|
|
|
 |
|
Vijay Balasubramanian
Department of Physics and Astronomy, University of Pennsylvania, USA
Wednesday 26 March 2008
16.00
Seminar Room B10 (Basement)
Alexandra House, 17 Queen Square, London, WC1N 3AR
Towards a theory of the structural and functional organization of the retina
The retina is a light-sensitive area of the central brain comprising ~65 types of cells and a complex web of microcircuitry. One hundred years of study since the work of Cajal have illuminated many details of the structural and functional organization of these circuits. I will argue that a theory of this organization can be developed by asking how information in natural scenes can be efficiently processed, subject to the metabolic, spatial, temporal and noise constraints inherent in biological computation. I will pay particular attention to metabolic constraints, and will describe our efforts to quantitatively measure the cost of communication in the optic nerve. The examples that I will discuss include: (a) the relative scarcity of Blue cones and the retina’s indifference to Red/ Green cone ratio, (b) the shape of individual retinal ganglion cell receptive fields, (c) the organization of these receptive fields into mosaics covering the visual space, (d) the separation into distinct cell types, each creating its own mosaic, and (e) the distribution of information traffic across the different channels in the optic nerve. Our analyses are based on a new, calibrated, high resolution database of chromatic images from a baboon habitat in the Okavango Delta, Botswana.