There are only a few organizational principles that allow the number of groups (K) to scale beyond the number of neurons (N). Polychronization ( http://www.izhikevich.org/publications/spnet.pdf ). This is e.g. different from synfire chains in which the number of groups equals the number of neurons. I don't remember much about the capacity analysis of standard reservoir computing methods (ESN, LSM, ELM), but I thought…
Is ELM reservoir computing?
Yes, if you consider the most salient part of reservoir computing method a random projection matrix that is quenched (kept fixed).