This circuit has been studied in detail by neurophysiologists, and several of its properties have been found to be altered during development in mouse models of Fragile-X syndrome, including parvalbumin-positive interneuron number (Selby et al., 2007), GABA receptor reversal potential (He et al., 2014), dendritic spine dynamics (Cruz-Martín et al., 2010), and L4 excitatory input (Bureau et al., 2008), reviewed by Contractor et al., 2015. Here, PVALB is linked to fragile X syndrome.