The Effect of Dynamic Synapses on Spatio-temporal Receptive Fields in Visual Cortex

Temporal dynamics are a well known feature of synaptic transmission. Recently temporal dynamics of synaptic transmission has been reported in neocortex. Here we examine the possible effects of these dynamics on the spatio-temporal receptive fields of simple cells in VI. We do this by examining a simple model of a cortical neuron that depends on an oriented thalamocortical projection. In our model, the receptive field (RF) structure is encoded either as a structured presynaptic probability of release or as a structured postsynaptic efficacy. We show that these different assumptions about the origin of receptive field structure lead to very different spatio-temporal dynamics. The structured efficacy model (SE) leads to tuning curves that are unimodal, and although the response magnitude changes in time, the preferred orientation does not. On the other hand, the structured probability model (PR) leads to tuning curves which are not unimodal and change their preferred orientation in time. We show that the temporal code induced by the dynamic synapses can be used for distinguishing between different input that induce the same average firing rate.