Fig. 2: Quantification of projection heterogeneity using single-neuron data.

A Schematic representation of the heterogeneity for the projections to a pair of homotopic downstream regions. From an upstream region U, one subset of neurons, u_i (red), extends projections to the intrahemispheric downstream target D_i, while a different subset, u_c (blue), projects to the contralateral downstream D_c. The degree of overlap between u_i and u_c, indicated by shared neurons (magenta), is calculated as the proportion of intersecting neurons relative to the lesser of the two subsets. Projection heterogeneity is then quantified by subtracting this proportional overlap from one. B Projection heterogeneity among various upstream-downstream region pairings, including 11 PFC regions as upstream and 43 cortical regions as downstream, calculated from the single-neuron data. C Overall heterogeneity for projections to each of the 43 homotopic downstream pairs. D Schematic representation of the heterogeneity for the projections to multiple downstream regions that are mutually heterotopic. The top schema delineates an upstream region projecting to four downstream regions via neuron subsets (red-u₁, yellow-u₂, green-u₃, and blue-u₄). The bottom distribution function represents P(N = i), the percentage of neurons projecting to N = i number of downstream regions. The values of P across varying values of N indicate the degree of heterogeneity: a greater proportion of neurons targeting fewer downstream regions (higher P at smaller i) and a smaller proportion targeting more regions (lower P at larger i) reflects larger heterogeneity. E Comparative heterogeneity profile of ipsilateral versus contralateral projections, calculated from single-neuron dataset across all upstream regions. F Heterogeneity for ipsilateral and contralateral projections from four example upstream regions: ACAv, ACAd, MOs, ORBvl. More examples are presented in Supplementary Fig. 3. Source data of (B–E, F) are provided as a Source Data file.