Verum and sham acupuncture exert distinct cerebral activation in pain processing areas: a crossover fMRI investigation in healthy volunteers

Although acupuncture is effective for treating pain, its site-specificity is questioned. The aim was to compare the cerebral responses of needling applied to an acupuncture point to the needling of a sham point, using functional magnetic resonance imaging (fMRI). Twenty-one healthy male volunteers were enrolled. Manual stimulation of the acupuncture (ST44) and sham points on the dorsum of the left foot was applied during fMRI in a crossover manner. fMRI data analysis was performed contrasting the ST44 and the sham conditions. Stimulation intensity, subjective discrimination of the needling site and the incidence of "Qi" sensation were additionally recorded. Stimulation of ST44 acupoint, in comparison to the sham procedure, was associated with an increased fMRI-activation in the primary somatosensory, the inferior parietal and the prefrontal cortex and the posterior insula. Sham needling was associated with increased activation in the anterior cingulate cortex and the anterior insula. Verum acupuncture increased the activity of discriminative somatosensory and cognitive pain processing areas of the brain, whereas sham needling activated the areas responsible for affective processing of pain. This may explain favorable effects of verum acupuncture in clinical studies about treatment of chronic pain patients.