Hello Bjoern & Frank,

first of all, sorry for my late reply.

Depending on your description I can not really reconstruct your  
experiment setting.
Ideally, please provide a minimal example.
Interesting additional information would be:
- In the case with STDP: how large are EPSPs in experiments without  
spiking? Larger than in the case without STDP?
- Provide details regarding your stimulation protocol.

Reminders that may help:
- If you change the order of connecting external spike sources to  
hardware neurons, different synapses are assigned on hardware. Due to  
fixed-pattern noise across synapses (static parameter variations due  
to production imperfections) EPSPs on the membrane potential are  
likely to differ in size.
- Depending on the number of synapses (and their synaptic weight),  
leak currents pull the membrane potential to the respective reversal  
potential.
Solution: Try to use as identical network configurations in both  
experiments as possible, e.g., do not provide input to the plastic  
synapse in your static case. Alternatively, compensate for the  
different excitabilities of the neuron (caused by leak currents) by  
adjusting synaptic weights.

Regarding the "sampling frequency" of the STDP controller:
This frequency defines how fast the global weight update controller  
steps through the rows of synapses.
The default value is maximum frequency to achieve the highest temporal  
resolution of possible weight changes.
For most use cases I recommend this setting.
For details, see: http://arxiv.org/abs/1201.6255

Kind regards,

Thomas


Zitat von "Deiseroth, Bjoern" <[log in to unmask]>:

> Hello there!
>
> I'm trying to implement some particular behavior, which only occurs  
> every now and then, even for quite simple networks.
> Is there some measured value, with how much noise the system runs?  
> Like in terms of mV variation of a neurons capacity? Or variation in  
> time-to-reach-max-capacity? And how is it effected by activating  
> things like STP or STDP?
>
> Simple UC:
>
> -          A single source neuron excites a single  
> IF_facets_hardware1 neuron with 15*minExcWeight(). Resulting  
> max-capacity lies around -68 to -66 mV. Nice, I can work with that!
>
> -          When some STDP synapse is placed (somewhere offside these  
> 2 neurons with 1 classical synapse), suddenly the post-connected  
> neuron spikes, sometimes (as in top of figure below). Seemingly it  
> also depends on the exact spike-injection time of its source neuron.  
> When the source array is set to 10 ms, the post neuron spikes  
> sometimes, at 15 ms, it never does..
>
>
>
> I figured/ read so far, that there is some sampling going thru each  
> neuron, even those not connected with STDP.
> With
> pynn.hardware.hwa.autoSTDPFrequency = runtime/2
> one may set the exact sample points.
> What exactly happens on those samplings? In the top of the attached  
> figure, I sample every 50ms, below every 10ms..
> At first I thought I should only sample after each "iteration" is  
> done, to avoid STDP noise, and as I don't need immediate STDP  
> changes. It looked like whenever sampling occurs, the remaining EPSP  
> (and IPSP?) approaching a neuron is reset.
> But actually the bottom figure comes closer to the "real case",  
> where post never spikes?
>
>
> Thanks a lot and kind regards
> Bjoern & Frank
>
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