Thank you, John!!

Thank you, Jason!

Sebastian! Thank you!! :)

Thank you, Kelsey!

Jumping Bobcat Slow Motion | Planet Earth II YouTube video by BAMBI

To celebrate our new pre-print from @fabricionicola.bsky.social, a few of my favorite animal jumps…

www.biorxiv.org/content/10.6...

youtu.be/OX9GTi-wQ6I

Understanding these modular substrates may help reveal how the nervous system builds complex actions and open new avenues for restoring coordinated movement after neurological injury.

You can read the full story here: www.biorxiv.org/content/10.6...

By showing that a spinal interneuron population can reliably reshape movement during an ongoing natural behavior by engaging a coordinated movement pattern, this work moves modular motor control from a descriptive concept to a circuit-level mechanism.

We show that genetically defined spinal neurons can access coordination patterns characteristic of motor modules, which act as preconfigured templates that the nervous system can recruit and modulate to generate context-dependent movement.

Overall, these results suggest a hierarchical organization of movement:

Behavior is organized into phases (temporal segmentation)
Phases are expressed through motor modules
Modules manifest as muscle synergies
Muscle synergies are implemented by neural circuits

Not all spinal interneurons can alter the ongoing natural behavior.

However, dILB6 can reliably reshape movement at any point in the jump, revealing a spinal population capable of accessing a specific motor module during natural behavior.

But can these neurons shape an ongoing natural behavior?

Using closed-loop optogenetics, we briefly activated these interneurons during propulsion or flight.

V3 had no effect on the movement.

In contrast, dILB6 strongly altered hindlimb kinematics during propulsion and flight.

We next asked whether these neurons can generate movement modules.

Using optogenetic stimulation of genetically defined populations, we found that V3 evoked triple-joint hindlimb extension, while dILB6 evoked triple-joint flexion.

These resemble the modules observed during propulsion and flight.

To identify neurons potentially involved in jumping, we mapped cFOS activity across the lumbar spinal cord during the behavior.

This revealed several candidate neuronal populations.

Are these modules driven entirely by neuronal activity?

Inhibiting (L5) during jump. Propulsion failed. During flight, hip and ankle movements were disrupted, but knee motion remained intact.

There is a hybrid neural-mechanical control, mediated by phase-specific, separable neural mechanisms.

We next asked whether these modules adapt to task demands.

Increasing jump distance scaled extensor activation during propulsion, while flexion during flight remained unchanged.

Thus, propulsion and flight follow distinct tuning rules, consistent with separable neural control.

Two coordination patterns emerged.

During propulsion, the hip, knee, and ankle extend together.

During flight, all three flex.

Muscle activity mirrored these joint movements, revealing a simple dual-module organization: an extensor burst for propulsion, and a flexor burst for flight.

If jumping is organized into coordination modules, the joints and muscles that generate the movement should reflect this structure.

We therefore examined hindlimb joint angles and muscle activity during propulsion and flight, the core phases of the jump.

We used a dynamical model to track how body posture evolves during the jump.

Three dominant movement modes emerged: one during preparation, one during propulsion, and one during flight.

This shows that jumping unfolds through a modular sequence of coordinated body configurations.

Together, these results show that the jump passes through four constrained whole-body coordination states.

To understand how posture evolves during the jump, we analyzed whole-body geometry across trials and over time.

During propulsion, animals adopted a similar posture across trials, showing minimal variability. The similarity matrix further revealed blocks of stable body configurations.

If jumping is built from components, how are they organized during the behavior?

Jumping is often described as unfolding through phases: preparation, propulsion, flight, and landing.

But are these phases intrinsic features of the full-body movement, or simply convenient labels?

Evolution offers a clue.

Early amphibians jump by simply extending their hindlimbs, landing in a belly flop.

Later species added controlled landing.

Reptiles, birds, and mammals added a preparatory countermovement.

This suggests that jumping may be composed of separable movement components.

All experiments were conducted under approved institutional animal care protocols.

This work was done during my postdoc in Ariel Levine’s lab at NIH/NINDS, with an incredible team of collaborators. Lily Li, Tiernon Riesenmy, Randall Pursley, @rbrianroome.bsky.social , @vulcnethologist.bsky.social , @ariellevine.bsky.social

Mammals have hundreds of joints and muscles. Controlling them individually would be nearly impossible.

How does the nervous system organize such complexity into coherent actions?

Our new study explores this question through a natural behavior: jumping.

Exercise rewires the brain — boosting the body’s endurance The more mice exercise, the more connections form between some neurons in their brains, study finds.

Exercise pumps up your muscles — but it might also be pumping up your neurons

go.nature.com/4r94ftv

Anyone got a video of a hare having the shit scared out of it by a curlew — ah, don’t worry, got one anyway!

Brown squirrel launching itself off of a tree

Hup

Hup