www.neuron.yale.edu

What is the standard way a synapse (Exp2Syn or Alpha) reacts on a second (3.,...) presynaptic impulse? How is conductance calculated then?

I don't think there is a standard way.

In expsyn and exp2syn every event leads to the same conductance change and these changes sum linearly. Judging from the code the AlphaSynapse is taylored to produce one single synaptic event.

On ModelDB you can find Ted Carnevale's implementation of a synapse showing short term plasticity:
http://senselab.med.yale.edu/senselab/m ... model=3815
Elsewhere in this forum you can also find description of saturating AMPA current (also from Ted Carnevale):
http://www.neuron.yale.edu/phpBB2/viewt ... light=ampa
However, given a synapse you can easily determine the behaviour of the conductance by visual inspection:

1. create a section
2. add the synapse of interest
3. voltage clamp the section
4. hook up a NetStim
5. run
6. Play around with netstim and the parameters of the synapse
7. Don't forget to create a graph somewhere along the way

On the more advanced level the source code of the mechanism you mentioned can be found in the \src\nrnoc subdirectory, which together with the online help should allow you to determine the behaviour.

AlphaSynapse is a "single shot" mechanism--it produces a single conductance
transient that occurs at a predetermined time (a time that the implementor specifies).

With the advent of NEURON's event delivery system, it became possible to implement
point processes that can be driven by input events. What happens when an event
arrives is described in the NET_RECEIVE block (for a synaptic mechanism, an
event perturbs a kinetic scheme or differential equation that ultimately governs the
time course of a synaptic conductance). This allows highly efficient simulation
of spike-triggered synaptic transmission, as well as the implementation of even more
efficient models of artificial spiking cells. This is all discussed in chapters 10 and 11
of The NEURON Book (can be ordered from Cambridge University Press, Amazon,
etc.). You may find this paper
Hines, M.L. and Carnevale, N.T. Discrete event simulation in the NEURON
environment. Neurocomputing 58-60:1117-1122, 2004
(preprint available from http://www.neuron.yale.edu/neuron/bib/nrnpubs.html)
to be a useful introduction to the NET_RECEIVE block and related topics such as
the NetCon (Network Connection) class. Then read
expsyn.mod, exp2syn.mod, and exp4syn.mod
(find these on your own computer in
c:\nrn58\src\nrnoc\ for MSWin
or
nrn-5.8/src/nrnoc/expsyn.mod for UNIX/Linux
)
and see if it doesn't begin to make sense.

--Ted

Thank you for the rapid answers. They were helpful to understand.