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This Article Full Text Full Text (PDF) All Versions of this Article: 107/5/1513    most recent 91580.2008v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map 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 Google Scholar Articles by Beck, S. Articles by Hallett, M. PubMed PubMed Citation Articles by Beck, S. Articles by Hallett, M.

Surround inhibition depends on the force exerted and is abnormal in focal hand dystonia

¹Human Motor Control Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland; ; ²Department of Clinical Neurology and Neurophysiology, University of Freiburg, Germany; ; ³Spinal Cord Injury Centre, University Hospital Balgrist, Zürich, Switzerland; and ; ⁴Department of Neurology, University of New Mexico, Albuquerque, New Mexico

Submitted 9 December 2008 ; accepted in final form 25 August 2009

There is evidence that surround inhibition (SI), a neural mechanism to enhance contrast between signals, may play a role in primary motor cortex during movement initiation, while it is deficient in patients with focal hand dystonia (FHD). To further characterize SI with respect to different force levels, single- and paired-pulse transcranial magnetic stimulation was applied at rest and during index finger movement to evoke potentials in the nonsynergistic, abductor policis muscle. In Experiment 1, in 19 healthy volunteers, SI was tested using single-pulse transcranial magnetic stimulation. Motor-evoked potentials at rest were compared with those during contraction using four different force levels [5, 10, 20, and 40% of maximum force (F_max)]. In Experiments 2 and 3, SI and short intracortical inhibition (SICI) were tested, respectively, in 16 patients with FHD and 20 age-matched controls for the 10% and 20% F_max levels. SI was most pronounced for 10% F_max and abolished for the 40% F_max level in controls, whereas FHD patients had no SI at all. In contrast, a loss of SICI was observed in FHD patients, which was more pronounced for 10% F_max than for 20% F_max. Our results suggest that SI is involved in the generation of fine finger movements with low-force levels. The greater loss of SICI for the 10% F_max level in patients with FHD than for the 20% F_max level indicates that this inhibitory mechanism is more abnormal at lower levels of force.

transcranial magnetic stimulation; short intracortical inhibition; fine finger movement; movement selection