Bistability and rhythmicity in the feeding circuit. A: Circuit diagram of the feeding CPG. We expanded our previous ten-cell model  by representing B31 and B63 with two-compartments (soma and axon compartments), incorporating a modulatory synapse from B63 to B31, and implementing an autapse in B31 (new elements in red). See Panel B for additional details. The circuit was implemented in SNNAP . Cellular and synaptic properties matched empirical data. Fill colors indicate cells that fire in phase. B: Hurwitz et al.  characterized and modeled membrane currents in the nonspiking soma of B31. We expanded that model by including a second-messenger system, which activated an inward current (new elements in red). C1: A 1-s depolarization of B63 (not shown) elicited a plateau-like potential in B31, which drove rhythmic activity (e.g., bursting in B64). C2: Without the autapse, B31 failed to manifest a plateau-like potential and rhythmic activity was blocked.