Communication channel

This example demonstrates how to create a connections from one neuronal ensemble to another that behaves like a communication channel (that is, it transmits information without changing it).

Network diagram:

[Input] ---> (A) ---> (B)

An abstract input signal is fed into a first neuronal ensemble \(A\), which then passes it on to another ensemble \(B\). The result is that spiking activity in ensemble \(B\) encodes the value from the Input.

In [1]:
import numpy as np
import matplotlib.pyplot as plt
%matplotlib inline

import nengo

Step 1: Create the Network

In [2]:
# Create a 'model' object to which we can add ensembles, connections, etc.
model = nengo.Network(label="Communications Channel")
with model:
    # Create an abstract input signal that oscillates as sin(t)
    sin = nengo.Node(np.sin)

    # Create the neuronal ensembles
    A = nengo.Ensemble(100, dimensions=1)
    B = nengo.Ensemble(100, dimensions=1)

    # Connect the input to the first neuronal ensemble
    nengo.Connection(sin, A)

    # Connect the first neuronal ensemble to the second
    # (this is the communication channel)
    nengo.Connection(A, B)

Step 2: Add Probes to Collect Data

Even this simple model involves many quantities that change over time, such as membrane potentials of individual neurons. Typically there are so many variables in a simulation that it is not practical to store them all. If we want to plot or analyze data from the simulation we have to “probe” the signals of interest.

In [3]:
with model:
    sin_probe = nengo.Probe(sin)
    A_probe = nengo.Probe(A, synapse=.01)  # ensemble output
    B_probe = nengo.Probe(B, synapse=.01)

Step 3: Run the Model!

In [4]:
with nengo.Simulator(model) as sim:

Step 4: Plot the Results

In [5]:
plt.figure(figsize=(9, 3))
plt.subplot(1, 3, 1)
plt.ylim(0, 1.2)
plt.subplot(1, 3, 2)
plt.ylim(0, 1.2)
plt.subplot(1, 3, 3)
plt.ylim(0, 1.2)
(0, 1.2)

These plots show the idealized sinusoidal input, and estimates of the sinusoid that are decoded from the spiking activity of neurons in ensembles A and B.

Step 5: Using a Different Input Function

To drive the neural ensembles with different abstract inputs, it is convenient to use Python’s “Lambda Functions”. For example, try changing the sin = nengo.Node line to the following for higher-frequency input:

sin = nengo.Node(lambda t: np.sin(2*np.pi*t))