spike_generator – Generate spikes from an array with spike-times


A spike generator can be used to generate spikes at specific times which are given to the spike generator as an array.


If the spike trains have a very high rate, we recommend using the spike_generator. For rates similar to regular neurons, use spike train injector.

Spike times are given in milliseconds as an array. The spike_times array must be sorted with the earliest spike first. All spike times must be strictly in the future. Trying to set a spike time in the past or at the current time step will cause a NEST error. Setting a spike time of 0.0 will also result in an error.

Multiple occurrences of the same time indicate that more than one event is to be generated at this particular time.

Additionally, spike_weights can be set. This is an array as well. It contains one weight value per spike time. If set, the spikes are delivered with the respective weight multiplied with the weight of the connection. To disable this functionality, the spike_weights array can be set to an empty array.

The spike generator supports spike times that do not coincide with a time step, that is, are not falling on the grid defined by the simulation resolution. There are three options that control how spike times that do not coincide with a step are handled (see also examples below):

Option 1: precise_times default: false

If false, spike times will be rounded to simulation steps, i.e., multiples of the resolution. The rounding is controlled by the two other flags. If true, spike times will not be rounded but represented exactly as a combination of step and offset. This should only be used if all neurons receiving the spike train can handle precise timing information. In this case, the other two options are ignored.

Option 2: allow_offgrid_times default: false

If false, spike times will be rounded to the nearest step if they are less than tic/2 from the step, otherwise NEST reports an error. If true, spike times are rounded to the nearest step if within tic/2 from the step, otherwise they are rounded up to the end of the step. This setting has no effect if precise_times is true.

Option 3: shift_now_spikes default: false

This option is mainly for use by the PyNN-NEST interface. If false, spike times rounded down to the current point in time will be considered in the past and ignored. If true, spike times that are rounded down to the current time step are shifted one time step into the future.

Note that GetStatus will report the spike times that the spike_generator will actually use, i.e., for grid-based simulation the spike times rounded to the appropriate point on the time grid. This means that GetStatus may return different spike_times values at different resolutions.


            params={"spike_times": [1.0, 2.0, 3.0]})

Instructs the spike generator to generate events at 1.0, 2.0, and 3.0 milliseconds, relative to the device-timer origin.


Assume that NEST works with default resolution (step size) of 0.1 ms and default tic length of 0.001 ms. Then, spikes times not falling onto the grid will be handled as follows for different option settings:

           params={"spike_times": [1.0, 1.9999, 3.0001]})

—> spikes at steps 10 (==1.0 ms), 20 (==2.0 ms) and 30 (==3.0 ms)

           params={"spike_times": [1.0, 1.05, 3.0001]})

—> Error! Spike time 1.05 not within tic/2 of step

           params={"spike_times": [1.0, 1.05, 3.0001],
           "allow_offgrid_times": True})
—> spikes at steps 10, 11 (mid-step time rounded up),

30 (time within tic/2 of step moved to step)

           params={"spike_times": [1.0, 1.05, 3.0001],
           "precise_times": True})
—> spikes at step 10, offset 0.0; step 11, offset -0.05;

step 31, offset -0.0999

Assume we have simulated 10.0 ms and simulation time is thus 10.0 (step 100). Then, any spike times set at this time must be later than step 100.

           params={"spike_times": [10.0001]})
—> spike time is within tic/2 of step 100, rounded down to 100 thus

not in the future; spike will not be emitted

           params={"spike_times": [10.0001],
           "precise_times": True})

—> spike at step 101, offset -0.0999 is in the future

           params={"spike_times": [10.0001, 11.0001],
           "shift_now_spikes": True})
—> spike at step 101, spike shifted into the future, and spike at step

110, not shifted, since it is in the future anyways

All stimulation devices share the parameters start and stop, which control the stimulation period. The property origin is a global offset that shifts the stimulation period. All three values are set as times in ms.

  • For spike-emitting devices, only spikes with times t that fulfill \(\mathrm{start} < t \leq \mathrm{stop}\) are emitted. Spikes that have timestamp of \(t = \mathrm{start}\) are not emitted.

  • For current-emitting devices, the current is activated and deactivated such that the current first affects the target dynamics during the update step \((\mathrm{start}, \mathrm{start}+h]\), that is, an effect can be recorded at the earliest at time \(\mathrm{start}+h\). The last interval during which the current affects the target’s dynamics is \((\textrm{stop}-h, \textrm{stop}]\).

The property stimulus_source defaults to an empty string. It can be set to the name of a stimulation backend, in which case it will take its parameters from the configured backend instead of from the internally stored values. More details on available backends and their properties can be found in the guide to stimulating the network.



A string specifying an arbitrary textual label for the device. Stimulation backends might use the label to generate device specific identifiers like filenames and such. Default: "".


A positive floating point number used as the reference time in ms for start and stop. Default: 0.0.


A positive floating point number specifying the activation time in ms, relative to origin. Default: 0.0.


A string specifying the name of the stimulation backend from which to get the data for updating the stimulus parameters of the device. By default, the device uses its internally stored parameters for updating the stimulus. Default: "".


A floating point number specifying the deactivation time in ms, relative to origin. The value of stop must be greater than or equal to start. Default: infinity.


List of spike times in ms.


List of corresponding spike weights, the unit depends on the receiver. (e.g., nS for conductance-based neurons or pA for current based ones)


List of multiplicities of spikes, same length as spike_times; mostly for debugging.


See above.


See above.


See above.

Set spike times from a stimulation backend

The spike times for this stimulation device can be updated with input coming from a stimulation backend. The data structure used for the update holds just an array of spike times in ms.



See also

Device, Spike, Generator

Examples using this model