A manuscript has been submitted and a pre-print now exists for this project!
Figure: Through electrical stimulation (A) we can causally generate action potentials in specific muscles (B) while leaving the activity of other muscles unchanged. Applying this technique in a flapping animal can lead to a motor program rewrite, (C), where new action potentials are produced at specific controlled timings (D).
If an individual muscle independently controls specific features of kinematics or dynamics, then precise behavioral outcomes can be directly ascribed to precisely timed spikes sent to that muscle. But if control is orchestrated across many muscles simultaneously such that the action of one muscle changes the potential of another muscle to do control, then the transformation of a precise change in spike timing into movement will depend on the context created by the spiking patterns in the rest of the motor program.
To answer these questions, we performed spike-resolved electromyography and precise stimulation of individual spikes in the hawkmoth Manduca sexta during tethered flapping. Combining correlational study of visually-induced turns with causal manipulation of spike timing, we discovered likely coordination patterns for pitch turns, investigated if these correlational patterns can individually drive pitch control, and studied whether the precise spike timing of power muscles can lead to pitch maneuvers. We observed that significant timing changes of the main downstroke muscles, the dorsolongitudinal muscles (DLMs) were associated with whether a moth was pitching up or down. Causally inducing this timing change in the DLMs with electrical stimulation produced a consistent, mechanically relevant feature in pitch torque, establishing that power muscles in Manduca play a role in controlling pitch. Because changes were evoked in unconstrained flapping in only the DLMs, however, these pitch torque features left large unexplained variation. We found this unexplained variation indicates significant functional overlap in pitch control. Precise timing of one power muscle does not produce a precise turn but must be coordinated with specific changes in the timing of other muscles. This demonstrates the importance of coordination across the entire motor program for flight.
