For example, we recently used this neonatal virus injection approach to express GCaMP6s in barrel cortex of wild-type and Fmr1 knockout mice (a model of Fragile X Syndrome), which allowed us to record the spontaneous and whisker-evoked activity of L2/3 neurons at P14-16 (He et al., 2017). This evidence concerns the gene FMR1 and fragile X syndrome.