title: Neural Adaptations Associated with Interlimb Transfer in a Ballistic Wrist Flexion Task.
abstract: Cross education is the process whereby training of one limb gives rise to increases in the subsequent performance of its opposite counterpart. The execution of many unilateral tasks is associated with increased excitability of corticospinal projections from primary motor cortex (M1) to the opposite limb. It has been proposed that these effects are causally related. Our aim was to establish whether changes in corticospinal excitability (CSE) arising from prior training of the opposite limb determine levels of interlimb transfer. We used three vision conditions shown previously to modulate the excitability of corticospinal projections to the inactive (right) limb during wrist flexion movements performed by the training (left) limb. These were: (1) mirrored visual feedback of the training limb; (2) no visual feedback of either limb; and (3) visual feedback of the inactive limb. Training comprised 300 discrete, ballistic wrist flexion movements executed as rapidly as possible. Performance of the right limb on the same task was assessed prior to, at the mid point of, and following left limb training. There was no evidence that variations in the excitability of corticospinal projections (assessed by transcranial magnetic stimulation (TMS)) to the inactive limb were associated with, or predictive of, the extent of interlimb transfer that was expressed. There were however associations between alterations in muscle activation dynamics observed for the untrained limb, and the degree of positive transfer that arose from training of the opposite limb. The results suggest that the acute adaptations that mediate the bilateral performance gains realized through unilateral practice of this ballistic wrist flexion task are mediated by neural elements other than those within M1 that are recruited at rest by single-pulse TMS.
authors.affiliation: Trinity College Institute of Neuroscience and School of Psychology, Trinity College DublinDublin, Ireland; School of Psychology, Queen's University BelfastNorthern Ireland, UK; Neural Control of Movement Lab, ETH ZurichZurich, Switzerland.
authors.forename: Kathy L
authors.initials: KL
authors.lastname: Ruddy
authors.affiliation: Trinity College Institute of Neuroscience and School of Psychology, Trinity College DublinDublin, Ireland; Department of Neurocognitive Psychology, Goethe UniversityFrankfurt, Germany.
authors.forename: Anne K
authors.initials: AK
authors.lastname: Rudolf
authors.affiliation: Trinity College Institute of Neuroscience and School of Psychology, Trinity College DublinDublin, Ireland; Faculty of Human Movement Sciences, Vrije University AmsterdamAmsterdam, Netherlands.
authors.forename: Barbara
authors.initials: B
authors.lastname: Kalkman
authors.affiliation: Trinity College Institute of Neuroscience and School of Psychology, Trinity College Dublin Dublin, Ireland.
authors.forename: Maedbh
authors.initials: M
authors.lastname: King
authors.affiliation: Faculty of Human Movement Sciences, Vrije University Amsterdam Amsterdam, Netherlands.
authors.forename: Andreas
authors.initials: A
authors.lastname: Daffertshofer
authors.affiliation: Centre for Sensorimotor Performance, School of Human Movement Studies, University of Queensland Brisbane, QLD, Australia.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Carroll
authors.affiliation: Trinity College Institute of Neuroscience and School of Psychology, Trinity College DublinDublin, Ireland; School of Psychology, Queen's University BelfastNorthern Ireland, UK.
authors.forename: Richard G
authors.initials: RG
authors.lastname: Carson
keywords: contralateral adaptations; corticospinal; cross education; mirror training; primary motor cortex