Meeting Abstract
102.4 Thursday, Jan. 7 Chasing the Cockroach: How reflexes enhance running PROCTOR, Joshua/L*; HOLMES, Philip; Princeton University jproctor@princeton.edu
Neuromuscular systems are stabilized and controlled by both feedforward and feedback signals. Feedforward pathways driven by central pattern generators (CPGs), in conjunction with mechanical reaction forces and nonlinear muscle properties, suffice to produce stable stereotypical gaits. (1) These preflexive mechanisms combine with neural reflexes originating in proprioceptive sensors to yield robust behavior in uncertain environments. Experiments, though, have shown that feedback is present and important for both slow and rapid running. (2,3) The focus of the current study is to understand how neural feedback, reflexes, can affect the motor program of the cockroach. We have developed a one dimensional neuromechanical model that represents a single actuated joint consisting of a neural system periodically activating agonist/antagonist muscles. We consider two types of feedback representative of sensory feedback in the cockroach: phasic or spike-timing, and tonic or firing rate. Phasic feedback encodes state information, such as position, in the timing of individual spikes. In contrast, firing rates can encode graded measures of force or other continuous variables. Using this single actuated joint model, we can investigate how the output of the neural system is changed by different sensory feedback. Results show that both phasic and tonic feedback can shift the relative phasings of the motoneurons thereby affecting the motion of the joint. These changes seen in the model can be qualitatively matched to experimental observations in the cockroach. These sensory systems have also been implemented in a complex hexapedal model and demonstrates that the system with feedback is more robust than the one without. References (1) P. Holmes, R.J. Full, D. Koditschek, and J. Guckenheimer. (2) S. Sponberg and R.J. Full. (3) S.N. Zill, A.L. Ridgel, R.A. DiCaprio, and S.F. Frazier.
