title: Evidence for sustained cortical involvement in peripheral stretch reflex during the full long latency reflex period.
abstract: Adaptation of reflexes to environment and task at hand is a key mechanism in optimal motor control, possibly regulated by the cortex. In order to locate the corticospinal integration, i.e. spinal or supraspinal, and to study the critical temporal window of reflex adaptation, we combined transcranial magnetic stimulation (TMS) and upper extremity muscle stretch reflexes at high temporal precision. In twelve participants (age 49 ± 13 years, eight male), afferent signals were evoked by 40 ms ramp and subsequent hold stretches of the m. flexor carpi radialis (FCR). Motor conduction delays (TMS time of arrival at the muscle) and TMS-motor threshold were individually assessed. Subsequently TMS pulses at 96% of active motor threshold were applied with a resolution of 5-10 ms between 10 ms before and 120 ms after onset of series of FCR stretches. Controlled for the individually assessed motor conduction delay, subthreshold TMS was found to significantly augment EMG responses between 60 and 90 ms after stretch onset. This sensitive temporal window suggests a cortical integration consistent with a long latency reflex period rather than a spinal integration consistent with a short latency reflex period. The potential cortical role in reflex adaptation extends over the full long latency reflex period, suggesting adaptive mechanisms beyond reflex onset.
authors.affiliation: Department of Rehabilitation Medicine, Leiden University Medical Center B0-Q, P.O. Box 9600, 2300 RC Leiden, The Netherlands; Department of Biomechanical Engineering, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, 2628 CD Delft, The Netherlands. Electronic address: M.J.L.Perenboom@lumc.nl.
authors.forename: M J L
authors.initials: MJ
authors.lastname: Perenboom
authors.affiliation: Department of Biomechanical Engineering, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, 2628 CD Delft, The Netherlands; School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Van de Ruit
authors.affiliation: Department of Rehabilitation Medicine, Leiden University Medical Center B0-Q, P.O. Box 9600, 2300 RC Leiden, The Netherlands.
authors.forename: J H
authors.initials: JH
authors.lastname: De Groot
authors.affiliation: Department of Biomechanical Engineering, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, 2628 CD Delft, The Netherlands; MIRA, Institute for Biomechanical Technology and Technical Medicine, University of Twente, 7500 AE Enschede, The Netherlands.
authors.forename: A C
authors.initials: AC
authors.lastname: Schouten
authors.affiliation: Department of Rehabilitation Medicine, Leiden University Medical Center B0-Q, P.O. Box 9600, 2300 RC Leiden, The Netherlands.
authors.forename: C G M
authors.initials: CG
authors.lastname: Meskers
mesh_terms: D000328:Adult; D000368:Aged; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011930:Reaction Time; D012026:Reflex, Stretch; D050781:Transcranial Magnetic Stimulation; D014953:Wrist; D055815:Young Adult
keywords: Cortical involvement; Stretch reflex; Transcranial magnetic stimulation