title: Cortical mechanisms of unilateral voluntary motor inhibition in humans.
abstract: While motor control is very often a goal-oriented event, little is known about the mechanisms underlying the termination of motor performance. To investigate what type of cortical activation underlies the muscle relaxation required to terminate the act, we performed single- and double-pulse transcranial magnetic stimulation (TMS) studies during voluntary muscle relaxation in nine normal volunteers. Subjects maintained a weak isometric contraction of the right first dorsal interosseous muscle (FDI), and either increased the level of contraction (Contraction), terminated the contraction (Relaxation), or maintained it (No-go) depending on a visual cue. Motor evoked potentials (MEP) and the silent period (SP) were recorded from the FDI during motor activity. To measure intra-cortical inhibition (ICI), we also performed double-pulse TMS, applying subthreshold conditioning stimuli at interstimulus intervals of 2 ms. When single-pulse TMS was given just prior to muscle relaxation (-21 to -70 ms), the MEP was reduced while the SP was unchanged. Intra-cortical inhibition was smaller just prior to the muscle relaxation. Unilateral voluntary muscle relaxation may not be associated with activation of the intracortical inhibitory system, but rather with the possible excitation of the corticospinal system, which can inhibit motoneurons disynaptically. These findings suggest that multiple inhibitory mechanisms act in diverse ways to achieve motor inhibition.
authors.affiliation: Human Brain Research Center, Kyoto University Graduate School of Medicine, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan.
authors.forename: Tahamina
authors.initials: T
authors.lastname: Begum
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Mima
authors.forename: Tatsuhide
authors.initials: T
authors.lastname: Oga
authors.forename: Hidemi
authors.initials: H
authors.lastname: Hara
authors.forename: Takeshi
authors.initials: T
authors.lastname: Satow
authors.forename: Akio
authors.initials: A
authors.lastname: Ikeda
authors.forename: Takashi
authors.initials: T
authors.lastname: Nagamine
authors.forename: Hidenao
authors.initials: H
authors.lastname: Fukuyama
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Shibasaki
mesh_terms: D000328:Adult; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D009126:Muscle Relaxation / Q000502:physiology; D050781:Transcranial Magnetic Stimulation