Title : A triplet model of spike - timing dependent plasticity generalizes the BCM rule to spatio - temporal inputs

Synaptic strength depresses for low, and potentiates for high activation of the postsynaptic neuron. This feature is a key property of the well-known Bienenstock-Cooper-Munro (BCM) synaptic rule, which has been shown to maximize the selectivity of the postynaptic neuron, and thereby offers a possible explanation for experience-dependent cortical plasticity such as orientation selectivity. However, this BCM framework is rate-based and a significant amount of recent work has shown that synaptic plasticity depends on the precise timing of presynaptic and postsynaptic spikes. In this paper we consider a triplet model of Spike-Timing Dependent Plasticity (STDP) which depends on the interactions of three precisely-timed spikes. Triplet STDP has been shown to describe experimentally-observed plasticity which the classical STDP rule, based on pairs of spikes, has failed to capture. In the case of rate-based patterns, we show a tight correspondence between the triplet STDP rule and the BCM rule. We demonstrate the selectivity property of the triplet STDP rule analytically for orthogonal inputs and numerically for non-orthogonal inputs. Moreover, in contrast to BCM, we show that triplet STDP can also elicit selectivity to input patterns consisting of higherorder spatio-temporal correlations. This property is crucial given the large amount of higher-order correlations measured in the brain. We studied the triplet STDP model in a biologically-inspired setting from receptive field theory, where orientation and directions selectivity arise due to the sensitivity of triplet STDP to spatio-temporal correlations.