On the anatomical basis of field size, contrast sensitivity, and orientation selectivity in macaque striate cortex: A model study

Abstract

Neurons in layer 4C in macaque striate cortex show a differential change in receptive field size and achromatic contrast sensitivity with depth, and exhibit orientation selective responses in the upper 4Cα sublayer. Using a computational model we first demonstrate that the observed change in receptive field size and contrast sensitivity can arise from a differential convergence of afferents from the P and M subdivisions of the lateral geniculate nucleus onto layer 4C spiny stellate cells - if one postulates that the two anatomically identified M1 and M2 subpopulations of the M afferents differentially project to different depth in the 4Cα subdivision. Number ratios and response properties of both M subpopulations are predicted and may now be tested experimentally. We then show that realistic orientation selective responses in upper 4Cα can emerge intracortically as a result of local lateral interactions, which are anisotropic, between spiny stellate cells and inhibitory interneurons. The model assumes that orientation bias and tuning are generated by the same cortical circuits and predicts a receptive field dynamics with an initial non orientation specific response.