  We demonstrate that the information contained in the spike occurrence times
of a population of neurons can be broken up into a series of terms, each of
which reflect something about potential coding mechanisms. This is possible 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 strategies. We find a transition between two coding r{\'e}gimes,
depending upon the size of the relevant observation timescale. For time windows
shorter than the timescale of the stimulus-induced response fluctuations, there
exists a spike count coding phase, where the purely temporal information is of
third order in time. For time windows much longer than the characteristic
timescale, there can be additional timing information of first order, leading
to a temporal coding phase in which timing information may affect the
instantaneous information rate.
  We study the relative contributions of the dynamic firing rate and
correlation variables to the full temporal information; the interaction of
signal and noise correlations in temporal coding; synergy between spikes and
between cells; and the effect of refractoriness. We illustrate the utility of
the technique by analysis of a few cells from the rat barrel cortex.
