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, ḡ_inh, of the depressing synapse. For small ḡ_inh, the network has a short-period solution controlled by intrinsic cellular properties. For large ḡ_inh, the solution has a much longer period and is controlled by properties of the synapse. We show that in an intermediate range of ḡ_inh values both stable periodic solutions exist simultaneously. Thus the network can switch oscillatory modes either by changing ḡ_inh or, for fixed ḡ_inh, by changing initial conditions.