Autaptic excitation contributes to bistability and rhythmicity in the neural circuit for feeding in Aplysia

The feeding circuit in Aplysia is a useful model system for studying the neuronal bases of cognitive functions such as sensory processing, generation of behavior, motivation, decision making, learning, and memory [1,2]. The goals of the present study are to develop a biologically-realistic model of the feeding circuit and to investigate the ways in which component processes contribute to circuit function. To begin, we developed a model of the central pattern generator (CPG) that mediates rhythmicity in the feeding circuit (Fig. ​(Fig.1A).1A). Simulations indicated that two positive-feedback loops (the B31 autapse and the synaptic interactions between B31 and B63) introduced bistability into the membrane potential of the B31 soma (Figures ​(Figures1B,1B, 1C1). In addition, simulations indicated that this plateau-like potential was the ‘deciding factor’ for initiating rhythmic activity (Fig. ​(Fig.1C).1C). Simulations also helped identify features of the model that warrant further empirical investigation; e.g., the simulated amplitude of the plateau-like potential was less than empirical observations.