S1-3.10 Jan. 5 Effect of Rewriting the Neural Code to Muscles in Running and Stationary Insects. SPONBERG, S.*; SPENCE, A.; MULLENS, C.; FULL, R. J.; Univ. of California, Berkeley firstname.lastname@example.org
While recent studies on isolated muscles discovered that single muscles can perform a variety of functions, we lack an understanding of how motor activation patterns are decoded through the musculo-skeletal system to affect animal locomotion. Here we define the control potential, termed effective field to parallel sensory neuron receptive fields, of individual muscles during two typical behaviors, station-keeping and running. We added direct muscle stimulation (spikes) in a phase-locked manner to muscles in behaving cockroaches, (Blaberus discoidalis) while measuring their dynamics using a 3-axis microaccelerometer backpack and videography. To modulate the neural code in behaving animals, we chose muscle 137, a femoral extensor of the middle leg because of its likely role as a control muscle. We measured the mechanical response to four naturally observed activation profiles. Activation of muscle 137 leads primarily to roll and lateral velocity responses with accelerations in the vertical and lateral directions (p<0.0001). Comparison of muscle effective fields showed that muscle 137 can provide finely graded control responses during station-keeping (p=0.007), but only gross level influences during high-speed running. Surprisingly, injecting even a single spike of stimulation to the muscle during station-keeping significantly altered the dynamics, whereas stimulation during rapid running produced significantly lower relative responses. Rewriting the neural code in the same way to a muscle under different behavioral conditions results in different effects on body mechanics. Because neural signals must act through the animalís musculo-skeletal system, an understanding of control requires neuromechanical integration. NSF FIBR grant and the Fannie and John Hertz Foundation.