Bistable Oscillations Arising from Synaptic Depression

Synaptic depression is a common form of short-term plasticity in the central and peripheral nervous systems. We show that in a network of two reciprocally connected neurons a single depressing synapse can produce two distinct oscillatory regimes. These distinct periodic behaviors can be studied by varying the maximal conductance, ḡinh, of the depressing synapse. For small ḡinh, the network has a short-period solution controlled by intrinsic cellular properties. For large ḡinh, the solution has a much longer period and is controlled by properties of the synapse. We show that in an intermediate range of ḡinh values both stable periodic solutions exist simultaneously. Thus the network can switch oscillatory modes either by changing ḡinh or, for fixed ḡinh, by changing initial conditions.