A variable size population of synapses.
This component is a population rather than a single synapse, in that one synapse element is created for each different index on incoming spikes.
The individual synapses then evolve according to the properties of the population to which they belong. These include the reversal potential, Erev, initial conductance, G_0, rise time, fall time and duration as for , spike response functions).
If the voltageDependent flag is set, then the conductance caused by a single synapse gated on the post-synaptic potential with equivalent gating charge z and half-open potential Vhalf.
If the saturates flag is set, then the single synapses can saturate under repeated stimulation. For computational convenience, this is not implemented by imposing the maximal conductance, but rather by specifying a saturationFactor indicating what fraction of the post-synaptic receptors are involved in transmission of a single event. Another event occurring immediately would be scaled down by (1 - saturationFactor). The available receptors are assumed to recover at the same rate as the decay of the synaptic conductance (fallTime). Thus, a saturation factor of zero means that conductances sum indefinitely. A saturation factor of 1 means that two spikes in rapid succession have the same effect as a single spike.
If specified, the profile set in the G_ModRule selector is used to implement spike time dependent synaptic plasticity using the arrival times of spikes on the afferent and back propagating ports. The profile is interpreted as a percentage modification to be applied as a function of the time between afferent and back-propagating spikes. Thus, the positive part of the profile is used for the cases when the back-propagating spike follows an afferent spike; the negative part for the case when a back-propagating spike precedes an afferent spike. When several spikes occur on one port between spikes on the other, only the first and last are used for conductance modification. That is, the modification rule only takes effect for "pre followed by post" or "post followed by pre" sequences, not for "pre followed by pre" or "post followed by post" sequences.
The conductance modification saturates at G_max, the exact behavior being given by the following code fragment:
double trel = backPropSpikeTime - afferentSpikeTime;
double delta = 0.01 * G_ModProf.valueAt(trel);
double f = -1 + 2/(1+ Math.exp(-delta));
if (f > 0) conductance += f * (G_Max - conductance);
if (f < 0) conductance += f * conductance;