stdp_nn_symm_synapse – Synapse type for spike-timing dependent plasticity with symmetric nearest-neighbour spike pairing scheme =============================================================================================================================== Description +++++++++++ ``stdp_nn_symm_synapse`` is a connector to create synapses with spike time dependent plasticity with the symmetric nearest-neighbour spike pairing scheme [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, and when a postsynaptic spike occurs, it is accounted in the facilitation rule with the nearest preceding presynaptic one (instead of pairing with all spikes, like in ``stdp_synapse``). For a clear illustration of this scheme see fig. 7A 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`` and increases to 1 on a pre-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 :ref:`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 References ++++++++++ .. [1] Morrison A., Aertsen A., Diesmann M. (2007) Spike-timing dependent plasticity in balanced random networks, Neural Comput. 19:1437--1467 .. [2] Morrison A., Diesmann M., and Gerstner W. (2008) Phenomenological models of synaptic plasticity based on spike timing, Biol. Cybern. 98, 459--478 See also ++++++++ :doc:`Synapse `, :doc:`Spike-Timing-Dependent Plasticity `