Cluster synchronization destruction and chaos in an inhomoceneous active medium

We show that in an inhomogeneous self-sustained oscillatory medium the destruction of perfect clusters of partial synchronization, that is induced both by varying the control parameter and by noise, leads to the onset of chaotic behavior. We study the mechanisms of chaos formation in both cases. It is demonstrated that as parameters change, the transition to chaos in the deterministic medium can result from a hard (subcritical) period-doubling bifurcation and can be accompanied by intermittency. The noise-induced initiation of chaotic dynamics can be related with the existence of non-attracting chaotic motions in the vicinity of a regular regime.