Meeting Abstract
Animals actively control locomotion through their motor program-the set of all neuromuscular activations controlling the limbs. In most vertebrates and slow moving animals, variations in the muscle activation amplitude, measured as spike rate encoding, are thought to be the dominating mechanisms of control. However, the role of activation timing has been implicated in the control of many invertebrates, even in the function of the main flight muscles of insects, which receive very few activating potentials. Both muscle activation time and muscle activation magnitude (spike number or rate) are now known to exhibit fluctuations associated with variations in behavior. Nonetheless, the relative importance of temporal vs. rate encoding across the whole of a motor program has remained elusive because most recordings only consider a few of the possible motor commands at any time. To meet this challenge we obtained a nearly complete spike-resolved motor program of the hawk moth, Manduca sexta. Examination of the muscle structure and anatomy as well as prior work on muscle function in hawk moths indicates that the primary neuromuscular determinants of wing motion during flight should arise from only 10 thoracic muscles. We took differential electromyogram recordings during open-loop tethered flight while the moth visually tracked a robotic flower stimulus. Using spike-sorting analysis, we identified spike-resolved firing from each muscle on a wing-stroke-to-wing-stroke basis. We isolated the effects of timing and rate relative to the motion of the flower. Precise control of timing may be an especially critical component of control when locomotor frequency increases and bandwidth constraints of neural systems are significant.
