Rank Order Coding

Abstract

The idea that neurones transmit information using a rate code is extremely entrenched in the neuroscience community. The vast majority of neurophysiological studies simply describe neural responses in terms of firing rate, and while studies using Peri-Stimulus Time Histograms (PSTHs) are fairly common, only rarely does one get to see the underlying spikes in the form of a raster display. Even rarer are studies that provide information about how spikes are generated across a population of neurones. One consequence of this strong bias is that many alternative coding schemes, and particularly those involving patterns of activity distributed across populations of neurones, have simply not been considered seriously. It is now virtually 30 years since the publication of Perkel and Bullocks' review of Neural Coding in which a whole range of candidate coding schemes were discussed1. Few of these various candidate codes have been disproved experimentally. Even today, when increasing numbers of researchers are interested in the potential of temporal coding schemes and in particular the role played by synchrony2,3, few question the underlying assumption that this synchrony is imposed on an underlying rate code.