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This Article Full Text Full Text (PDF) All Versions of this Article: 581/1/189    most recent jphysiol.2006.123356v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Prabhu, G. Articles by Lemon, R. Search for Related Content PubMed PubMed Citation Articles by Prabhu, G. Articles by Lemon, R. Related Collections Neuroscience

¹ Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, Queen Square, London WC1N 3BG, UK
² Dipartimento di Neuroscienze, Università degli Studi di Parma, Parma, Italy
³ Institute of Cognitive Neuroscience and Department of Psychology, UCL, Queen Square, London WC1N 3AR, UK

Transcranial magnetic stimulation (TMS) was used to investigate corticospinal excitability during the preparation period preceding visually guided self-paced grasping. Previously we have shown that while subjects prepare to grasp a visible object, paired-pulse TMS at a specific interval facilitates motor-evoked potentials (MEPs) in hand muscles in a manner that varies with the role of the muscle in shaping the hand for the upcoming grasp. This anticipatory modulation may reflect transmission of inputs to human primary motor cortex (M1) for visuomotor guidance of hand shape. Conversely, single-pulse TMS is known to suppress MEPs during movement preparation. Here we investigate the time course of single- and paired-pulse MEP modulation. TMS was delivered over M1, at different time intervals after visual presentation of either a handle or a disc to healthy subjects. Participants were instructed to view the object, and later to grasp it when given a cue. During grasp there was a specific pattern of hand muscle activity according to the object grasped. MEPs were evoked in these muscles by TMS delivered prior to grasp. Paired-pulse MEPs were facilitated, whilst single-pulse MEPs were suppressed. The pattern of facilitation matched the object-specific pattern of muscle activity for TMS pulses delivered 150 ms or more after object presentation. However, this effect was not present when TMS was delivered immediately after object presentation, or if the delivery of TMS was given separately from the cue to perform the grasp action. These results suggest that object-related information for preparation of appropriate hand shapes reaches M1 only immediately preceding execution of the grasp.

(Received 23 October 2006; accepted after revision 22 February 2007; first published online 1 March 2007)
Corresponding author R. Lemon: Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, Queen Square, London WC1N 3BG, UK.  Email: rlemon{at}ion.ucl.ac.uk

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				G. Prabhu, R. Lemon, and P. Haggard On-Line Control of Grasping Actions: Object-Specific Motor Facilitation Requires Sustained Visual Input J. Neurosci., November 14, 2007; 27(46): 12651 - 12654. [Abstract] [Full Text] [PDF]