Evidence of a preprogrammed deactivation of the hamstring muscles for triggering rapid changes of posture in humans

Normal subjects were asked to make rapid flexions of the legs from a stationary initial standing posture in a self-paced mode. Because this movement implicates a rapid change in posture, questions were asked about the type of central command which must include the rupture of the erect posture and the accomplishment of the goal directed movement. Movements of the different segments of the body were recorded and analyzed using the optoelectronic ELITE system. Electromyographic (EMG) activities of 8 muscles of the lower limb on one side were recorded, rectified and integrated. The time relationships of the different EMG signals (activation or deactivation) were analyzed with respect to selecte…

Does order and timing in performance of imagined and actual movements affect the motor imagery process? The duration of walking and writing task.

The purpose of the present study was to investigate the effects on the duration of imagined movements of changes in timing and order of performance of actual and imagined movement. Two groups of subjects had to actually execute and imagine a walking and a writing task. The first group first executed 10 trials of the actual movements (block A) and then imagined the same movements at different intervals: immediately after actual movements (block I-1) and after 25 min (I-2), 50 min (I-3) and 75 min (I-4) interval. The second group first imagined and then actually executed the tasks. The duration of actual and imagined movements, recorded by means of an electronic stopwatch operated by the subj…

''Forward to the past''

Carlini, Alessandro | Actis-Grosso, Rossana | Stucchi, Natale | Pozzo, Thierry; International audience; ''Our daily experience shows that the CNS is a highly efficient machine to predict the effect of actions into the future; are we so efficient also in reconstructing the past of an action? Previous studies demonstrated we are more effective in extrapolating the final position of a stimulus moving according to biological kinematic laws. Here we address the complementary question: are we more effective in extrapolating the starting position (SP) of a motion following a biological velocity profile? We presented a dot moving upward and corresponding to vertical arm movements that were masked i…

A methodology for assessing the effect of correlations among muscle synergy activations on task-discriminating information

Delis, Ioannis | Berret, Bastien | Pozzo, Thierry | Panzeri, Stefano; International audience; ''Muscle synergies have been hypothesized to be the building blocks used by the central nervous system to generate movement. According to this hypothesis, the accomplishment of various motor tasks relies on the ability of the motor system to recruit a small set of synergies on a single-trial basis and combine them in a task-dependent manner. It is conceivable that this requires a fine tuning of the trial-to-trial relationships between the synergy activations. Here we develop an analytical methodology to address the nature and functional role of trial-to-trial correlations between synergy activation…

Aging Affects the Mental Rotation of Left and Right Hands

BACKGROUND:Normal aging significantly influences motor and cognitive performance. Little is known about age-related changes in action simulation. Here, we investigated the influence of aging on implicit motor imagery. METHODOLOGY/PRINCIPAL FINDINGS:Twenty young (mean age: 23.9+/-2.8 years) and nineteen elderly (mean age: 78.3+/-4.5 years) subjects, all right-handed, were required to determine the laterality of hands presented in various positions. To do so, they mentally rotated their hands to match them with the hand-stimuli. We showed that: (1) elderly subjects were affected in their ability to implicitly simulate movements of the upper limbs, especially those requiring the largest amplit…

Hand trajectories of vertical arm movements in one- G and zero- G environments

The purpose of the present experiment was to study the way in which the central nervous system (CNS), represents gravitational force during vertical arm pointing movements. Movements in upward (against gravity) and downward (with gravity) directions, with two different mass loads (hand empty and with a hand-held 0.5-kg weight) were executed by eight subjects in a normal gravitational environment. Movements by two cosmonauts, in the two directions, were also tested in a state of weightlessness. Analyses focused upon finger trajectories in the saggital plane. Subjects in a normal gravitational environment showed curved paths for both directions and weight conditions. In addition, downward mov…

Cortical Areas Involved in Vertical Saccades With a 3 Teslas Functional Mri

Static postural control in children with developmental dyslexia

Correspondence to: Service d’Ophtalmologie, CHU de Dijon, 3 rue du Faubourg Raines, F-21000 Dijon, France. Tel.: +33 3 80 24 68 74; fax: +33 3 80 24 11 39.; International audience; The present investigation tries to better understand potential association and causal relationship between phonological and postural impairment due to developmental dyslexia. The study included 50 boys with developmental dyslexia and selected on the basis of their overall reading difficulties, and 42 control boys. Body sway during a quite standing posture eye open and eye closed on a force platform were tested in the two groups of subjects that were between 10 and 13 years of age. Analysis of classical parameters…

Hand trajectory formation during whole body reaching movements in man.

End-effector trajectory formation was studied during a reaching movement using the whole body. The movements of various parts of the body were measured with the optoelectronic ELITE system. Wrist reaching movement paths showed noticeable curvatures. The analysis of various marker onset latencies revealed that the wrist was the last to move, always after the head, knee or trunk, suggesting a subordinate role of the focal component with respect to the primary role of the equilibrium component. These results suggest that reaching wrist movements are subjected to whole-body equilibrium constraints in addition to constraints placed upon end-effector kinematics or the dynamic optimization of uppe…

Effects of loss of metatarsophalangeal joint mobility on gait in rheumatoid arthritis patients

Objective. To evaluate the effects of loss of range of motion (ROM) of the metatarsophalangeal (MTP) joint on the kinematic parameters of walking in rheumatoid arthritis (RA) patients. Methods. Inclusion of RA patients with inactive disease, no synovitis of the inferior limb and reduced ROM of the MTP joints. Evaluation of the ROM of the MTP dorsal and plantar flexion, and gait analysis using a three-dimensional computerized movement analysis. Calculation of gait parameters and maximal flexion and extension of the hips and knees during walking. Analysis 1 compared the ROM of dorsal and plantar flexion in patients with or without walking pain; 2 compared the gait parameters between patients …

Effects of movement direction upon kinematic characteristics of vertical arm pointing movements in man

Vertical arm pointing movements in two directions (upwards and downwards), imposing two different loads (unload and 0.5 kg) and speeds (normal and fast) have been studied in six subjects. Movements were recorded using an optoelectronic system. Data analysis concentrated upon finger-tip kinematics. Significant effects of movement direction were recorded upon velocity profiles. The acceleration time, computed relative to total movement time, was greater for downward movements than for upward movements. In contrast however, no effects of load or speed were observed. Movement time was not affected by movement direction or load, for both speeds tested. These results suggest different planning pr…

Comparison of actual and imagined execution of whole-body movements after a long exposure to microgravity

Five cosmonauts were tested 30 days before a six-month space flight and also on the 2nd and the 6th day after their return to Earth. Cosmonauts performed and imagined a task that involved climbing two stairs to step onto a platform, jumping down with both feet and walking normally for a distance of 4 m. Durations of actual and imagined movements were measured by an electronic stopwatch. Results indicated that cosmonauts performed actual and imagined movements with similar durations before and after the space flight. However, the 2nd day after their return to Earth, cosmonauts significantly increased the durations of both actual and imagined movements. The durations of the imagined and actua…

Motion perception in early glaucoma

Purpose: The aim of our study was to underline the changes in the movement perception for early glaucoma. Our working hypothesis consisted in inquiring if the impairment of the magnocellular pathway may modify the movement perception capabilities in the visual field, more particularly in its peripheral area.Methods: We included 14 healthy subjects and 14 patients with early primary open angle glaucoma. A moving target was presented on a semicircular screen (1.8 m diameter); participants were asked to localize the Ending Point (EP) of each movement. Each stimulus consisted in a white dot (0,72° of diameter) moving horizontally with the imposed velocity profile. Two different laws of motion w…

Action tunes body dimension in space: evidences from non-use and overuse

Finisguerra, Alessandra | Bassolino, Michela | Serino, Andrea | Pozzo, Thierry; International audience

Sensorimotor adaptation of point-to-point arm movements after spaceflight: the role of internal representation of gravity force in trajectory planning.

International audience; After an exposure to weightlessness, the central nervous system operates under new dynamic and sensory contexts. To find optimal solutions for rapid adaptation, cosmonauts have to decide whether parameters from the world or their body have changed and to estimate their properties. Here, we investigated sensorimotor adaptation after a spaceflight of 10 days. Five cosmonauts performed forward point-to-point arm movements in the sagittal plane 40 days before and 24 and 72 h after the spaceflight. We found that, whereas the shape of hand velocity profiles remained unaffected after the spaceflight, hand path curvature significantly increased 1 day after landing and return…

Prolonged exposure to microgravity modifies limb endpoint kinematics during the swing phase of human walking

Many neurophysiological and behavioural studies suggested that the lower limb endpoint might be a centrally represented variable within the gravity reference frame and effectively controlled during the locomotion. This investigation examines the effects of prolonged exposure to microgravity upon lower limb endpoint kinematics. Seven cosmonauts were tested before and the 2nd day after a 6 month orbital mission. The spatio-temporal patterns of the limb extremity (malleolus) were analysed during the swing phase of the walk using a motion analysis system. Paths and velocity profiles of endpoint displacements were computed and compared for both the pre- and post-flight walking sessions. The resu…

Quantitative assessment of stereotyped and challenged locomotion after lesion of the striatum: a 3D kinematic study in rats.

Background Although the striatum is in position to regulate motor function, the role of the structure in locomotor behaviour is poorly understood. Therefore, a detailed analysis of locomotion- and obstacle avoidance-related parameters was performed after unilateral lesion of the striatum in rats. Methods and Results Using the three dimensional motion capture technology, kinematics of walking and clearing obstacles, head and body orientation were analyzed before and up to 60 days after the lesion. Recordings were performed in treadmill running rats with or without obstacles attached to the treadmill belt. The lesion, which was induced by the direct injection of the mitochondrial toxin malona…

Do equilibrium constraints modulate postural reaction when viewing imbalance?

Abstract Action observation and action execution are tightly coupled on a neurophysiological and a behavioral level, such that visually perceiving an action can contaminate simultaneous and subsequent action execution. More specifically, observing a model in postural disequilibrium was shown to induce an increase in observers’ body sway. Here we reciprocally questioned the role of observers’ motor system in the contagion process by comparing participants’ body sway when watching displays of antero-posterior vs. lateral imbalance. Indeed, during upright standing, biomechanical constraints differ along the antero-posterior (A-P) and medio-lateral (M-L) axes; hence an impact of observers’ post…

''The role of action in space and body representations''

Bassolino, Michela | Finisguerra, Alessandra | Pozzo, Thierry; International audience

Similar planning strategies for whole-body and arm movements performed in the sagittal plane

The present paper looks for kinematic similarities between whole-body and arm movements executed in the sagittal plane. Eight subjects performed sit-to-stand (STS) and back-to-sit (BTS) movements at their preferred speed in the sagittal plane. Kinematics analysis focused on shoulder motion revealed that STS was composed of a straight, forward displacement followed by a curved, upward displacement while BTS was characterized by a curved, downward and straight, backward displacement. Curvature of the upward displacement was significantly greater than the downward one. Analysis of shoulder-velocity profiles showed that movement duration was significantly longer for BTS compared with STS and th…

Publisher Correction: Anticipatory postural adjustments during joint action coordination

There is a current claim that humans are able to effortlessly detect others' hidden mental state by simply observing their movements and transforming the visual input into motor knowledge to predict behaviour. Using a classical paradigm quantifying motor predictions, we tested the role of vision feedback during a reach and load-lifting task performed either alone or with the help of a partner. Wrist flexor and extensor muscle activities were recorded on the supporting hand. Early muscle changes preventing limb instabilities when participants performed the task by themselves revealed the contribution of the visual input in postural anticipation. When the partner performed the unloading, a co…

Daily modulation of the speed–accuracy trade-off

International audience; Goal-oriented arm movements are characterized by a balance between speed and accuracy. The relation between speed and accuracy has been formalized by Fitts’ law and predicts a linear increase in movement duration with task constraints. Up to now this relation has been investigated on a short-time scale only, that is during a single experimental session, although chronobiological studies report that the motor system is shaped by circadian rhythms. Here, we examine whether the speed–accuracy trade-off could vary during the day. Healthy adults carried out arm-pointing movements as accurately and fast as possible toward targets of different sizes at various hours of the …

Improvement and generalization of arm motor performance through motor imagery practice

This study compares the improvement and generalization of arm motor performance after physical or mental training in a motor task requiring a speed-accuracy tradeoff. During the pre- and post-training sessions, 40 subjects pointed with their right arm as accurately and as fast as possible toward targets placed in the frontal plane. Arm movements were performed in two different workspaces called right and left paths. During the training sessions, which included only the right path, subjects were divided into four training groups (n = 10): (i) the physical group, subjects overtly performed the task; (ii) the mental group, subjects imagined themselves performing the task; (iii) the active cont…

Continuous, bilateral Achilles' tendon vibration is not detrimental to human walk.

Sensory feedback from the moving limbs contributes to the regulation of animal and human locomotion. However, the question of the specific role of the various modalities is still open. Further, functional loss of leg afferent fibres due to peripheral neuropathy does not always lead to major alteration in the gait pattern. In order to gain further insight on proprioceptive control of human gait, we applied vibratory tendon stimulation, known to recruit spindle primary afferent fibres, to both triceps surae muscles during normal floor walk. This procedure would disturb organisation and execution of walking, especially if spindles fire continuously and subjects are blindfolded. Vibration induc…

Children with Dyslexia Have Altered Cross-Modal Processing Linked to Binocular Fusion. A Pilot Study

Patrick Quercia, 1 Thierry Pozzo, 2 Alfredo Marino, 3 Anne Laure Guillemant, 1 Céline Cappe, 4 Nicolas Gueugneau 1 1Université de Bourgogne, Dijon, Campus Universitaire, UFR STAPS, BP 27877, F-21078 Dijon, France; INSERM U1093, Cognition, Action et Plasticité Sensorimotrice, Dijon F-21078, France; 2Center for Translational Neurophysiology, Istituto Italiano di Tecnologia, Ferrara, Italy; 3Private Consultant, Vicenza 36100, Italie; 4Brain and Cognition Research Center, CerCo, CNRS UMR 5549, Toulouse, FranceCorrespondence: Patrick QuerciaMedical Office, 15 Rue du Clair Matin, Beaune 21200, FranceTel +33 6 87822741Email doc.quercia@gmail.comIntroduction: The ca…

<p>Children with Dyslexia Have Altered Cross-Modal Processing Linked to Binocular Fusion. A Pilot Study</p>

Introduction The cause of dyslexia, a reading disability characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities, is unknown. A considerable body of evidence shows that dyslexics have phonological disorders. Other studies support a theory of altered cross-modal processing with the existence of a pan-sensory temporal processing deficit associated with dyslexia. Learning to read ultimately relies on the formation of automatic multisensory representations of sounds and their written representation while eyes fix a word or move along a text. We therefore studied the effect of brief sounds on vision with a modification of binocular f…

''Motor Resonance Mechanisms Are Preserved In Alzheimer's Disease Patients''

Bisio, A. | Casteran, M. | Ballay, Y. | Manckoundia, P. | Mourey, F. | Pozzo, T.; International audience; ''This study aimed to better characterize the sensorimotor mechanisms underlying motor resonance, namely the relationship between motion perception and movement production in patients suffering from Alzheimer's disease (AD). This work first gives a kinematic description of AD patients' upper limb movements, then it presents a simple paradigm in which a dot with different velocities is moved in front of the participant who is instructed to point to its final position when it stopped. AD patients' actions, as well as healthy elderly participants, were similarly influenced by the dot veloc…

Visual gravity influences arm movement planning.

International audience; When submitted to a visuomotor rotation, subjects show rapid adaptation of visually guided arm reaching movements, indicated by a progressive reduction in reaching errors. In this study, we wanted to make a step forward by investigating to what extent this adaptation also implies changes into the motor plan. Up to now, classical visuomotor rotation paradigms have been performed on the horizontal plane, where the reaching motor plan in general requires the same kinematics (i.e., straight path and symmetric velocity profile). To overcome this limitation, we considered vertical and horizontal movement directions requiring specific velocity profiles. This way, a change i…

Decline in motor prediction in elderly subjects: right versus left arm differences in mentally simulated motor actions.

This study investigates the effects of age upon the temporal features of executed and imagined movements performed with the dominant (D; right) and nondominant (ND; left) arms. Thirty right-handed subjects were divided into two groups: (i) the young group (n=15; mean age: 22.5+/-2.5 years) and (ii) the elderly group (n=15; mean age: 70.2+/-2.2 years). The motor task, involving arm pointing movements among four pairs of targets (.5cm, 1cm, 1.5cm and 2cm), imposed strong spatiotemporal constraints. During overt performance, young and elderly subjects modulated movement duration according to the size of targets, despite the fact that movement speed decreased with age as well as in the left arm…

Cerebral Dynamics during the Observation of Point-Light Displays Depicting Postural Adjustments

Objective: As highly social creatures, human beings rely part of their skills of identifying, interpreting, and predicting the actions of others on the ability of perceiving biological motion. In the present study, we aim to investigate the electroencephalographic (EEG) cerebral dynamics involved in the coding of postural control and examine whether upright stance would be codified through the activation of the temporal-parietal cortical network classically enrolled in the coding of biological motion. Design: We registered the EEG activity of 12 volunteers while they passively watched point light displays (PLD) depicting quiet stable (QB) and an unstable (UB) postural situations and their r…

Boosting Action Observation and Motor Imagery to Promote Plasticity and Learning

Neural Plasticity, 2018

Functional Electrical Stimulation Alters the Postural Component of Locomotor Activity in Healthy Humans

International audience; Knowledge of the effects of Functional Electrical Stimulation (FES) of different intensity on postural stability during walking in healthy subjects is necessary before these relationships in patients with postural disorders can be assessed and understood. We examined healthy subjects in Control group walking on a treadmill for 40 min and in FES group provided with 30 min of stimulation, which intensity increased every 10 min. The main difference between Control and FES group was the progressive increase of trunk oscillations in sagittal, frontal, and horizontal planes and an increase of relative stance duration in parallel with FES intensity increase. Both Control an…

Space-by-Time Modular Decomposition Effectively Describes Whole-Body Muscle Activity During Upright Reaching in Various Directions

The modular control hypothesis suggests that motor commands are built from precoded modules whose specific combined recruitment can allow the performance of virtually any motor task. Despite considerable experimental support, this hypothesis remains tentative as classical findings of reduced dimensionality in muscle activity may also result from other constraints (biomechanical couplings, data averaging or low dimensionality of motor tasks). Here we assessed the effectiveness of modularity in describing muscle activity in a comprehensive experiment comprising 72 distinct point-to-point whole-body movements during which the activity of 30 muscles was recorded. To identify invariant modules o…

Arm end-point trajectories under normal and micro-gravity environments.

Abstract The purpose of the present experiment was to study the way in which the CNS represents gravitational force during vertical arm pointing movements. Movements in upward and downward directions were executed by two cosmonauts in normal-gravity and weightlessness. Analyses focused upon finger kinematics in the sagittal plane. In normal-gravity, downward direction movements showed smaller curvatures and greater relative times to peak velocity ( AT MT ) when compared with upward direction movements. Data from the weightlessness experiments showed that whilst downward movements decreased their curvature during space flight, curvatures of upward movements changed slightly. Furthermore, AT …

Effects of kinematics constraints on hand trajectory during whole-body lifting tasks

Trajectories of the hands and whole-body center of mass were studied during whole-body lifting tasks. The movements of different parts of the body were monitored with the ELITE system. Subjects were instructed to lift to shoulder height an object placed at one of two distances (5-45 cm) before them on the floor. The lifts were performed both with and without kinematics constraints (i.e. to produce a straight hand trajectory while lifting, and to lift without any instructions, respectively). Hand trajectories were roughly straight when performed under the constrained condition, but curved when performed without instruction. Hand velocity curves showed bell-shaped profiles. In both groups, bo…

Anticipatory Postural Adjustments and kinematic arm features when postural stability is manipulated

International audience; Beyond the classical paradigm that presents the Anticipatory Postural Adjustments (APAs) as a manner to create forces that counteract disturbances arising from the moving segment during a pointing task, there is a controversial discussion about the role APAs to facilitate the movement and perform a task accurately. In addition, arm kinematics features are classically used to infer the content of motor planning for the execution and the control of arm movements, The present study aimed to disentangle the conflicting role of APAs during an arm-pointing task in which the subjects reach a central diode that suddenly turns on, while their postural stability was manipulate…

Le projet SimAction

Resume Le projet SimAction avait pour but de developper de nouvelles methodes d’aide au reentrainement moteur en exploitant les mecanismes de couplage entre perception et execution de l’action. L’objectif etait de creer des outils d’entrainement par observation complementaires aux methodes conventionnelles basees sur le reentrainement physique. Les outils developpes devaient dans un premier temps etre orientes vers une population âgee. Ce projet a permis un travail en interaction entre des physiologistes du mouvement, des cliniciens, des equipes de recherche specialisees en informatique, traitement de l’image, science cognitive et ergonomie, ainsi que deux industriels. Au cours de ce projet…

Proprioception oculaire et dyslexie de développement

But de l’etude L’objectif de ce travail est d’evaluer la presence d’anomalies de la proprioception constituant le syndrome de deficience posturale au sein d’une population d’enfants atteints de dyslexie de developpement. Patients et methodes Soixante patients de sexe masculin, âges en moyenne de 11 ans et 9 mois, ont ete inclus dans l’etude. Le diagnostic de dyslexie de developpement a ete confirme par un examen neuropsychologique a l’aide d’epreuves standardisees. Apres un interrogatoire visant a rechercher les signes fonctionnels evocateurs d’une anomalie proprioceptive, les patients ont fait l’objet d’un examen clinique ophtalmologique et postural en 9 etapes precisement decrites. Result…

Does the coordination between posture and movement during human whole-body reaching ensure center of mass stabilization?

The whole-body center of mass (CoM) has been classically regarded as the stabilized reference value for human voluntary movements executed upon a fixed base of support. Axial synergies (opposing displacements of head and trunk with hip segments) are believed to minimize antero-posterior (A/P) CoM displacements during forward trunk movements. It is also widely accepted that anticipatory postural adjustments (APAs) create forces of inertia that counteract disturbances arising from the moving segment(s). In the present study, we investigated CoM stabilization by axial synergies and APAs during a whole-body reaching task. Subjects reached towards an object placed on the ground in front of them …

Encoding of human action in Broca's area.

International audience; Broca's area has been considered, for over a century, as the brain centre responsible for speech production. Modern neuroimaging and neuropsychological evidence have suggested a wider functional role is played by this area. In addition to the evidence that it is involved in syntactical analysis, mathematical calculation and music processing, it has recently been shown that Broca's area may play some role in language comprehension and, more generally, in understanding actions of other individuals. As shown by functional magnetic resonance imaging, Broca's area is one of the cortical areas activated by hand/mouth action observation and it has been proposed that it may …

Direction-dependent activation of the insular cortex during vertical and horizontal hand movements

International audience; The planning of any motor action requires a complex multisensory processing by the brain. Gravity - immutable on Earth - has been shown to be a key input to these mechanisms. Seminal fMRI studies performed during visual perception of falling objects and self-motion demonstrated that humans represent the action of gravity in parts of the cortical vestibular system; in particular, the insular cortex and the cerebellum. However, little is known as to whether a specific neural network is engaged when processing non-visual signals relevant to gravity. We asked participants to perform vertical and horizontal hand movements without visual control, while lying in a 3T-MRI sc…

Mentally represented motor actions in normal aging. I. Age effects on the temporal features of overt and covert execution of actions.

The present study examines the temporal features of overt and covert actions as a function of normal aging. In the first experiment, we tested three motor tasks (walking, sit-stand-sit, arm pointing) that did not imply any particular spatiotemporal constraints, and we compared the duration of their overt and covert execution in three different groups of age (mean ages: 22.5, 66.2 and 73.4 years). We found that the ability of generating motor images did not differentiate elderly subjects from young subjects. Precisely, regarding overt and covert durations, subjects presented similarities for the walking and pointing tasks and dissimilarities for the stand-sit-stand task. Furthermore, the tim…

The embodied consciousness

Consciousness is a polysemous concept including among others self-awareness (of his body ...), the awareness of the environment around us, the awareness of the other or even narrative awareness (a kind of inner monologue that can be part of more extended temporalities). To this list could be added the consciousness attached to each sensory organ in which visual perception would be overrepresented. Compared to the consciousness linked to vestibular sensory signals or proprioception (if however these can generate separate consciousnesses), "visual awareness" lends itself more easily to introspection. In Occident, all these consciousnesses generally refer to a knowledge of self by duplication …

Dissociating effect of upper limb non-use and overuse on space and body representations.

Accurate and updated representations of the space where the body acts, i.e. the peripersonal space (PPS), and the location and dimension of body parts (body representation, BR) are essential to perform actions. Because both PPS and BR are involved in motor execution and display the same plastic proprieties after the use of a tool to reach far objects, it has been suggested that they overlap in a unique representation of the body in a space devoted to action. Here we determined whether manipulating actions in space, without modifying body metrics, i.e. through immobilization, induces a dissociation of the plastic properties of PPS and BR. In 39 healthy subjects we evaluated PPS and BR for th…

Tri-dimensional and triphasic muscle organization of whole-body pointing movements.

Previous kinematic and kinetic studies revealed that, when accomplishing a whole-body pointing task beyond arm's length, a modular and flexible organization could represent a robust solution to control simultaneously target pointing and equilibrium maintenance. Here, we investigated the underlying mechanisms that produce such a coordinative kinematic structure. We monitored the activity of a large number of muscles spread throughout subjects' bodies while they performed pointing movements beyond arm's length, either with or without imposition of postural or pointing constraints. Analyses revealed that muscle signals lied on a tri-dimensional hyper-plane and were temporally organized accordi…

Measuring Aksak Rhythm and Synchronization in Transylvanian Village Music by Using Motion Capture

<p>Techniques based on motion capture can be useful in <span><span style="font-size: x-small;">analyzing a wide range of musical styles and practices</span></span>: in this case, Transylvanian village music. We focused on a repertoire known as “Gypsy songs of sorrow”, played by professional Gypsy musicians during parties and celebrations of their own community. Two parameters were the object of study: rhythmic duration, and synchronization between musicians (a violinist and a viola player). Results show that rhythm is a local variant of <em>aksak</em> and is based on two duration units (S=short, L=long) which respect the formula 2:3 < S:L &am…

''Alterations with Movement Duration in the Kinematics of a Whole Body Pointing Movement''

Casteran, Matthieu | Manckoundia, Patrick | Pozzo, Thierry | Thomas, Elizabeth; International audience; ''Our aim was to investigate how the organization of a whole body movement is altered when movement duration (MD) is varied. Subjects performed the same whole body pointing movement over long, normal and short MDs. The kinematic trajectories were then analyzed on a normalized time base. A principal components analysis (PCA) revealed that the degree of coordination between the elevation angles of the body did not change with MD. This lack of significant differences in the coordination was interesting given that small spatial and temporal differences were observed in the individual kinemati…

Aging affects the mental simulation/planning of the "rising from the floor" sequence.

We investigated the effect of aging on the ability to mentally simulate/plan a complex sequential action of the whole body, namely "rising from the floor". Forty-four non-demented elderly people (mean age: 85.2±5.5 years) and 20 young people (mean age: 26.6±4.9 years) were included in the study. They were required to put in order six images representing the main movements necessary to get up from a sitting position on the floor. We showed that older subjects had poorer performance-both in terms of proportion of success and response time-than their younger counterparts. These results are in line with previous findings showing age-related alterations in action simulation/action planning proce…

Improvement of motor performance by observational training in elderly people.

Action observation influences action execution; this strong coupling is underlined by an overlap of cortical areas activated during observation and execution of action, and is dependent of specific motor experience. The goal of the present study was to verify if action observation can be used for rehabilitation of elderly people. We tested this question with a protocol of observational practice of 2 frequently used movements: walking and sit-to-stand/back-to-sit. Both tasks were performed at normal and maximal speed before and after training, by 8 elderly subjects. Observational practice led to an increase in walking velocity via an increase in step frequency, but without modification of st…

Modular Control of Pointing beyond Arm's Length

Hand reaching and bipedal equilibrium are two important functions of the human motor behavior. However, how the brain plans goal-oriented actions combining target reaching with equilibrium regulation is not yet clearly understood. An important question is whether postural control and reaching are integrated in one single module or controlled separately. Here, we show that postural control and reaching motor commands are processed by means of a modular and flexible organization. Principal component and correlation analyses between pairs of angles were used to extract global and local coupling during a whole-body pointing beyond arm's length. A low-dimensional organization of the redundant ki…

<p>Alteration in binocular fusion modifies audiovisual integration in children</p>

Background: In the field of multisensory integration, vision is generally thought to dominate audiovisual interactions, at least in spatial tasks, but the role of binocular fusion in audiovisual integration has not yet been studied. Methods: Using the Maddox test, a classical ophthalmological test used to subjectively detect a latent unilateral eye deviation, we checked whether an alteration in binocular vision in young patients would be able to change audiovisual integration. The study was performed on a group of ten children (five males and five females aged 11.3±1.6 years) with normal binocular vision, and revealed a visual phenomenon consisting of stochastic disappearanceof part of a vi…

Influence of Transcranial Direct Current Stimulation on Psychomotor Symptoms in Major Depression

Background: Transcranial direct current stimulation (tDCS) applied to the left dorsolateral prefrontal cortex (dlPFC) might be a promising treatment strategy for depression. As disturbances in psychomotor activity are one of the key features of unipolar depression are, we aimed to evaluate the behavioral effects of ten tDCS sessions over a 5-day period on psychomotor retardation in depressed patients. Methods: Twenty-three treatment-resistant depressed patients received either active or sham anodal tDCS to the left dorsolateral prefrontal cortex (2 mA, 10 sessions over 1 week). Psychomotor functioning was registered by means of observer ratings (Salp&ecirc

Effect of fatigue on the precision of a whole-body pointing task.

We addressed the issue of the possible degradation of the aiming precision of a whole-body pointing task, when movement coordination is deranged by selective fatigue of the postural task component. The protocol involved continuous repetition (0.1 Hz frequency) of rapid whole-body pointing trials toward a target located beyond arm length, starting from stance and requiring knee flexion. Six healthy human subjects repeated the trials until exhaustion. Such repetition led to electromyography signs of fatigue in rectus femoris (active in body lowering and raising), but not in deltoid (prime mover for arm reaching component). Rectus femoris fatigue affected the equilibrium control strategy, sinc…

''Modulation of Anticipatory Postural Activity For Multiple Conditions of A Whole-body Pointing Task''

Tolambiya, A. | Chiovetto, E. | Pozzo, T. | Thomas, E.; International audience; ''This is a study on associated postural activities during the anticipatory segments of a multijoint movement. Several previous studies have shown that they are task dependant. The previous studies, however, have mostly been limited in demonstrating the presence of modulation for one task condition, that is, one aspect such as the distance of the target or the direction of reaching. Real-life activities like whole-body pointing, however, can vary in several ways. How specific is the adaptation of the postural activities for the diverse possibilities of a whole-body pointing task? We used a classification paradig…

Visual inference of arm movement is constrained by motor representations

International audience; Several studies support the idea that motion inference is strongly motor dependent. In the present study, we address the role of biomechanical constraints in motion prediction and how this implicit knowledge can interfere in a spatial prediction task. Right-handed (RHS) and left-handed subjects (LHS) had to estimate the final position of a horizontal arm movement in which the final part of the trajectory was hidden. Our study highlighted a direction effect: end point prediction accuracy was better to infer the final position of horizontal motion directed toward the median line of human body. This finding suggests that the spatial prediction of end point is mapped ont…

The representation of gravitational force during drawing movements of the arm

The purpose of the present experiment was to study the way in which the central nervous system (CNS) represents gravitational force (GF) during vertical drawing movements of the arm. Movements in four different directions: (a) upward vertical (0 degrees), (b) upward oblique (45 degrees), (c) downward vertical (180 degrees) and (d) downward oblique (135 degrees), and at two different speeds, normal and fast, were executed by nine subjects. Data analysis focused upon arm movement kinematics in the frontal plane and gravitational torques (GTs) exerted around the shoulder joint. Regardless of movement direction, subjects showed straight-line paths for both speed conditions. In addition, movemen…

Does the centre of mass remain stable during complex human postural equilibrium tasks in weightlessness?

In normal gravity conditions the execution of voluntary movement involves the displacement of body segments as well as the maintenance of a stable reference value for equilibrium control. It has been suggested that centre of mass (CM) projection within the supporting base (BS) is the stabilised reference for voluntary action, and is conserved in weightlessness. The purpose of this study was to determine if the CM is stabilised during whole body reaching movements executed in weightlessness. The reaching task was conducted by two cosmonauts aboard the Russian orbital station MIR, during the Franco-Russian mission ALTAIR, 1993. Movements of reflective markers were recorded using a videocamera…

Sensory functions and Alzheimer's disease: a multi-disciplinary approach

Relations between sensory functions and Alzheimer's disease are still under-explored. To understand them better, the Fondation Médéric Alzheimer has brought together a multi-disciplinary expert group. Aristote's five senses must be enhanced by today's knowledge of proprioception, motor cognition and pain perception. When cognition breaks down, the person with dementia perceives the world around her with her sensory experience, yet is unable to integrate all this information to understand the context. The treatment of multiple sensory inputs by the brain is closely linked to cognitive processes. Sensory deficits reduce considerably the autonomy of people with dementia in their daily life and…

Rémanence de l’effet vibratoire durant la marche humaine

Les effets de la vibration musculaire peuvent generalement persister apres la fin de la stimulation. L’extinction de ce post-effet fut etudie durant la marche humaine. Six sujets ont realise une tâche locomotrice (six pas successifs) en condition temoin, et apres la vibration (70 Hz) bilaterale des tendons d’Achille. La frequence du pas est augmentee (diminution de la duree de la phase d’appui) alors que la longueur de l’enjambee tend a decroitre. La duree relative de la phase d’appui evolue vers les valeurs normales a mesure des repetitions. Ces resultats demontrent que les effets de la vibration perseverent apres la fin de la stimulation. De plus, en raison de la dynamique du processus de…

Initial information prior to movement onset influences kinematics of upward arm pointing movements

International audience; To elaborate a motor plan and perform online control in the gravity field, the brain relies on priors and multisensory integration of information. In particular, afferent and efferent inputs related to the initial state are thought to convey sensorimotor information to plan the upcoming action. Yet it is still unclear to what extent these cues impact motor planning. Here we examined the role of initial information on the planning and execution of arm movements. Participants performed upward arm movements around the shoulder at three speeds and in two arm conditions. In the first condition, the arm was outstretched horizontally and required a significant muscular comm…

Voluntary Imitation in Alzheimer’s Disease Patients

International audience; Although Alzheimer's disease (AD) primarily manifests as cognitive deficits, the implicit sensorimotor processes that underlie social interactions, such as automatic imitation, seem to be preserved in mild and moderate stages of the disease, as is the ability to communicate with other persons. Nevertheless, when AD patients face more challenging tasks, which do not rely on automatic processes but on explicit voluntary mechanisms and require the patient to pay attention to external events, the cognitive deficits resulting from the disease might negatively affect patients' behavior. The aim of the present study was to investigate whether voluntary motor imitation, i.e.…

Motor Resonance Mechanisms during Action Imitation in Depression

Objectives Major depressive disorder has been associated with impairments in social cognition. However, studies exploring the processing of social information focused on facial discrimination. The aim of this study was to better characterize the sensorimotor mechanisms underlying motor resonance in depressed patients. Method Twenty-three right-handed patients meeting DSM-IV criteria for unipolar depression were compared to 14 matched healthy controls. In a simple imitation paradigm, the kinematic features of movements in natural condition were compared to those of motions performed after the observation of a moving dot. Reaction time and pointing velocity were considered to evaluate if the …

Kinematic features of movement tunes perception and action coupling

How do we extrapolate the final position of hand trajectory that suddenly vanishes behind a wall? Studies showing maintenance of cortical activity after objects in motion disappear suggest that internal model of action may be recalled to reconstruct the missing part of the trajectory. Although supported by neurophysiological and brain imaging studies, behavioural evidence for this hypothesis is sparse. Further, in humans, it is unknown if the recall of internal model of action at motion observation can be tuned with kinematic features of movement. Here, we propose a novel experiment to address this question. Each stimulus consisted of a dot moving either upwards or downwards, and correspond…

Cognitive demands impair postural control in developmental dyslexia: A negative effect that can be compensated

Children with developmental dyslexia exhibit delayed reading abilities and various sensori-motor deficits. The way these various symptoms interact remain poorly understood. The objective of this study was twofold. First, we aimed to investigate whether postural control was impaired in dyslexic children when cognitive demands are increased. Second, we checked whether this effect could be reduced significantly by a treatment aiming to recalibrate ocular proprioception. Twelve dyslexic and fifteen treated dyslexic children (>3 months of treatment) were compared with twelve non-dyslexic children in two conditions (mean age: 11.6 ± 2.1, 12.5 ± 1.5 and 10.6 ± 1.7 years respectively). In a first c…

Motor recruitment during action observation: Effect of interindividual differences in action strategy

Abstract Visual processing of other’s actions is supported by sensorimotor brain activations. Access to sensorimotor representations may, in principle, provide the top-down signal required to bias search and selection of critical visual features. For this to happen, it is necessary that a stable one-to-one mapping exists between observed kinematics and underlying motor commands. However, due to the inherent redundancy of the human musculoskeletal system, this is hardly the case for multijoint actions where everyone has his own moving style (individual motor signature—IMS). Here, we investigated the influence of subject’s IMS on subjects’ motor excitability during the observation of an actor…

The sensorimotor and cognitive integration of gravity.

In order to demonstrate that gravity is not only a load acting locally and continuously on the body limbs, but is also used by higher levels of the nervous system as a dynamic orienting reference for the elaboration of the motor act, a review of several experiments conducted both in 1 g and 0 g are presented. During various locomotor tasks, the strategy that consists of stabilizing the head with respect to gravity illustrates one of the solutions used by the CNS to optimize the control of dynamic equilibrium. A question which remains to be solved when considering experimental results obtained in weightlessness concerns, however, the maintenance of motor schema that has evolved under normal …

Kinematic and dynamic processes for the control of pointing movements in humans revealed by short-term exposure to microgravity.

The generation of accurate motor commands requires implicit knowledge of both limb and environmental dynamics. The action of gravity on moving limb segments must be taken into account within the motor command, and may affect the limb trajectory chosen to accomplish a given motor task. Exactly how the CNS deals with these gravitoinertial forces remains an open question. Does the CNS measure gravitational forces directly, or are they accommodated in the motor plan by way of internal models of physical laws? In this study five male subjects participated. We measured kinematic and dynamic parameters of upward and downward arm movements executed at two different speeds, in both normal Earth grav…

Contrôle du centre de masse lors de pointage de tout le corps chez le sujet jeune et âgé sain

Quantitative evaluation of muscle synergy models: a single-trial task decoding approach.

Delis, Ioannis | Berret, Bastien | Pozzo, Thierry | Panzeri, Stefano; International audience; ''Muscle synergies, i.e., invariant coordinated activations of groups of muscles, have been proposed as building blocks that the central nervous system (CNS) uses to construct the patterns of muscle activity utilized for executing movements . Several efficient dimensionality reduction algorithms that extract putative synergies from electromyographic (EMG) signals have been developed. Typically, the quality of synergy decompositions is assessed by computing the Variance Accounted For (VAF). Yet, little is known about the extent to which the combination of those synergies en codes task discriminating…

Prism adaptation by mental practice

International audience; The prediction of our actions and their interaction with the external environment is critical for sensorimotor adaptation. For instance, during prism exposure, which deviates laterally our visual field, we progressively correct movement errors by combining sensory feedback with forward model sensory predictions. However, very often we project our actions to the external environment without physically interacting with it (e.g., mental actions). An intriguing question is whether adaptation will occur if we imagine, instead of executing, an arm movement while wearing prisms. Here, we investigated prism adaptation during mental actions. In the first experiment, participa…

The role of anticipatory postural adjustments during whole body forward reaching movements

THE purpose of this study was to examine the role of anticipatory postural adjustments (APAs) in the execution of forward oriented whole body reaching movements. From the standing position, eight healthy subjects were asked to reach an object placed at 45 cm from the feet, at both naturally paced and fast speeds. Electromyographic signals of six antagonistic muscles were analysed in conjunction with centre of mass (CM) displacements, centre of foot pressure displacements and resultant ground reaction forces. Results revealed that APAs created necessary angular momentum of body segments for effective task execution. These results suggest that APAs can initiate movements conducted from a fixe…

Investigating centre of mass stabilisation as the goal of posture and movement coordination during human whole body reaching

In the light of experimental results showing significant forward centre of mass (CoM) displacements within the base of support, this study investigated if whole body reaching movements can be executed whilst keeping the CoM fixed in the horizontal axis. Using kinematic simulation techniques, angular configurations were recreated from experimental data imposing two constraints: a constant horizontal position of the CoM and an identical trajectory of the hand to grasp an object. The comparison between recorded and simulated trials showed that stabilisation of the CoM was associated with greater backward hip displacements, which became more marked with increasing object distance. This was in c…

Interhemispheric inhibition during mental actions of different complexity.

International audience; Several investigations suggest that actual and mental actions trigger similar neural substrates. Yet, neurophysiological evidences on the nature of interhemispheric interactions during mental movements are still meagre. Here, we asked whether the content of mental images, investigated by task complexity, is finely represented in the inhibitory interactions between the two primary motor cortices (M1s). Subjects' left M1 was stimulated by means of transcranial magnetic stimulation (TMS) while they were performing actual or mental movements of increasing complexity with their right hand and exerting a maximum isometric force with their left thumb and index. Thus, we sim…

''Investigating reduction of dimensionality during single-joint elbow movements: a case study on muscle synergies''

Chiovetto, Enrico | Berret, Bastien | Delis, Ioannis | Panzeri, Stefano | Pozzo, Thierry; International audience; ''A long standing hypothesis in the neuroscience community is that the central nervous system (CNS) generates the muscle activities to accomplish movements by combining a relatively small number of stereotyped patterns of muscle activations, often referred to as" muscle synergies." Different definitions of synergies have been given in the literature. The most well-known are those of synchronous, time-varying and temporal muscle synergies. Each one of them is based on a different mathematical model used to factor some EMG array recordings collected during the execution of variety…

Deciphering the functional role of spatial and temporal muscle synergies in whole-body movements

AbstractVoluntary movement is hypothesized to rely on a limited number of muscle synergies, the recruitment of which translates task goals into effective muscle activity. In this study, we investigated how to analytically characterize the functional role of different types of muscle synergies in task performance. To this end, we recorded a comprehensive dataset of muscle activity during a variety of whole-body pointing movements. We decomposed the electromyographic (EMG) signals using a space-by-time modularity model which encompasses the main types of synergies. We then used a task decoding and information theoretic analysis to probe the role of each synergy by mapping it to specific task …

Training the Motor Cortex by Observing the Actions of Others During Immobilization

International audience; Limb immobilization and nonuse are well-known causes of corticomotor depression. While physical training can drive the recovery from nonuse-dependent corticomotor effects, it remains unclear if it is possible to gain access to motor cortex in alternative ways, such as through motor imagery (MI) or action observation (AO). Transcranial magnetic stimulation was used to study the excitability of the hand left motor cortex in normal subjects immediately before and after 10 h of right arm immobilization. During immobilization, subjects were requested either to imagine to act with their constrained limb or to observe hand actions performed by other individuals. A third gro…

Does Observation of Postural Imbalance Induce a Postural Reaction?

Import JabRef | WosArea Life Sciences and Biomedicine - Other Topics; International audience; Background: Several studies bring evidence that action observation elicits contagious responses during social interactions. However automatic imitative tendencies are generally inhibited and it remains unclear in which conditions mere action observation triggers motor behaviours. In this study, we addressed the question of contagious postural responses when observing human imbalance. Methodology/Principal Findings: We recorded participants' body sway while they observed a fixation cross (control condition), an upright point-light display of a gymnast balancing on a rope, and the same point-light di…

Kinematics of obstacle clearance in the rat

Although the rat has become the favourite animal model in preclinical research on locomotion, studies designed to assess the strategy used by rats to avoid obstacle are lacking. Using an optoelectronic 3D motion analysis system, we therefore, compared the step pattern, timing and length variables of locomotor cycles, trajectories and joint angles of limbs when rats step between and over obstacles (3 cm-high) fixed on a treadmill belt (25 cm/s). Motion in all four limbs of adult animals with an initial age of 11 weeks was serially recorded for a period of 10 weeks. The results showed that obstacle clearance is associated with the reorganization of the basic step pattern resulting in increase…

An ensemble analysis of electromyographic activity during whole body pointing with the use of support vector machines.

Import JabRef | WosArea Life Sciences and Biomedicine - Other Topics; International audience; We explored the use of support vector machines (SVM) in order to analyze the ensemble activities of 24 postural and focal muscles recorded during a whole body pointing task. Because of the large number of variables involved in motor control studies, such multivariate methods have much to offer over the standard univariate techniques that are currently employed in the field to detect modifications. The SVM was used to uncover the principle differences underlying several variations of the task. Five variants of the task were used. An unconstrained reaching, two constrained at the focal level and two …

Simulating mechanical consequences of voluntary movement upon whole-body equilibrium: the arm-raising paradigm revisited.

Voluntary arm-raising movement performed during the upright human stance position imposes a perturbation to an already unstable bipedal posture characterised by a high body centre of mass (CoM). Inertial forces due to arm acceleration and displacement of the CoM of the arm which alters the CoM position of the whole body represent the two sources of disequilibrium. A current model of postural control explains equilibrium maintenance through the action of anticipatory postural adjustments (APAs) that would offset any destabilising effect of the voluntary movement. The purpose of this paper was to quantify, using computer simulation, the postural perturbation due to arm raising movement. The m…

The Relation between Geometry and Time in Mental Actions

Mental imagery is a cognitive tool that helps humans take decisions by simulating past and future events. The hypothesis has been advanced that there is a functional equivalence between actual and mental movements. Yet, we do not know whether there are any limitations to its validity even in terms of some fundamental features of actual movements, such as the relationship between space and time. Although it is impossible to directly measure the spatiotemporal features of mental actions, an indirect investigation can be conducted by taking advantage of the constraints existing in planar drawing movements and described by the two-thirds power law (2/3PL). This kinematic law describes one of th…

Energy-related optimal control accounts for gravitational load: comparing shoulder, elbow, and wrist rotations.

International audience; Gaveau J, Berret B, Demougeot L, Fadiga L, Pozzo T, Papaxanthis C. Energy-related optimal control accounts for gravitational load: comparing shoulder, elbow, and wrist rotations. J Neurophysiol 111: 4-16, 2014. First published October 16, 2013; doi: 10.1152/jn.01029.2012.-We permanently deal with gravity force. Experimental evidences revealed that moving against gravity strongly differs from moving along the gravity vector. This directional asymmetry has been attributed to an optimal planning process that optimizes gravity force effects to minimize energy. Yet, only few studies have considered the case of vertical movements in the context of optimal control. What kin…

Gait-dependent motor memory facilitation in covert movement execution

In the current study, we examined whether sensorimotor information stored in short-term memory may influence the temporal features between overt and covert execution of human locomotor movements and, furthermore, to examine to what extent such influence may depend on the ongoing gait activity. The subjects (n=20) who participated in the experiment were separated in two groups and instructed to walk (overt execution) or imagine walking (covert execution) along three locomotor paths: horizontal, uphill and downhill. The subjects of the first group, labeled in block, performed all the covert trials before executing the corresponding overt trials, while the subjects of the second group, labeled…

Identification of Spatial-Temporal Muscle Synergies from EMG Epochs of Various Durations: A Time-Warped Tensor Decomposition

Extraction of muscle synergies from electromyography (EMG) recordings relies on the analysis of multi-trial muscle activation data. To identify the underlying modular structure, dimensionality reduction algorithms are usually applied to the EMG signals. This process requires a rigid alignment of muscle activity across trials that is typically achieved by the normalization of the length of each trial. However, this time-normalization ignores important temporal variability that is present on single trials as result of neuromechanical processes or task demands. To overcome this limitation, we propose a novel method that simultaneously aligns muscle activity data and extracts spatial and tempor…

FUNCTIONAL EFFECT OF SHORT-TERM IMMOBILIZATION: KINEMATIC CHANGES AND RECOVERY ON REACHING-TO-GRASP

Abstract Although previous investigations agree in showing significant cortical modifications related to short-term limb immobilization, little is known about the functional changes induced by non-use. To address this issue, we studied the kinematic effect of 10 h of hand immobilization. In order to prevent any movement, right handed healthy participants wore on their dominant hand a soft bandage. They were requested to perform the same reaching-to-grasping task immediately after immobilization, 1 day before (baseline 1) and in other two following days without non-use (baseline 2 and baseline 3). While no differences were found among baseline conditions, an increase of the total duration of…

Standing up from a chair as a dynamic equilibrium task: a comparison between young and elderly subjects.

The purpose of this study was to analyze and compare the features of center of mass (CoM) control along anterior/posterior axis in young and elderly subjects during sit-to-stand (STS). From a sitting position, seven healthy young subjects and seven healthy elderly subjects were asked to stand up from a chair under different experimental conditions (visual conditions: normal and blindfolded; speed: normal and as fast as possible). Analysis of results was based upon the concept of a “dynamic equilibrium area” (DEA), which in turn identified the dynamic limits of balance. The results showed that both the maximal CoM velocity in the horizontal axis and the CoM velocity at the instant of seat-of…

The Inactivation Principle: Mathematical Solutions Minimizing the Absolute Work and Biological Implications for the Planning of Arm Movements

An important question in the literature focusing on motor control is to determine which laws drive biological limb movements. This question has prompted numerous investigations analyzing arm movements in both humans and monkeys. Many theories assume that among all possible movements the one actually performed satisfies an optimality criterion. In the framework of optimal control theory, a first approach is to choose a cost function and test whether the proposed model fits with experimental data. A second approach (generally considered as the more difficult) is to infer the cost function from behavioral data. The cost proposed here includes a term called the absolute work of forces, reflecti…