Figure 12. Path length economy of neocortical axons was suboptimal though superior to wire-minimized arbors.

(A) Coronal view of example spiny cell axon arbor (left) and its MST (right): upper, shows wire length minimization generally increased path length from parent cell body along arbor to each bouton (dot colour codes for path length, see scale bar), and, lower, histograms show this results in a shift in path length distribution of these arbors from positively skewed to one more dispersed and symmetric. (Anatomical axes: A, anterior; D, dorsal; L, lateral; M, medial; P, posterior). (B) Surface view of example basket cell axon arbor (left) and its MST (right) shows, upper, a similar increase in path length (note different colour scale to (A)) compared with spiny axon arbor with wire minimization, and, lower, a spread in path length distribution. (C) Path length economy (γ) of spiny (left) and basket cells axons (right) was suboptimal (γ_AXON = P_STAR/P_AXON, where P_AXON is average path length from parent soma to each bouton in the arbor) though significantly greater than wire-minimization arbors regardless of whether or not (γ_MST = P_STAR/P_MST) these inserted additional vertices (branch points) according to Steiner minimal tree criteria (γ_ESMT = P_STAR/P_ESMT) or the actual axon bifurcations or nodes (γ_MSTnodes = P_STAR/P_MSTnodes) were used.