in forehead analgesia to sharpness, whereas the ipsilateral forehead analgesia to pressure-pain may arise due to activation of coeruleospinal pain control. These findings suggest that pain modulation involves unilaterally extending mechanisms in addition to local and generalized controls. The dissociated changes to sharpness and pressure-pain indicate distinct cutaneous and deep central pain pathways.