Mechanisms of intersegmental coordination in leech locomotion

Abstract

Swimming movements in the leech are characterized by a traveling wave that sweeps rostrocaudally along the animal. Intersegmental phase lags in body movement are approximately constant, near 20° per segment, thus ensuring that one wave length is expressed for normal cycle periods (0.4 s to 2.0 s). The central pattern generator, a chain of tightly-coupled oscillators, is composed of interneurons that make interganglionic contacts, which provide coordinating links in both directions. A computer model that incorporates the observed rostrocaudally-decreasing cycle periods, realistic signal conduction delays and multiple channels of coupling along the nerve cord demonstrates that many of the features of intersegmental coordination in the leech can be explained by the known intersegmental interactions and the gradient in the cycle period of the segmentally iterated oscillator circuits.