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Erin Koch, Jianzhong Jin, Jose-Manuel Alonso, Qasim Zaidi; Functional implications of orientation maps in visual cortex. Journal of Vision 2016;16(12):563. doi: https://doi.org/10.1167/16.12.563.
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© ARVO (1962-2015); The Authors (2016-present)
Stimulus orientation is mapped in the primary visual cortex of primates and carnivores in a pinwheel pattern, with iso-orientation domains rotating around pinwheel centers. The circuit functions and perceptual implications of this orientation map remain unclear, as it is absent in many mammals such as rodents. We used simultaneous recordings from horizontally arranged neurons in cat visual cortex using linear arrays (32 electrodes, 100 microns apart), to distinguish horizontal tracks running through iso-orientation domains showing limited changes in orientation preference and narrow orientation tuning, from those running near pinwheel centers showing rapid changes in orientation preference and broad tuning. The results showed that two fundamental properties of visual cortical responses, contrast saturation and cross-orientation suppression, are closely related to the functional organization of orientation maps, and are stronger within iso-orientation domains than pinwheel centers. Model simulations showed that these relations emerge when two robust intra-cortical computations – distance-weighted excitation from oriented neurons, and local divisive-inhibition from unoriented neurons – are applied with identical parameters to different orientation neighborhoods in cortex. Excitation enhances narrower tuning, cross-orientation suppression and response maximum in iso-orientation domains, as compared to pinwheel centers. Inhibition serves to make iso-orientation domains more sensitive to small contrasts, and more compressive to high contrasts, as compared to pinwheel centers. We conclude that pooled cortical outputs from iso-orientation domains and pinwheel centers differ not only in orientation diversity/selectivity but also in linearity of contrast response and suppression of responses to complex patterns. Image processing experiments demonstrated that outputs from narrow-tuned iso-orientation cells could be used in extra-striate cortex to build cells selective to edges and contours, whereas outputs from broad-tuned pinwheel cells could build extra-striate cells sensitive to textures and patterns.
Meeting abstract presented at VSS 2016
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