title: Using voluntary motor commands to inhibit involuntary arm movements.
abstract: A hallmark of voluntary motor control is the ability to stop an ongoing movement. Is voluntary motor inhibition a general neural mechanism that can be focused on any movement, including involuntary movements, or is it mere termination of a positive voluntary motor command? The involuntary arm lift, or 'floating arm trick', is a distinctive long-lasting reflex of the deltoid muscle. We investigated how a voluntary motor network inhibits this form of involuntary motor control. Transcranial magnetic stimulation of the motor cortex during the floating arm trick produced a silent period in the reflexively contracting deltoid muscle, followed by a rebound of muscle activity. This pattern suggests a persistent generator of involuntary motor commands. Instructions to bring the arm down voluntarily reduced activity of deltoid muscle. When this voluntary effort was withdrawn, the involuntary arm lift resumed. Further, voluntary motor inhibition produced a strange illusion of physical resistance to bringing the arm down, as if ongoing involuntarily generated commands were located in a 'sensory blind-spot', inaccessible to conscious perception. Our results suggest that voluntary motor inhibition may be a specific neural function, distinct from absence of positive voluntary motor commands.
authors.affiliation: Institute of Cognitive Neuroscience, University College London, London, UK Institute of Neuroinformatics, University of Zurich and ETH Zurich, Switzerland Neuroscience Center Zurich, University of Zurich and ETH Zurich, Switzerland arko@ini.uzh.ch.
authors.forename: Arko
authors.initials: A
authors.lastname: Ghosh
authors.affiliation: Institute of Neurology, University College London, London, UK.
authors.forename: John
authors.initials: J
authors.lastname: Rothwell
authors.affiliation: Institute of Cognitive Neuroscience, University College London, London, UK.
authors.forename: Patrick
authors.initials: P
authors.lastname: Haggard
mesh_terms: D000293:Adolescent; D000328:Adult; D001132:Arm / Q000502:physiology; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology; D009068:Movement / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D012018:Reflex / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D014836:Volition / Q000502:physiology*
keywords: Kohnstamm; arm movement; involuntary contraction; motor cortex; voluntary control; voluntary inhibition