FOS and viral infectious disease: To visualize the target brain areas (i.e., Cg1, PrL, and IL) of ChR2 or EYFP virus infection and c-Fos protein expression after photostimulation, the ChR2 virus infection was marked with green fluorescence, c-Fos expression was marked with red fluorescence, and ChR2 and c-Fos expression in the Cg1, PrL, and IL was merged (Supplementary Figure 2A).