In many species, adjacent topographic maps in sensory neocortex are found to be oriented as roughly mirror-image copies of one another. Here we use a computational model to show for the first time that, in principle, adjacent cortical topographic maps that are mirror-image symmetric along two dimensions can arise from activity-dependent changes if the distribution radius of afferents sufficiently exceeds that of horizontal intracortical interactions. We also find that infrequently, other types of intermap symmetry and previously unexpected map relationships (such as interlocking rotation, in which two adjacent maps become intertwined) can occur. These results support the hypothesis that activity-dependent synaptic changes play a more important role in forming the orientations of adjacent cortical maps than is currently recognized.

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