The role of sub-maximal force production in the enslaving phenomenon

Slobounov, Semyon; Johnston, Jamie A.; Chiang, Hsueh-Sheng; Ray, William J.

doi:10.1016/s0006-8993(02)03288-2

Cited by 40 publications

(35 citation statements)

References 17 publications

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“…Most findings were consistent with previous reports, including 1) enslaving increased with the force of target finger during voluntary force production (Slobounov et al 2002;Danion et al 2003); 2) The TMS-induced force increment showed an inverted U-shaped dependence on the background force (from 3% to 50%) during voluntary force production by the index finger (Danion et al 2003). Danion et al (Danion et al 2003) reported the same pattern with the maximal increment for the index finger at its 35% MVC.…”

Section: Discussionsupporting

confidence: 91%

Movement-specific enhancement of corticospinal excitability at subthreshold levels during motor imagery

2006

Exp Brain Res

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This study examined modulation of corticospinal excitability during both actual and imagined movements. Seven young healthy subjects performed actual (3% to 50% maximal voluntary contraction) and imagined index finger force production, and rest. Individual responses to focal transcranial magnetic stimulation (TMS) in four fingers (index, middle, ring, and little) were recorded for all three tested conditions. The force increments at the threshold of activation were derived from regression analysis, representing the TMS-induced response at the threshold activation of the corticospinal pathways. The increment in the index finger during motor imagery was larger than that at rest, but smaller than that at the threshold of activation. On the other hand, the increment in the uninstructed (middle, ring and little), slave fingers during motor imagery was larger than that at rest, but not different from that at the threshold of activation. These contrasting results suggest that the degree of imagery-induced enhancement in corticospinal excitability was significantly less than what could be predicted for threshold levels from regression analysis, but only for the index finger, and not the adjacent slave fingers. It is concluded that corticospinal excitability for the explicitly instructed index finger is specifically enhanced at subthreshold levels during motor imagery.

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Section: Discussionsupporting

confidence: 91%

Movement-specific enhancement of corticospinal excitability at subthreshold levels during motor imagery

2006

Exp Brain Res

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“…In contrast to the unchanged forces produced by instructed finger after fatigue (Fig 2A), uninstructed finger forces (ENSL) increased significantly after index finger fatigue, evident in I/I, I/L, and L/I tasks when the fatigued index finger produced the same absolute force but at a higher relative level. Slobounov et al (2002) reported previously that ENSL increased with the level of force production in unfatigued muscles. Our results, demonstrating increased ENSL after fatigue, confirm and extend this result.…”

Section: Effects Of Fatigue On Enslaving Forces and Matching Errorsmentioning

confidence: 66%

Perception of finger forces within the hand after index finger fatiguing exercise

Park

Leonard

2007

Exp Brain Res

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The effect of fatigue on finger force perception within a hand during ipsilateral finger force matching was examined. Thirteen subjects were instructed to match a reference force of an instructed finger using the same or different finger within the hand before and after index finger fatigue. Absolute reference force targets for the index or little finger were identical during pre-and post-fatigue sessions. Fatigue was induced by a 60-s sustained maximal voluntary contraction (MVC) of the index finger. Index finger MVC decreased approximately 29%, while there was a non-significant (about 5%) decrease in the little finger MVC. The results showed that: 1) The absolute reference and matching forces of the instructed fingers were not significantly changed after fatigue, while the total forces (sum of instructed and uninstructed finger forces) were increased after fatigue. 2) The relative forces (with respect to corresponding pre-and post-fatigue MVCs) of the index finger increased significantly in both reference and matching tasks, while the relative forces of the little finger remained unchanged after fatigue. 3) Matching errors remained unchanged after fatigue when the fatigued index finger produced the reference force, while the errors increased significantly when the fatigued index finger produced the matching force. 4) Enslaving (difference between total and instructed finger forces) increased significantly after fatigue, especially during force production by the fatigued index finger and when the little finger produced matching forces at higher force levels. 5) Enslaving significantly increased matching errors particularly after fatigue. Taken together, our results suggest that absolute finger forces within the hand are perceived within the CNS during ipsilateral finger force matching. Perception of absolute forces of the fatigued index finger is not altered after fatigue. The ability of the fatigued index finger to reproduce little finger forces is impaired to a certain degree, however. The impairment is likely to be attributable to altered afferent/ efferent relationships of the fatigued index finger.

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“…Increased inhibition may occur and this appears to depend on the level of co-activation. Stronger movements result in more co-activation (Slobounov et al 2002) which would oppose SI more strongly. In addition, in previous studies during movement, only nonsignificant changes of group mean MEP amplitude in the nonrelated hand muscle were found together with a corresponding significant increase in the movement-related muscles FDS, FDI, EIP (Sohn and Hallett 2004a;Voller et al 2005).…”

Section: Discussionmentioning

confidence: 99%

“…Although it is generally assumed that fingers move independently, it has been shown that humans hardly ever move one finger alone (Fish and Soechting 1992;Soechting and Flanders 1992;Engel et al 1997). Co-activation in muscles not related to the movement has, in part, a central cortical origin (HagerRoss and Schieber 2000;Slobounov et al 2002), which we refer to as unintentional co-activation. The concept of SI in the human motor system is that unwanted movements in surrounding muscles during voluntary actions are suppressed (Hallett 2003).…”

Section: Introductionmentioning

confidence: 94%

Short-latency afferent inhibition during selective finger movement

et al. 2005

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During individual finger movement, two opposite phenomena occur at the level of the central nervous system that could affect other intrinsic hand muscle representations, unintentional co-activation, and surround inhibition (SI). At rest, excitability in the motor cortex (M1) is inhibited at about 20 ms after electric stimulation of a peripheral nerve [short-latency afferent inhibition (SAI)]. We sought to determine whether SAI changes during selective index finger movement. Effects were measured by the response to transcranial magnetic stimulation in two functionally distinct target muscles of the hand [abductor digiti minimi muscle (ADM), first dorsal interosseus muscle (FDI)]. An increase in SAI in the ADM during index finger movement compared to at rest could help explain the genesis of SI. Electrical stimulation was applied to either the little finger (homotopic for ADM, heterotopic for FDI) or the index finger (heterotopic for ADM, homotopic for FDI). During index finger movement, homotopic SAI was present only in the ADM, and the effect of peripheral stimulation was greater when there was less co-activation. Heterotopic SAI found at rest disappeared with movement. We conclude that during movement, homotopic SAI on the muscle in the surround of the intended movement may contribute to SI.

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The role of sub-maximal force production in the enslaving phenomenon

Cited by 40 publications

References 17 publications

Movement-specific enhancement of corticospinal excitability at subthreshold levels during motor imagery

Movement-specific enhancement of corticospinal excitability at subthreshold levels during motor imagery

Perception of finger forces within the hand after index finger fatiguing exercise

Short-latency afferent inhibition during selective finger movement

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