Field Discontinuities and Islands in a Model of Cortical Map Formation

The existence of field discontinuities, i.e. discontinuities in cortical maps of the retina is well established by neurophysiological investigations in a variety of species [1, 2, 3, 4]. In cat, additional geometric anomalies known as islands or type-II organization have been observed [2, 3]. The ontogenesis of these visual representations is studied in a model of activity-dependent self-organizing maps. The field discontinuities and islands are explained by the occurrence of dynamical instabilities depending on the geometry of the cortical area. A comparison with neurophysiological data from a variety of species shows that field discontinuities indeed occur in areas of elongated shape only. The approach also explains the large degree of interindividual variability observed in cats by the coexistence of several solutions of the model. These results demonstrate that field discontinuities and islands can be explained by the same developmental mechanism.