Fig. 6: Projection patterns and anatomical insights from primary axonal tracts.

A Schematic illustration showing the axonal morphology, highlighting the blue-colored primary axonal tract, which is the long projecting axonal path after excluding distal short segments. A neuron may contain multiple tracts, such as the secondary tract highlighted in dark orange. B Schematic visualization of three distinct projection patterns at the population level: convergent, divergent, and parallel, determined based on the comparative spread in space of somas and terminals. Soma positions are indicated by red dots, while arrowheads denote the terminal points of primary axonal tracts. The blue lines connecting them represent the primary axonal tracts. C 2D projections of primary axonal tracts of 25 projection-based subtypes in cortex, striatum, and thalamus. The label on the left specifies the s-type (for CP neurons) or projection classes. Circular red dots represent the somas, while triangular black dots denote the tract termini. In-between tracts are colored randomly. A line plot of the spatial spread (radius) change from the somas to the terminals along the corresponding tracts is appended on the right side for each project type. D Horizontal view of projection pattern maps by source (left) and target (right) regions. The regions are colored by the projection pattern type. E 3D scatter plot of the terminal point locations for three clusters identified for the L5 ET projecting cortical SSp-m neurons using K-Means clustering based on their terminal points, with the respective spatial spread profiles plotted on the right. The terminal points of the three classes are colored in red (C1), green (C2), and blue (C3). Source data are provided as a Source Data file.