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


Beck, S; Schubert, M; Pirio Richardson, S; Hallett, M (2009). Surround inhibition depends on the force exerted and abnormalities in focal hand dystonia. Journal of Applied Physiology, 107(5):1513-1518.

Abstract

There is evidence that surround inhibition (SI), a neural mechanism to enhance contrast between signals, may play a role in primary motor cortex (M1) 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 (TMS) was applied at rest and during index finger movement to evoke potentials in the non-synergistic, abductor policis muscle (APB). In Experiment 1, in nineteen healthy volunteers, SI was tested using single pulse TMS. Motor evoked potentials (MEPs) at rest were compared to those during contraction using four different force levels (5%, 10%, 20% and 40% of maximum force (Fmax)). In Experiment 2 and 3, SI and short intracortical inhibition (SICI) were tested, respectively, in sixteen patients with FHD and twenty age-matched controls for the 10% and 20% Fmax level. The results show that SI was most pronounced for 10% Fmax and abolished for the 40% Fmax level in controls, while FHD patients had no SI at all. In contrast, a loss of SICI was observed in FHD patients, which was more pronounced for 10% Fmax than for 20% Fmax. The current findings suggest that SI is involved in the generation of fine finger movements with low force levels. The greater loss of SICI for the 10% Fmax level in patients with FHD compared to 20% Fmax indicates that this inhibitory mechanism is more abnormal at lower levels of force. Key words: transcranial magnetic stimulation, fine finger movement, movement selection, short intracortical inhibition.

Abstract

There is evidence that surround inhibition (SI), a neural mechanism to enhance contrast between signals, may play a role in primary motor cortex (M1) 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 (TMS) was applied at rest and during index finger movement to evoke potentials in the non-synergistic, abductor policis muscle (APB). In Experiment 1, in nineteen healthy volunteers, SI was tested using single pulse TMS. Motor evoked potentials (MEPs) at rest were compared to those during contraction using four different force levels (5%, 10%, 20% and 40% of maximum force (Fmax)). In Experiment 2 and 3, SI and short intracortical inhibition (SICI) were tested, respectively, in sixteen patients with FHD and twenty age-matched controls for the 10% and 20% Fmax level. The results show that SI was most pronounced for 10% Fmax and abolished for the 40% Fmax level in controls, while FHD patients had no SI at all. In contrast, a loss of SICI was observed in FHD patients, which was more pronounced for 10% Fmax than for 20% Fmax. The current findings suggest that SI is involved in the generation of fine finger movements with low force levels. The greater loss of SICI for the 10% Fmax level in patients with FHD compared to 20% Fmax indicates that this inhibitory mechanism is more abnormal at lower levels of force. Key words: transcranial magnetic stimulation, fine finger movement, movement selection, short intracortical inhibition.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Balgrist University Hospital, Swiss Spinal Cord Injury Center
Dewey Decimal Classification:610 Medicine & health
Language:English
Date:November 2009
Deposited On:29 Sep 2009 08:37
Last Modified:05 Apr 2016 13:21
Publisher:American Physiological Society
ISSN:0161-7567
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1152/japplphysiol.91580.2008
PubMed ID:19713426

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