All patients will be evaluated for study eligibility at visit 1 (baseline). Baseline assessment includes individual IBS symptoms (pain/discomfort, bloating, constipation, and diarrhea) as perceived by patients will be scored. The syndrome of IBS patients will also be recorded and analyzed based on the Chinese medicine theories. All patients will then undergo baseline rectal barostat for thresholds of rectal sensation. At visit 2, eligible patients will be randomly assigned to either (1) electroacupuncture or (2) sham electroacupuncture treatment groups. Functional Magnetic Resonance Imaging (fMRI) scanning will be performed before, during and after the electroacupuncture or sham electroacupuncture treatment.