Acupuncture can mobilize endogenous opioid system and produce analgesia. However, there is some variability of the analgesic effect between individuals, which is related with cholecystokin level of the subject. In the present study, we try to use functional magnetic resonance imaging (fMRI) to address the question by which neuropathways CCK influences acupuncture induced analgesia. Two different frequencies of transcutaneous electric acupoint stimulation (TEAS) were administered to normal human body. TEAS was used instead of traditional acupuncture for its similar analgesic effect and convenience of parameter adjustment. Our previous studies have indicated that low and high frequency TEAS generated effects through different neuropathways, in which some nuclei of midbrain, thalamus and hypothalamus played an important role. 25 healthy volunteers were randomly divided into two groups to receive low and high frequency TEAS respectively. Data from functional MRI scanning (EPI sequence, TR=3000 ms, TE=45 ms, Flip angle: 90°) were collected at the same time of stimulation. Basal and after TEAS pain thresholds were measured by radiant heat withdrawal test 1～3 days before fMRI examination and changes of pain threshold were calculated as the index of analgesic effect of TEAS. Functional data were processed with cross correlation of timecourse and stimulation curve after registration, normalization and detrending. The averaged signal intensity of every interested region was linear regressed according to the change of pain threshold. We found that in low frequency TEAS group, activation intensity of contralateral primary and supplementary motor areas (MI and SMA), bilateral secondary somatosensory area (SⅡ), contralateral thalamus and anterior cingulate cortex (BA 24), ipsilateral superior temporal gyrus, insula had a significant linear correlation with the change of pain threshold. Furthermore, the signal intensity of bilateral hippocampus and the change of pain threshold had a negative linear correlation. While in th
