A unified approach to the study of temporal, correlational and rate coding
Abstract
We demonstrate that the complete (Mackay and McCulloch, 1952) information contained in the spike times of a population of neurons can be broken up into a series of terms which have physiological significance. This occurs in the coding r{\'e}gime in which few spikes are emitted in the relevant time window. This approach allows us to study the additional information contributed by spike timing beyond that present in the spike counts, to examine the contributions to the whole information of different statistical properties of spike trains, such as firing rates and correlation functions, and forms the basis for a new quantitative procedure for the analysis of simultaneous multiple neuron recordings. It also provides theoretical constraints upon neural coding. We find that there is a transition between two coding r{\'e}gimes depending on the size of the relevant observation timescale with respect to the characteristic timescale of stimulus-induced response fluctuations. For time windows shorter than the timescale of the stimulus-induced fluctuations, the additional purely temporal information is of third order, and hence spike counts necessarily dominate the population information. For time-windows much longer than the characteristic timescale, the additional timing information can be of first order, and thus affect the instantaneous information rate. It is also found that, over short timescales, the temporal structure of correlations contributes less to temporal coding than the temporal variations of the firing rates.Keywords
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