Figure 5.

Changes in branch probability, branch distribution, and branch length throughout simulations of chick retinotectal map development. (A) Graph depicting branch probability for a chick map development simulation using the branchdensity parameter. The initial branch probabilities are shown for three retinal positions (heavy upper lines, iteration 1). Branch probability decreases during map development, and becomes more topographically biased as a result of added repellents from branches and arbors themselves (thin lower lines, iteration 200). (B) The actual branch distribution shown for all axons originating from central retina at the beginning (iteration 1) and end (iteration 200) of a simulation run using the branchdensity parameter. At iteration 1 branches are widely distributed across the OT, though biased for mid-OT (green). At iteration 200 the branch distribution peaks at the position of the TZ (red). (C) Total branch length (total length of all branches present at each iteration) is calculated after each iteration during the simulation and graphed. Total branch length rises quickly at the start of the simulation and eventually levels out, as higher amounts of added repellents restrict branching further. Note that despite the essentially stable overall total branch length from relatively early time points, topographic branch specificity continues to increase. This suggests branches at latter stages are removed from ectopic locations and replaced by branches formed at more topographically correct locations, thus maintaining close to net zero change in total branch length. In addition, total branch length increases negligibly at later stages indicating that the simulation is stable. [Color scheme can be viewed in the online issue, which is available at www.interscience.wiley.com.]