Effect of synaptic plasticity on orientation selectivity in the primary visual cortex

G. MATO; S. GONZALO COGNO

Chicago

Conferencia; 45th Meeting Society for Neuroscience; 2015

Society for Neuroscience

Orientation selectivity is ubiquitous in the primary visual cortex (V1) of mammals. In cats and monkeys, V1 displays spatially ordered maps of orientation preference. Instead, in mice, squirrels and rats, orientation selective neurons in V1 are not spatially organized, giving rise to a seemingly random pattern usually referred to as a salt-and-pepper layout. The fact that such different organizations can sharpen orientation tuning leads to question the structural role of the intracortical connections; specifically the influence of plasticity and the generation of functional connectivity. In this work, we analyse the effect of plasticity processes on orientation selectivity for both scenarios. We study a computational model of layer 2/3 and a reduced one-dimensional model of orientation selective neurons, both in the balanced state. We analyse two plasticity mechanisms. The first one involves spike-timing dependent plasticity (STDP), and the second one the reconnection of the interactions according to the preferred orientations of the neurons; this last rule gives rise to functional connectivity. We find that under certain conditions STDP can indeed improve selectivity but it works in a somehow unexpected way, that is, effectively decreasing the modulated part of the intracortical connectivity as compared to the non-modulated part. The degree of functional connectivity generated by the plasticity process depends on the selectivity in the initial condition. As in the balanced state the degree of selectivity is inversely proportional to the functional connectivity we have a self stabilizing process that tends to a fixed value of selectivity in the final state. For the reconnection mechanism we also find that increasing functional connectivity leads in fact to a decrease in orientation selectivity if the network is in a stable balanced state. Both counterintuitive results are a consequence of the dynamics of the balanced state. We also find that selectivity can be increased by a reconnection process if the resulting connections give rise to an unstable balanced state for a given Fourier mode. We compare these findings with recent experimental results.