Unraveling the mechanisms of surround suppression in early visual processing

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.

Surround Modulation Properties of Tectal Neurons in Pigeons Characterized by Moving and Flashed Stimuli

“…Taken together, visual neurons in both avian OT and the preliminary stages of the visual system of mammals, including retina [ 63 , 64 , 65 , 66 ], SC [ 22 , 67 ], LGN [ 33 , 68 ] and V1 [ 32 , 69 , 70 ], have similar RF structures, most of which presented a concentric organization characterized by an excitatory CRF surrounded by an inhibitory eCRF. The main difference between birds and mammals is that most V1 neurons are orientation selective which means that they respond best to particular orientation stimuli but not to the orthogonal orientation [ 71 ].…”

“…The surround modulation properties reported in mammals are almost related to the nature of neurons, which are selective to orientation or spatial frequency [ 22 , 32 , 33 ]. In avians, neurons in OT mostly respond to motion [ 34 , 35 ] or change in luminance [ 36 , 37 ].…”

Mechanisms of Surround Suppression Effect on the Contrast Sensitivity of V1 Neurons in Cats

“…Although a considerable number of studies at the cellular level have shown that surround suppression (SS) may depend on multiple information encoding from feed-forward, lateral, and feedback connections [14,66,76,80,81,[90][91][92][93], the underlying mechanisms are not fully understood [3,19]. For example, it is unclear whether SS results from an enhanced inhibition or a weakened excitation or both in the neural circuitry [3].…”

“…A neuron's response to dissimilar stimuli presented simultaneously in the cRF and sRF is usually stronger than that to similar stimuli [6,7], and it is commonly thought that SS plays a critical role in the perception of visual saliency, detection of object boundaries, and figure-ground segregation [3,[7][8][9][10][11][12]. However, the neural mechanisms that SS mediates visual information processing have not been fully understood [3,[13][14][15][16][17][18][19].…”

The combination of feedforward and feedback processing accounts for contextual effects in visual cortex

“…These models ( e . g ., Dipoppa et al, 2018; Keller et al, 2020a; Li and Young, 2021; Mossing et al, 2021; Obeid and Miller, 2021b; Rubin et al, 2015; Schwabe et al, 2006, 2010; Shushruth et al, 2012b) differ as to whether they treat space discretely ( i . e .…”