Meeting Abstract
26.3 Friday, Jan. 4 Sensory feedback loops in lamprey swimming TYTELL, E.D.*; COHEN, A.H.; Univ. of Maryland, College Park; Univ. of Maryland, College Park tytell@umd.edu
In fishes, undulatory swimming is produced by sets of spinal interneurons constituting a central pattern generator (CPG). The CPG can produce the basic pattern for locomotion in the absence of sensory information, but is strongly affected by sensory input. For instance, proprioceptive feedback from mechanosensory �edge cells� on the margin of the lamprey spinal cord can reset the CPG�s rhythm or entrain it to a different frequency. The CPG�s output, in turn, activates the muscles, bending the body, and providing proprioceptive input back to the CPG itself. This feedback loop was studied in two ways. First, the input-output relationship between sensory information and the CPG rhythm was investigated during fictive swimming in the isolated spinal cord. The cord was bent sinusoidally back and forth at several points along its length. Bending at caudal segments entrains the CPG so that each side starts a burst just before it is maximally stretched, which is approximately the same phase relationship observed between muscle activity and bending in freely swimming lampreys. Bending at rostral segments, in contrast, results in bursts on each side just after that side is maximally shortened and is beginning to stretch, nearly 50% out of phase with the pattern observed in free swimming. Second, the closed-loop behavior of the spinal cord was investigated by filtering the CPG bursts (its output) in real time with a computer and using the filtered bursts to determine the bending applied to the spinal cord (the CPG input). Filtering was done with a variable phase lag linear filter to test the CPG�s stability with different phase relationships between motor output and movement. Additionally, the resonant properties of the lamprey body were simulated in the computer to determine if the CPG frequency would converge to the body�s resonant frequency, which would be useful for efficient swimming.
