1. A system for determining functional synapses from predetermined synapses of connections between two cells in a neuronal circuit, comprising: a processor configured to determine, from the predetermined synapses, the functional synapses by: admitting, in a first step with a first probability, given structural touches to a second step as potential synapses, followed by selecting, with a second probability in the second step, synapses of the potential synapses as predetermined synapses; and leaving a portion of the connections unused such that the functional synapses are determined with a third probability from the synapses being selected in the second step, wherein the third probability is independent of a number of the predetermined synapses.