Acupuncture is a commonly used therapy for treating functional diarrhea (FD), although there is limited knowledge on the mechanism. The objectives of this study were to investigate the differences in brain activities elicited by acupuncture between FD patients and healthy controls (HC) so as to explore the possible mechanism. Eighteen FD patients and eighteen HC received 10 sessions of acupuncture treatment at ST25 acupoints. Functional magnetic resonance imaging (fMRI) scans were, respectively, performed before and after acupuncture. The defecation frequency, Bristol stool form scale (SBFS), and MOS 36-item Short Healthy Survey (SF-36) were employed to evaluate the clinical efficacy. After acupuncture, the FD patients showed a significant decrease in defecation frequency and BSFS score. The regional homogeneity (ReHo) map showed a decrease in the paracentral lobule and postcentral gyrus, and an increase in the angular gyrus, insula, anterior cingulate cortex (ACC), and precuneus in the FD group. Moreover, the changes in ReHo values in the ACC were correlated with the reduction in defecation frequency. Decreasing functional connectivity among the ACC, insula, thalamus, and orbital frontal cortex only existed in the FD group. Conclusively, acupuncture alleviated defecation frequency and improved stool formation in FD patients. The efficacy might result from the regulation of the homeostasis afferent processing network. 1. Introduction Functional diarrhea (FD), one of the functional gastrointestinal disorders (FGID), is characterized by chronic diarrhea in the absence of structural or biochemical abnormalities that explain the symptoms [1]. According to the 2006 Rome III criteria, FD is defined as loose or watery stools without pain occurring in at least 75% of the stools [2]. The prevalence of FD ranges from 1.72% to 3.7% [3–5]. FD significantly influences the quality life of patients and consumes many healthcare resources [6]. Because of the unclear etiology and pathogenesis, the therapeutic options for FD are limited. As a result, complementary or alternative therapies are attractive to both patients and practitioners. Acupuncture, an important traditional Chinese medicine (TCM) therapy, has been used to treat gastrointestinal symptoms for centuries in China. Now it has been increasingly accepted as a complementary and alternative treatment for functional gastrointestinal disorders in western countries [7, 8]. ST25 (Tianshu), an important acupoint in the stomach meridian of the Foot Yangming, is commonly used to treat intestinal illnesses, such as
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