scholarly journals Case Studies in Neuroscience: The central and somatosensory contributions to finger interdependence and coordination: lessons from a study of a “deafferented person”

2019 ◽  
Vol 121 (6) ◽  
pp. 2083-2087 ◽  
Author(s):  
Cristian Cuadra ◽  
Ali Falaki ◽  
Robert Sainburg ◽  
Fabrice R. Sarlegna ◽  
Mark L. Latash
Keyword(s):  
Peripheral Neuropathy ◽  
Equilibrium Point ◽  
Force Production ◽  
Total Force ◽  
Equilibrium Point Hypothesis ◽  
Somatosensory Feedback ◽  
Central Origin ◽  
Neural Origin ◽  
Zero Values ◽  
Large Fiber

We tested finger force interdependence and multifinger force-stabilizing synergies in a patient with large-fiber peripheral neuropathy (“deafferented person”). The subject performed a range of tasks involving accurate force production with one finger and with four fingers. In one-finger tasks, nontask fingers showed unintentional force production (enslaving) with an atypical pattern: very large indices for the lateral (index and little) fingers and relatively small indices for the central (middle and ring) fingers. Indices of multifinger synergies stabilizing total force and of anticipatory synergy adjustments in preparation to quick force pulses were similar to those in age-matched control females. During constant force production, removing visual feedback led to a slow force drift to lower values (by ~25% over 15 s). The results support the idea of a neural origin of enslaving and suggest that the patterns observed in the deafferented person were reorganized based on everyday manipulation tasks. The lack of significant changes in the synergy index shows that synergic control can be organized in the absence of somatosensory feedback. We discuss the control of the hand in deafferented persons within the α-model of the equilibrium-point hypothesis and suggest that force drift results from an unintentional drift of the control variables to muscles toward zero values. NEW & NOTEWORTHY We demonstrate atypical patterns of finger enslaving and unchanged force-stabilizing synergies in a person with large-fiber peripheral neuropathy. The results speak strongly in favor of central origin of enslaving and its reorganization based on everyday manipulation tasks. The data show that synergic control can be implemented in the absence of somatosensory feedback. We discuss the control of the hand in deafferented persons within the α-model of the equilibrium-point hypothesis.

Limits to the Control of the Human Thumb and Fingers in Flexion and Extension

2010 ◽  
Vol 103 (1) ◽  
pp. 278-289 ◽  
Author(s):  
W. S. Yu ◽  
H. van Duinen ◽  
S. C. Gandevia
Keyword(s):  
Control System ◽  
Healthy Subjects ◽  
Neural Control ◽  
Force Production ◽  
Total Force ◽  
Neural Drive ◽  
Antagonist Muscles ◽  
Hand Performance ◽  
The Difference ◽  
Flexion And Extension

In humans, hand performance has evolved from a crude multidigit grasp to skilled individuated finger movements. However, control of the fingers is not completely independent. Although musculotendinous factors can limit independent movements, constraints in supraspinal control are more important. Most previous studies examined either flexion or extension of the digits. We studied differences in voluntary force production by the five digits, in both flexion and extension tasks. Eleven healthy subjects were instructed either to maximally flex or extend their digits, in all single- and multidigit combinations. They received visual feedback of total force produced by “instructed” digits and had to ignore “noninstructed” digits. Despite attempts to maximally flex or extend instructed digits, subjects rarely generated their “maximal” force, resulting in a “force deficit,” and produced forces with noninstructed digits (“enslavement”). Subjects performed differently in flexion and extension tasks. Enslavement was greater in extension than in flexion tasks ( P = 0.019), whereas the force deficit in multidigit tasks was smaller in extension ( P = 0.035). The difference between flexion and extension in the relationships between the enslavement and force deficit suggests a difference in balance of spillover of neural drive to agonists acting on neighboring digits and focal neural drive to antagonist muscles. An increase in drive to antagonists would lead to more individualized movements. The pattern of force production matches the daily use of the digits. These results reveal a neural control system that preferentially lifts fingers together by extension but allows an individual digit to flex so that the finger pads can explore and grasp.

scholarly journals Synergies in the space of control variables within the equilibrium-point hypothesis

Neuroscience ◽  
2016 ◽  
Vol 315 ◽  
pp. 150-161 ◽  
Author(s):  
S. Ambike ◽  
D. Mattos ◽  
V.M. Zatsiorsky ◽  
M.L. Latash
Keyword(s):  
Equilibrium Point ◽  
Control Variables ◽  
Equilibrium Point Hypothesis

scholarly journals Equifinality and its violations in a redundant system: multifinger accurate force production

2013 ◽  
Vol 110 (8) ◽  
pp. 1965-1973 ◽  
Author(s):  
Luke Wilhelm ◽  
Vladimir M. Zatsiorsky ◽  
Mark L. Latash
Keyword(s):  
Force Production ◽  
Uncontrolled Manifold ◽  
Total Force ◽  
Redundant System ◽  
Uncontrolled Manifold Hypothesis ◽  
Final State ◽  
Performance Variables ◽  
Force Mode ◽  
Finger Forces ◽  
The Individual

We explored a hypothesis that transient perturbations applied to a redundant system result in equifinality in the space of task-related performance variables but not in the space of elemental variables. The subjects pressed with four fingers and produced an accurate constant total force level. The “inverse piano” device was used to lift and lower one of the fingers smoothly. The subjects were instructed “not to intervene voluntarily” with possible force changes. Analysis was performed in spaces of finger forces and finger modes (hypothetical neural commands to fingers) as elemental variables. Lifting a finger led to an increase in its force and a decrease in the forces of the other three fingers; the total force increased. Lowering the finger back led to a drop in the force of the perturbed finger. At the final state, the sum of the variances of finger forces/modes computed across repetitive trials was significantly higher than the variance of the total force/mode. Most variance of the individual finger force/mode changes between the preperturbation and postperturbation states was compatible with constant total force. We conclude that a transient perturbation applied to a redundant system leads to relatively small variance in the task-related performance variable (equifinality), whereas in the space of elemental variables much more variance occurs that does not lead to total force changes. We interpret the results within a general theoretical scheme that incorporates the ideas of hierarchically organized control, control with referent configurations, synergic control, and the uncontrolled manifold hypothesis.

scholarly journals Neuropathy in Chronic Renal Failure

2013 ◽  
Vol 28 (2) ◽  
pp. 116-127
Author(s):  
Md Munzur Alahi ◽  
Md Pervez Amin ◽  
Md Ahmed Ali ◽  
Md Kafiluddin ◽  
Quamruddin Ahmad
Keyword(s):  
Renal Failure ◽  
Chronic Renal Failure ◽  
Peripheral Neuropathy ◽  
Axonal Degeneration ◽  
Muscle Wasting ◽  
Autonomic Failure ◽  
Neurological Complications ◽  
Vibration Sense ◽  
Pathologic Features ◽  
Large Fiber

Peripheral neuropathy is common in chronic renal failure patients and it’s early detection and treatment reduces the sufferings of these patients. Studies of neuropathy in ESKD have demonstrated prevalence rates which vary from 60 to 100%. The striking pathologic features of peripheral neuropathy in patients of CRF are axonal degeneration in the most distal nerve trunks with secondary segmental demyelination. The most frequent clinical features are those of large-fiber involvement, with paresthesias, reduction in deep tendon reflexes, impaired vibration sense, weakness and muscle wasting. Patients of CRF may present with mononeuropathies or autonomic failure also. The exact cause of nerve involvement has not been identified but the middle molecule hypothesis is widely accepted. Dialysis in any form fails to improve the neuropathy but renal transplantation does improve the neurological complications. This review details the various features of neuropathy in patients of chronic renal failure. DOI: http://dx.doi.org/10.3329/bjn.v28i2.17183 Bangladesh Journal of Neuroscience 2012; Vol. 28 (2): 116-127

scholarly journals Evolution of Motor Control: From Reflexes and Motor Programs to the Equilibrium-Point Hypothesis

2008 ◽  
Vol 19 (1) ◽  
pp. 3-24 ◽  
Author(s):  
Mark Latash
Keyword(s):  
Motor Control ◽  
Equilibrium Point ◽  
Voluntary Movements ◽  
Motor Programs ◽  
Equilibrium Point Hypothesis ◽  
Motor Synergies ◽  
Recent Developments ◽  
Active Motor ◽  
Control Theories

Evolution of Motor Control: From Reflexes and Motor Programs to the Equilibrium-Point HypothesisThis brief review analyzes the evolution of motor control theories along two lines that emphasize active (motor programs) and reactive (reflexes) features of voluntary movements. It suggests that the only contemporary hypothesis that integrates both approaches in a fruitful way is the equilibrium-point hypothesis. Physical, physiological, and behavioral foundations of the EP-hypothesis are considered as well as relations between the EP-hypothesis and the recent developments of the notion of motor synergies. The paper ends with a brief review of the criticisms of the EP-hypothesis and challenges that the hypothesis faces at this time.

scholarly journals Stability of multifinger action in different state spaces

2014 ◽  
Vol 112 (12) ◽  
pp. 3209-3218 ◽  
Author(s):  
Sasha Reschechtko ◽  
Vladimir M. Zatsiorsky ◽  
Mark L. Latash
Keyword(s):  
Force Production ◽  
Total Force ◽  
Force Output ◽  
Large Magnitude ◽  
State Spaces ◽  
Theoretical Scheme ◽  
Lower Stability ◽  
Mode Space ◽  
Finger Forces

We investigated stability of action by a multifinger system with three methods: analysis of intertrial variance, application of transient perturbations, and analysis of the system's motion in different state spaces. The “inverse piano” device was used to apply transient (lifting-and-lowering) perturbations to individual fingers during single- and two-finger accurate force production tasks. In each trial, the perturbation was applied either to a finger explicitly involved in the task or one that was not. We hypothesized that, in one-finger tasks, task-specific stability would be observed in the redundant space of finger forces but not in the nonredundant space of finger modes (commands to explicitly involved fingers). In two-finger tasks, we expected that perturbations applied to a nontask finger would not contribute to task-specific stability in mode space. In contrast to our expectations, analyses in both force and mode spaces showed lower stability in directions that did not change total force output compared with directions that did cause changes in total force. In addition, the transient perturbations led to a significant increase in the enslaving index. We consider these results within a theoretical scheme of control with referent body configurations organized hierarchically, using multiple few-to-many mappings organized in a synergic way. The observed volatility of enslaving, greater equifinality of total force compared with elemental variables, and large magnitude of motor equivalent motion in both force and mode spaces provide support for the concept of task-specific stability of performance and the existence of multiple neural loops, which ensure this stability.

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