  Occurrence of strong or mass synchronization of a large number of neuronal
populations in the brain characterizes its pathological states. In order to
establish an understanding of the mechanism underlying such pathological
synchronization we present a model of coupled populations of phase oscillators
representing the interacting neuronal populations. Through numerical analysis,
we discuss the occurrence of mass synchronization in the model, where a source
population which gets strongly synchronized drives the target populations onto
mass synchronization. We hypothesize and identify a possible cause for the
occurrence of such a synchronization, which is so far unknown: Pathological
synchronization is caused not just because of the increase in the strength of
coupling between the populations but also because of the strength of the strong
synchronization of the drive population. We propose a demand-controlled method
to control this pathological synchronization by providing a delayed feedback
where the strength and frequency of the synchronization determines the strength
and the time delay of the feedback. We provide an analytical explanation for
the occurrence of pathological synchronization and its control in the
thermodynamic limit.
