||Background: Myofascial pain of the jaw is a frequently encountered chronic pain syndrome. Recent trends have shown that alternative medicine, such as acupuncture, is becoming a popular treatment modality for this syndrome; however, little is known about the physiology behind acupuncture. Functional magnetic resonance imaging (fMRI) has been used with wide success in the mapping of human brain functions to better understand treatment and disease. Objective: To examine the effects of acupuncture at LI 4 on brain activations through fMRI on patients with chronic myofascial pain. Intervention: Manual stimulation of LI 4 with dry needling acupunture or sham acupuncture after clenching for 2 minutes while undergoing fMRI. Main Outcome Measures: All blood oxygen level dependent (BOLD)-related signal contrasts were made between the rest period after clenching and the first 5 minutes of acupuncture treatment. Results: Acupuncture induced significant activation of the primary sensory cortex and significant deactivation of the limbic system. Conclusions: Acupuncture performed at LI4 deactivated the limbic system, suggesting that acupuncture decreases the activity of brain sites related to pain.