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Fig. 15.3. Scaling cortical density. Five LISSOM orientation maps from networks with different densities are shown. The parameters for each network were first calculated using Equation 15.3, and each network was then trained independently on the same random stream of input patterns. The number of connections in these networks ranged from 2 × 10⁶ to 3 × 10⁸ (requiring 2 MB to 317 MB of memory), and the simulation time from 10 minutes to 5 hours. Despite this wide range of simulation scales, the final organized maps are both qualitatively and quantitatively similar, as long as their size is above a certain minimum (about 64 × 64 in this case). Larger networks take significantly more memory and simulation time, but offer greater detail and allow multiple dimensions such as orientation, ocular dominance, and direction selectivity to be represented simultaneously.