title: Equilibrium-based movement endpoints elicited from primary motor cortex using repetitive microstimulation.
abstract: High-frequency, long-duration intracortical microstimulation (HFLD-ICMS) is increasingly being used to deduce how the brain encodes coordinated muscle activity and movement. However, the full movement repertoire that can be elicited from the forelimb representation of primary motor cortex (M1) using this method has not been systematically determined. Our goal was to acquire a comprehensive M1 forelimb representational map of movement endpoints elicited with HFLD-ICMS, using stimulus parameters optimal for evoking stable forelimb spatial endpoints. The data reveal a 3D forelimb movement endpoint workspace that is represented in a patchwork fashion on the 2D M1 cortical surface. Although cortical maps of movement endpoints appear quite disorderly with respect to movement space, we show that the endpoint locations in the workspace evoked with HFLD-ICMS of two adjacent cortical points are closer together than would be expected if the organization were random. Although there were few obvious consistencies in the endpoint maps across the two monkeys tested, one notable exception was endpoints bringing the hand to the mouth, which was located at the boundary between the hand and face representation. Endpoints at the extremes of the monkey's workspace and locations above the head were largely absent. Our movement endpoints are best explained as resulting from coactivation of agonist and antagonist muscles driving the joints toward equilibrium positions determined by the length-tension relationships of the muscles.
authors.affiliation: University of Kansas Medical Center, Department of Molecular and Integrative Physiology, Kansas City, Kansas 66160.
authors.forename: Gustaf M
authors.initials: GM
authors.lastname: Van Acker
authors.affiliation: University of Kansas, Bioengineering Graduate Program, Lawrence, Kansas 66045, and.
authors.forename: Sommer L
authors.initials: SL
authors.lastname: Amundsen
authors.affiliation: University of Kansas Medical Center, Department of Molecular and Integrative Physiology, Kansas City, Kansas 66160.
authors.forename: William G
authors.initials: WG
authors.lastname: Messamore
authors.affiliation: University of Kansas Medical Center, Department of Molecular and Integrative Physiology, Kansas City, Kansas 66160.
authors.forename: Hongyu Y
authors.initials: HY
authors.lastname: Zhang
authors.affiliation: University of Kansas, Bioengineering Graduate Program, Lawrence, Kansas 66045, and University of Kansas, Department of Mechanical Engineering, Lawrence, Kansas 66045.
authors.forename: Carl W
authors.initials: CW
authors.lastname: Luchies
authors.affiliation: University of Kansas Medical Center, Department of Molecular and Integrative Physiology, Kansas City, Kansas 66160, pcheney@kumc.edu.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Cheney
mesh_terms: D000818:Animals; D001132:Arm / Q000294:innervation / Q000502:physiology; D001931:Brain Mapping; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D004576:Electromyography; D008253:Macaca mulatta; D009044:Motor Cortex / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D011817:Rabbits
keywords: ICMS; corticomotor mapping; corticospinal; electromyography; intracortical microstimulation; primary motor cortex