The Journal of Neuroscience, October 1, 2002, 22(19):8726-8738
The Influence of Different Retinal Subcircuits on the
Nonlinearity of Ganglion Cell Behavior
Matthias H.
Hennig1,
Klaus
Funke2, and
Florentin
Wörgötter1
1 Institute for Neuronal Computational Intelligence and
Technology, Department of Psychology, University of Stirling, Stirling,
FK9 4LA, United Kingdom, and 2 Institut für
Physiologie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
Y-type retinal ganglion cells show a pronounced, nonlinear,
frequency-doubling behavior in response to modulated sinewave gratings.
This is not observed in X-type cells. The source of this spatial
nonlinear summation is still under debate. We have designed a realistic
biophysical model of the cat retina to test the influence of different
retinal cell classes and subcircuits on the linearity of ganglion cell
responses. The intraretinal connectivity consists of the fundamental
feedforward pathway via bipolar cells, lateral horizontal cell
connectivity, and two amacrine circuits. The wiring diagram of X- and
Y-cells is identical apart from two aspects: (1) Y-cells have a wider
receptive field and (2) they receive input from a nested amacrine
circuit consisting of narrow- and wide-field amacrine cells. The model
was tested with contrast-reversed gratings. First and second harmonic
response components were determined to estimate the degree of
nonlinearity. By means of circuit dissection, we found that a high
degree of the Y-cell nonlinear behavior arises from the spatial
integration of temporal photoreceptor nonlinearities. Furthermore, we
found a weaker and less uniform influence of the nested amacrine
circuit. Different sources of nonlinearities interact in a
multiplicative manner, and the influence of the amacrine circuit is
~25% weaker than that of the photoreceptor. The model predicts
that significant nonlinearities occur already at the level of
horizontal cell responses. Pharmacological inactivation of the amacrine
circuit is expected to exert a milder effect in reducing ganglion cell nonlinearity.
Key words:
receptive field; rectification; ganglion cell; amacrine
cell; cat retina; model
Copyright © 2002 Society for Neuroscience 0270-6474/02/22198726-13$05.00/0