Warning

This is A PREVIEW for NEST 3.0 and NOT an OFFICIAL RELEASE! Some functionality may not be available and information may be incomplete!

spike_generator – A device which generates spikes from an array with spike-times

Description

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

Spike times are given in milliseconds, and 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.

Spike times may not coincide with a time step, i.e., are not a multiple of the simulation resolution. Three options control how spike times that do not coincide with a step are handled (see examples below):

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.

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.

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.

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.

Example:

nest.Create("spike_generator",
            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.

Example:

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:

nest.Create("spike_generator",
           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)

nest.Create("spike_generator",
           params={"spike_times": [1.0, 1.05, 3.0001]})

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

nest.Create("spike_generator",
           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)

nest.Create("spike_generator",
           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.

nest.Create("spike_generator",
           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

nest.Create("spike_generator",
           params={"spike_times": [10.0001],
           "precise_times": True})

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

nest.Create("spike_generator",
           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

Parameters

The following properties can be set in the status dictionary.

origin

ms

Time origin for device timer

start

ms

Earliest possible time stamp of a spike to be emitted

stop

ms

Earliest time stamp of a potential spike event that is not emitted

spike_times

ms

Spike-times

spike_weights

synaptic weights

Corresponding spike-weights, the unit depends on the receiver

spike_multiplicities

integer

Multiplicities of spikes, same length as spike_times; mostly for debugging

precise_times

boolean

see above

allow_offgrid_times

boolean

see above

shift_now_spikes

boolean

see above

Sends

SpikeEvent