To do so, we engineered MCs in AD mice with the expression of channelrhodopsin‐2‐E123A (ChR2), a modified version of a light‐gated excitatory ion channel by injecting the rAAV1/2‐DIO‐ChR2/GFP virus into the dentate gyrus of AD/Calb2‐CRE mice, in which CRE was expressed specifically in MCs of AD mice under a control of calbindin‐2 (Calb2) promoter (AD/ChR2 mice, Figure 3a,b). The gene discussed is CALB2; the disease is Alzheimer disease.