Paper detail

Generic Behaviour of Strongly Reinforced Polya Urns : Convergence and Stability

We consider, as proposed and studied in Hofstad et.\ al.\ \cite{HHKR}, a class of graph-based "interacting urn"-type Polya urn model inspired by neuronal processing in the brain where a signal enters the brain at some (randomly) chosen neuron and is transmitted to a (random) single neighbouring neuron with a probability depending on the relative `efficiency' of the synapses connecting the neurons, and in doing so the efficiency of the utilized synapse is improved/reinforced. We study the structures (or architectures) and relative efficiency of the neuronal networks that can arise from repeating this process a very large number of times in a "strong reinforcement regime". Under the most general conditions, we prove in the affirmative a part of the main open conjecture in \cite{HHKR} i.e. the zero probability of convergence of the corresponding "urn process" to any 'unstable' equilibrium. Under very generic conditions, i.e., for an open and dense subset of parameters with full measure, we also prove the full open conjecture by showing the finiteness of the equilibrium set and hence the unit probability of convergence of the "urn process" to some 'stable' equilibrium.