Meeting Abstract

40.3  Friday, Jan. 4  Direct Manipulation of Extensor Muscle Phase Affects Leg Swing Trajectory, Foot Placement and Turning Dynamics in a Running Insect MULLENS, CH*; SPONBERG, S; FULL, RJ; Univ. of California, Berkeley cmullens@berkeley.edu

Real time rewriting of the motor code to a muscle can reveal its causal effects on individual leg and whole body dynamics. We target a putative control muscle, the femoral extensor muscle 137 in the middle leg of a cockroach (Blaberus discoidalis). Despite its anatomical designation as a femoral extensor, muscle 137 is hypothesized to absorb energy during running. Previously, we have shown that adding muscle action potentials (MAPs) at a constant phase to muscle 137 in the leg of a running cockroach can alter muscle function and prolong stance effects on center of mass (COM) dynamics. It has been proposed that neural feedback to this muscle could also control swing dynamics and the swing-to-stance transition event of the subsequent stride. We modulated the motor code with variable phase advances from normal running by adding MAPs prior to the onset of normal activity. As onset phase was advanced in muscle 137, leg swing duration was prematurely terminated, resulting in a posterior shift of leg anterior extreme position. We observed resultant changes in dynamics that included an increased rotational velocity toward the stimulated leg (P = 0.017) and increased roll away from the stimulated leg (P = 0.003). These effects correspond to the dynamics of initiating a turn toward the stimulated leg. It is likely that energy absorption from muscle 137 during swing prevents typical stance initiation and, therefore, force production in the subsequent stride. The resulting net torque of the tripod of the legs in that stride could produce the observed turning dynamics. NSF FIBR grant and the Fannie and John Hertz Foundation.