Coupled oscillators in an isolated pacemaker neuron?

The effects were examined of brief lengthening perturbations of different amplitudes on the pacemaker activity of the slowly adapting stretch receptor organ of crayfish. The analysis indicates that perturbation effects: (i) when elicited by low amplitudes, depend on the delivery time (or phase) of the perturbation relative to the last spike, while those evoked by larger amplitudes are phase-independent; (ii) tend to decrease, below the value of the natural interspike interval or pacemaker period, the interval at which the perturbation is delivered, anticipating the occurrence of the next spike; (iii) which follow the first poststimulus spike consist of phase-dependent lengthenings of interspike intervals which are greater for the first and decrease gradually in length in the following post-perturbation intervals; (iv) are gradually compensated because the pre-perturbation phase tends to be recovered in the interspike intervals following the perturbation and spikes gradually tend to occur closer to the instants when they would have fired without the perturbation. Although other models may explain the above behavior, phase compensation suggests strongly that at least two oscillators (i.e., an unperturbable oscillator and a stimulus sensitive one) underlie the pacemaker activity of the slowly adapting organ.