# 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.

Warning

This synaptic plasticity rule does not take precise spike timing into account. When calculating the weight update, the precise spike time part of the timestamp is ignored.

## 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