Sensory information guides locomotion. This observation is often explored with respect to how the primary senses such as vision or olfaction guide navigation. Recently we published the surprising finding that the sense of balance plays a fundamental role in determining when animals move.  Furthermore, the challenge of maintaining stable posture appears key to understanding the development of locomotion (Ehrlich & Schoppik, 2018). In this seminar I’ll share our in-progress investigations into where and how the brain transforms sensed posture into locomotion. We targeted our observations and perturbations to defined populations of neurons from the sensory periphery to brainstem premotor areas using a set of transgenic zebrafish. We used a high-speed volumetric lightsheet imaging developed by our collaborators in the Hillman Lab at Columbia University (Swept, Confocally-Aligned Planar Excitation, or SCAPE) to measure the responses of neurons to postural changes. Finally, we tested the necessity of candidate populations by chemogenetic or optical ablation methods followed by behavioral observation. Our preliminary results offer new insights into how the nervous system transforms sensed posture into locomotion.My lab studies how the neural circuits that permit stable locomotion develop and function. We address these questions in the larval zebrafish, a small model vertebrate that allows exceptional access to the developing nervous system. Our experiments combine a variety of methodologies including behavioral observation, genetic perturbations, optical/electrical measurements of neural activity, and computational models.

Next, I’ll discuss a new set of experiments investigating the development of coordination. Here too we found that balance plays an unexpectedly foundational role in determining the way developing animals come to move. We investigated the development of locomotion in the larval zebrafish to understand how and why coordination might develop. We found that older larvae use their bodies and fins synergistically to climb in the water column. Younger larvae could climb similarly, but preferred not to — with detriment to balance. Without fins, larvae were able to climb but were not able to maintain their preferred horizontal posture. Mutant larvae without a functional vestibular system did not synergize fin and body movements. Computational modeling illustrates how findominated climbing comes to improve balance, though it requires more effort. Together these findings link the sense of balance to coordinated locomotion: as they develop, zebrafish improve postural stability by optimizing fin-body coordination. We propose that the need to balance drives the development of coordinated locomotion. 

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