Aplysia bursting neurons as endogenous oscillators. II. Synchronization and entrainment by pulsed inhibitory synaptic input

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Abstract
The characteristics of the phase response curves (PRC) for single pulses of inhibitory synaptic input to a single bursting neuron were used to predict higher order interactions between an interneuron and the population of endogenous bursters. The ability of the interneuron to both phase advance and delay the bursting oscillator indicated that the interneuron would synchronize activity in the network of bursting neurons, and under certain conditions, would entrain bursting neurons at intervals shorter than their free run period. The asymmetry of the PRC (the occurrence of phase delay at most phases of the cycle) indicated that the limits of stable entrainment would be asymmetrical (that it would be easier to entrain a bursting neuron at intervals longer than its free run period). The shift of the PRC upward (toward more phase delay) when the duration of synaptic inhibition was increased indicated that the limits of stable entrainment would shift toward longer entrainment intervals. The dependence of the phase shift on the precise phase of the burst cycle in the PRC indicated the precise phase locking of the bursting neuron to the input from the interneuron within the region of stable entrainment. Synchronization and entrainment of the left upper quadrant bursting cell network by inhibitory input is compared to similar phenomena in other neural networks.