Gravity-efficient motor control is associated with contraction-dependent intracortical inhibition

• Published in: iScience Vol. 26; no. 7; p. 107150
• Main Authors: Gueugneau, Nicolas, Martin, Alain, Gaveau, Jérémie, Papaxanthis, Charalambos
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 21.07.2023; Elsevier
• Subjects: Neuroscience; Space medicine; Neuroscience; Space medicine
• ISSN: 2589-0042; 2589-0042
• DOI: 10.1016/j.isci.2023.107150

In humans, moving efficiently along the gravity axis requires shifts in muscular contraction modes. Raising the arm up involves shortening contractions of arm flexors, whereas the reverse movement can rely on lengthening contractions with the help of gravity. Although this control mode is universal, the neuromuscular mechanisms that drive gravity-oriented movements remain unknown. Here, we designed neurophysiological experiments that aimed to track the modulations of cortical, spinal, and muscular outputs of arm flexors during vertical movements with specific kinematics (i.e., optimal motor commands). We report a specific drop of corticospinal excitability during lengthening versus shortening contractions, with an increase of intracortical inhibition and no change in spinal motoneuron responsiveness. We discuss these contraction-dependent modulations of the supraspinal motor output in the light of feedforward mechanisms that may support gravity-tuned motor control. Generally, these results shed a new perspective on the neural policy that optimizes movement control along the gravity axis. [Display omitted] •Unconstrained vertical, gravity-oriented, movements show optimal kinematics•Upward and downward movements rely on shortening and lengthening contractions•Neuromuscular control of such vertical movements is contraction-dependent•Intracortical – rather than spinal – mechanisms subserve this control Space medicine; Neuroscience