Unraveling the mechanisms of surround suppression in early visual processing.

Yao Li,Lai-Sang Young,Dongzhuo Douglas Zhou

doi:10.1371/journal.pcbi.1008916

Abstract

This paper uses mathematical modeling to study the mechanisms of surround suppression in the primate visual cortex. We present a large-scale neural circuit model consisting of three interconnected components: LGN and two input layers (Layer 4Ca and Layer 6) of the primary visual cortex V1, covering several hundred hypercolumns. Anatomical structures are incorporated and physiological parameters from realistic modeling work are used. The remaining parameters are chosen to produce model outputs that emulate experimentally observed size-tuning curves. Our two main results are: (i) we discovered the character of the long-range connections in Layer 6 responsible for surround effects in the input layers; and (ii) we showed that a net-inhibitory feedback, i.e., feedback that excites I-cells more than E-cells, from Layer 6 to Layer 4 is conducive to producing surround properties consistent with experimental data. These results are obtained through parameter selection and model analysis. The effects of nonlinear recurrent excitation and inhibition are also discussed. A feature that distinguishes our model from previous modeling work on surround suppression is that we have tried to reproduce realistic lengthscales that are crucial for quantitative comparison with data. Due to its size and the large number of unknown parameters, the model is computationally challenging. We demonstrate a strategy that involves first locating baseline values for relevant parameters using a linear model, followed by the introduction of nonlinearities where needed. We find such a methodology effective, and propose it as a possibility in the modeling of complex biological systems.

Highlights

The goal of this paper is to discover mechanisms behind certain phenomena in visual neuroscience via mathematical modeling and simulations
The visual signal from the retina is relayed through the lateral geniculate nucleus (LGN), and enters the primary visual cortex directly
A phenomenon called surround suppression, which means a reduction of neuronal activities in response to stimuli of increasing size, is well-observed in all layers of the primate primary visual cortex

Summary

Introduction

The goal of this paper is to discover mechanisms behind certain phenomena in visual neuroscience via mathematical modeling and simulations. V1 cells are known to have very small apertures, meaning the part of the visual field about which information is relayed directly to each cell is very small, no more than a fraction of a degree This part of the visual field is known as the cell’s classical receptive field (CRF). Cells in V1 respond vigorously to certain small stimuli centered at their CRF but their firing rates are attenuated when the eye is presented with a larger size stimulus of the same kind. This phenomenon is known as surround suppression: stimulating the cortical region around a cell can suppress the cell’s response. We demonstrate below how this can be improved with the addition of a suitably chosen nonlinearity

Objectives

Methods

Results

Discussion

Conclusion