Participation of ipsilateral cortical descending influences in bimanual wrist movements in humans
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RESEARCH ARTICLE
Participation of ipsilateral cortical descending influences in bimanual wrist movements in humans L. Zhang3 · L. Duval1,2 · F. Hasanbarani2,4 · Y. Zhu5 · X. Zhang5 · D. Barthelemy2,6 · N. Dancause1 · A. G. Feldman1,2 Received: 25 January 2020 / Accepted: 29 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract There are contralateral and less studied ipsilateral (i), indirect cortical descending projections to motoneurons (MNs). We compared ipsilateral cortical descending influences on MNs of wrist flexors by applying transcranial magnetic stimulation (TMS) over the right primary motor cortex at actively maintained flexion and extension wrist positions in uni- and bimanual tasks in right-handed participants (n = 23). The iTMS response includes a short latency (~ 25 ms) motor evoked potential (iMEP), a silent period (iSP) and a long latency (~ 60 ms) facilitation called rebound (iRB). We also investigated whether the interaction between the two hands while holding an object in a bimanual task involves ipsilateral cortical descending influences. In the unimanual task, iTMS responses in the right wrist flexors were unaffected by changes in wrist position. In the bimanual task with an object, iMEPs in the right wrist flexors were larger when the ipsilateral wrist was in flexion compared to extension. Without the object, only iRB were larger when the ipsilateral wrist was extended. Thus, ipsilateral cortical descending influences on MNs were modulated only in bimanual tasks and depended on how the two hands interacted. It is concluded that the left and right cortices cooperate in bimanual tasks involving holding an object with both hands, with possible involvement of oligo- and poly-synaptic, as well as transcallosal projections to MNs. The possible involvement of spinal and transcortical stretch and cutaneous reflexes in bimanual tasks when holding an object is discussed in the context of the well-established notion that indirect, referent control underlies motor actions. Keywords Motor cortex · Transcranial magnetic stimulation · Referent control
Introduction Communicated by Winston D. Byblow. L. Zhang and L. Duval contributed equally to this work. * A. G. Feldman [email protected] 1
Department of Neuroscience, University of Montreal, Montreal, Canada
2
Centre for Interdisciplinary Research in Rehabilitation (CRIR), IRGLM, Institut de Readaptation Gingras-Lindsay de Montreal, 6300 Darlington, Montreal, Canada
3
Institut für Neuroinformatik, Ruhr-Universität Bochum, Bochum, Germany
4
School of Physical and Occupational Therapy, McGill University, Montreal, Canada
5
Faculty of Medicine, University of Montreal, Montreal, Canada
6
Ecole de Readaptation, University of Montreal, Montreal, Canada
Contralateral (c) as well as ipsilateral (i) pathways from the primary motor cortex (M1) project to motoneurons (MNs) of arm muscles (Rosenzweig et al. 2009). Multiple pathways can carry ipsilateral cortical descending influences to MNs. For instance, the br
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