[NEST Users] Re: `tsodyks_synapse` and `tsodyks2_synapse` models have different behavior for short term depression

Hi Pavel,

you are right. Indeed, I assumed that $\Delta{}t_n=t_n-t_{n-1}$, rather than $\Delta{}t_n=t_{n+1}-t_n$, as used in the paper. Well spotted. This makes much more sense now. Sorry for the confusion. I agree that the current NEST implementation is hence wrong, obviously the result of an earlier "fix", as Charl explained. I had a quick look at Charl's PR and think this will solve the problem.

Best Tom

On 17.12.24 12:22, Pavel Haman wrote:

Hello Tom and Charl,

thank you for your time, explanations and replies. You confirmed what I thought was happening.

I quickly checked the paper (Maass and Markram, 2002; doi:10.1016/S0893-6080(01)00144-7) and equations (1-5). I think that the model should not update weights with delay of one spike, since $\Delta t_n$ in the equations is actually $t_{n+1}-t_{n}$, i.e. referring to the new spike (it is explained in the sentence before equations), not to older spikes. (I believe here could be the issue, since interpreting $\Delta t_n$, as I would naturally do, as $t_{n}-t_{n-1}$ leads to this one spike delay of updates)

Effective weight for spike $n+1$, $A_{n+1}$ is given as $A_{n+1}= A u_{n+1} R_{n+1}$ and $u_{n+1}$ depends on the times of the new spike $t_{n+1}$ and previous spike $t_{n}$

I will check Charl's PR later this week.

All the best, Pavel

po 16. 12. 2024 v 22:19 odesílatel Charl Linssen <nest-users@turingbirds.com mailto:nest-users@turingbirds.com> napsal:

A little follow-up: I made a pull request with a suggested fix for
this issue: https://github.com/nest/nest-simulator/pull/3384
<https://github.com/nest/nest-simulator/pull/3384>

Tom, Pavel, would you mind having a look to see if this addresses
the issue?

Again, much obliged!
Charl


On Mon, Dec 16, 2024, at 11:14, Charl Linssen wrote:
 > Hi Tom,
 >
 > Thanks for your input on this! I was just looking at the code
too. It
 > seems that the order of updates (first update adaptation variables,
 > then send spike, versus first send spike, then update adaptation
 > variables) was changed, in order to prevent the adaptation from
kicking
 > in for the very first spike to ever go through the synapse. See
 > https://github.com/nest/nest-simulator/pull/1672/
<https://github.com/nest/nest-simulator/pull/1672/>.) Notice that
 > t_lastspike is initialised to zero, rather than some "special" value
 > like -1. It is possible that this fix was erroneous, in that it
ends up
 > affecting not just the first-ever spike, but also subsequent
spikes. I
 > am investigating a bit more, but if you are convinced that the
current
 > behaviour is the correct one, then I can stop investigating.
 >
 > Much obliged!
 > Charl
 >
 >
 > On Mon, Dec 16, 2024, at 11:01, Tom Tetzlaff wrote:
 >> 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_tsodyks2_synapse.html <https://nest-simulator.readthedocs.io/en/stable/auto_examples/evaluate_tsodyks2_synapse.html>),
 >> 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_tsodyks2_synapse.html <https://nest-simulator.readthedocs.io/en/stable/auto_examples/evaluate_tsodyks2_synapse.html>
 >>>
 >>> 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@nest-simulator.org
<mailto:users@nest-simulator.org>
 >>> To unsubscribe send an email to users-leave@nest-simulator.org
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 >>
 >> --
 >> ---
 >>
 >> 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
<https://www.fz-juelich.de/profile/tetzlaff_t>
 >>
 >>
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