What The Retina Might Know About Natural Scenes

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Biological organisms collect information from the natural environment that is necessary for their survival. A significant fact about the design of the neural systems responsible for collecting this data is their massive parallelism. For example, the retina expresses at least 15 kinds of parallel information channels which transmit different kinds of information relevant to behaviour to the brain, rather than using a few general purpose cables with a suitably complicated code. A prototypical example is the segregation of ON and OFF pathways in the visual system to process information in bright vs. dark features of a scene. The parallel channels are strikingly heterogeneous, spanning a 50-fold range in nerve fiber diameter and a 10-fold range in voltage spike firing rate. What determines this choice of massively parallel design, and the particular channels that are expressed? This project will explore a basic hypothesis: parallel channels exist to minimize the metabolic and spatial costs necessary to extract behaviorally relevant information from natural stimuli and transmit it to the brain. To accomplish this goal, the PI intends to 1) examine timing precision, reproducibility, information rate, and information per spike encoded by different retinal neurons, 2) study how neuronal circuit structure relates to the structure of natural images, and 3) measure spatial and metabolic costs of different channels and examine how parallelism affects information transmission. The project intends to develop new theory and analysis techniques to study spatio-temporal constraints in neural coding, adaptation to changing stimulus statistics and the biophysics of why large, expensive cells appear to be needed to transmit information at high average rates.This project, joining theoretical physics and experimental biology, will have a broad inter-disciplinary impact by: (a) training physics graduate students in the problems and techniques of neuroscience, and (b) transferring analytical and theoretical tools of physics to neuroscientists. The PI is also involved in encouraging such synergy between physics and biology by organizing joint physics-neuroscience workshops at Penn and at the Kavli Institute for Theoretical Physics.