Effects of oscillator frequency on phase-locking in the lamprey central pattern generator.

The central pattern generator (CPG) for locomotion can be thought of as a chain of segmental oscillators coupled together that produces the basic locomotor pattern. The isolated spinal cord of the lamprey is an excellent preparation in which to formulate general principles for the operation of the CPG. The stability of the preparation and the ease with which surgical lesions can be made in the cord have allowed the study of the coordinating system with a convenience unobtainable in more complex vertebrates. Mathematical models have been developed to help analyze the CPG and other systems of coupled oscillators. The models have pointed to two important parameters for determining the relative timing of a system of coupled oscillators: the nature of the coupling and the difference in frequency among the oscillators. The latter is dealt with here. In lampreys, the frequency differences of the segmental oscillators along the cord can be quite large. This factor is shown to be related to changes in the intersegmental phase lags during serotonin modulation of fictive swimming. An understanding of some effects of the frequency difference is also shown to have been important in helping to formulate a protocol for the demonstration of functional regeneration in the isolated spinal cord preparation.