Crossover inhibition in the retina: circuitry that compensates for nonlinear rectifying synaptic transmission |
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Authors: | Alyosha Molnar Hain-Ann Hsueh Botond Roska Frank S Werblin |
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Institution: | (1) School of Electrical and Computer Engineering (ECE), Cornell University, Ithaca, NY 14853, USA;(2) Department of Bioengineering, University of California at Berkeley, Berkeley, CA 94720, USA;(3) Neural Circuit Laboratories, Friedrich Miescher, Institute for Biomedical Research, Maulbeerstrasse 66, 4058 Basel, Switzerland;(4) Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA; |
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Abstract: | In the mammalian retina, complementary ON and OFF visual streams are formed at the bipolar cell dendrites, then carried to
amacrine and ganglion cells via nonlinear excitatory synapses from bipolar cells. Bipolar, amacrine and ganglion cells also receive a nonlinear inhibitory input from amacrine cells. The most common form of such inhibition crosses over from the opposite visual stream: Amacrine
cells carry ON inhibition to the OFF cells and carry OFF inhibition to the ON cells (”crossover inhibition”). Although these
synapses are predominantly nonlinear, linear signal processing is required for computing many properties of the visual world
such as average intensity across a receptive field. Linear signaling is also necessary for maintaining the distinction between
brightness and contrast. It has long been known that a subset of retinal outputs provide exactly this sort of linear representation
of the world; we show here that rectifying (nonlinear) synaptic currents, when combined thorough crossover inhibition can
generate this linear signaling. Using simple mathematical models we show that for a large set of cases, repeated rounds of
synaptic rectification without crossover inhibition can destroy information carried by those synapses. A similar circuit motif
is employed in the electronics industry to compensate for transistor nonlinearities in analog circuits. |
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