a, 3D rendering of nine GrC axons, nine PCs, and the locations of synapses (white lines) connecting them. Note, unlabeled axonal varicosities are presynaptic to non-PC neurons (e.g., molecular layer interneurons). b, Calculation of Hamming similarity as a pairwise metric to compare the similarity of two binary patterns. The example compares the postsynaptic connectivity pattern between two PCs from different parallel fibers (PFs) where a “1” denotes a connection and a “0” denotes the lack of connection. c, Box plot (25th, 50th and 75th percentiles with whiskers extended to points within 1.5 IQRs) of the ratio of GrC→PC synapses to the total number of times a GrC axon and PC pair contact (touch) one another (Methods). Left: synapse ratio per GrC. Right: synapse ratio per PC. d, Similarity of GrC inputs between pairs of PCs with at least 30 common GrC axon contacts comparing shuffled input connectivity, non-local GrC axons, and local GrC axons. All three populations are significantly different (p = 1.25 × 10−56, Kruskal-Wallis test; p = 0.00433, shuffle vs. non-local GrC axons; p = 9.16 × 10−32, non-local GrC axons vs. local GrC axons; p = 4.91 × 10−61, shuffle vs. non-local GrC axons; Dunn’s post hoc tests, Bonferroni corrected for multiple comparisons).