Computations in the vertebrate retina: gain enhancement, differentiation and motion discrimination

An understanding of brain function will ultimately require an understanding of the elementary information processing operations performed by synapses, membranes and neurons. Such knowledge, in addition to its intrinsic interest, will be instrumental for a full comprehension of the algorithms and computational procedures used by the brain to solve visual and other perceptual problems. The vertebrate retina is a very attractive model system for approaching the question of the information processing role of biological mechanisms of nerve cells. The retina provides the visual input to the brain and is its main interface with the outside world. Its anatomy and physiology are relatively well known. We also have a fairly good idea of some of the information processing operations, i.e., the computations, performed by the retina. A complete circuit diagram of the retina is not available, but it is now possible to identify a few simple computations that the retina performs and to relate them to specific biophysical mechanisms and circuit elements on the basis of theoretical work, computer simulations and experimental data. In this paper we consider three operations carried out by most retinae: amplification, temporal differentiation and computation of the direction of motion of visual patterns