Synaptic perturbation and entrainment of gastric mill rhythm of the spiny lobster

1. The gastric mill rhythm of the lobster stomatogastric ganglion was perturbed with short trains of synaptic input from the inferior ventricular nerve (IVN) through fibers. The stimulus was delivered randomly for phase-response curve analysis or repetitively to ex-amine entrainment. The responses depend on the phase of the stimulus in the endogenous rhythm. 2. The stimulus may alter the internal co-ordination of the motor pattern. Stimuli that occur during a lateral gastric nerve-anterior lateral nerve-E-neuron (LG-GM-E) burst per-turb the burst internally and produce a pro-longed LG-GM-E burst, while those that occur during the silent interval between LG-GM-E bursts may evoke a triggered LG-GM-E burst. Spontaneous, prolonged, and triggered LG-GM-E bursts differ in their internal structure as well as the order of burst onsets and offsets. 3. The intercalated triggered LG-GM-E burst delays the occurrence of the subsequent spontaneous LG-GM-E burst, thus strongly resetting the rhythm. These resetting effects have been formalized by phase-response curve analysis. 4. Over limited constraints, cyclic IVN stimuli can entrain the rhythm. Repetitively delivered IVN stimuli have parametric effects on the rhythm that mask the predictive value of phase-response curve analysis for the de-termination of the phase relations during en-trainment