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Cerebral Cortex Advance Access originally published online on January 6, 2009
Cerebral Cortex 2009 19(9):2013-2024; doi:10.1093/cercor/bhn230
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© The Author 2009. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Role of Corticospinal Suppression during Motor Preparation

Julie Duque1,2,3 and Richard B. Ivry1,2

1 Department of Psychology, 2 Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720, USA, 3 Laboratory of Neurophysiology, Université catholique de Louvain, Brussels B-1200, Belgium

Address correspondence to Dr Julie Duque, PhD, Laboratory of Neurophysiology, UCL 5449, School of Medicine, University of Louvain, Avenue Hippocrate, 54 B-1200 Brussels, Belgium. Email: julie.duque@uclouvain.be.

Behavior arises from a constant competition between potential actions. For example, movements performed unimanually require selecting one hand rather than the other. Corticospinal (CS) excitability of the nonselected hand is typically decreased prior to movement initiation, suggesting that response selection may involve mechanisms that inhibit nonselected candidate movements. To examine this hypothesis, participants performed a reaction time task, responding with the left, right, or both indexes. Transcranial magnetic stimulation was applied over the right primary motor cortex (M1) to induce motor-evoked potentials (MEPs) in a left hand muscle at various stages during response preparation. To vary the time of response selection, an imperative signal was preceded by a preparatory cue that was either informative or uninformative. Left MEPs decreased following the cue. Surprisingly, this decrease was greater when an informative cue indicated that the response might require the left hand than when it indicated a right hand response. In the uninformative condition, we did not observe additional attenuation of left MEP after an imperative indicating a right hand response. These results argue against the "deselection" hypothesis. Rather, CS suppression seems to arise from "impulse control" mechanisms that ensure that responses associated with potentially selected actions are not initiated prematurely.

Key Words: action selection • inhibition • mirror movement • transcranial magnetic stimulation • unimanual movement


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