S7-1.3 Friday, Jan. 6 Neuromechanical phase lags in swimming lampreys TYTELL, E.D.*; HSU, C.-Y.; COHEN, A.H.; WILLIAMS, T.L.; FAUCI, L.J.; Johns Hopkins Univ.; Feng Chia Univ.; Univ. of Maryland, College Park; Princeton Univ.; Tulane Univ. email@example.com
When fish swim, they bend their bodies in a traveling mechanical wave that moves from head to tail. At the same time, they activate blocks of muscle successively, resulting in a wave of neural activity that moves down the body. The two waves do not usually move at the same speed, though, meaning that muscle activity and bending are relatively in phase rostrally, but grow increasingly out of phase caudally. The result of this neuromechanical phase lag is that when caudal muscle is active, it is overpowered by external fluid forces so that the muscle is lengthened and absorbs energy. Although this effect appears at first glance to be inefficient, it may actually facilitate swimming by stiffening the tail region against the fluid, resulting in a better transmission of force from the body into the wake. We developed a computational model of swimming lamprey in which a flexible body was fully coupled to the fluid environment, so that the body deformed in response to both internal muscular forces and external fluid forces. We found that such a model, with no sensory feedback, could develop a neuromechanical phase lag similar to that observed in fishes when the internal forces were relatively weak compared to the fluid forces. Models with a relatively large neuromechanical phase lag had a lower cost of transport at a steady speed, supporting the idea that the phase lag facilitates effective force transmission during steady swimming. However, our results were strongly dependent on the frequency of the swimming pattern, while fishes have been observed to maintain the phase lag over a wide range of frequencies. Therefore, we conjecture that neural feedback may be required to maintain a phase lag over the range of swimming frequencies.