Impact of movement and movement-related feedback on the lamprey central pattern generator for locomotion

A semi-reduced, minimally restrained lamprey preparation was used to investigate the impact of movement and movement-related feedback during D-glutamate-induced locomotion. The preparation consisted of the trunk alone with the spinal cord exposed to the bathing solution. Two conditions were compared using electromyography or nerve recording: (i) muscle and spinal cord, (ii) spinal cord alone supported by the notochord. Compared with the isolated spinal cord, movement in the presence of muscle consistently and significantly increased the frequency of the motor output and reduced the phase delay among the segments. In moving preparations, coupling among the segments was reduced by two staggered hemisections to permit the strength and direction of intersegmental coupling to be estimated. The estimates revealed that movement increased the total intersegmental coupling strength and increased the proportion of the coupling that was descending over those of the isolated spinal cord. The effects on the phase and frequency of bursting can be explained in the light of the excitation evoked by bending that we have reported previously. Thus, we demonstrate that movement and movement-related feedback that arise from spinally induced motor patterns can alter the form of the movement and the functional coupling strength among the segments of the lamprey spinal cord.