Using CSA with spatial populations

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This example shows a brute-force way of specifying connections between NEST populations with spatial data using Connection Set Algebra instead of the built-in connection routines.

Using the CSA requires NEST to be compiled with support for libneurosim. For details, see [1].

See Also

Using CSA for connection setup


First, we import all necessary modules.

import matplotlib.pyplot as plt
import nest

Next, we check for the availability of the CSA Python module. If it does not import, we exit with an error message.

    import csa

    haveCSA = True
except ImportError:
        "This example requires CSA to be installed in order to run.\n"
        + "Please make sure you compiled NEST using\n"
        + "  -Dwith-libneurosim=[OFF|ON|</path/to/libneurosim>]\n"
        + "and CSA and libneurosim are available."
    import sys


We define a factory that returns a CSA-style geometry function for the given layer. The function returned will return for each CSA-index the position in space of the given neuron as a 2- or 3-element list.

This function stores a copy of the neuron positions internally, entailing memory overhead.

def geometryFunction(population):
    positions = nest.GetPosition(population)

    def geometry_function(idx):
        return positions[idx]

    return geometry_function

We create two spatial populations that have 20x20 neurons of type iaf_psc_alpha.

pop1 = nest.Create("iaf_psc_alpha", positions=nest.spatial.grid([20, 20]))
pop2 = nest.Create("iaf_psc_alpha", positions=nest.spatial.grid([20, 20]))

For each population, we create a CSA-style geometry function and a CSA metric based on them.

g1 = geometryFunction(pop1)
g2 = geometryFunction(pop2)
d = csa.euclidMetric2d(g1, g2)

The connection set cg describes a Gaussian connectivity profile with sigma = 0.2 and cutoff at 0.5, and two values (10000.0 and 1.0) used as weight and delay, respectively.

cg = csa.cset(csa.random * (csa.gaussian(0.2, 0.5) * d), 10000.0, 1.0)

We can now connect the populations using the Connect function with the conngen rule. It takes the IDs of pre- and postsynaptic neurons (pop1 and pop2), the connection set (cg) and a dictionary that map the parameters weight and delay to positions in the value set associated with the connection set (params_map).

params_map = {"weight": 0, "delay": 1}
connspec = {"rule": "conngen", "cg": cg, "params_map": params_map}
nest.Connect(pop1, pop2, connspec)

Finally, we use the PlotTargets function to show all targets in pop2 starting at the center neuron of pop1.

cntr = nest.FindCenterElement(pop1)
nest.PlotTargets(cntr, pop2)

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