A Model Of Orientation Selectivity In Mouse Primary Visual Cortex(V1)

Recent experiments have shown that mouse primary visual cortex(V1)is very different from that of cat or monkey,including response properties—one of which is that contrast invariance in the orientation selectivity(OS)of the neurons' firing rates is replaced in mouse with contrast-dependent sharpening(broadening)of OS in excitatory(inhibitory)neurons.These differences indicate a different circuit design for mouse V1 than that of cat or monkey.Here we develop a large-scale computational model of an effective input layer of mouse V1 based on experimental data.The model successfully reproduces experimentally observed response properties-for example,distributions of firing rates,orientation tuning widths,and response modulations of simple and complex neurons,including the contrast dependence of orientation tuning curves.Analysis of the model results shows that strong feedback inhibition and strong orientation-preferential cortical excitation to the excitatory population are the predominant mechanisms underlying the contrastsharpening of OS in excitatory neurons,while the contrast-broadening of OS in inhibitory neurons results from a strong but nonpreferential cortical excitation to these inhibitory neurons,with the resulting contrast-broadened inhibition producing a secondary enhancement on the contrast-sharpened OS of excitatory neurons.Further in discussion,we provide the model with different setups,which cater to the differences among various experiments as well as alternatives to the assumptions made in the original setup,and we find the mechanisms based on our model analysis still stand.More importantly,based on the understanding of these mechanisms,we show that compared with other animals,adjusting the detailed balances between the predominant mechanisms can also lead to contrast invariance in the excitatory neurons in mouse V1 –providing insights for future studies on contrast dependence(invariance)in various species.Implications to the encoding of the OS information by the proposed mechanism is also discussed.