title: The mapping of eccentricity and meridional angle onto orthogonal axes in the primary visual cortex: an activity-dependent developmental model.
abstract: Primate vision research has shown that in the retinotopic map of the primary visual cortex, eccentricity and meridional angle are mapped onto two orthogonal axes: whereas the eccentricity is mapped onto the nasotemporal axis, the meridional angle is mapped onto the dorsoventral axis. Theoretically such a map has been approximated by a complex log map. Neural models with correlational learning have explained the development of other visual maps like orientation maps and ocular-dominance maps. In this paper it is demonstrated that activity based mechanisms can drive a self-organizing map (SOM) into such a configuration that dilations and rotations of a particular image (in this case a rectangular bar) are mapped onto orthogonal axes. We further demonstrate using the Laterally Interconnected Synergetically Self Organizing Map (LISSOM) model, with an appropriate boundary and realistic initial conditions, that a retinotopic map which maps eccentricity and meridional angle to the horizontal and vertical axes respectively can be developed. This developed map bears a strong resemblance to the complex log map. We also simulated lesion studies which indicate that the lateral excitatory connections play a crucial role in development of the retinotopic map.
authors: Computational Neuroscience Laboratory, Department of Biotechnology, Indian Institute of Technology Madras Chennai, India.
authors: Ryan T
authors: RT
authors: Philips
authors: Computational Neuroscience Laboratory, Department of Biotechnology, Indian Institute of Technology Madras Chennai, India.
authors: V Srinivasa
authors: VS
authors: Chakravarthy
keywords: LISSOM; V1; complex-logarithmic; development; plasticity; retinotopy; self-organizing