Feedback Synapse to Cone and Light Adaptation

Part of Advances in Neural Information Processing Systems 3 (NIPS 1990)

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Josef Skrzypek


Light adaptation (LA) allows cone vIslOn to remain functional between twilight and the brightest time of day even though, at anyone time, their intensity-response (I-R) characteristic is limited to 3 log units of the stimu(cid:173) lating light. One mechanism underlying LA, was localized in the outer seg(cid:173) ment of an isolated cone (1,2). We found that by adding annular illhmination, an I-R characteristic of a cone can be shifted along the intensity domain. Neural network involving feedback synapse from horizontal cells to cones is involved to be in register with ambient light level of the periphery. An equivalent electrical circuit with three different transmembrane channels leakage, photocurrent and feedback was used to model static behavior of a cone. SPICE simulation showed that interactions between feedback synapse and the light sensitive conductance in the outer segment can shift the I-R curves along the intensity domain, provided that phototransduction mechan(cid:173) ism is not saturated during maximally hyperpolarized light response.