In one mouse visual cortex volume, like-to-like synapses formed on basal and apical dendrites in proportion to axon–dendrite contact, for within-area, feedforward and feedback axons

Question: Ding et al. (2025) found in the MICrONS mouse visual cortex volume that excitatory neurons with similar visual responses connect more often than neurons whose axon and dendrite pass equally close (like-to-like). Is this rule a property of basal dendrites, apical dendrites, or both? Data: the Ding et al. functional connectomics table (148 proofread presynaptic neurons, 294,727 connected and proximity-control pairs), 9,944 MICrONS v1507 synapses of these pairs, and public v661 skeletons of 11,010 cells with basal and apical node labels. Method: for each pair and compartment we measured the dendrite length within 5 um of the axon (co-travel) and counted synapses. A Poisson model with co-travel as exposure and one intercept per presynaptic neuron gave a like-to-like coefficient b per compartment (log synapses per um of co-travel per SD of similarity). A written plan fixed the primary measure, models and nulls before any compartment result. Results: like-to-like held on both compartments. For digital-twin signal correlation, b was 0.18 (95% CI 0.13 to 0.23) on basal and 0.14 (0.09 to 0.19) on apical dendrites; both exceeded all 2,000 within-neuron permutations (null SD 0.014 and 0.020). In vivo movie-response correlation gave 0.13 and 0.13. In 4,350 connected pairs whose axon passed both compartments (4,959 synapses), the apical share of synapses followed the apical share of co-travel; the similarity effect on that share was -0.020 log-odds per SD (CI -0.079 to 0.037; p = 0.45), against about -0.15 if like-to-like were on basal dendrites only. The raw basal coefficient was 0.04 larger, but a null that splits each pair's synapses by co-travel alone gave the same difference (0.033 +/- 0.015; p = 0.56). The result held for distal apical dendrite (b = 0.16), for within-area, feedforward and feedback axons, for co-travel radii of 3 and 10 um, with a free co-travel exponent and with intercepts per neuron, area and layer. Exploratory: pairs with nearer receptive fields had fewer basal synapses per um (b = -0.07) than apical (-0.03); this did not survive the within-pair test or the free-exponent model. Conclusion: an axon makes more synapses per um of contact onto neurons with similar responses and places them on basal and apical dendrites in proportion to where it touches them. Limits: one mouse; 148 axons; similarity from calcium imaging and a model of the same recordings; automatic apical labels on v661 skeletons; few distal tuft synapses (941).

connectomics · MICrONS · like-to-like connectivity · apical dendrite · basal dendrite · functional connectomics · mouse visual cortex · feedback connections · synapse placement · Peters' rule · dendritic compartments