FREQUENCY REGULATION OF A SLOW RHYTHM BY A FAST PERIODIC INPUT

Many nervous systems contain rhythmically active subnetworks that inte ract despite oscillating at widely different frequencies. The stomatog astric nervous system of the crab Cancer borealis produces a rapid pyl oric rhythm and a considerably slower gastric mill rhythm. We construc t and analyze a conductance-based compartmental model to explore the a ctivation of the gastric mill rhythm by the modulatory commissural neu ron 1 (MCN1). This model demonstrates that the period of the MCN1-acti vated gastric mill rhythm, which was thought to be determined entirely by the interaction of neurons in the gastric mill network, can be str ongly influenced by inhibitory synaptic input from the pacemaker neuro n of the fast pyloric rhythm, the anterior burster (AB) neuron. Surpri singly, the change of the gastric mill period produced by the pyloric input to the gastric mill system can be many times larger than the per iod of the pyloric rhythm itself. This model illustrates several mecha nisms by which a fast oscillatory neuron may control the frequency of a much slower oscillatory network. These findings suggest that it is p ossible to modify the slow rhythm either by direct modulation or indir ectly by modulating the faster rhythm.