Extended Data Figure 5. MF collateral axons connectivity to GrCs.

a, 3D rendering of a MF (red) bouton, with an axon collateral making synapses onto a GrC (blue) dendrite near a claw. Asterisks denote the location of synapses. b, Rendering of a MF bouton with no axon collaterals. c, Distribution of number of collaterals per MF bouton (n = 63); a MF bouton can have multiple axon collaterals, and each collateral may or may not make synapses onto GrCs. d, Box plot (25th, 50th and 75th percentiles with whiskers extended to points within 1.5 IQRs) of the number of MF-GrC connections: per MF bouton (n = 63), per axon collateral (n = 8), and per each bouton in a collateral (n = 16). e, Box plot of the number of synapses in each MF-GrC connection: per MF bouton (n = 978), per collateral (n = 28), and per bouton in collateral axons (n = 51). Due to the low frequency of axon collaterals, GrC targets, and the number of synapses per GrC target, it is unlikely that MF axon collaterals to GrCs represent a major route of signal propagation. f, Example of an axon collateral making synapses to a GrC on the trunk, and with more synapses formed on the claw. g, Example of a connection on the trunk of the dendrite, with no claw. h, Joint probability distribution of the synapse location of MF axon collaterals onto GrCs (on claw vs. trunk) and whether or not the dendrite made a claw onto the same MF bouton, or did not have claws (unformed claws). These examples of MF axon collateral connections to GrCs could represent different states of MF→GrC rewiring, supporting the hypothesis that MF→GrC wiring adapts to changing MF input representation^6,42. Scale bars are 10 μm.