Involvement of Opioid Receptors and α2-Adrenoceptors in Inhibitory Pain Modulation Processes: A Double-Blind Placebo-Controlled Crossover Study

HFS not only evokes local signs of central sensitization but also triggers a broader ipsilateral antinociceptive mechanism mediated by opioid receptors. Dysfunction of this lateralized pain modulation process might contribute to painful unilateral disorders such as migraine or complex regional pain syndrome.