Figure 11. Examples of wiring ‘shortcuts’ by wire-minimization algorithms.

(A) Low economy spiny axon arbor (left upper) wiring was significantly shortened by MST (left lower) shortcuts linking bouton-rich terminal patches while avoiding bouton-free primary and secondary axon collaterals. Magnified central region (right) shows numerous wiring differences in the flow direction from soma to tips between overlaid axon (grey arrows) and MST (red arrows) arbors. (B) High economy spiny cell axon arbor (left upper) wiring was only slightly shortened because MST (left lower) could find fewer shortcuts because of the more uniform bouton distribution over the sparsely branched axon arbor. Magnified central region axon and MST overlay (right) illustrates few differences in wiring pattern flow between these arbors. (C) Cell type-specific differences in wiring shortcuts: for a typical basket cell axons wiring shortcuts zig-zag between boutons ‘strings’ on terminal branches but avoid the main bouton-free axon collateral (upper), while for a typical spiny cell branch boutons are found on all orders of branching permitting very few shortcuts (lower). (Key: axon  =  grey lines, graph  =  red lines, boutons  =  yellow dots; anatomical axes: A, anterior; D, dorsal; L, lateral; M, medial; P, posterior).