Neural computation from retina to visual cortex

California Institute Of Technology, Pasadena CA

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Abstract

Project Summary This research aims at understanding how visual information is processed in the eye and brain. Vision begins in the retina, a complex network of neurons in the back of the eye where visual images are converted into streams of action potentials that travel through the fibers of the optic nerve to the brain. There the signals pass through the thalamus to the visual cortex, where much larger circuits of neurons are brought to bear. Recent research has changed our view of the retina: Whereas it used to be considered a simple prefilter for the visual image, new results suggest that the retina computes quite specific features of the scene and conveys those to the brain through many parallel channels. The proposed research will build on this work, both to further our understanding of how the retina converts images into spike trains, and to investigate how this code for visual scenes can be used by the brain for further processing. This will be addressed in a collaborative project that combines experimental as well as theoretical and computational approaches. The specific aims are: (1) to unify diverse functions of the retina under a common mathematical formalism, and use this to discover new functions; (2) to determine how our brain might process retinal signals for rapid understanding of a new scene; (3) to explain how our fine vision can be so acute, given that the eyes are never holding still. If successful, this research will offer benefits on multiple fronts. First, it will expand our notions of what a neural circuit like the retina can compute and how the information is encoded in its output, an important goal of systems neuroscience. Second, it will help resolve two mysteries of visual processing, relating to both its remarkable speed and its high acuity. Third, progress in these areas will benefit brain science in general. Many of the circuit motifs encountered in the retina are repeated in other brain areas, and may well serve similar network-level functions. Finally, an improved understanding of early visual function can change how one thinks about visual diseases and therapy. For example, it now appears that certain functions previously assigned to the visual cortex already happen in the retina; if so, then retinal dysfunction could also have much more elaborate effects on visual experience. Conversely, in efforts to treat retinal degeneration by electronic or genetic prostheses one needs to know which aspects of retinal function the prosthesis should emulate to support visual perception.