Dr. Valeriya Gritsenko (Speaker in person)

Abstract:

Accurate movement requires more than producing the joint torques needed to move the limb. The nervous system must also stabilize a multijoint body whose segments mechanically interact and whose loading changes with gravity. This talk presents a unified neuromechanical framework in which motor commands combine predictive compensation for gravitational and intersegmental moments with the regulation of limb impedance. Experiments across normal and altered gravity show that static muscle activation and antagonist co-contraction change together with gravitational load, while phasic muscle activation drives motion with separate contributions to co-contraction. Experiments with TMS further show that corticospinal excitability anticipates resistive interaction moments and scales with the gravitational moments required during posture and reaching, supporting a descending contribution to both limb dynamics compensation and postural control. These results reveal why motor commands cannot be understood as a direct mapping from desired motion to muscle torque: co-contraction generates stiffness and damping that stabilize the limb but are invisible to inverse dynamics. Together, these findings support a dual control architecture that balances predictive force compensation with impedance regulation, allowing the nervous system to counteract resistive interaction moments, exploit gravity and assistive interaction moments, and maintain robust movement across changing mechanical environments.

Affiliation: West Virginia University, School of Medicine

Google Calendar invite: https://calendar.app.google/eSCaMHGQUhy42JDJ8