THE POWER RATIO AND THE INTERVAL MAP - SPIKING MODELS AND EXTRACELLULAR RECORDINGS

We describe a new, computationally simple method for analyzing the dyn amics of neuronal spike trains driven by external stimuli. The goal of our method is to test the predictions of simple spike-generating mode ls against extracellularly recorded neuronal responses. Through a new statistic called the power ratio, we distinguish between two broad cla sses of responses: (1) responses that can be completely characterized by a variable firing rate, (for example, modulated Poisson and gamma s pike trains); and (2) responses for which firing rate variations alone are not sufficient to characterize response dynamics (for example, le aky integrate-and-fire spike trains as well as Poisson spike trains wi th long absolute refractory periods). We show that the responses of ma ny visual neurons in the cat retinal ganglion, cat lateral geniculate nucleus, and macaque primary visual cortex fall into the second class, which implies that the pattern of spike times can carry significant i nformation about visual stimuli. Our results also suggest that spike t rains of X-type retinal ganglion cells, in particular, are very simila r to spike trains generated by a leaky integrate-and-fire model with a dditive, stimulus-independent noise that could represent background sy naptic activity.