  Many natural systems including the brain comprise coupled non-uniformly
stimulated elements. In this paper we show that heterogeneously driven networks
of excitatory-inhibitory units exhibit striking collective phenomena, including
spontaneous oscillations upon coupling. On varying the coupling strength a
novel transition is seen wherein the pattern symmetries of stimulated and
unstimulated groups undergo mutual exchange. The system exhibits coexisting
chaotic and non-chaotic attractors - an intriguing result in view of earlier
reports of varying degrees of chaoticity in the brain.
