Anatol Feldman

• PhD, DSc
• Professor at Université de Montréal

Background After a central nervous system lesion, the ability to control muscle activation and relaxation in specific joint ranges may be impaired. The underlying mechanism of this sensorimotor impairment is related to a decreased ability to regulate the tonic stretch reflex threshold (TSRT) through descending and peripheral control processes. In d...

Background Coordination between arm movements and postural adjustments is crucial for reaching-while-stepping tasks involving both anticipatory postural adjustments (APAs) and compensatory movements to effectively propel the whole-body forward so that the hand can reach the target. Stroke impairs the ability to coordinate the action of multiple bod...

The referent control theory (RCT) for action and perception is an advanced formulation of the equilibrium-point hypothesis. The RCT suggests that rather than directly specifying the desired motor outcome, the nervous system controls action and perception indirectly by setting the values of parameters of physical and physiological laws. This is done...

Human locomotion may result from monotonic shifts in the referent position, R, of the body in the environment. R is also the spatial threshold at which muscles can be quiescent but are activated depending on the deflection of the current body configuration Q from R. Shifts in R are presumably accomplished with the participation of proprioceptive an...

We tested the hypothesis that the ipsilateral corticospinal system, like the contralateral corticospinal system, controls the threshold muscle length at which wrist muscles and the stretch reflex begin to act during holding tasks. Transcranial magnetic stimulation was applied over the right primary motor cortex in 21 healthy subjects holding a smoo...

Unperturbed human locomotion presumably results from feedforward shifts in stable body equilibrium in the environment, thus avoiding falling and subsequent catching considered in alternative theories of locomotion. Such shifts are achieved by relocation of the referent body configuration at which multiple muscle recruitment begins. Rather than bein...

Background Motor performance is a complex process controlled in task-specific spatial frames of reference (FRs). Movements can be made within the framework of the body (egocentric FR) or external space (exocentric FR). People with stroke have impaired reaching, which may be related to deficits in movement production in different FRs. Objective To...

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 i...

Conventional explanations of the vestibulo-ocular reflex (VOR), eye and head movements are re-visited by considering two alternative frameworks addressing the question of how the brain controls motor actions. Traditionally, biomechanical and/or computational frameworks reflect the views of several prominent scholars of the past, including Helmholtz...

Objectives The corticospinal system (CS) regulates muscle activation through shifts in muscle-level tonic stretch-reflex thresholds (TSRT). This ability is impaired in stroke and contributes to sensorimotor impairments such as spasticity. We determined the role of CS in elbow flexor activity regulation in healthy and post-stroke subjects. We also d...

Reaching from standing requires simultaneous adjustments of focal and postural task elements. We investigated the ability of people with stroke to stabilize the endpoint trajectory while maintaining balance during standing reaches. Nineteen stroke and 11 age-equivalent healthy subjects reached toward a target (n=30 trials) located beyond arm length...

Previous studies suggest that visual information is essential for balance and stability of locomotion. We investigated whether visual deprivation is met with active reactions tending to minimize worsening balance and stability during walking in humans. We evaluated effects of vision on kinetic characteristics of walking on a treadmill-ground reacti...

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 ref...

Feldman AG. Indirect, referent control of motor actions underlies directional tuning of neurons.

To evaluate normal and impaired control of anticipatory grip force (GF) modulation, we compared GF production during horizontal arm movements in healthy and post-stroke subjects, and, based on a physiologically feasible dynamic model, determined referent control variables underlying the GF–arm motion coordination in each group. 63% of 13 healthy an...

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, th...

Objectives: Deficits in regulation of tonic stretch reflex thresholds (TSRTs) after stroke occur in elbow flexors and extensors leading to spasticity in specific joint ranges. Threshold deregulation may also be responsible for other deficits such as abnormal activation of passively shortening muscles. Goals were to characterize activation of short...

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 gravit...

Previous motor learning studies based on adapting movements of the hemiparetic arm in stroke subjects have not accounted for spasticity occurring in specific joint ranges (spasticity zones), resulting in equivocal conclusions about learning capacity. We compared the ability of participants with stroke to rapidly adapt elbow extension movements to c...

Objectives: Voluntary movements post-stroke are affected by abnormal muscle activation due to exaggerated stretch reflexes (SRs). We examined the ability of post-stroke subjects to regulate SRs in spastic muscles. Methods: Elbow flexor and extensor EMGs and joint angle were recorded in 13 subjects with chronic post-stroke spasticity. Muscles wer...

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 mod...

Purpose/Hypothesis : The ability of people to re-learn motor tasks after stroke involving the more-affected spastic upper limb (UL) is an essential component of motor recovery. The studies involving the more-affected side have failed to account for the presence of angular zones in which spasticity interferes with movement production. Previous studi...

Postural stabilization is provided by stretch reflexes, intermuscular reflexes, and intrinsic muscle properties. Taken together, these posture-stabilizing mechanisms resist deflections from the posture at which balance of muscle and external forces is maintained. Empirical findings suggest that for each muscle, these mechanisms become functional at...

New & noteworthy: Motor actions may result from minimization of the deflection of the actual body configuration from the centrally specified referent body configuration, in the limits of neuromuscular and environmental constraints. The minimization process may maintain reaching trajectory and accuracy regardless of the number of body segments invo...

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...

Background: A major challenge in stroke rehabilitation is determining effective strategies for optimizing upper limb motor recovery. Reaching accuracy and stability is ensured by appropriate spatiotemporal arm-trunk coordination. We hypothesized that coordination would be disrupted in stroke and related to damage in descending command signals rath...

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 pre-programs motor commands required for actions and uses a copy of them called efference copy (EC) to also influe...

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 instructe...

In this book, I have described a theory of action and perception—referent control. Strictly based on experimental material, the theory places action and perception in the context of physical laws to offer solutions of several classical problems in behavioral neuroscience. This approach also results in the rejection of theories in behavioral neurosc...

Empirical data on neural control of motor action and perception have not yet been put into the context of a coherent theory. Dr. Feldman's goal for the proposed book is to illustrate that the field is now at a stage where the data can be used to formulate some core principles that underlie action and perception and to present the foundation of a sc...

In this chapter, I will describe experiments in humans and animals supporting the notion that the nervous system exercises parametric control of motor actions (see Chap. 2). It will be demonstrated that by changing task-specific parameters, the system allows physical laws to take their course to generate motor outcome without pre-programming of EMG...

In this chapter, I will introduce the basic neurophysiological rule (BNR) to extend the explanation of the physiological origin of referent variables R, λ, and C already described for the single joint level to more global forms of referent control. These forms can be used to guide multi-muscle and multi-joint actions. One such a form—the referent a...

A specific form of parametric control described in the previous section—referent or threshold position control of motor actions—can be considered as the foundation of a physiologically feasible theory of action. As a first step towards this goal, we need to explain how electro-chemical mono- and poly-synaptic influences on α-MNs from descending and...

This quotation (http:// www. quotationspage. com/ faq. php#85) is reminiscent of the Gödel’s incompleteness theorem in mathematics: In any axiomatic system of postulates there would always be some statements the validity of which could not be established within this system (Kennedy 2011). Einstein’s quote points to similar limitations in other bran...

Some ideas outlined in this book emerged in the unique scientific atmosphere created by a group of scientists that is now known in the West as the Moscow Biological School. As an historical and scientific phenomenon, this School deserves to be described in a separate book (Berkinblit and Latash 2005; see also Stuart 2005). As a proud member of this...

The co-existence of divergent theories of action and perception is indicative of a confusion, rather than of a consensus in the understanding of basic principles of brain functioning. This situation in behavioral neurosciences is comparable to one that existed in the natural sciences before Galileo and Newton. This book is an attempt to overcome th...

The notion of referent control helps solve both problems of action as well as some problems of perception or better to say, problems of action-perception coupling since it has been recognized for over a century that perception and action are interdependent (Helmholtz 1866). Previous attempts to solve action-perception problems that will be consider...

Humans and animals can repeatedly reach the same motor goal by combining different joint rotations (motor equivalency; Lashley 1951; Bernstein 1935), an important feature allowing behavioral flexibility in everyday life. Bernstein (1967) emphasized the necessity of solving the redundancy problem by answering the question of how the nervous system c...

According to previous studies, muscles become active in response to deviations from a threshold (referent) position of body segments. To test the hypothesis that corticospinal pathways set and reset the referent position in a task-specific way, we evaluated corticospinal influences at wrist positions established before and after voluntary motion as...

When arm and trunk segments are involved in reaching for objects within arm's reach, vestibulospinal pathways compensate for trunk motion influence on arm movement. This compensatory arm-trunk synergy is characterised by a gain coefficient of 0 to 1. Vestibular patients have less efficient arm-trunk synergies and lower gains. To assess the clinical...

. By involving additional degrees of freedom, the nervous system may preserve hand trajectories when making pointing movements with or without trunk displacement. Previous studies indicate that the potential contribution of trunk movement to hand displacement for movements made within arm reach is neutralized by appropriate compensatory shoulder an...

Motor learning studies in subjects with stroke have mainly focused on the less-impaired arm to separate confounding influences of motor deficits from motor learning capabilities. One previous study assessed motor learning (error correction) in the hemiparetic arm using a one trial learning paradigm ─ rapid adaptation of arm motion to a new load. It...

The equilibrium control hypothesis (λ model) is considered with special reference to the following concepts: (a) the length-force invariant characteristic (IC) of the muscle together with central and reflex systems subserving its activity; (b) the tonic stretch reflex threshold (λ) as an independent measure of central commands descending to alpha a...

The paretic arm of subjects with stroke has a decreased ability to quickly adapt to and recover from perturbations during rhythmical arm swinging. We investigated whether bilateral coupling in the synchronous motion of two arms may facilitate the restoration of rhythmical movement of the paretic arm in subjects with chronic hemiparesis due to strok...

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 t...

Falls during walking are a major cause of injury in post-stroke individuals, and walking faster may further decrease gait stability. We compared gait stability between high-functioning post-stroke individuals and controls at matched speeds. We also evaluated the effect of a speed increase on gait stability in post-stroke individuals. Ten stroke sub...

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 lo...

Most falls in older adults occur when walking, specifically following a trip. This study investigated the short- and longer term responses of young (n = 24, 27.6 ± 4.5 yr) and older adults (n = 18, 69.1 ± 4.2 yr) to a trip during gait at comfortable speed and the role of interlimb coordination in recovery from tripping. Subjects walked on a self-pa...

This paper presents preliminary results of our ongoing work on the biomimetic muscle-like behaviour of poly(sodium acrylate) (PSA) hydrogels. Using Hill's model as a basic framework, interpenetrating network (IPN) hydrogels consisting of a contractile PSA network and an elastic poly(vinyl alcohol) PVA network were desinged. The hydrogels so formed...

Previous findings suggest that, by influencing the subthreshold state of motoneurons, the corticospinal pathways can set and reset the threshold position at which wrist muscle recruitment begins. Here we assumed that the corticospinal system can change the threshold position in a similar way before anticipated perturbation to pre-determine an appro...

Advances to the equilibrium-point (EP) theory and solutions to several classical problems of action and perception are suggested and discussed. Among them are (1) the posture-movement problem of how movements away from a stable posture can be made without evoking resistance of posture-stabilizing mechanisms resulting from intrinsic muscle and refle...

Locomotion is presumably guided by feed-forward shifts in the referent body location in the desired direction in the environment. We propose that the difference between the actual and the referent body locations is transmitted to neurons that virtually diminish this difference by appropriately changing the referent body configuration, i.e. the body...

We used the framework of the equilibrium-point hypothesis (in its updated form based on the notion of referent configuration) to investigate the multi-digit synergies at two levels of a hypothetical hierarchy involved in prehensile actions. Synergies were analyzed at the thumb-virtual finger (VF) level (VF is an imaginary digit with the mechanical...

It has previously been established that muscles become active in response to deviations from a threshold (referent) position of the body or its segments, and that intentional motor actions result from central shifts in the referent position. We tested the hypothesis that corticospinal pathways are involved in threshold position control during inten...

Dans cet article nous proposons un certain nombre d’arguments permettant de repondre a la question fondamentale : comment le systeme nerveux controle-t-il un systeme complexe constitue d’un grand nombre de muscles et d’articulations ? Nous pensons qu’il est essentiel d’examiner les problemes lies au controle moteur a partir d’un cadre theorique con...

It is known that hand transport and grasping are functionally different but spatially coordinated components of reach-to-grasp (RTG) movements. As an extension of this notion, we suggested that body segments involved in RTG movements are controlled as a coherent ensemble by a global minimization process associated with the necessity for the hand to...

We studied multi-joint coordination during tasks of transporting real and imaginary objects with two arms. One of the arms was unexpectedly arrested in one-third of trials performed. In the absence of perturbation, multi-joint synergies stabilizing the distance between the arms early and late in the movement were seen in both conditions and even we...

According to a view that has dominated the field for over a century, the brain programs muscle commands and uses a copy of these commands [efference copy (EC)] to adjust not only resulting motor action but also ongoing perception. This view was helpful in formulating several classical problems of action and perception: (1) the posture-movement prob...

This section is a collection of papers devoted to the equilibrium-point (EP) hypothesis. The first chapter (by Feldman and Levin) is a brief account of the past and present status of the hypothesis with suggestions for further development. The EP hypothesis emerged in the unique scientific atmosphere created by a group of researchers that is now kn...

This chapter is a brief account of fundamentals of the equilibrium-point hypothesis or more adequately called the threshold control theory (TCT). It also compares the TCT with other approaches to motor control. The basic notions of the TCT are reviewed with a major focus on solutions to the problems of multi-muscle and multi-degrees of freedom redu...

Marrow cavities in all bones of newborn mammals contain haematopoietic tissue and stromal microenvironment that support haematopoiesis (haematopoietic microenvironment), known as red bone marrow (BM). From the early postnatal period onwards, the haematopoietic microenvironment, mainly in tubular bones of the extremities, is replaced by mesenchymal...

We investigated intra- and inter-evaluator reliability to quantify spasticity based on the tonic stretch reflex threshold (TSRT) and the correlation between TSRT and resistance to stretch. Spasticity was evaluated in 20 subjects with chronic stroke-related spasticity using a portable device and the Modified Ashworth Scale (MAS). Evaluations were do...

Fatigue affects the capacity of muscles to generate forces and is associated with characteristic changes in EMG signals. It may also influence interjoint and intermuscular coordination. To understand better the global effects of fatigue on multijoint movement, we studied movement kinematics and EMG changes in healthy volunteers asked to hammer repe...

Abundance of muscle spindles is most likely related to gradual recruitment and functional specialization of motor units, as well as to their fundamental role in reflex intermuscular interaction and cooperation with other sensory systems. Spindle afferents per se usually convey ambiguous kinesthetic information to the brain. Experimental data indica...

The ability of dopamine replacement to restore rapid motor adjustments in Parkinson's disease (PD) was investigated. Medicated and non-medicated patients performed finger-to-nose movements while simultaneously bending the trunk forward, without vision. Trunk motion was blocked unexpectedly, necessitating rapid adjustments in arm trajectories. Patie...

The grip force holding an object between fingers usually increases before or simultaneously with arm movement thus preventing the object from sliding. We experimentally analyzed and simulated this anticipatory behavior based on the following notions. (1) To move the arm to a new position, the nervous system shifts the threshold position at which ar...

The vestibulospinal system likely plays an essential role in motor equivalence--the ability to reach the desired motor goal despite intentional or imposed changes in the number of body segments involved in the task. To test this hypothesis, we compared the ability of healthy subjects and patients with unilateral vestibular lesions (surgical acousti...

It is generally assumed that proprioceptive feedback plays a crucial role in limb posture and movement. However, the role of afferent signals from extraocular muscles (EOM) in the control of eye movement has been a matter of continuous debate. These muscles have atypical sensory receptors in several species and it has been proposed that they are no...

Introduction Optimal practice and feedback elements are essential requirements for maximal motor recovery in patients with motor deficits due to central nervous system lesions. Methods A virtual environment (VE) was created that incorporates practice and feedback elements necessary for maximal motor recovery. It permits varied and challenging prac...

The answer to the question of how the nervous system controls multiple muscles and body segments while solving the redundancy problem in choosing a unique action from the set of many possible actions is still a matter of controversy. In an attempt to clarify the answer, we review data showing that motor actions emerge from central resetting of the...

Marrow cavities in all the bones of newborn mammals contain active hematopoietic tissue, known as red bone marrow. From the early postnatal period onwards, the hematopoietic tissue, mainly in the bones of the extremities, is gradually replaced by non-hematopoietic mesenchymal cells that accumulate lipid drops, known as yellow or fatty bone marrow....

Introduction. While walking, we perceive the environment as motionless despite the shift in the visual image on the retina. In order to perceive the environmental constancy, an appropriate internal transformation of optic flow is needed. To be efficient, such sensory transformation should be initiated somewhat before the gait onset. This hypothesis...

We addressed the fundamental questions of which variables underlie the control of arm movement and how they are stored in motor memory, reproduced and modified in the process of adaptation to changing load conditions. Such variables are defined differently in two major theories of motor control (internal models and threshold control). To resolve th...

Changing the steady-state configuration of the body or its segments may be an important function of central pattern generators for locomotion and other rhythmical movements. Thereby, muscle activation, forces, and movement may emerge following a natural tendency of the neuromuscular system to achieve the current steady-state configuration. To verif...

It is usually assumed that proprioceptive feedback comes to motoneurons too late to contribute to the initial activity of agonist muscles during fast arm movements, leading to the suggestion that this feedback is only efficient in slow movements and postural control. The argument does not take into account that the changes in the motoneuronal membr...

We describe an immersive and interactive experimental protocol developed in a virtual reality environment using the CAREN system. The environment allows the user to receive enhanced feedback about the quality and outcome of varied pointing movements made in a virtual elevator. Features of the virtual environment (representation of the user's body m...

Natural laws express the relationships between certain variables called state variables. Constrained by natural laws these variables cannot be specified directly by the nervous system, as illustrated by the failure of the force control theory that relies on the idea of direct programming of kinematics and muscle torques. Natural laws include parame...

Title: Central generator oscillating between two steady states underlies rhythmic arm movements.

Work-related musculo-skeletal disorders have been previously related to movement repetition, inadequate postures, non-ergonomic environments, muscular imbalance and fatigue. However, no direct link between fatigue and injury has been experimentally shown. To address this problem, we compared the effects of fatigue and injury on the kinematics of re...

To address the question of how arm posture is controlled, we analyzed shoulder-elbow unloading responses in the horizontal plane for different directions of the initial load. The initial load, produced by a double-joint manipulandum, was suddenly diminished to 1of 12 randomly presented levels (60 to -10% of the initial load; in 6 out of 12 cases th...

It has been suggested that multijoint movements result from the specification of a referent configuration of the body. The activity of muscles and forces required for movements emerge depending on the difference between the actual and referent body configurations. We identified the referent arm configurations specified by the nervous system to brin...

Introduction: Rhythmical arm movements may be produced in a pendulum-like manner by central destabilization of the system at one equilibrium position. Alternatively, they may result from transitions between two equilibrium positions that define the spatial boundaries of movement. Methods: Standing subjects swung one or both arms from the shoulder j...