A Computational Model of Direction Selectivity in Macaque V1 Cortex Based on Dynamic Differences between On and Off Pathways

This paper is about neural mechanisms of direction selectivity (DS) in macaque primary visual cortex, V1. We present data (on male macaque) showing strong DS in a majority of simple cells in V1 layer 4C alpha, the cortical layer that receives direct afferent input from the magnocellular division of the lateral geniculate nucleus (LGN). Magnocellular LGN cells are not direction-selective. To understand the mechanisms of DS, we built a large-scale, recurrent model of spiking neurons called DSV1. Like its predecessors, DSV1 reproduces many visual response properties of V1 cells including orientation selectivity. Two important new features of DSV1 are (1) DS is initiated by small, consistent dynamic differences in the visual responses of OFF and ON Magnocellular LGN cells, and (2) DS in the responses of most model simple cells is increased over those of their feedforward inputs; this increase is achieved through dynamic interaction of feedforward and intracortical synaptic currents without the use of intracortical direction-specific connections. The DSV1 model emulates experimental data in the following ways: (1) most 4C alpha Simple cells were highly direction-selective but 4C alpha Complex cells were not; (2) the preferred directions of the model's direction-selective Simple cells were invariant with spatial and temporal frequency (TF); (3) the distribution of the preferred/opposite ratio across the model's population of cells was very close to that found in experiments. The strong quantitative agreement between DS in data and in model simulations suggests that the neural mechanisms of DS in DSV1 may be similar to those in the real visual cortex.

Automated summary

This paper investigates the neural mechanisms of direction selectivity (DS) in the macaque primary visual cortex, V1. The authors present data showing strong DS in a majority of simple cells in V1 layer 4C alpha, which receives input from the magnocellular division of the lateral geniculate nucleus (LGN). They built a large-scale, recurrent model called DSV1 to understand the mechanisms of DS and found that DS is initiated by dynamic differences in the visual responses of OFF and ON Magnocellular LGN cells, and the increase in DS in model cells is achieved through the interaction of feedforward and intracortical currents without direction-specific connections. The model's simulations match experimental data well, suggesting similar neural mechanisms in DSV1 and the real visual cortex.