Some of the Effects of Acupuncture in Knee Pain May be Due to Activation of the Reward System

Acupuncture is an ancient therapy with a variety of different explanatory models. A cascade of physiologic effects has been reported, both in the peripheral and the central nervous system, following the insertion of a needle. Clinical trials testing the specific claims of acupuncture have generally tried to focus on testing the efficacy of applying specific techniques and/or specified points. However, different conditions may respond differently to different modes of stimulation. Also, insertion of needles into the body can stimulate effects not dependent on the locations of stimulation. Recently, it was demonstrated that both superficial and deep needling (with de qi/Hibiki) resulted in amelioration of patellofemoral pain and an increased feeling of wellbeing. One area in the brain that is affected by acupuncture stimulation is the limbic system. The limbic system consists of a group of brain structures, including the hippocampus, amygdala, and their interconnections, and connections with the hypothalamus, septal area, and portions of the tegmentum. It contains many of the centres related to emotion and reward. The pleasurable aspect of the acupuncture experience has largely been ignored as it has been considered to be part of its antinociceptive effects. It has previously been reported that physical exercise and electroacupuncture in animals result in modulation of the peptidergic content in limbic structures. These results are supported by recent animal studies in Japan that have clearly demonstrated that acupuncture results in the activation of the reward system. These findings are supported by positron emission tomography studies in patients, which showed that the insula ipsilateral to the site of needling was activated, as well as the dorsolateral prefrontal cortex, the anterior cingulate and the midbrain. Taken together, these results suggest that acupuncture, as well as the patient's expectation and belief regarding a potentially beneficial treatment, modulate activity in the reward system.