Geometrical relationships among multiple cortical maps, such as those between ocular dominance and orientation maps, are a prominent feature of the brain's functional architecture. It is also well known that there is a strong bias of cortical responses toward the contralateral eye during early postnatal development. We wondered therefore whether and how such an imbalance of cortical responsiveness in a developing animal might influence the mutual geometrical relationships between orientation and ocular dominance maps in adult animals. The results of our study indicate the existence of a strong tendency for the peaks of the ipsilateral eye domains to coincide with the location of point singularities (pinwheel centers) in orientation maps. No such relationship was found for the peaks of contralateral eye domains. Computational studies reproduced similar asymmetry in the coincidence under the contralateral eye bias of inputs. Our study raised the idea that the pinwheel centers play an important role for retaining the weaker ipsilateral eye inputs during normal development.

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It has been reported that the OFF responses of cells in the visual pathway are stronger, on average, than the ON responses early in the life of cats and ferrets. In this study, we theoretically investigate the effects of this imbalance in activity on the orientation map formation. We carry out computer simulations based on our previously proposed self-organization model, in which the correlated activities between ON- and OFF-center cells in the lateral geniculate nucleus regulate the formation of orientation maps in the visual cortex. When imbalance between the activities of these ON- and OFF-center cells is assumed, we obtain orientation maps with spatial periodicity, as observed in the experiments. On the other hand, when balanced activities are assumed, orientation maps do not show periodicity. This suggests that the imbalance in activities between ON- and OFF-center cells contributes to the elaboration of orientation maps during the critical period.

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