There is 2006 paper "Polychronization: Computation with Spikes" E. Izhikevich. that describes one simulation they have done in silico and it explains how exactly distribution of activity happens and why you can't run out of memory. Basically the small group of neurons, say 10, can represent much larger amount of information say 1000 because they can fire in different orders, that is what they call poly-synchronous activity.