The role of self-excitation in the development of topographic order

A connectionist type model is presented for explaining the development of the topographically ordered retinotectal connections of the visual system of the frog. The structure of a tectal column were taken into account inplicitly. Simulations suggest that the self-excitatory intracolumnar connections play an important role in the formation of the topography.

Based on a large number of experiments, the development of highly ordered afferent pathway of the optic tectum seems to be activity-dependent. Activity-dependent mechanisms mainly effect via modification of synaptic strengths, due to temporal correlation of the activities between the pre- and post-synaptic side. All the previous activity-dependent models deal with the spatial correlation of the images refected onto the retina, which is generally true in natural images, but have not been proofed in images after retinal transformation. The movement of objects is always conntinous. This feature can provide a possibility to establish topogaphically ordered projections, if the receiving system can recognize and make use of it. The reverberatory loops created by large-pear shaped cells,soma provide the biological basis of self-excitation. The simulations show, in the case of self-excitation the system is able to recognize the topology of the visual field by the conntinuity of the object's movement.

Zoltán Somogyvári was working on this project.