Measuring representational distances -- the spike-train metrics approach

A fundamental problem in studying population codes is how to compare population activity patterns. Population activity patterns are not just spatial, but spatiotemporal. Thus, a principled approach to the problem of the comparison of population activity patterns begins with the comparison of the temporal activity patterns of a single neuron, and then, to the extension of the scope of this comparison to populations spread across space. Since 1926 when Adrian and Zotterman reported that the firing rates of somatosensory receptor cells depend on stimulus strength, it has become apparent that a significant amount of the information propagating through the sensory pathways is encoded in neuronal firing rates. However, while it is easy to define the average firing rate for a cell over the lengthy presentation of a time-invariant stimulus, it is more difficult to quantify the temporal features of spike trains. With an experimental data set extracting a time-dependent rate function is model dependent since calculating it requires a choice of a binning or smoothing procedure.