Turning behavior in lamprey in response to descending unilateral commands: Experiments and modeling

Steering maneuvers in vertebrates are characterized by asymmetric modulation of the cycle duration and the intensity of the symmetric rhythmic locomotor activity. In the lamprey in vitro model system, turns can be evoked by electrical skin stimuli applied to one side of the head, which give rise to descending unilateral excitatory commands. Turns are observed as increased activity on one side of the spinal cord, followed by a rebound on the other. We investigated the generation of turns in single-segment models of the lamprey locomotor spinal network, and were able to reproduce all main experimental results. Sufficient mechanisms to explain changes in the locomotor rhythm, including rebound, are asymmetric activation of crossing inhibitory neurons, accompanied by a calcium influx in these neurons.