Response variability and timing precision of neuronal spike trains in vivo

We report that neuronal spike trains can exhibit high, stimulus- dependent temporal precision even while the trial-to-trial response variability, measured in several traditional ways, remains substantially independent of the stimulus. We show that retinal ganglion cells and neurons in the lateral geniculate nucleus (LGN) of cats in vivo display both these aspects of firing behavior, which have previously been reported to be contradictory. We develop a simple model that treats neurons as 'leaky' integrate-and-fire devices and show that it too, can exhibit both behaviors. We consider the implications of our findings for the problem of neural coding.