Cross-correlation between neurons: a source of information about the nervous system

Impulse trains of spiking neurons are a stochastic process; however, the impulse trains of related neurons are generally not statistically independent. Cross-correlation may be due to either a common input that affects the firing of both cells, or to direct synaptic influence of the one neuron upon the other. By analyzing the distributions of intervals preceding and those following the coincident firings relative to that of all the intervals between impulses in each train, it is possible to infer restrictions upon the ways in which the correlating influence interacts with other sources of variability for each cell. This is applied to pairs of cells in two systems, one in which the coincident firing is due to an input common to the two cells, and one in which one cell is presynaptic to the other.