Dear Jan, At the beginning of my code I save connections using: nest.DumpLayerConnections(ll_exc,ll_exc,SYN_MODEL_LATCONN_EXC_EXC,'latconn_ll_exc_exc.txt') At the end of execution I use: nest.DumpLayerConnections(ll_exc,ll_exc,SYN_MODEL_LATCONN_EXC_EXC,'latconn_ll_exc_exc_end.txt') that is, just writting to a new file. Now I realized that between Run() calls, I update (using SetStatus()) the rate of a poisson_generator that send spikes to my ll_exc layer ... May be that is the reason? What is sure is that I do not change anything of my ll_exc layer between Run() calls. To solve this, I seen at stimulation backends, but cannot realize the name of the file (not sure what node_id refers to) and how to define the "rate" value inside {data_path}/{data_prefix}{label}/{node_id}.txt ... If I have 10k poisson_generators (each one with its one rate) do I have to create 10k files? I am using NEST 3.3 compiled with mpi. Thanks a lot in advance. Xavier

Hi Jochen, Yesterday night I checked that the problem is that I update the "rate" parameter of a poisson_generator inside the Prepare()/Update() block. That is, with a simple code like that, the poisson_generator does not generate any spike. Hence my neurons do not spike, the speed execution is really fast and STDP synapses do not change their weight: # Neurons creation neurons = nest.Create("iaf_psc_alpha", ...) #Connect neurons uisng STDP synapses conn_dict = {...} syn_dict = {"synapse_model":"stdp_synapse"} nest.Connect(neurons,neurons, conn_dict, syn_dict ) #Connection with a poisson_generator in order to stimulate neurons pg = nest.Create("poisson_generator",...) nest.Connect(pg,neurons, ...) nest.Prepare() for i in range(10): nest.SetStatus(pg,'rate',i*1000) nest.Run(100) nest.Cleanup() But using Simulate() (without Prepare() and Cleanup()), the neurons spike and change their STDP connections: ... for i in range(10): nest.SetStatus(pg,'rate',i*1000) nest.Simulate(100) Hence, it was my fault! I tried to use Prepare() / Cleanup() because I do not want spike_recorder to clean the data in the ascii file after every Simulate() call... hence I took a look at stimulation backends, but I think it is not going to solve my problem. Please, could you include some flag in order to append data to spike_recorders after every Simulate() (i.e. Cleanup()) call? Some of us have post-processing external code (C++ in my case) to post-process data from all the spike_recorder files generated by NEST 2.0 ... Now, having to gather this information from much more files (changing spike_recorder prefix file name after every Simulate() ) increase the complexity of our post-processing code. Thanks a lot in advance! Xavier