It is shown analytically that there exists a natural basis in terms of which the nonperturbative time evolution of an important class of driven four-level systems in the strong-coupling regime decouples and essentially reduces to the corresponding time evolution in the weak-field regime, exhibiting simple Rabi oscillations between the different relevant quantum states. The predictions of the model are corroborated by an exact numerical calculation. 33.15.Hp, 02.30.Mv, 73.40.Gk