Biophysics of Computation: Neurons, Synapses and Membranes

Synapses, membranes and neurotransmitters play an important role in processing information in the nervous system. We do not know, however, what biophysical mechanisms are critical for neuronal computations, what elementary information processing operations they implement, and which sensory or motor computations they underlie. In this paper, we outline an approach to these problems. We will review a number of different biophysical mechanisms such as synaptic interactions between excitation and inhibition, dendritic spines, non-impulse generating membrane nonlinearities and transmitter-regulated voltage channels. For watch one, we discuss the information processing operations that may be implemented. All of these mechanisms act either within a few milliseconds, such as the action potential or synaptic transmission, or over several hundred milliseconds or even seconds, modulating some property of the circuit. In some cases we will suggest specific examples where a biophysical mechanism underlies a given computation. In particular, we will discuss the neuronal operations, and their implementation, underlying direction selectivity in the vertebrate retina