# stdp_nn_restr_synapse – Synapse type for spike-timing dependent plasticity with restricted symmetric nearest-neighbour spike pairing scheme¶

## Description¶

`stdp_nn_restr_synapse`

is a connector to create synapses with spike time
dependent plasticity with the restricted symmetric nearest-neighbour spike
pairing scheme (fig. 7C in [1]).

When a presynaptic spike occurs, it is taken into account in the depression part of the STDP weight change rule with the nearest preceding postsynaptic one, but only if the latter occurred not earlier than the previous presynaptic one. When a postsynaptic spike occurs, it is accounted in the facilitation rule with the nearest preceding presynaptic one, but only if the latter occurred not earlier than the previous postsynaptic one. So, a spike can participate neither in two depression pairs nor in two potentiation pairs.

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 relies on an additional variable - the postsynaptic
eligibility trace [1] (implemented on the postsynaptic neuron side). It
decays exponentially with the time constant `tau_minus`

and increases to 1 on
a post-spike occurrence (instead of increasing by 1 as in `stdp_synapse`

).

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