stdp_triplet_synapse – Synapse type with spike-timing dependent plasticity (triplets)
=====================================================================================

Description
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``stdp_triplet_synapse`` is a connection with spike time dependent
plasticity accounting for spike triplet effects (as defined in [1]_).

Notes:

- Presynaptic traces ``r_1`` and ``r_2`` of [1]_ are stored in the connection as
  ``Kplus`` and ``Kplus_triplet`` and decay with time-constants ``tau_plus`` and
  ``tau_plus_triplet``, respectively.
- Postsynaptic traces ``o_1`` and ``o_2`` of [1]_ are acquired from the postsynaptic
  neuron states ``Kminus_`` and ``triplet_Kminus_`` which decay on time-constants
  ``tau_minus`` and ``tau_minus_triplet``, respectively. These two time-constants
  can be set as properties of the postsynaptic neuron.
- This version implements the 'all-to-all' spike interaction of [1]_. The
  'nearest-spike' interaction of [1]_ can currently not be implemented
  without changing the postsynaptic archiving-node (clip the traces to a
  maximum of 1).

.. warning::

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

Parameters
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=================  ======  ===========================================
 tau_plus          real    Time constant of short presynaptic trace
                           (tau_plus of [1]_)
 tau_plus_triplet  real    Time constant of long presynaptic trace
                           (tau_x of [1]_)
 Aplus             real    Weight of pair potentiation rule
                           (A_plus_2 of [1]_)
 Aplus_triplet     real    Weight of triplet potentiation rule
                           (A_plus_3 of [1]_)
 Aminus            real    Weight of pair depression rule
                           (A_minus_2 of [1]_)
 Aminus_triplet    real    Weight of triplet depression rule
                           (A_minus_3 of [1]_)
 Wmax              real    Maximum allowed weight
=================  ======  ===========================================

=============== ======  ===========================================
**States**
-------------------------------------------------------------------
 Kplus          real    Pre-synaptic trace (r_1 of [1]_)
 Kplus_triplet  real    Triplet pre-synaptic trace (r_2 of [1]_)
=============== ======  ===========================================

Transmits
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SpikeEvent

References
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.. [1] Pfister JP, Gerstner W (2006). Triplets of spikes in a model
       of spike timing-dependent plasticity.  The Journal of Neuroscience
       26(38):9673-9682. DOI: https://doi.org/10.1523/JNEUROSCI.1425-06.2006

See also
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:doc:`Synapse <index_synapse>`, :doc:`Spike-Timing-Dependent Plasticity <index_spike-timing-dependent plasticity>`