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