Synergy between short-term and long-term plasticity explains direction-selectivity in visual cortex

Abstract

In this study, we examine whether short-term plasticity (STP) mediates learning rules governing long-term synaptic plasticity (LTSP). More specifically, we examine how the initial vesicle release probability can mediate long-term changes in synaptic strength. Given the importance of calcium-dependent modulation of synaptic transmission, as well as the temporal information to cortical computation, we examine whether STP can set the initial condition in modulating network connectivity strength and stability via spike-timing-dependent plasticity (STDP). Taking as a starting point the well-established Tsodyks-Markram (TM) rule for STP, we implement a model of two interconnected units receiving a train of incoming spikes first mediated by a mechanism of presynaptic STP. Extending the TM model, we then implement a mechanism of postsynaptic LTSP. By treating the two mechanisms synergistically, we manipulate the initial vesicle release probability of presynaptic STP and find that this process modulates long-term depression-mediated weight convergence, thus mediating the activity of postsynaptic responses. Furthermore, we show that an interaction between STP and LTSP jointly mediate neocortical synapses in explaining direction selectivity. Overall, results suggest that calcium-dependent modulation of synaptic strength mediates important consequences of neocortical response properties.