Spike count histograms for two neurons after 1,600 presentations of pattern A during the recall epoch. Offset is time in milliseconds from start of pattern presentation. A neuron that is not part of a polychronous group associated with pattern A (upper panel) fires at random times during replay of the pattern. Some neurons consistently fire at a particular time during pattern replay, producing peaks in the spiking count histogram. These peaks indicate that the neuron fires as part of a stimulus-related polychronous group. The timing of peaks over multiple neurons produces a spatiotemporal signature of group activation in response to the stimulus.