Psychophysical and neurophysiological responses to acupuncture stimulation to incorporated rubber hand

From a neuroscientific perspective, the sensations induced by acupuncture are not only the product of the bottom-up modulation of simple needling at somatosensory receptors, but also of the reciprocal interaction of top-down modulation from the brain. The present study investigated whether acupuncture stimulation to incorporated body parts produces brain responses that are similar to the responses observed following acupuncture stimulation to the real hand. The present study included 17 participants who watched a rubber hand being synchronously stroked with their unseen left hand to induce incorporation of the rubber hand into their body. After the experimental modification of body ownership, acupuncture needle stimulation was applied to the LI4 acupoint on the incorporated rubber hand while brain activity was measured with functional magnetic resonance imaging (fMRI). When the rubber hand was fully incorporated with the real body, acupuncture stimulation to the rubber hand resulted in the experience of the DeQi sensation as well as brain activations in the dorsolateral prefrontal cortex (DLPFC), insula, secondary somatosensory cortex (SII), and medial temporal (MT) visual area. The insular activation was associated with the DeQi sensation from the rubber hand. The psychophysical and neurophysiological responses associated with acupuncture stimulation to the incorporated rubber hand were influenced by an enhanced bodily awareness of the hand, which was likely due to top-down modulation from the interoceptive system in the brain.