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Fig. 5.12. Long-range lateral connections in the orientation map. The lateral inhibitory connection weights of four sample neurons from the marked regions in Figure 5.9 are shown in the top row, situated in the orientation map as shown in the bottom row. The small white square in both figures identifies the neuron; the black outline on top indicates the extent of these connections before self-organization, and the white outline on the map plot shows their extent after self-organization and pruning. On top, the color coding represents the connected neuron's orientation, selectivity, and connection strength, as in Figure 5.7; the map encodes orientation and selectivity as in Figure 5.9c. The connection histogram (CH) in the middle shows how many connections come from neurons of each orientation. For every neuron, the strongest connections originate from the neuron's nearby neighbors, as indicated by the large, bright central area in each weight plot. The long-range connection patterns differ depending on where the neuron is located in the orientation map. (a) Neurons in the middle of an OR patch receive connections from neurons with similar preferences, aligned along the orientation preference of the neuron (for this neuron, about 65^o, i.e. blue). (b) At pinwheel centers, the connections come from all directions and orientations and are nearly isotropic. The histogram is nearly flat, with small peaks near orientations that happen to be overrepresented in the pinwheel. (c) Connections at saddle points extend along the two orientations of the saddle, in this case red (0^o) and blue (65^o). The neuron also makes connections with intermediate orientations and directions; these connections match its own OR preference (30^o, purple), and result in one broad peak in the histogram. (The connections of this neuron are cut off along the bottom because it is located near the bottom of the map.) (d) Connections of neurons at fractures are also elongated along the two directions of the neighboring orientation patches. The neuron plotted in (d) is on a fracture between yellow-green (130^o) and blue-purple (40^o), and makes connections with both of these orientations. In contrast to saddle points, it does not connect with intermediate orientations and directions, resulting in two distinct peaks in the orientation histogram. While the connection patterns in iso-orientation patches have already been confirmed in biology, the patterns at the other map features are predictions for future experiments.