Computational study identifies spinal circuit that modulates stretch reflexes

How did the bodies of animals, including ours, become such fine-tuned movement machines? How vertebrates coordinate the eternal tug-o-war between involuntary reflexes and seamless voluntary movements is a mystery that Francisco Valero-Cuevas' Lab in USC Alfred E. Mann Department of Biomedical Engineering, set out to understand.

Do you remember the pediatrician tapping your knee to see if you had a strong involuntary knee-jerk reaction? This was to test the stretch reflexes in your spinal cord, which resist muscle stretching to give you muscle tone to hold your body up against gravity for example, fast corrections after tripping. So, how exactly those reflexes are modulated or inhibited to allow smooth, voluntary movement has been debated since Charles Scott Sherrington's foundational work in the 1880s (yes, the 1880s!). This new work cuts directly into critical debates about how the ancient spinal cord and the relatively new human brain interact to produce smooth movements and how some neurological conditions disrupt this fine balance and produce slow, inaccurate, jerky, etc. movements in neurological conditions.

The study, led by Biomedical engineering doctoral student Grace Niyo, sheds light on a possible undiscovered system or circuitry at play within the spinal cord that, when working properly, "modulates" reflexes during voluntary movements. The study, Niyo says, proposes "a theoretically new mechanism to modulate spinal reflexes at the same spinal cord level as stretch reflexes."

Valero-Cuevas says, "We are constantly benefiting from, and modulating stretch reflexes, whether we realize it or not as we stand, move and act."

He explains, "Although our brain is highly sophisticated, we need to recognize the value and power of the ancient spinal cord-;which has allowed all vertebrates to thrive for millions of years before large brains were even possible. We would like to understand how the spinal cord is able to regulate smooth movements, even with minimal brain control, as we know happens in amphibians and reptiles. This perspective could have important implications for understanding, and possibly treating, movement disorders in neurological conditions that affect the brain, spinal cord, or both-;and also for creating biologically-inspired prostheses or robots that move smoothly using simulated spinal cords."

The study's additional co-authors include Lama I. Almofeez, a PhD student in the USC Alfred E Man Department of Biomedical Engineering and Andrew Erwin, who at the time of the study was a Post-doctoral scholar in the USC Division of Biokinesiology and Physical Therapy.

Source:

University of Southern California

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