FMR1 and fragile X syndrome: As reported in Fig. 5E the spontaneous activity of FAST cells, most probably neurons, was significantly stronger in FXS cultures; indeed both the amplitude (Fig. 5E left) and the frequency (Fig. 5E middle and right) of calcium events were significantly higher in FMRP-KO neurons respect to FMRP-WT neurons, with no difference in synchronized firing, thus suggesting the possible overexcitability of the FXS cortical network.