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Cerebral Cortex Advance Access originally published online on October 10, 2007
Cerebral Cortex 2008 18(6):1395-1406; doi:10.1093/cercor/bhm173
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© 2007 The Authors
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Memory Formation in the Motor Cortex Ipsilateral to a Training Hand

J Duque1,2, R Mazzocchio1,3, K Stefan1, F Hummel1,4, E Olivier2 and Leonardo G. Cohen1

1 Human Cortical Physiology Section and Stroke Neurorehabilitation Clinic, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20817, USA, 2 Laboratoire de Neurophysiologie, Université catholique de Louvain, B-1200 Brussels, Belgium, 3 Sezione di Neurofisiologia Clinica, Dipartimento di Scienze Neurologiche e del Comportamento, Universita’ di Siena, I-53100 Siena, Italy, 4 Cortical Physiology Research Group, Department of Neurology, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany

Address correspondence to Dr Leonardo G. Cohen, Human Cortical Physiology Section, Stroke Neurorehabilitation Clinic, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20817, USA. Email: cohenl{at}ninds.nih.gov

Cortical reorganization within the primary motor cortex (M1) contralateral to a practicing hand has been extensively investigated. The extent to which the ipsilateral M1 participates in these plastic changes is not known. Here, we evaluated the influence of unilateral hand practice on the organization of the M1 ipsilateral and contralateral to the practicing hand in healthy human subjects. Index finger movements elicited by single-pulse transcranial magnetic stimulation (TMS) delivered to each M1 were evaluated before and after practice of unilateral voluntary index finger abduction motions. Practice increased the proportion and acceleration of TMS-evoked movements in the trained direction and the amplitude of motor-evoked potentials (MEPs) in the abduction agonist first dorsal interosseous (FDI) muscle in the practicing hand and decreased the proportion and acceleration of TMS-evoked abduction movements and MEP amplitudes in the abduction agonist FDI in the opposite resting hand. Our findings indicate that unilateral hand practice specifically weakened the representation of the practiced movement in the ipsilateral M1 to an extent proportional to the strengthening effect in the contralateral M1, a result that varied with the practicing hand's position. These results suggest a more prominent involvement of interacting bilateral motor networks in motor memory formation and probably acquisition of unimanual motor skills than previously thought.

Key Words: inhibition • ipsilateral M1 • motor learning • plasticity • TMS • training


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