(A) For granular and supragranular layers, developmental changes in the connectivity of local circuits are illustrated. Excitatory neurons are illustrated in black. PV+ (blue), SST+ (burgundy), and VIP+ (green) inputs are color coded, along with neuromodulatory inputs such as acetylcholine (purple). Excitatory TC inputs are shown in black. Developmental age and time are annotated at the bottom. L4 changes in interneuron connectivity precede L2/3 changes (Jiang et al., 2010), with PV maturation in L2/3 correlated in time to CP onset and closure (Fagiolini et al., 2004). L2/3 connectivity matures during this period (Cossell et al., 2015; Ko et al., 2013). SST+ connectivity to PV+ neurons, initially strong, grows weaker during this time and loses sensitivity to cholinergic modulation (Yaeger et al., 2019).
(B) Mature connectivity is summarized.