From 2013 to 2016, the field focused on (1) early life stress, panic disorder, alexithymia, functional somatic syndrome; (2) collagenous colitis and malabsorption syndrome; (3) functional connectivity, anterior cingulate cortex, and catecholamine; (4) Dientamoeba fragilis and Bifidobacterium infantis 35624; (5) fecal microbiota transplantation (FMT); (6) visceral hyperalgesia and substance P; (7) interstitial cells of Cajal; (8) low-grade inflammation, paracellular permeability, and oxidative stress; and (9) δ opioid receptor and ion transport. Here, TAC1 is linked to collagenous colitis.