Fig. 5: FN^E–IO neurons send widespread projections to downstream motor and nonmotor regions.

a, Experimental strategy for tracing FN^E–IO neuron projections. b, Widespread axonal collaterals from FN^E–IO neurons in the MY, PN, MB and TH. Histological images from three mice (magenta, yellow and cyan indicate individual mice) are aligned to the Allen Mouse Brain CCF. Asterisk in the medulla indicates the mcMAO region, in which AAVretro-Cre was injected. c, Brain-wide distribution of the axonal collaterals from FN^E–IO neurons (n = 3 mice). The fraction of collateral is normalized to the total axonal labeling of individual mice. d, Overview of FN^E–IO neuron projections from single-neuron tracing experiments (Methods). Two distinct groups are assigned based on their unique projection patterns—both groups collateralize to the MY, PN and cerebellar cortex, but only neurons in group 2 project to the MB and TH. e, Axon density matrix of individual neurons. Each column represents one FN^E–IO neuron, and each row represents one downstream target. Projection density is normalized to the total number of axons for each cell. Several key regions are highlighted on the right. f, Objective visual inspection summarizes the projection motifs for group 1 and group 2 FN^E–IO neurons. Representative projection targets are denoted by bars and dots with different sizes indicating different densities. CB, cerebellum; MY, medulla; PN, pons; MB, midbrain; TH, thalamus; HY, hypothalamus.

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