Modeling the origins of spatial and temporal variability in visual cortical representations

by Juan Daniel Florez Weidinger
Doctoral thesis
Date of Examination:2013-10-24
Date of issue:2013-11-25
Advisor:Prof. Dr. Fred Wolf
Referee:Prof. Dr. Detlev Schild
Referee:Prof. Dr. Stefan Treue
Persistent Address: http://dx.doi.org/10.53846/goediss-4124

 

 

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Abstract

English

Response characteristics of orientation-tuned neurons in the visual cortex appear to be similar in mammalian lineages widely separated in evolution. The spatial arrangement of preferences across the cortex, however, shows fundamental differences. While in primates and carnivores orientation preferences form orientation maps, in rodents they are spatially interspersed. The developmental processes and evolutionary origins of these two opposite layout-types remain enigmatic. In this thesis I introduce a class of models that can generate both types of functional organization found in the primary visual cortex of mammals. The conditions on the intra-cortical interaction for the generation of interspersed layouts are analytically calculated and confirmed in a biologically detailed model: an interspersed organization is actively generated when local circuits are predominantly suppressive. The model is further expanded to include representations to both eyes and to modulate the degree of plasticity during the critical period. Numerical simulations show that the final arrangement of orientations shows a weak negative correlation between nearest neighbours and that it suffers from a substantial dynamical lability of neuronal selectivities compared to columnar architectures. Interspersed layouts in general exhibit superior stimulus coverage but cause higher wiring costs to maintain a selective like-to-like connectivity. A model in which cortical organization is assumed to optimize a composite cost function that penalizes reductions in stimulus coverage and excessive wiring length depending on cortex size is introduced. A transition from interspersed layouts to columnar architecture above a critical area size is predicted by the optimization model.
Keywords: Visual cortex; Orientation tuning; Rodents; Disorganized; Pattern formation; Intra-cortical interaction; Modeling; Binocular matching
 
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