Variable and Asymmetric Range of Enslaving: Fingers Can Act Independently over Small Range of Flexion

Noort, Josien C. van den; Beek, Nathalie van; Kraan, Thomas van der; Veeger, H.E.J.; Stegeman, Dick F.; Veltink, Petrus H.; Maas, Huub

doi:10.1371/journal.pone.0168636

Cited by 18 publications

(9 citation statements)

References 39 publications

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“…To our knowledge, no other studies investigating finger force enslaving with a similar task as in our experiment have been reported. However, in agreement with our findings Van den Noort et al [ 21 ] found that the index finger could flex independently, i.e. without movements of the non-instructed fingers, for some range.…”

Section: Discussionsupporting

confidence: 94%

“…They claimed that enslaving effect should have been different between two mentioned tasks if peripheral connections between tendons of extrinsic muscles had effect on enslaving (because there are no apparent connections between intrinsic muscles in contrast with extrinsic muscles) [ 6 ]. In contrast, other studies involving finger movement [ 15 , 21 ]indicated substantial contributions of mechanical connections. Lang and Schieber [ 15 ]showed that the enslaving effect was generally similar during passive (i.e., the finger was flexed and extend by an external force) and active (i.e., voluntary moved) finger flexion movements.…”

Section: Introductionmentioning

confidence: 79%

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Timing and extent of finger force enslaving during a dynamic force task cannot be explained by EMG activity patterns

2017

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Finger enslaving is defined as the inability of the fingers to move or to produce force independently. Such finger enslaving has predominantly been investigated for isometric force tasks. The aim of this study was to assess whether the extent of force enslaving is dependent on relative finger movements. Ten right-handed subjects (22–30 years) flexed the index finger while counteracting constant resistance forces (4, 6 and 8 N) orthogonal to the fingertip. The other, non-instructed fingers were held in extension. EMG activities of the mm. flexor digitorum superficialis (FDS) and extensor digitorum (ED) in the regions corresponding to the index, middle and ring fingers were measured. Forces exerted by the non-instructed fingers increased substantially (by 0.2 to 1.4 N) with flexion of the index finger, increasing the enslaving effect with respect to the static, pre-movement phase. Such changes in force were found 260–370 ms after the initiation of index flexion. The estimated MCP joint angle of the index finger at which forces exerted by the non-instructed fingers started to increase varied between 4° and 6°. In contrast to the finger forces, no significant changes in EMG activity of the FDS regions corresponding to the non-instructed fingers upon index finger flexion were found. This mismatch between forces and EMG of the non-instructed fingers, as well as the delay in force development are in agreement with connective tissue linkages being slack when the positions of the fingers are similar, but pulled taut when one finger moves relative to the others. Although neural factors cannot be excluded, our results suggest that mechanical connections between muscle-tendon structures were (at least partly) responsible for the observed increase in force enslaving during index finger flexion.

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Section: Discussionsupporting

confidence: 94%

Section: Introductionmentioning

confidence: 79%

Timing and extent of finger force enslaving during a dynamic force task cannot be explained by EMG activity patterns

2017

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“…It is not particularly obvious why the ringer finger is appreciated as the center of clique-formation of the fingers and upper limb, but this might relate to previous findings showing relatively enlarged cortical representations for the ring finger in S1 during somatosensation [55]. One possible explanation might be that the ring finger’s constrained freedom of movement [56–58] could result in the ring finger acting as a ‘common denominator’ for various multi-digit movements, leading to the observed digit interconnectedness surrounding the ring finger [59,60]. On the basis of betweenness centrality coefficients the shoulder and wrist are characterized as central, and therefore as important body parts.…”

Section: Discussionmentioning

confidence: 99%

Moving in on human motor cortex. Characterizing the relationship between body parts with non-rigid population Response Fields

Schellekens

Bakker

et al. 2020

Preprint

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For cortical motor activity, the relationships between different body part representations is unknown. Through reciprocal body part relationships, functionality of cortical motor areas with respect to whole body motor control can be characterized. In the current study, we investigate the relationship between body part representations within individual neuronal populations in motor cortices, following a 7 Tesla fMRI 18-body-part motor experiment in combination with our newly developed non-rigid population Response Field (pRF) model and graph theory. The non-rigid pRF metrics reveal somatotopic structures in all included motor cortices covering frontal, parietal, medial and insular cortices and that neuronal populations in primary sensorimotor cortex respond to fewer body parts than secondary motor cortices. Reciprocal body part relationships are estimated in terms of uniqueness, clique-formation, and importance. We report unique response profiles for the knee, a clique of body parts surrounding the ring finger, and a central role for the shoulder and wrist. These results reveal associations among body parts from the perspective of the central nervous system, while being in agreement with intuitive notions of body part usage.

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“…Moreover, the extent of finger movement individualization is unlikely to have driven variability in the cortical tuning curves. While anatomical enslavement in the hand affects individual finger movements at higher angular flexion, detailed hand kinematics data have demonstrated that, for low angular flexion of individual fingers, analogous to those used for button presses during the fMRI tasks, a high degree of independent finger movement is possible in the human hand [ 36 ].…”

Section: Discussionmentioning

confidence: 99%

A Mechanistic Link from GABA to Cortical Architecture and Perception

et al. 2017

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SummaryUnderstanding both the organization of the human cortex and its relation to the performance of distinct functions is fundamental in neuroscience. The primary sensory cortices display topographic organization, whereby receptive fields follow a characteristic pattern, from tonotopy to retinotopy to somatotopy [1]. GABAergic signaling is vital to the maintenance of cortical receptive fields [2]; however, it is unclear how this fine-grain inhibition relates to measurable patterns of perception [3, 4]. Based on perceptual changes following perturbation of the GABAergic system, it is conceivable that the resting level of cortical GABAergic tone directly relates to the spatial specificity of activation in response to a given input [5, 6, 7]. The specificity of cortical activation can be considered in terms of cortical tuning: greater cortical tuning yields more localized recruitment of cortical territory in response to a given input. We applied a combination of fMRI, MR spectroscopy, and psychophysics to substantiate the link between the cortical neurochemical milieu, the tuning of cortical activity, and variability in perceptual acuity, using human somatosensory cortex as a model. We provide data that explain human perceptual acuity in terms of both the underlying cellular and metabolic processes. Specifically, higher concentrations of sensorimotor GABA are associated with more selective cortical tuning, which in turn is associated with enhanced perception. These results show anatomical and neurochemical specificity and are replicated in an independent cohort. The mechanistic link from neurochemistry to perception provides a vital step in understanding population variability in sensory behavior, informing metabolic therapeutic interventions to restore perceptual abilities clinically.

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Variable and Asymmetric Range of Enslaving: Fingers Can Act Independently over Small Range of Flexion

Cited by 18 publications

References 39 publications

Timing and extent of finger force enslaving during a dynamic force task cannot be explained by EMG activity patterns

Timing and extent of finger force enslaving during a dynamic force task cannot be explained by EMG activity patterns

Moving in on human motor cortex. Characterizing the relationship between body parts with non-rigid population Response Fields

A Mechanistic Link from GABA to Cortical Architecture and Perception

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