eLife Assessment:
This manuscript uses a genetically-encoded calcium indicator to assess neural activity across a population of axons connecting the fly's brain to its ventral nerve cord while the tethered fly behaves on a floating ball. Changes in fluorescence signal correlate better with states such as walking, resting, and grooming than with particular limb movements or joint angles, suggesting that specific descending neurons represent the larger behavioral subdivisions. The preparation and large-scale analysis represent a significant step forward in determining how the brain compresses sensory and state information to convey commands to the ventral nervous system for behavior execution by motor circuits.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. The reviewers remained anonymous to the authors.)