FMR1 and fragile X syndrome: To determine whether spontaneous network activity patterns are altered in the developing visual cortex of FXS mice we performed in vivo calcium imaging in the primary visual cortex of lightly anesthetized Fmr1 knockout mice (Fmr1–/y) and wild type littermate controls (Fmr1+/y) at postnatal day (P) 8–14 (Figure 1).