# stdp_nn_pre_centered_synapse – Synapse type for spike-timing dependent plasticity with presynaptic-centered nearest-neighbour spike pairing scheme¶

## Description¶

stdp_nn_pre_centered_synapse is a connector to create synapses with spike time dependent plasticity with the presynaptic-centered nearest-neighbour spike pairing scheme, as described in 1.

Each presynaptic spike is taken into account in the STDP weight change rule with the nearest preceding postsynaptic one and the nearest succeeding postsynaptic one (instead of pairing with all spikes, like in stdp_synapse). So, when a presynaptic spike occurs, it is accounted in the depression rule with the nearest preceding postsynaptic one; and when a postsynaptic spike occurs, it is accounted in the facilitation rule with all preceding presynaptic spikes that were not earlier than the previous postsynaptic spike. For a clear illustration of this scheme see fig. 7B in 2.

The pairs exactly coinciding (so that presynaptic_spike == postsynaptic_spike + dendritic_delay), leading to zero delta_t, are discarded. In this case the concerned pre/postsynaptic spike is paired with the second latest preceding post/presynaptic one (for example, pre=={10 ms; 20 ms} and post=={20 ms} will result in a potentiation pair 20-to-10).

The implementation involves two additional variables - presynaptic and postsynaptic traces 2. The presynaptic trace decays exponentially over time with the time constant tau_plus, increases by 1 on a pre-spike occurrence, and is reset to 0 on a post-spike occurrence. The postsynaptic trace (implemented on the postsynaptic neuron side) decays with the time constant tau_minus and increases to 1 on a post-spike occurrence.

## Parameters¶

tau_plus |
ms |
Time constant of STDP window, potentiation (tau_minus defined in postsynaptic neuron) |

lambda |
real |
Step size |

alpha |
real |
Asymmetry parameter (scales depressing increments as alpha*lambda) |

mu_plus |
real |
Weight dependence exponent, potentiation |

mu_minus |
real |
Weight dependence exponent, depression |

Wmax |
real |
Maximum allowed weight |

## Transmits¶

SpikeEvent