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Fig. 6.12. Reorganization of the orientation map after a cortical lesion. These plots show the retinotopic organization (calculated from settled responses as in Figure 6.7) and the orientation preferences of the central 70 × 70 region of the 142 × 142 cortex. The dotted white line in (a) shows the area that will be lesioned. Immediately after the lesion, the map spreads out slightly into the lesioned area, because the neurons near the lesion boundary respond to inputs previously represented by the lesioned neurons. This expansion can be observed by comparing corresponding areas around the lesion in (a) and (b), such as the lesion's top boundary. Over time (c), the map expands farther into the lesioned area, regaining some of the lost function. Neurons whose preferred orientations are perpendicular to the lesion boundary change the most because they have the most connections cropped by the boundary. For example, along the top of the lesion, the neurons colored cyan and green on the right side (with vertical preferences) shift their RFs significantly inward, whereas the red, orange, and purple neurons on the left side (with nearly horizontal preferences) do not change much. Thus, the model gives a possible computational explanation for the observed reorganization processes in biology (Section 6.1.2; Merzenich et al. 1990). It further predicts that the specific patterns of expansion depend on the orientation preferences of the neurons around the lesion, and that the extent of recovery depends on how large the lesion is compared with lateral excitation and the afferent receptive fields. An animated demo of the reorganization process can be seen at ...