pascal fries describes “activated neural groups [that] oscillate and thereby undergo rhythmic excitability fluctuations that produce temporal windows for communication. only coherently oscillating neuronal groups can interact effectively, because their communication windows for input and for output are open at the same times, [subserving] our cognitive flexibility.” Fries, P.: “a mechanism for cognitive dynamics; neuronal communication through neuronal coherence.” trends in cognitive sciences 9, 474-480, november 2005.