16 Dec
2024
16 Dec
'24
11:01 a.m.
Dear Pavel,
I can confirm you observation, and I share your surprise. Intuitively,
one would expect that the synaptic state should return to the initial
state after the long period of silence. However, after consulting the
source papers (todyks_synapse: doi:10.1523/JNEUROSCI.20-01-j0003.2000,
tsodyks2_synapse: doi:10.1016/S0893-6080(01)00144-7) and looking at the
NEST code, I conclude that what the example shows is indeed the intended
behaviour.
A key difference between tsodyks_synapse and todyks2_synapse is the
order of update steps: upon arrival of the presynaptic spike,
tsodyks_synapse first updates the synapse state (x,y,z,u; see lines
258-277 in tsodyks_synapse.h), and then reports the new weight (line 285
in tsodyks_synapse.h). In tsodyks2_synapse, this is reversed: first, the
synaptic weight is computed based on the current (i.e., the old) synapse
state (line 236 in tsodyks2_synapse.h), and then the synapse state is
updated (lines 243,244 in tsodyks2_synapse.h). When the first spike of
the second burst of presynaptic spikes arrives in the example
(https://nest-simulator.readthedocs.io/en/stable/auto_examples/evaluate_tsod…),
the recovery value of tsodyks2_synapse still is where it was at the end
of the first burst of spikes (before the break). This is exactly how the
model is defined in (Maass and Markram, 2002;
doi:10.1016/S0893-6080(01)00144-7; see equations (1-5)). It needs one
more spike to really "recover".
I hope this clarifies things a bit.
Best
Tom
On 12.12.24 12:05, Pavel Haman wrote:
Hello,
I have followed the example script comparing `tsodyks_synapse` and `tsodyks2_synapse`
models, which can be found here:
https://nest-simulator.readthedocs.io/en/stable/auto_examples/evaluate_tsod…
Using the parameter set for depression instead of facilitation I found that
`tsodyks2_synapse` model leads to weird peaks of synaptic currents (at least I would not
expect that for short term depression) - during the second stimulation the weight
rescaling seems to be shifted by one spike compared to tsodyks_synapse (as if parameter
"u" would be updated after rescaling the weight instead of before).
Does anybody know why is there this difference between the two synapse models?
Thank you.
All the best,
PH
_______________________________________________
NEST Users mailing list -- users(a)nest-simulator.org
To unsubscribe send an email to users-leave(a)nest-simulator.org
--
---
Dr. Tom Tetzlaff
Institute for Advanced Simulation (IAS-6)
Computational and Systems Neuroscience
Jülich Research Centre
Jülich, Germany
https://www.fz-juelich.de/profile/tetzlaff_t
-----------------------------------------------------------------------
-----------------------------------------------------------------------
Forschungszentrum Jülich GmbH
52425 Jülich
Sitz der Gesellschaft: Jülich
Eingetragen im Handelsregister des Amtsgerichts Düren Nr. HR B 3498
Vorsitzender des Aufsichtsrats: MinDir Stefan Müller
Geschäftsführung: Prof. Dr. Astrid Lambrecht (Vorsitzende),
Karsten Beneke (stellv. Vorsitzender), Dr. Ir. Pieter Jansens
-----------------------------------------------------------------------
-----------------------------------------------------------------------