Implementation of volume_transmitter to record and manage spike times and multiplicity of neurons releasing a neuromodulator (volume_transmitter is not included in the current release version of NEST)
Part of definition of volume_transmitter to record and manage spike times and multiplicity of neurons releasing a neuromodulator, which is needed for neuromodulated synaptic plasticity (volume transmitter and neuromodulated synapses are not included in the release version of NEST at the moment)