The calculation of frequency-shift functions for chains of coupled oscillators, with application to a network model of the lamprey locomotor pattern generator.

Chains of coupled limit-cycle oscillators are considered, in which the coupling is assumed to be weak and only between adjacent oscillators. For such a system the change in frequency of an oscillator due to the coupling can be expressed, up to first order in the coupling strength, by functions that depend only on the phase difference between the coupled oscillators. In this article a numerical algorithm is developed for the evaluation of these functions (the H-functions) in terms of a single oscillator and the interactions between coupled oscillators. The technique is applied to a connectionist model for the locomotor pattern generator in the lamprey spinal cord. An H-function so derived is compared to a function derived empirically (the C-function) from simulations of the same system. The phase lags that develop between adjacent oscillators in a simulated chain are compared with those predicted theoretically, and it is shown that coupling that is functionally "strong" is nonetheless weak enough to behave as predicted.