Two oscillation modes exist only when both synapses are depressing. The maximal synaptic conductance of one synapse was varied by ramping it up (●) and then down (▵) over a total period of 300 sec. A, Both synapses are depressing. GLP→PD was fixed at 0.8 mS/cm2, and GPD→LP was varied between 0 and 10 mS/cm2. B, The PD to LP synapse was depressing, and the LP to PD synapse was static. GLP→PD was fixed at 0.8 mS/cm2, and GPD→LP was varied between 0 and 15 mS/cm2. C, The LP to PD synapse was depressing, and the PD to LP synapse was static. GPD→LP was fixed at 10 mS/cm2, and GLP→PD was varied between 0 and 1.5 mS/cm2. D, Synapses are as in C, butGLP→PD was fixed at 0.8 mS/cm2, and GPD→LP was varied between 0 and 15 mS/cm2.