  We investigate the synchronization dynamics of two coupled noise-driven
FitzHugh-Nagumo systems, representing two neural populations. For certain
choices of the noise intensities and coupling strength, we find cooperative
stochastic dynamics such as frequency synchronization and phase
synchronization, where the degree of synchronization can be quantified by the
ratio of the interspike interval of the two excitable neural populations and
the phase synchronization index, respectively. The stochastic synchronization
can be either enhanced or suppressed by local time-delayed feedback control,
depending upon the delay time and the coupling strength. The control depends
crucially upon the coupling scheme of the control force, i.e., whether the
control force is generated from the activator or inhibitor signal, and applied
to either component. For inhibitor self-coupling, synchronization is most
strongly enhanced, whereas for activator self-coupling there exist distinct
values of the delay time where the synchronization is strongly suppressed even
in the strong synchronization regime. For cross-coupling strongly modulated
behavior is found.
