Microglial activation and ensuing neuroinflammation have been shown to participate in delirium‐associated cognitive impairment.[20] However, microglial activation had no or negligible contribution to the regulation of cognition by the intestinal clock because the number and morphology of Iba1+ cells as well as the levels of inflammatory factors (such as Il‐1β, Tnfα, and Ccl8) in the hippocampus and in primary microglial cells were not different between Bmal1‐iKO and control mice (Figure S5A–E, Supporting Information). Here, BMAL1 is linked to delirium.