1
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Benamati A, Ricotta JM, De SD, Latash ML. Three Levels of Neural Control Contributing to Performance-stabilizing Synergies in Multi-finger Tasks. Neuroscience 2024; 551:262-275. [PMID: 38838976 DOI: 10.1016/j.neuroscience.2024.05.044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2023] [Revised: 05/28/2024] [Accepted: 05/30/2024] [Indexed: 06/07/2024]
Abstract
We tested a hypothesis on force-stabilizing synergies during four-finger accurate force production at three levels: (1) The level of the reciprocal and coactivation commands, estimated as the referent coordinate and apparent stiffness of all four fingers combined; (2) The level of individual finger forces; and (3) The level of firing of individual motor units (MU). Young, healthy participants performed accurate four-finger force production at a comfortable, non-fatiguing level under visual feedback on the total force magnitude. Mechanical reflections of the reciprocal and coactivation commands were estimated using small, smooth finger perturbations applied by the "inverse piano" device. Firing frequencies of motor units in the flexor digitorum superficialis (FDS) and extensor digitorum communis (EDC) were estimated using surface recording. Principal component analysis was used to identify robust MU groups (MU-modes) with parallel changes in the firing frequency. The framework of the uncontrolled manifold hypothesis was used to compute synergy indices in the spaces of referent coordinate and apparent stiffness, finger forces, and MU-mode magnitudes. Force-stabilizing synergies were seen at all three levels. They were present in the MU-mode spaces defined for MUs in FDS, in EDC, and pooled over both muscles. No effects of hand dominance were seen. The synergy indices defined at different levels of analysis showed no correlations across the participants. The findings are interpreted within the theory of control with spatial referent coordinates for the effectors. We conclude that force stabilization gets contributions from three levels of neural control, likely associated with cortical, subcortical, and spinal circuitry.
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Affiliation(s)
- Anna Benamati
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy; Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA
| | - Joseph M Ricotta
- Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA
| | - Sayan D De
- Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA
| | - Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA.
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2
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Guberman S, Latash ML. The Role of Imitation, Primitives, and Spatial Referent Coordinates in Motor Control: Implications for Writing and Reading. Motor Control 2024:1-15. [PMID: 38364817 DOI: 10.1123/mc.2023-0122] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2023] [Revised: 12/13/2023] [Accepted: 01/05/2024] [Indexed: 02/18/2024]
Abstract
We review a body of literature related to the drawing and recognition of geometrical two-dimensional linear drawings including letters. Handwritten letters are viewed not as two-dimensional geometrical objects but as one-dimensional trajectories of the tip of the implement. Handwritten letters are viewed as composed of a small set of kinematic primitives. Recognition of objects is mediated by processes of their creation (actual or imagined)-the imitation principle, a particular example of action-perception coupling. The concept of spatial directional field guiding the trajectories is introduced and linked to neuronal population vectors. Further, we link the kinematic description to the theory of control with spatial referent coordinates. This framework allows interpreting a number of experimental observations and clinical cases of agnosia. It also allows formulating predictions for new experimental studies of writing.
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Affiliation(s)
- Shelia Guberman
- Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, San Jose, CA, USA
| | - Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, University Park, PA, USA
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3
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Pascucci F, Cesari P, Bertucco M, Latash ML. Postural adjustments to self-triggered perturbations under conditions of changes in body orientation. Exp Brain Res 2023:10.1007/s00221-023-06671-0. [PMID: 37479771 PMCID: PMC10386932 DOI: 10.1007/s00221-023-06671-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Accepted: 07/10/2023] [Indexed: 07/23/2023]
Abstract
We studied anticipatory and compensatory postural adjustments (APAs and CPAs) associated with self-triggered postural perturbations in conditions with changes in the initial body orientation. In particular, we were testing hypotheses on adjustments in the reciprocal and coactivation commands, role of proximal vs. distal muscles, and correlations between changes in indices of APAs and CPAs. Healthy young participants stood on a board with full support or reduced support area and held a standard load in the extended arms. They released the load in a self-paced manned with a standard small-amplitude arm movement. Electromyograms of 12 muscles were recorded and used to compute reciprocal and coactivation indices between three muscle pairs on both sides of the body. The subject's body was oriented toward one of three targets: straight ahead, 60° to the left, and 60° to the right. Body orientation has stronger effects on proximal muscle pairs compared to distal muscles. It led to more consistent changes in the reciprocal command compared to the coactivation command. Indices of APAs and CPAs showed positive correlations across conditions. We conclude that the earlier suggested hierarchical relations between the reciprocal and coactivation command could be task-specific. Predominance of negative or positive correlations between APA and CPA indices could also be task-specific.
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Affiliation(s)
- Francesco Pascucci
- Department of Engineering for Innovation Medicine, University of Verona, Verona, Italy
| | - Paola Cesari
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Via Felice Casorati 43, 37131, Verona, Italy.
| | - Matteo Bertucco
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Via Felice Casorati 43, 37131, Verona, Italy
| | - Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, University Park, PA, 16802, USA
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4
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Abolins V, Latash ML. Unintentional Force Drifts as Consequences of Indirect Force Control with Spatial Referent Coordinates. Neuroscience 2021; 481:156-165. [PMID: 34774968 DOI: 10.1016/j.neuroscience.2021.11.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Revised: 10/16/2021] [Accepted: 11/02/2021] [Indexed: 11/29/2022]
Abstract
We explored the phenomenon of unintentional force drifts in the absence of visual feedback. Based on the idea of direct force control with internal models and on the idea of indirect force control with referent coordinates to the involved muscle groups, contrasting predictions were drawn for changes in the drift magnitude when acting against external spring loads. Fifteen young subjects performed typical accurate force production tasks by pressing with the Index finger at 20% of maximal voluntary contraction (MVC) in isometric conditions and while acting against one of the three external springs with different stiffness. The visual feedback on the force was turned off after 5 s. At the end of each 20-s trial, the subjects relaxed and then tried to reproduce the final force level. The force drifts were significantly smaller in the spring conditions, particularly when acting against more compliant springs. The subjects were unaware of the force drifts and, during force matching, produced forces close to the initial force magnitude, which were not different across the conditions. There was a trend toward larger drifts during performance by the dominant hand. We view these observations as strong arguments in favor of the theory of control with spatial referent coordinates. In particular, force drifts were likely consequences of drifts of referent coordinates to both agonist and antagonist muscles. The lack of drift effects on both perception-to-report and perception-to-act fit the scheme of kinesthetic perception based on the interaction of efferent (referent coordinate) and afferent processes.
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Affiliation(s)
- Valters Abolins
- Cyber-Physical Systems Laboratory, Institute of Electronics and Computer Science, Riga LV-1006, Latvia.
| | - Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA.
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5
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Santello M. Pushing the boundaries of a physical approach for the study of sensorimotor control: Comment on "Laws of nature that define biological action and perception" by Mark L. Latash. Phys Life Rev 2021; 37:7-9. [PMID: 33676230 DOI: 10.1016/j.plrev.2021.02.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2021] [Accepted: 02/18/2021] [Indexed: 01/29/2023]
Affiliation(s)
- Marco Santello
- School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ 85287-9709, USA.
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6
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Zhang L, Duval L, Hasanbarani F, Zhu Y, Zhang X, Barthelemy D, Dancause N, Feldman AG. Participation of ipsilateral cortical descending influences in bimanual wrist movements in humans. Exp Brain Res 2020; 238:2359-2372. [PMID: 32766959 DOI: 10.1007/s00221-020-05899-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2020] [Accepted: 07/29/2020] [Indexed: 01/09/2023]
Abstract
There are contralateral and less studied ipsilateral (i), indirect cortical descending projections to motoneurons (MNs). We compared ipsilateral cortical descending influences on MNs of wrist flexors by applying transcranial magnetic stimulation (TMS) over the right primary motor cortex at actively maintained flexion and extension wrist positions in uni- and bimanual tasks in right-handed participants (n = 23). The iTMS response includes a short latency (~ 25 ms) motor evoked potential (iMEP), a silent period (iSP) and a long latency (~ 60 ms) facilitation called rebound (iRB). We also investigated whether the interaction between the two hands while holding an object in a bimanual task involves ipsilateral cortical descending influences. In the unimanual task, iTMS responses in the right wrist flexors were unaffected by changes in wrist position. In the bimanual task with an object, iMEPs in the right wrist flexors were larger when the ipsilateral wrist was in flexion compared to extension. Without the object, only iRB were larger when the ipsilateral wrist was extended. Thus, ipsilateral cortical descending influences on MNs were modulated only in bimanual tasks and depended on how the two hands interacted. It is concluded that the left and right cortices cooperate in bimanual tasks involving holding an object with both hands, with possible involvement of oligo- and poly-synaptic, as well as transcallosal projections to MNs. The possible involvement of spinal and transcortical stretch and cutaneous reflexes in bimanual tasks when holding an object is discussed in the context of the well-established notion that indirect, referent control underlies motor actions.
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Affiliation(s)
- L Zhang
- Institut für Neuroinformatik, Ruhr-Universität Bochum, Bochum, Germany
| | - L Duval
- Department of Neuroscience, University of Montreal, Montreal, Canada
- Centre for Interdisciplinary Research in Rehabilitation (CRIR), IRGLM, Institut de Readaptation Gingras-Lindsay de Montreal, 6300 Darlington, Montreal, Canada
| | - F Hasanbarani
- Centre for Interdisciplinary Research in Rehabilitation (CRIR), IRGLM, Institut de Readaptation Gingras-Lindsay de Montreal, 6300 Darlington, Montreal, Canada
- School of Physical and Occupational Therapy, McGill University, Montreal, Canada
| | - Y Zhu
- Faculty of Medicine, University of Montreal, Montreal, Canada
| | - X Zhang
- Faculty of Medicine, University of Montreal, Montreal, Canada
| | - D Barthelemy
- Centre for Interdisciplinary Research in Rehabilitation (CRIR), IRGLM, Institut de Readaptation Gingras-Lindsay de Montreal, 6300 Darlington, Montreal, Canada
- Ecole de Readaptation, University of Montreal, Montreal, Canada
| | - N Dancause
- Department of Neuroscience, University of Montreal, Montreal, Canada
| | - A G Feldman
- Department of Neuroscience, University of Montreal, Montreal, Canada.
- Centre for Interdisciplinary Research in Rehabilitation (CRIR), IRGLM, Institut de Readaptation Gingras-Lindsay de Montreal, 6300 Darlington, Montreal, Canada.
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7
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Abolins V, Stremoukhov A, Walter C, Latash ML. On the origin of finger enslaving: control with referent coordinates and effects of visual feedback. J Neurophysiol 2020; 124:1625-1636. [PMID: 32997555 DOI: 10.1152/jn.00322.2020] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
When a person tries to press with a finger, other fingers of the hand produce force unintentionally. We explored this phenomenon of enslaving during unintentional force drifts in the course of continuous force production by pairs of fingers of a hand. Healthy subjects performed accurate force production tasks by finger pairs Index-Middle, Middle-Ring, and Ring-Little with continuous visual feedback on the combined force of the instructed (master) fingers or of the noninstructed (enslaved) fingers. The feedback scale was adjusted to ensure that the subjects did not know the difference between these two, randomly presented, conditions. Across all finger pairs, enslaved force showed a drift upward under feedback on the master finger force, and master force showed a drift downward under feedback on the enslaved finger force. The subjects were unaware of the force drifts, which could reach over 50% of the initial force magnitude over 15 s. Across all conditions, the index of enslaving increased by ∼50% over the trial duration. The initial moment of force magnitude in pronation-supination was not a consistent predictor of the force drift magnitude. These results falsify the hypothesis that the counter-directional force drifts reflected drifts in the moment of force. They suggest that during continuous force production, enslaving increases with time, possibly due to the spread of excitation over cortical finger representations or other mechanisms, such as increased synchronization of firing of α-motoneurons innervating different compartments of extrinsic flexors. These changes in enslaving, interpreted at the level of control with referent coordinates for the fingers, can contribute to a variety of phenomena, including unintentional force drifts.NEW & NOTEWORTHY We report a consistent slow increase in finger enslaving (force production by noninstructed fingers) when visual feedback was presented on the force produced by either two instructed fingers or two noninstructed fingers of the hand. In contrast, force drifts could be in opposite directions depending on the visual feedback. We interpret enslaving and its drifts at the level of control with referent coordinates for the involved muscles, possibly reflecting spread of cortical excitation.
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Affiliation(s)
- Valters Abolins
- Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania.,Institute of Electronics and Computer Science, Riga, Latvia
| | - Alex Stremoukhov
- Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania
| | - Caroline Walter
- Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania
| | - Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania
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8
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Laws of nature that define biological action and perception. Phys Life Rev 2020; 36:47-67. [PMID: 32868159 DOI: 10.1016/j.plrev.2020.07.007] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2020] [Accepted: 07/29/2020] [Indexed: 12/12/2022]
Abstract
We describe a physical approach to biological functions, with the emphasis on the motor and sensory functions. The approach assumes the existence of biology-specific laws of nature uniting salient physical variables and parameters. In contrast to movements in inanimate nature, actions are produced by changes in parameters of the corresponding laws of nature. For movements, parameters are associated with spatial referent coordinates (RCs) for the effectors. Stability of motor actions is ensured by the abundant mapping of RCs across hierarchical control levels. The sensory function is viewed as based on an interaction of efferent and afferent signals leading to an iso-perceptual manifold where percepts of salient sensory variables are stable. This approach offers novel interpretations for a variety of known neurophysiological and behavioral phenomena and makes a number of novel testable predictions. In particular, we discuss novel interpretations for the well-known phenomena of agonist-antagonist co-activation and vibration-induced illusions of both position and force. We also interpret results of several new experiments with unintentional force changes and with analysis of accuracy of perception of variables produced by elements of multi-element systems. Recently, this approach has been expanded to interpret motor disorders including spasticity and consequences of subcortical disorders (such as Parkinson's disease). We suggest that the approach can be developed for cognitive functions.
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9
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Guillaud E, Faure C, Doat E, Bouyer LJ, Guehl D, Cazalets JR. Ancestral persistence of vestibulospinal reflexes in axial muscles in humans. J Neurophysiol 2020; 123:2010-2023. [PMID: 32319843 DOI: 10.1152/jn.00421.2019] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Most studies addressing the role of vestibulospinal reflexes in balance maintenance have mainly focused on responses in the lower limbs, while limited attention has been paid to the output in trunk and back muscles. To address this issue, we tested whether electromyographic (EMG) responses to galvanic vestibular stimulations (GVS) were modulated similarly in back and leg muscles, in situations where the leg muscle responses to GVS are known to be attenuated. Body sway and surface EMG signals were recorded in the paraspinal and limb muscles of humans (n = 19) under three complementary conditions. During treadmill locomotion, EMG responses in the lower limbs were observed only during stance, whereas responses in trunk muscles were observed during all phases of the locomotor cycle. During upright standing, a slight head contact abolished the responses in the lower limbs, while the responses remained present in back muscles. Similarly, during parabolic flight-induced microgravity, EMG responses in lower limb muscles were suppressed but remained in axial muscles despite the abolished gravitational otolithic drive. Our results suggest a differentiated control of axial and appendicular muscles when a perturbation is detected by vestibular inputs. The persistence and low modulation of axial muscle responses suggests that a hard-wired reflex is functionally efficient to maintain posture. By contrast, the ankle responses to GVS occur only in balance tasks when proprioceptive feedback is congruent. This study using GVS in microgravity is the first to present an approach delineating feedforward vestibular control in unconstrained environment.NEW & NOTEWORTHY This study addresses the extent of conservation of trunk muscle control in humans. Results show that galvanic vestibular stimulation-evoked vestibular responses in trunk muscles remain strong in conditions where leg muscle responses are downmodulated (walking, standing, microgravity). This suggests a phylogenetically conserved blueprint of sensorimotor organization, with strongly hardwired vestibulospinal inputs to axial motoneurons and a higher degree of flexibility in the later emerging limb control system.
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Affiliation(s)
- Etienne Guillaud
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Université de Bordeaux, CNRS UMR 5287, Bordeaux, France
| | - Céline Faure
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Université de Bordeaux, CNRS UMR 5287, Bordeaux, France.,Center for Interdisciplinary Research in Rehabilitation and Social Integration (CIRRIS), Faculty of Medicine, Université Laval, Quebec City, Quebec, Canada
| | - Emilie Doat
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Université de Bordeaux, CNRS UMR 5287, Bordeaux, France
| | - Laurent J Bouyer
- Center for Interdisciplinary Research in Rehabilitation and Social Integration (CIRRIS), Faculty of Medicine, Université Laval, Quebec City, Quebec, Canada
| | - Dominique Guehl
- CHU de Bordeaux, Service d'explorations fonctionnelles du système nerveux, Bordeaux, France
| | - Jean-René Cazalets
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Université de Bordeaux, CNRS UMR 5287, Bordeaux, France
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10
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Chan-Viquez D, Hasanbarani F, Zhang L, Anaby D, Turpin NA, Lamontagne A, Feldman AG, Levin MF. Development of vertical and forward jumping skills in typically developing children in the context of referent control of motor actions. Dev Psychobiol 2020; 62:711-722. [PMID: 31957019 DOI: 10.1002/dev.21949] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2019] [Revised: 12/14/2019] [Accepted: 12/23/2019] [Indexed: 12/20/2022]
Abstract
The empirically based referent control theory of motor actions provides a new framework for understanding locomotor maturation. Mature movement patterns of referent control are characterized by periods of minimization of activity across multiple muscles (global electromyographic [EMG] minima) resulting from transient matching between actual and referent body configurations. We identified whether locomotor maturation in young children was associated with (a) development of referent control and (b) children's frequency of participation in everyday activities evaluated by parents. Kinematics and EMG activity were recorded from typically developing children (n = 15, 3-5 years) and young adults (n = 10, 18-25 years) while walking, vertical or forward jumping. Presence and location of global EMG minima in movement cycles, slopes of ankle vertical/sagittal displacements, and shoulder displacement ratios were evaluated. Children had fewer global EMG minima compared to adults during specific phases of vertical and forward jumps. Ankle displacement profiles for walking and jumping forward were related to each other in adults, whereas those for walking and vertical jumping were related in children. Higher frequency of participation was significantly correlated with more mature jumping patterns in children. A decrease in the number of global EMG minima and changes in ankle movement patterns could be indicators of locomotor immaturity in typically developing children.
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Affiliation(s)
- Daniela Chan-Viquez
- School of Physical and Occupational Therapy, McGill University, Montreal, QC, Canada.,Center for Interdisciplinary Research in Rehabilitation of Greater Montreal (CRIR), Montreal, QC, Canada
| | - Fariba Hasanbarani
- School of Physical and Occupational Therapy, McGill University, Montreal, QC, Canada.,Center for Interdisciplinary Research in Rehabilitation of Greater Montreal (CRIR), Montreal, QC, Canada
| | - Lei Zhang
- Center for Interdisciplinary Research in Rehabilitation of Greater Montreal (CRIR), Montreal, QC, Canada.,Department of Neuroscience, University of Montreal, Montreal, QC, Canada
| | - Dana Anaby
- School of Physical and Occupational Therapy, McGill University, Montreal, QC, Canada.,Center for Interdisciplinary Research in Rehabilitation of Greater Montreal (CRIR), Montreal, QC, Canada
| | - Nicolas A Turpin
- Center for Interdisciplinary Research in Rehabilitation of Greater Montreal (CRIR), Montreal, QC, Canada.,Department of Neuroscience, University of Montreal, Montreal, QC, Canada
| | - Anouk Lamontagne
- School of Physical and Occupational Therapy, McGill University, Montreal, QC, Canada.,Center for Interdisciplinary Research in Rehabilitation of Greater Montreal (CRIR), Montreal, QC, Canada
| | - Anatol G Feldman
- Center for Interdisciplinary Research in Rehabilitation of Greater Montreal (CRIR), Montreal, QC, Canada.,Department of Neuroscience, University of Montreal, Montreal, QC, Canada
| | - Mindy F Levin
- School of Physical and Occupational Therapy, McGill University, Montreal, QC, Canada.,Center for Interdisciplinary Research in Rehabilitation of Greater Montreal (CRIR), Montreal, QC, Canada
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11
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Feldman AG. Indirect, referent control of motor actions underlies directional tuning of neurons. J Neurophysiol 2018; 121:823-841. [PMID: 30565957 DOI: 10.1152/jn.00575.2018] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Many neurons of the primary motor cortex (M1) are maximally sensitive to "preferred" hand movement directions and generate progressively less activity with movements away from these directions. M1 activity also correlates with other biomechanical variables. These findings are predominantly interpreted in a framework in which the brain preprograms and directly specifies the desired motor outcome. This approach is inconsistent with the empirically derived equilibrium-point hypothesis, in which the brain can control motor actions only indirectly, by changing neurophysiological parameters that may influence, but remain independent of, biomechanical variables. The controversy is resolved on the basis of experimental findings and theoretical analysis of how sensory and central influences are integrated in the presence of the fundamental nonlinearity of neurons: electrical thresholds. In the presence of sensory inputs, electrical thresholds are converted into spatial thresholds that predetermine the position of the body segments at which muscles begin to be activated. Such thresholds may be considered as referent points of respective spatial frames of reference (FRs) in which neurons, including motoneurons, are centrally predetermined to work. By shifting the referent points of respective FRs, the brain elicits intentional actions. Pure involuntary reactions to perturbations are accomplished in motionless FRs. Neurons are primarily sensitive to shifts in referent directions, i.e., shifts in spatial FRs, whereas emergent neural activity may or may not correlate with different biomechanical variables depending on the motor task and external conditions. Indirect, referent control of posture and movement symbolizes a departure from conventional views based on direct preprogramming of the motor outcome.
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Affiliation(s)
- Anatol G Feldman
- Department of Neuroscience, University of Montreal , Montreal, Quebec , Canada.,Institut de Réadaptation Gingras-Lindsay de Montréal, Centre for Interdisciplinary Research in Rehabilitation of Greater Montreal (CRIR) , Montreal, Quebec , Canada.,Jewish Rehabilitation Hospital, CRIR, Laval, Quebec, Canada
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12
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Zhang L, Feldman AG, Levin MF. Vestibular and corticospinal control of human body orientation in the gravitational field. J Neurophysiol 2018; 120:3026-3041. [PMID: 30207862 DOI: 10.1152/jn.00483.2018] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Body orientation with respect to the direction of gravity changes when we lean forward from upright standing. We tested the hypothesis that during upright standing, the nervous system specifies the referent body orientation that defines spatial thresholds for activation of multiple muscles across the body. To intentionally lean the body forward, the system is postulated to transfer balance and stability to the leaned position by monotonically tilting the referent orientation, thus increasing the activation thresholds of ankle extensors and decreasing their activity. Consequently, the unbalanced gravitational torque would start to lean the body forward. With restretching, ankle extensors would be reactivated and generate increasing electromyographic (EMG) activity until the enhanced gravitational torque would be balanced at a new posture. As predicted, vestibular influences on motoneurons of ankle extensors evaluated by galvanic vestibular stimulation were smaller in the leaned compared with the upright position, despite higher tonic EMG activity. Defacilitation of vestibular influences was also observed during forward leaning when the EMG levels in the upright and leaned position were equalized by compensating the gravitational torque with a load. The vestibular system is involved in the active control of body orientation without directly specifying the motor outcome. Corticospinal influences originating from the primary motor cortex evaluated by transcranial magnetic stimulation remained similar at the two body postures. Thus, in contrast to the vestibular system, the corticospinal system maintains a similar descending facilitation of motoneurons of leg muscles at different body orientations. The study advances the understanding of how body orientation is controlled. NEW & NOTEWORTHY The brain changes the referent body orientation with respect to gravity to lean the body forward. Physiologically, this is achieved by shifts in spatial thresholds for activation of ankle muscles, which involves the vestibular system. Results advance the understanding of how the brain controls body orientation in the gravitational field. The study also extends previous evidence of empirical control of motor function, i.e., without the reliance on model-based computations and direct specification of motor outcome.
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Affiliation(s)
- Lei Zhang
- Department of Neuroscience, University of Montreal , Montreal, Quebec , Canada.,Institut de Réadaptation Gingras-Lindsay de Montréal, Centre for Interdisciplinary Research in Rehabilitation of Greater Montreal (CRIR) , Montreal, Quebec , Canada.,Jewish Rehabilitation Hospital, CRIR, Laval, Quebec , Canada
| | - Anatol G Feldman
- Department of Neuroscience, University of Montreal , Montreal, Quebec , Canada.,Institut de Réadaptation Gingras-Lindsay de Montréal, Centre for Interdisciplinary Research in Rehabilitation of Greater Montreal (CRIR) , Montreal, Quebec , Canada.,Jewish Rehabilitation Hospital, CRIR, Laval, Quebec , Canada
| | - Mindy F Levin
- Jewish Rehabilitation Hospital, CRIR, Laval, Quebec , Canada.,School of Physical and Occupational Therapy, McGill University , Montreal, Quebec , Canada
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13
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Abstract
The phenomenon of agonist-antagonist muscle coactivation is discussed with respect to its consequences for movement mechanics (such as increasing joint apparent stiffness, facilitating faster movements, and effects on action stability), implication for movement optimization, and involvement of different neurophysiological structures. Effects of coactivation on movement stability are ambiguous and depend on the effector representing a kinematic chain with a fixed origin or free origin. Furthermore, coactivation is discussed within the framework of the equilibrium-point hypothesis and the idea of hierarchical control with spatial referent coordinates. Relations of muscle coactivation to changes in one of the basic commands, the c-command, are discussed and illustrated. A hypothesis is suggested that agonist-antagonist coactivation reflects a deliberate neural control strategy to preserve effector-level control and avoid making it degenerate and facing the necessity to control at the level of signals to individual muscles. This strategy, in particular, allows stabilizing motor actions by covaried adjustments in spaces of control variables. This hypothesis is able to account for higher levels of coactivation in young healthy persons performing challenging tasks and across various populations with movement impairments.
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Affiliation(s)
- Mark L Latash
- Department of Kinesiology, The Pennsylvania State University , University Park, Pennsylvania
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14
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Increasing mediolateral standing sway is associated with increasing corticospinal excitability, and decreasing M1 inhibition and facilitation. Gait Posture 2018; 60:135-140. [PMID: 29202358 DOI: 10.1016/j.gaitpost.2017.11.021] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 11/22/2017] [Accepted: 11/27/2017] [Indexed: 02/02/2023]
Abstract
In standing, corticospinal excitability increases and primary motor cortex (M1) inhibition decreases in response to anterior posterior or direction unspecific manipulations that increase task difficulty. However, mediolateral (ML) sway control requires greater active neural involvement. Therefore, the primary purpose of this study was to determine the pattern of change in neural excitability when ML postural task difficulty is manipulated and to test whether the neural excitability is proportional to ML sway magnitude across conditions. Tibialis anterior corticospinal excitability was quantified using motor evoked potential (MEP) and postural sway was indexed using ML center of pressure (COP) velocity. Additionally, we examined inhibition and facilitation processes in the primary motor cortex using the paired pulse short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) techniques respectively. Measurements were repeated in four conditions with quiet stance as a control. Differences between conditions were tested using one-way repeated measures ANOVAs, on log transformed data. Associations were quantified using Spearman's Rank Correlation Coefficient. There was a significant main effect of condition on all the neural excitability measures with MEP (p<0.001) being highest in the most difficult condition, and SICI (p=0.01), ICF (p<0.001) being lowest in the most difficult condition. Increasing ML COP velocity was significantly associated with increasing MEP amplitude (r=0.68, p<0.001), but decreasing SICI (r=0.24, p=0.03) and ICF (r=-0.54, p<0.001). Our results show that both corticospinal and M1 excitability in standing are scaled in proportion to ML task difficulty.
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Referent control of the orientation of posture and movement in the gravitational field. Exp Brain Res 2017; 236:381-398. [PMID: 29164285 DOI: 10.1007/s00221-017-5133-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Accepted: 11/13/2017] [Indexed: 10/18/2022]
Abstract
This study addresses the question of how posture and movement are oriented with respect to the direction of gravity. It is suggested that neural control levels coordinate spatial thresholds at which multiple muscles begin to be activated to specify a referent body orientation (RO) at which muscle activity is minimized. Under the influence of gravity, the body is deflected from the RO to an actual orientation (AO) until the emerging muscle activity and forces begin to balance gravitational forces and maintain body stability. We assumed that (1) during quiet standing on differently tilted surfaces, the same RO and thus AO can be maintained by adjusting activation thresholds of ankle muscles according to the surface tilt angle; (2) intentional forward body leaning results from monotonic ramp-and-hold shifts in the RO; (3) rhythmic oscillation of the RO about the ankle joints during standing results in body swaying. At certain sway phases, the AO and RO may transiently overlap, resulting in minima in the activity of multiple muscles across the body. EMG kinematic patterns of the 3 tasks were recorded and explained based on the RO concept that implies that these patterns emerge due to referent control without being pre-programmed. We also confirmed the predicted occurrence of minima in the activity of multiple muscles at specific body configurations during swaying. Results re-affirm previous rejections of model-based computational theories of motor control. The role of different descending systems in the referent control of posture and movement in the gravitational field is considered.
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Zhang L, Turpin NA, Feldman AG. Threshold position control of anticipation in humans: a possible role of corticospinal influences. J Physiol 2017; 595:5359-5374. [PMID: 28560812 DOI: 10.1113/jp274309] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2017] [Accepted: 05/26/2017] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Sudden unloading of preloaded wrist muscles elicits motion to a new wrist position. Such motion is prevented if subjects unload muscles using the contralateral arm (self-unloading). Corticospinal influences originated from the primary motor cortex maintain tonic influences on motoneurons of wrist muscles before sudden unloading but modify these influences prior to the onset and until the end of self-unloading. Results are interpreted based on the previous finding that intentional actions are caused by central, particularly corticospinal, shifts in the spatial thresholds at which wrist motoneurons are activated, thus predetermining the attractor point at which the neuromuscular periphery achieves mechanical balance with environment forces. By maintaining or shifting the thresholds, descending systems let body segments go to the equilibrium position in the respective unloading tasks without the pre-programming of kinematics or muscle activation patterns. The study advances the understanding of how motor actions in general, and anticipation in particular, are controlled. ABSTRACT The role of corticospinal (CS) pathways in anticipatory motor actions was evaluated using transcranial magnetic stimulation (TMS) of the primary motor cortex projecting to motoneurons (MNs) of wrist muscles. Preloaded wrist flexors were suddenly unloaded by the experimenter or by the subject using the other hand (self-unloading). After sudden unloading, the wrist joint involuntarily flexed to a new position. In contrast, during self-unloading the wrist remained almost motionless, implying that an anticipatory postural adjustment occurred. In the self-unloading task, anticipation was manifested by a decrease in descending facilitation of pre-activated flexor MNs starting ∼72 ms before changes in the background EMG activity. Descending facilitation of extensor MNs began to increase ∼61 ms later. Conversely, these influences remained unchanged before sudden unloading, implying the absence of anticipation. We also tested TMS responses during EMG silent periods produced by brief muscle shortening, transiently resulting in similar EMG levels before the onset and after the end of self-unloading. We found reduced descending facilitation of flexor MNs after self-unloading. To explain why the wrist excursion was minimized in self-unloading due to these changes in descending influences, we relied on previous demonstrations that descending systems pre-set the threshold positions of body segments at which muscles begin to be activated, thus predetermining the equilibrium point to which the system is attracted. Based on this notion, a more consistent explanation of the kinematic, EMG and descending patterns in the two types of unloading is proposed compared to the alternative notion of direct pre-programming of kinematic and/or EMG patterns.
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Affiliation(s)
- Lei Zhang
- Center for Interdisciplinary Research in Rehabilitation (CRIR), Institut de réadaptation Gingras-Lindsay de Montréal and Jewish Rehabilitation Hospital, Laval, Quebec, Canada.,Department of Neuroscience, University of Montréal, Quebec, Canada
| | - Nicolas A Turpin
- Center for Interdisciplinary Research in Rehabilitation (CRIR), Institut de réadaptation Gingras-Lindsay de Montréal and Jewish Rehabilitation Hospital, Laval, Quebec, Canada.,Department of Neuroscience, University of Montréal, Quebec, Canada
| | - Anatol G Feldman
- Center for Interdisciplinary Research in Rehabilitation (CRIR), Institut de réadaptation Gingras-Lindsay de Montréal and Jewish Rehabilitation Hospital, Laval, Quebec, Canada.,Department of Neuroscience, University of Montréal, Quebec, Canada
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Feldman AG, Levin MF. Spatial control of reflexes, posture and movement in normal conditions and after neurological lesions. J Hum Kinet 2016; 52:21-34. [PMID: 28149391 PMCID: PMC5260515 DOI: 10.1515/hukin-2015-0191] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/01/2016] [Indexed: 11/24/2022] Open
Abstract
Control of reflexes is usually associated with central modulation of their sensitivity (gain) or phase-dependent inhibition and facilitation of their influences on motoneurons (reflex gating). Accumulated empirical findings show that the gain modulation and reflex gating are secondary, emergent properties of central control of spatial thresholds at which reflexes become functional. In this way, the system pre-determines, in a feedforward and task-specific way, where, in a spatial domain or a frame of reference, muscles are allowed to work without directly prescribing EMG activity and forces. This control strategy is illustrated by considering reflex adaptation to repeated muscle stretches in healthy subjects, a process associated with implicit learning and generalization. It has also been shown that spasticity, rigidity, weakness and other neurological motor deficits may have a common source - limitations in the range of spatial threshold control elicited by neural lesions.
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Affiliation(s)
- Anatol G. Feldman
- Department of Neuroscience, University of Montreal, Montreal, Quebec, Canada
- Centre for Interdisciplinary Research in Rehabilitation (CRIR), Montreal, Quebec, Canada
| | - Mindy F. Levin
- School of Physical and Occupational Therapy, McGill University, Montreal, Quebec, Canada
- Centre for Interdisciplinary Research in Rehabilitation (CRIR), Montreal, Quebec, Canada
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Feldman AG. Active sensing without efference copy: referent control of perception. J Neurophysiol 2016; 116:960-76. [PMID: 27306668 PMCID: PMC5009211 DOI: 10.1152/jn.00016.2016] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Accepted: 06/06/2016] [Indexed: 11/22/2022] Open
Abstract
Although action and perception are different behaviors, they are likely to be interrelated, as implied by the notions of perception-action coupling and active sensing. Traditionally, it has been assumed that the nervous system directly preprograms motor commands required for actions and uses a copy of them called efference copy (EC) to also influence our senses. This review offers a critical analysis of the EC concept by identifying its limitations. An alternative to the EC concept is based on the experimentally confirmed notion that sensory signals from receptors are perceived relative to referent signals specified by the brain. These referents also underlie the control of motor actions by predetermining where, in the spatial domain, muscles can work without preprogramming how they should work in terms of motor commands or EC. This approach helps solve several problems of action and explain several sensory experiences, including position sense and the sense that the world remains stationary despite changes in its retinal image during eye or body motion (visual space constancy). The phantom limb phenomenon and other kinesthetic illusions are also explained within this framework.
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Affiliation(s)
- Anatol G Feldman
- Department of Neuroscience and Institute of Biomedical Engineering, University of Montreal, Montreal, QC, Canada; and Center for Interdisciplinary Research in Rehabilitation of Greater Montreal (CRIR), Montreal, QC, Canada
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Turpin NA, Levin MF, Feldman AG. Implicit learning and generalization of stretch response modulation in humans. J Neurophysiol 2016; 115:3186-94. [PMID: 27052586 DOI: 10.1152/jn.01143.2015] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 03/30/2016] [Indexed: 11/22/2022] Open
Abstract
Adaptation of neural responses to repeated muscle stretching likely represents implicit learning to minimize muscle resistance to perturbations. To test this hypothesis, the forearm was placed on a horizontal manipulandum. Elbow flexors or extensors compensated an external load and were stretched by 20° or 70° rotations. Participants were instructed not to intervene by intentionally modifying the muscle resistance elicited by stretching. In addition to phasic stretch reflexes (SRs), muscle stretching was associated with inhibitory periods (IPs) in the ongoing muscle activity starting at minimal latencies of ∼35 ms. The SR amplitude decreased dramatically across 5-12 trials and was not restored after a resting period of 3-5 min, despite the increase in stretch amplitude from 20° to 70°, but IPs remained present. When SRs were suppressed, stretching of originally nonstretched, antagonist muscles initiated after the rest period showed immediate SR suppression while IPs remained present in the first and subsequent trials. Adaptation to muscle stretching thus includes features characteristic of implicit learning such as memory consolidation and generalization. Adaptation may be achieved by central shifts in the threshold positions at which muscles begin to be activated. Shifts are thought to be prepared in advance and triggered with stretch onset. Threshold position resetting provides a comprehensive explanation of the results in the broader context of the control of posture, movement, and motor learning in the healthy and damaged nervous system.
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Affiliation(s)
- Nicolas A Turpin
- Department of Neurosciences, University of Montreal, Montreal, Quebec, Canada; Institute of Biomedical Engineering, University of Montreal, Montreal, Quebec, Canada; Center for Interdisciplinary Research in Rehabilitation (CRIR) of Greater Montreal, Montreal, Quebec, Canada
| | - Mindy F Levin
- School of Physical and Occupational Therapy, McGill University, Montreal, Quebec, Canada; and Center for Interdisciplinary Research in Rehabilitation (CRIR) of Greater Montreal, Montreal, Quebec, Canada
| | - Anatol G Feldman
- Department of Neurosciences, University of Montreal, Montreal, Quebec, Canada; Institute of Biomedical Engineering, University of Montreal, Montreal, Quebec, Canada; Center for Interdisciplinary Research in Rehabilitation (CRIR) of Greater Montreal, Montreal, Quebec, Canada
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Latash ML. Fifty Years of Physics of Living Systems. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 957:81-103. [PMID: 28035561 DOI: 10.1007/978-3-319-47313-0_5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The equilibrium-point hypothesis and its more recent version, the referent configuration hypothesis, represent the physical approach to the neural control of action. This hypothesis can be naturally combined with the idea of hierarchical control of movements and of synergic organization of the abundant systems involved in all actions. Any action starts with defining trajectories of a few referent coordinates for a handful of salient task-specific variables. Further, referent coordinates at hierarchically lower levels emerge down to thresholds of the tonic stretch reflex for the participating muscles. Stability of performance with respect to salient variables is reflected in the structure of inter-trial variance and phenomena of motor equivalence. Three lines of recent research within this framework are reviewed. First, synergic adjustments of the referent coordinate and apparent stiffness have been demonstrated during finger force production supporting the main idea of control with referent coordinates. Second, the notion of unintentional voluntary movements has been introduced reflecting unintentional drifts in referent coordinates. Two types of unintentional movements have been observed with different characteristic times. Third, this framework has been applied to studies of impaired movements in neurological patients. Overall, the physical approach searching for laws of nature underlying biological movement has been highly stimulating and productive.
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Affiliation(s)
- Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, Rec. Hall-267, University Park, Pennsylvania, 16802, USA.
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Levin MF. Deficits in spatial threshold control of muscle activation as a window for rehabilitation after brain injury. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 826:229-49. [PMID: 25330894 DOI: 10.1007/978-1-4939-1338-1_14] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Mindy F Levin
- School of Physical and Occupational Therapy, McGill University, 3654 Promenade SirWilliam Osler, Montreal, QC, H3G 1Y5, Canada,
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Motor control and position sense: action-perception coupling. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 826:17-31. [PMID: 25330882 DOI: 10.1007/978-1-4939-1338-1_2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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Feldman AG, Ilmane N, Sangani S, Raptis H, Esmailzadeh N. Action-perception coupling in kinesthesia: a new approach. Neuropsychologia 2013; 51:2590-9. [PMID: 24036358 DOI: 10.1016/j.neuropsychologia.2013.09.013] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Revised: 09/02/2013] [Accepted: 09/04/2013] [Indexed: 11/28/2022]
Abstract
According to recent findings, intentional motor actions are controlled by resetting the referent position, R, at which neuromuscular elements, including reflexes, begin to act. It is suggested that somatosensory afferents inform the brain about the deviation (P) of body segments from the centrally set referent position. To perceive the actual position (Q) of body segments and form the position sense (PS), the central and afferent signals are combined: Q=R+P. In previous studies, the R has been shown to remain invariant during involuntary changes in the wrist position elicited by sudden unloading of muscles, suggesting that only the afferent component is responsible for the PS during this reflex. In contrast, the central PS component, R, is predominantly responsible for PS during intentional motion in isotonic conditions. We tested the hypothesis that the R and P are interchangeable PS components such that involuntary changes in wrist position elicited by the unloading reflex can easily be reproduced by making intentional changes in wrist position in isotonic conditions, in the absence of vision. The PS rule also suggests that PS is independent of sense of effort, which was tested by asking subjects to reproduce elbow joint angles under different constant loads. We also tested the hypothesis that tendon vibration may elicit motion that may not be perceived by subjects (no-motion illusion). These hypotheses were confirmed in three experiments. It is concluded that the R and P are additive components of PS and that, contrary to the conventional view, PS is independent of the sense of effort or efference copy. The PS rule also explains kinesthetic illusions and the phantom limb phenomenon. This study advances the understanding of action-perception coupling in kinesthesia.
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Affiliation(s)
- Anatol G Feldman
- Department of Neurosciences, University of Montreal, Montreal, PQ, Canada H3S 2J4; Centre for Interdisciplinary Research in Rehabilitation (CRIR), Institut de réadaptation Gingras-Lindsay de Montréal, 6300 Darlington, Montreal, PQ, Canada H3S 2J4; Jewish Rehabilitation Hospital, Laval, PQ, Canada.
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Bilateral coupling facilitates recovery of rhythmical movements from perturbation in healthy and post-stroke subjects. Exp Brain Res 2013; 227:263-74. [DOI: 10.1007/s00221-013-3509-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2012] [Accepted: 04/02/2013] [Indexed: 10/26/2022]
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Nishikawa KC, Monroy JA, Powers KL, Gilmore LA, Uyeno TA, Lindstedt SL. A Molecular Basis for Intrinsic Muscle Properties: Implications for Motor Control. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 782:111-25. [DOI: 10.1007/978-1-4614-5465-6_6] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
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Mullick AA, Musampa NK, Feldman AG, Levin MF. Stretch reflex spatial threshold measure discriminates between spasticity and rigidity. Clin Neurophysiol 2012; 124:740-51. [PMID: 23146713 DOI: 10.1016/j.clinph.2012.10.008] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Revised: 10/02/2012] [Accepted: 10/02/2012] [Indexed: 10/27/2022]
Abstract
OBJECTIVE Muscle spasticity following stroke has been shown to result from limitations in the range of regulation of the tonic reflex spatial threshold (ST), i.e., the joint angle at which the stretch reflex begins to act due to descending and segmental influences on motoneurons. The purpose of this study was to determine whether spasticity due to stroke and rigidity due to parkinsonism can be discriminated based on the ST measure. METHODS Elbow muscles were stretched at different velocities in healthy, stroke (spasticity) and parkinsonism (rigidity) subjects. The elbow angle at which muscle activation began for each stretch velocity (dynamic ST) and the velocity sensitivity of the ST were measured. Dynamic ST values extrapolated to zero velocity defined the tonic ST. RESULTS Compared to healthy subjects, spasticity and rigidity were associated with a decrease in the range of central regulation of tonic STs. STs were hypersensitive in spastic muscles and either hypo- or inversely sensitive to stretch velocity in rigid muscles. CONCLUSIONS ST characteristics discriminate between neurological deficits of muscle tone. SIGNIFICANCE Results suggest that spasticity and rigidity result from deficits in descending facilitatory control combined with deficits in dynamic fusimotor or/and presynaptic control of Ia inputs to motoneurons.
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Affiliation(s)
- Aditi A Mullick
- School of Physical and Occupational Therapy, McGill University, Canada
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Ilmane N, Sangani S, Feldman AG. Corticospinal control strategies underlying voluntary and involuntary wrist movements. Behav Brain Res 2012; 236:350-358. [PMID: 22983216 DOI: 10.1016/j.bbr.2012.09.008] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2012] [Revised: 09/06/2012] [Accepted: 09/08/2012] [Indexed: 10/27/2022]
Abstract
The difference between voluntary and involuntary motor actions has been recognized since ancient times, but the nature of this difference remains unclear. We compared corticospinal influences at wrist positions established before and after voluntary motion with those established before and after involuntary motion elicited by sudden removal of a load (the unloading reflex). To minimize the effect of motoneuronal excitability on the evaluation of corticospinal influences, motor potentials from transcranial magnetic stimulation of the wrist motor cortex area were evoked during an EMG silent period produced by brief muscle shortening. The motoneuronal excitability was thus equalized at different wrist positions. Results showed that the unloading reflex was generated in the presence of a corticospinal drive, rather than autonomously by the spinal cord. Although the tonic EMG levels were substantially different, the corticospinal influences remained the same at the pre- and post-unloading wrist positions. These influences however changed when subjects voluntarily moved the wrist to another position. Previous studies showed that the corticospinal system sets the referent position (R) at which neuromuscular posture-stabilizing mechanisms begin to act. In self-initiated actions, the corticospinal system shifts the R to relay these mechanisms to a new posture, thus converting them from mechanisms resisting to those assisting motion. This solves the classical posture-movement problem. In contrast, by maintaining the R value constant, the corticospinal system relies on these posture-stabilizing mechanisms to allow involuntary responses to occur after unloading. Thus, central control strategies underlying the two types of motor actions are fundamentally different.
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Affiliation(s)
- Nabil Ilmane
- Département de Physiologie, Université de Montréal; Centre for Interdisciplinary Research in Rehabilitation (CRIR), Institut de réadaptation Gingras-Lindsay de Montréal and Jewish Rehabilitation Hospital,Laval, PQ, Canada
| | - Samir Sangani
- Département de Physiologie, Université de Montréal; Centre for Interdisciplinary Research in Rehabilitation (CRIR), Institut de réadaptation Gingras-Lindsay de Montréal and Jewish Rehabilitation Hospital,Laval, PQ, Canada
| | - Anatol G Feldman
- Département de Physiologie, Université de Montréal; Centre for Interdisciplinary Research in Rehabilitation (CRIR), Institut de réadaptation Gingras-Lindsay de Montréal and Jewish Rehabilitation Hospital,Laval, PQ, Canada.
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