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Defective proprioceptive integration may play a role in the pathophysiology of motor symptoms in Parkinson's disease (PD). Dysfunction related to proprioceptively-evoked postural reactions in PD patients is still a controversial issue, with only a limited number of studies to date and mostly discordant results. The aims of the present study were (1) to determine whether or not the proprioceptive defect in PD underlies postural impairment and (2) whether or not deep brain stimulation of the subthalamic nucleus (STN-DBS) affects proprioceptive integration. We examined proprioceptive integration during a postural task in 13 PD patients and 12 age-matched control subjects, using a muscle-tendon vibration paradigm. Analysis of the center of pressure displacement and kinematic data indicates a greater degree of postural destabilization and a reduced ability to maintain a vertical orientation in PD. We found a significant positive effect of STN-DBS on these postural features. Our findings indicate that Parkinson patients, even in the absence of any clinical evidence of instability, falls, or freezing, use proprioceptive information for postural control less efficiently than healthy subjects. Furthermore, STN-DBS was found to improve proprioceptive integration, with positive impacts on postural orientation and balance.

Introduction NF1 children have cognitive disorders, especially in executive functions, visuospatial, and language domains, the pathophysiological mechanisms of which are still poorly understood. Materials and methods A correlation study was performed from neuropsychological assessments and brain MRIs of 38 NF1 patients and 42 controls, all right-handed, aged 8–12 years and matched in age and gender. The most discriminating neuropsychological tests were selected to assess their visuospatial, metaphonological and visuospatial working memory abilities. The MRI analyses focused on the presence and location of Unidentified Bright Objects (UBOs) (1), volume analysis (2) and diffusion analysis (fractional anisotropy and mean diffusivity) (3) of the regions of interest including subcortical structures and posterior fossa, as well as shape analysis of subcortical structures (4). The level of attention, intelligence quotient, age and gender of the patients were taken into account in the statistical analysis. Then, we studied how diffusion and volumes parameters were associated with neuropsychological characteristics in NF1 children. Results NF1 children present different brain imaging characteristics compared to the control such as (1) UBOs in 68%, (2) enlarged total intracranial volume, involving all subcortical structures, especially thalamus, (3) increased MD and decreased FA in thalamus, corpus callosum and hippocampus. These alterations are diffuse, without shape involvement. In NF1 group, brain microstructure is all the more altered that volumes are enlarged. However, we fail to find a link between these brain characteristics and neurocognitive scores. Conclusion While NF1 patients have obvious pathological brain characteristics, the neuronal substrates of their cognitive deficits are still not fully understood, perhaps due to complex and multiple pathophysiological mechanisms underlying this disorder, as suggested by the heterogeneity observed in our study. However, our results are compatible with an interpretation of NF1 as a diffuse white matter disease.

In a bimanual task, proprioception provides information about position and movement of upper arms. Developmental studies showed improvement of proprioceptive accuracy and timing adjustments of muscular events from childhood to adulthood in bimanual tasks. However, the cortical maturational changes related to bimanual coordination is not fully understood. The aim of this study was to investigate cortical correlates underlying motor planning and upper limb stabilization performance at left (C3) and right (C4) sensorimotor cortices using event-related potential (ERP) analyses. We recruited 46 participants divided into four groups (12 children: 8–10 years, 13 early adolescents: 11–13 years, 11 late adolescents: 14–16 years and 10 young adults: 20–35 years). Participants performed a bimanual load-lifting task, where the left postural arm supported the load and the right motor arm lifted the load. Maximal amplitude of elbow rotation (MA%) of the postural arm, reaction time (RT) and EMG activity of biceps brachii bilaterally were computed. Laplacian-transformed ERPs of the electroencephalographic (EEG) signal response-locked to motor arm biceps EMG activity onset were analyzed over C3 and C4. We found a developmental effect for behavioral and EEG data denoted by significant decrease of MA% and RT with age, earlier inhibition of the biceps brachii of the postural arm in adults and earlier EEG activation/inhibition onset at C3/C4. Amplitude of the negative wave at C4 was higher in children and early adolescents compared to the other groups. In conclusion, we found a maturational process in cortical correlates related to motor planning and upper limb stabilization performance with interhemispheric lateralization appearing during adolescence. Findings may serve documenting bimanual performance in children with neurodevelopmental disorders.

Developmental dyslexia (DD) and developmental coordination disorder (DCD) are distinct diagnostic disorders. However, they also frequently co-occur and may share a common etiology. It was proposed conceptually a neural network framework that explains differences and commonalities between DD and DCD through impairments of distinct or intertwined cortico-subcortical connectivity pathways. The present study addressed this issue by exploring intrinsic cortico-striatal and cortico-cerebellar functional connectivity in a large (n = 136) resting-state fMRI cohort study of 8–12-year-old children with typical development and with DD and/or DCD. We delineated a set of cortico-subcortical functional circuits believed to be associated with the brain’s main functions (visual, somatomotor, dorsal attention, ventral attention, limbic, frontoparietal control, and default-mode). Next, we assessed, using general linear and multiple kernel models, whether and which circuits distinguished between the groups. Findings revealed that somatomotor cortico-cerebellar and frontoparietal cortico-striatal circuits are affected in the presence of DCD, including abnormalities in cortico-cerebellar connections targeting motor-related regions and cortico-striatal connections mapping onto posterior parietal cortex. Thus, DCD but not DD may be considered as an impairment of cortico-subcortical functional circuits.

Sensorimotor disorders have been frequently reported in children and adults with dyslexia over the past 30 years. The present study aimed to determine the impact of sensorimotor comorbidity risks in dyslexia by investigating the functional links between phonological and sensorimotor representations in young dyslexic adults. Using 52 dyslexic participants and 58 normo-readers, we investigated whether the underlying phonological deficit, which is reported in the literature, was associated with a general impairment of sensorimotor representations of articulatory and bodily actions. Internal action representations were explored through motor imagery tasks, consisting of measuring and comparing the durations of performed or imagined actions chosen from their current repertoire of daily life activities. To detect sensorimotor deficits, all participants completed the extended version of the M-ABC 2, as a reference test. We found sensorimotor impairments in 27% of the young adult dyslexics, then considered as sensorimotor comorbid, as opposed to much less in the normo-reader group (5%). While motor slowdown, reflecting motor difficulty, was present in all dyslexic adults, motor imagery performance was impacted only in the specific dyslexic subgroup with sensorimotor impairments. Moreover, in contrast with slowness, only the comorbid subgroup showed an increased variability in execution durations. The present study highlights the importance of the quality of perception-action coupling, questions the relevance of investigating sensorimotor impairment profiles beyond phonological deficits and provides new arguments supporting the perspective of multiple deficits approaches in dyslexia.

Le controle anticipe et le controle en ligne sont les deux facettes du controle predictif, bases sur les modeles internes, qui sont suspectes d’etre impactes dans les troubles des apprentissages. Nous avons examine le controle anticipe dans une tâche bimanuelle de delestage, qui teste la coordination entre la posture du bras qui soutient le poids et le bras manipulateur qui realise le delestage, chez des enfants dyslexiques (DD) et/ou dyspraxiques (DCD), compares a des enfants au developpement typique (TD). Il ressort de cette etude une meilleure stabilisation du bras postural, basee sur une inhibition plus precoce des muscles flechisseurs au cours du delestage volontaire, traduisant ainsi l’anticipation de l’effet destabilisateur du delestage, pour l’ensemble des sujets. En revanche, seul le groupe avec une comorbidite DD/DCD, presente une anticipation des muscles flechisseurs moins precoce que les autres groupes (Cignetti et al., 2018). Ainsi cette tâche permet de reveler que sans contrainte temporelle, tous les enfants sont capables de construire une representation interne de leur action, y compris les enfants DCD. Par ailleurs, lorsque les contraintes temporelles sont tres elevees, comme dans le cas d’un apprentissage moteur en 60 essais, les enfants DCD et DD/DCD presentent des performances moins elevees. La question de la comorbidite, qui est de plus en plus renseignee dans la litterature, permet de nuancer certains resultats anterieurs et devient une veritable question en matiere d’etiologie et de remediation.

Introduction La question posee chez le jeune adulte dyslexique est de savoir si une atteinte des representations phonemiques (imprecision des representations ou difficulte d’acces) est assortie d’une atteinte plus generale des representations internes de l’action. Materiel et methodes Pour repondre a cette question, nous avons teste 45 dyslexiques et 45 normolecteurs âges de 19 a 24 ans avec un protocole d’ideation motrice assorti d’une etude detaillee du controle postural. Au prealable la motricite manuelle fine et la motricite globale ont ete evaluees au moyen du MABC2 dans sa version etendue de 3 a 17 ans, pour tous les sujets. Diverses epreuves impliquant l’ensemble du corps, les membres superieurs ou encore le systeme articulatoire ont ete proposes. Le sujet chronometre lui-meme son action qu’elle soit executee ou imaginee. Resultats Les sujets normolecteurs presentent une isochronie dans les deux situations executee et imaginee pour les epreuves de locomotion, de redressement (assis-debout), de saisie d’objet, et de repetition de phrase, ce qui atteste la robustesse de la representation interne de l’action (Chabeauti et al., 2012). Les acquisitions des sujets dyslexiques sont en cours. Discussion/conclusion Au-dela des comparaisons des durees d’execution entre les deux groupes, qui pourraient traduire un ralentissement des sujets dyslexiques, et ainsi elargir le probleme de reglage temporel du controle phonemique au controle moteur, nous cherchons a determiner si cette isochronie est affectee plus specifiquement chez certains adultes dyslexiques, presentant des troubles moteurs detectes avec le MABC2, qui pourrait traduire un deficit plus global des representations sensorimotrices.

Introduction De nombreuses etudes rapportent que la scoliose idiopathique de l’adolescent (SIA) s’accompagne d’un defaut d’integration centrale des informations sensorielles [1] , [2] , [3] , [4] . Methode Afin de mieux comprendre si les processus d’integration proprioceptive sont impactes chez les sujets atteints de SIA, nous avons explore les bases neurales de l’integration proprioceptive en IRMf de stimulation, par vibration tendineuse, chez les enfants et les adolescents au developpement typiques [5] , [6] ainsi que chez 13 adolescents atteints de SIA (Assaiante et al., en preparation). La question principale etait de savoir si les reseaux responsables de l’integration proprioceptive presentent un dysfonctionnement ou un retard de maturation dans le cas de la scoliose. Resultats Il ressort de nos etudes neurodeveloppementales que les cartes d’activation cerebrales consecutives aux vibrations tendineuses rapportent des activations similaires chez les adolescents SIA, les enfants typiques et adolescents typiques, suggerant ainsi que les principaux reseaux impliques dans la construction de la representation du corps sont actifs et preserves. Neanmoins, les adolescents SIA presentent un pattern de connectivite fonctionnelle frontostriatale et frontoparietale plus diffus que les adolescents typiques ainsi qu’une epaisseur corticale des cortex frontaux et parietaux plus importante, rappelant ainsi les caracteristiques des sujets plus jeunes. Discussion/conclusion Plutot qu’un dysfonctionnement, ces resultats semblent etre plus en faveur d’un retard de maturation des reseaux qui contribuent a construire et a reactualiser la representation du corps en action.

Anticipatory postural adjustments (APAs) cancel the destabilizing effects of movement on posture. Across development, the maturation of APAs is characterized by an accurate adjustment of the timing parameters of electromyographic (EMG) response. The study aimed at investigating the maturation of cortical oscillations involved in the improvement of APAs efficiency. Thirty-six healthy participants (8–16 yr) performed the bimanual load-lifting task in which subjects are instructed to lift a load, placed on the left forearm, with the right hand. EMG data were acquired over the biceps brachii on the postural arm to the determine EMG response onset. Electroencephalographic signals were analyzed in the time-frequency domain by convolution with complex Gaussian Morlet wavelets. Electrophysiological signature of APAs in children and adolescents consisted of a mu-rhythm desynchronization over the sensorimotor cortex contralateral to the postural arm. Across development, the mu-rhythm desynchronization was characterized by a progressive shift forward of the onset of the desynchronization, lower amplitude, and velocity. These changes occurred along with an alteration of the timing of the EMG response, as shown by an earlier onset of the flexor inhibition with increasing age. The maturational changes in the Mu-oscillations might sustain the development of APAs. A possible role of the Mu-oscillation in the generation of postural command is discussed. NEW & NOTEWORTHY Across development, our study showed a progressive shift forward of the parameters of the mu-rhythm desynchronization. These changes occurred along with an alteration of the timing parameters of the electromyographic response, as shown by an earlier onset of the flexor inhibition with increasing age. The progressive development of APAs during childhood and adolescence might therefore be sustained by maturational electrophysiological changes that include mu-rhythm oscillation modifications in the postural sensorimotor cortex.

Background and aim Feedforward and online controls are two facets of predictive motor control from internal models, which is suspected to be impaired in learning disorders. We examined whether the feedforward component is affected in children (8–12 years) with developmental dyslexia (DD) and/or with developmental coordination disorder (DCD) compared to typically developing (TD) children. Methods Children underwent a bimanual unloading paradigm during which a load supported to one arm, the postural arm, was either unexpectedly unloaded by a computer or voluntary unloaded by the subject with the other arm. Results All children showed a better stabilization (lower flexion) of the postural arm and an earlier inhibition of the arm flexors during voluntary unloading, indicating anticipation of unloading. Between-group comparisons of kinematics and electromyographic activity of the postural arm revealed that the difference during voluntary unloading was between DD-DCD children and the other groups, with the former showing a delayed inhibition of the flexor muscles. Conclusion Deficit of the feedforward component of motor control may particularly apply to comorbid subtypes, here the DD-DCD subtype. The development of a comprehensive framework for motor performance deficits in children with learning disorders will be achieved only by dissociating key components of motor prediction and focusing on subtypes and comorbidities.

Introduction La posture est consideree comme un element essentiel dans la phonation pour optimiser la communication. En situation de forcage vocal, lorsque le locuteur doit surmonter des difficultes comme la distance de son auditeur, son inattention ou le bruit ambiant, des modifications globales apparaissent au niveau de la posture, telle que la perte de la verticalite et de l’alignement postural. Une perturbation fonctionnelle de la coordination posture-voix peut alors amener le sujet a utiliser des solutions posturales generatrices de tensions. Le but de cette etude est de determiner si les mouvements du corps sont une consequence de l’effort vocal ou bien une strategie a part entiere pour optimiser l’effort de communication. Materiel et methode Nous avons entrepris une etude de correlations entre les marqueurs de la phonation, enregistres au moyen du systeme d’enregistrement EVA (SQLab, LPL, Aix-en-Provence) et ceux de la posture, enregistres au moyen d’un systeme automatique d’analyse de mouvement (SMART) chez 20 jeunes femmes realisant trois tâches de communication verbale avec des difficultes croissantes d’effort vocal. Resultats Les parametres vocaux augmentent effectivement en fonction des difficultes de l’environnement de communication. Les parametres cinematiques (amplitudes et durees des mouvements corporels) augmentent avec l’effort vocal. Enfin, parametres vocaux et cinematiques sont intimement correles avec une anticipation posturale. Discussion/Conclusion Ainsi, tâches posturale et vocale sont coordonnees et l’anticipation posturale est consideree comme une veritable strategie de communication qui consiste a capter l’attention de l’auditeur afin qu’il puisse se focaliser sur le contenu du message [1] .

There is evidence that adolescence is a critical period in development, most likely involving important modifications of the body schema and of the sensorimotor representations. The present study addressed this issue, by investigating the differences between adolescents and adults regarding the integration of proprioceptive information at both perceptual and postural levels and the visual recognition of human movement. Proprioceptive integration was examined using muscle-tendon vibration that evoked either a postural response or an illusory sensation of movement. The ability to recognize human movement was investigated from a paradigm where the participants had to discern between human movements performed with and without gravity. The study produced three main findings. First, the adolescents had larger postural responses to tendon vibrations than the adults, with visual information enabling them to reduce this exaggerated postural reaction. Second, the adolescents had a greater illusory perception of movement compared with the adults. Third, the adolescents had the same perceptual ability as adults in the human movement perception task. In conclusion, we were able to highlight notable differences between adolescents and young adults, which confirms the late maturation of multisensory integration for postural control and the privileged visual contribution to postural control.

The massive shift in writing habits calls for a better understanding of the possible consequences of typing practice on language processing, including reading. To assess a possible impact of typing knowledge on word recognition, we built a set of words and pseudowords differing by their ratio of bimanual transitions between letters, an index of typing difficulty for experts. An effect of typing difficulty was observed in expert participants who were actually typing the items and not in a control group of hunt-and-peck typists. We then tested whether word recognition, measured with the task of lexical decision, was impacted by the typing difficulty of words. We found that lexical decision latencies varied as a function of typing difficulty, but differently for experts and non-experts. The effect was mostly driven by pseudowords. This suggests that motor representations built during the practice of typing have a collateral effect on visual recognition processes. The implications for education are discussed.

Proprioceptive processing is important for appropriate motor control, providing error-feedback and internal representation of movement for adjusting the motor command. Although proprioceptive functioning improves during childhood and adolescence, we still have few clues about how the proprioceptive brain network develops. Here, we investigated developmental changes in the functional organization of this network in early adolescents (n = 18, 12 ± 1 years), late adolescents (n = 18, 15 ± 1), and young adults (n = 18, 32 ± 4), by examining task-evoked univariate activity and patterns of functional connectivity (FC) associated with seeds placed in cortical (supramarginal gyrus) and subcortical (dorsal rostral putamen) regions. We found that although the network is already well established in early adolescence both in terms of topology and functioning principles (e.g., long-distance communication and economy in wiring cost), it is still undergoing refinement during adolescence, including a shift from diffuse to focal FC and a decreased FC strength. This developmental effect was particularly pronounced for fronto-striatal connections. Furthermore, changes in FC features continued beyond adolescence, although to a much lower extent. Altogether, these findings point to a protracted developmental time course for the proprioceptive network, which breaks with the relatively early functional maturation often associated with sensorimotor networks.

International audience; During action, Anticipatory Postural Adjustments (APAs) cancel the consequences of a movement on postural stabilization. Their muscular expression is characterized by early changes in the activity of the postural muscles, before the movement begins. To explore the mechanisms enabling the acquisition of APAs, a learning paradigm was designed in which the voluntary lifting of a load with one hand triggered the unloading of another load suspended below the contralateral forearm. The aim of this study was to investigate changes in the muscular expression that uncovers the progressive learning of new APAs. A trial-by-trial analysis of kinematic and electromyographic signals recorded on the right arm was conducted in twelve adults through six sessions of learning. Kinematic results reported an enhancement of the postural stabilization across learning. The main EMG pattern found during learning consisted of a flexor inhibition, where latency was shifted towards an earlier occurrence in parallel with the improvement of the postural performance. A linear regression analysis conducted between the inhibition latency and the maximal amplitude of elbow rotation showed that the earlier the inhibition onset, the better the postural stabilization. This study revealed that the progressive shift of the postural flexor inhibition latency could be considered as a reliable neurophysiological marker of the progressive learning of new APAs. Importantly, this marker could be used to track motor learning abnormalities in pathology. We relate our findings to the update of a forward predictive model of action, defined as a system that predicts beforehand the consequences of the action on posture.

Transcranial magnetic stimulation (TMS) parameters were recorded in a lower limb muscle and correlated with the gait parameters of 25 patients with Parkinson's disease (PD) with and without dopamine substitution treatment (DST) and 10 control subjects. Single and paired-pulse TMS were recorded in the tibialis anterior muscle (TA). Gait analysis was performed using a 3D motion analysis system. Parkinsonian patients (PP) did not differ from the control subjects (CS) in terms of relaxed motor threshold, active motor threshold (AMT), cortical silent period (CSP), motor-evoked potential (MEP) amplitude and area, or paired-pulse TMS with short interstimulus intervals (ISI). At longer ISIs, paired-pulse TMS showed that the amplitudes of the conditioned MEPs were lower in untreated PP than in CS. DST partially compensated for this difference. Gait analysis showed that the gait of PP undergoing no treatment was slower and the stride length shorter than normal. Both of these parameters improved under DST, however. Analysis of data obtained on all the subjects combined showed that both of the latter parameters were correlated with the paired-pulse MEP amplitude and area at longer ISIs. In PP, the cortical areas responsible for the lower limb movements seem to undergo intracortical facilitation (ICF) impairments, whereas the intracortical inhibition process is normal. The ICF level was found to be associated to the stride length and the velocity. The fact that only these two gait parameters were found to be dopa responsive indicates that dopaminergic treatment may improve gait disorders by restoring the ICF.

Gait and speech are automatic motor activities which are frequently impaired in Parkinson's disease. Obvious clinical similarities exist between these disorders but were never investigated. We propose to determine whether there exist any common features in Parkinson's disease between spatiotemporal gait disorders and temporal speech disorders. Gait and speech were analysed on 11 Parkinsonian patients (PP) undergoing deep-brain stimulation of the subthalamic nucleus (STN-DBS) and 11 control subjects under three conditions of velocity (natural, slow and speed). The patients were tested with and without l-dopa and stimulator ON or OFF. Locomotor parameters were recorded using an optoelectronic system. Speech parameters were recorded with a headphone while subjects were reading a short paragraph. The results confirmed that PP walk and read more slowly than controls. Patient's difficulties in modulating walking and speech velocities seem to be due mainly to an inability to internally control the step length and the interpause-speech duration (ISD). STN-DBS and levodopa increased patients' walking velocity by increasing the step length. STN-DBS and levodopa had no effect on speech velocity but restored the patients' ability to modulate the ISD. The walking cadence and speech index of rythmicity tended to be lower in patients and were not significantly improved by STN-DBS or levodopa. Speech and walking velocity as well as ISD and step length were correlated in both groups. Negative correlations between speech index of and walking cadence were observed in both groups. Similar fundamental hypokinetic impairment and probably a similar rhythmic factor similarly affected the patients' speech and gait. These results suggest a similar physiopathological process in both walking and speaking dysfunction.

In the current study, we adopted the hypothesis that the body scheme disturbances occurring during adolescence might lead subjects to transiently neglect proprioceptive information and that adolescents might rely more strongly on vision to control their orientation and stabilize their body. To check this point, we asked adolescents 14–15 years to maintain vertical stance while very slow sinusoidal oscillations in the frontal plane were applied to the supporting platform at 0.01 Hz (below the detection threshold of the semicircular canal system) and at 0.06 Hz (above) with the eyes open and closed. Two postural components, orientation and segmental stabilization, were analyzed at the head, shoulder, trunk, and pelvis levels. At the lowest frequency without vision, the performances of adolescents were much less efficient than those of adults. Moreover, this study showed that vision plays a predominant role in adolescents’ control of orientation and body stabilization. At 0.06 Hz without vision, a clearcut difference was observed between the strategies used by girls and boys; specifically, the maturation of the segmental stabilization processes was found to be more advanced in girls than in boys. However, no such difference was observed at 0.01 Hz. Lastly, comparisons between the data obtained in adolescents and those previously obtained in young adults (Vaugoyeau, Viel, Amblard, Azulay, & Assaiante, 2008) clearly show that adolescents use different postural strategies and that they are not yet capable of reaching comparable postural performance levels to those observed in adults. Because adolescents were not able to use the proprioceptive information available to improve their postural control, we concluded that they showed a maturational lag in comparison with adults. This suggests that the mechanisms underlying postural control are still maturing during adolescence, which might constitute a transient period of proprioceptive neglect in sensory integration of postural control.

Posture is often affected in Parkinson's disease. Postural abnormalities belong to the motor axial involvement. Generally, postural dysfunction induces clinical impairment at the latest stages of the disease, except in late-onset idiopathic Parkinson's disease and in atypical parkinsonian syndromes. Posture may be affected in its orientation component (stooped posture, camptocormia, Pisa syndrome) or in its balance component (loss of postural reflexes). Overall, postural impairment is poorly improved by levodopa, which implies that it is unlikely due to the nigrostriatal dopaminergic denervation. Several methods of investigation have been proposed but are generally not available in clinical practice. Medical treatment and deep brain stimulation (DBS) of the subthalamic nucleus or globus pallidus pars interna are less efficient on axial than on distal motor signs. The pedonculopontine nucleus seems promising as a new target for DBS in combination with the subthalamic nucleus. Physical therapy is, in most cases, the best way to improve postural dysfunction.

Resume Les troubles de la marche sont frequents en neurologie. Leur semiologie clinique permet parfois d'etablir des correlations anatomocliniques et d'en deduire une etiologie avec ou sans l'aide d'examens complementaires. De nombreuses classifications basees sur l’examen clinique ont ete proposees mais ne permettent pas dans de nombreux cas de trancher. L’apport des techniques recentes d’analyse quantifiee du mouvement appliquees a la locomotion ou de systemes specifiques est interessant tant au point de vue de la connaissance des mecanismes physiologiques du controle posturolocomoteur, de leur acquisition tout au long du developpement chez l’enfant que de la determination des mecanismes physiopathologiques impliques dans les troubles de la marche pathologiques ou lies au vieillissement.

To determine why parkinsonian patients (PP) present some difficulties to initiate locomotion, a diagonal step has been investigated in two tasks in five control subjects (CS) and in ten PP. In the first task, the subjects had to perform one diagonal step without change in their orientation (WR); in the second task, they had to perform one diagonal step with a body rotation in the step direction (RO). The defended hypothesis is that the gait initiation deficits in Parkinson disease are a consequence of their difficulties to coordinate al the component of a complex movement. The analysed parameters were the duration of the postural and movement phases, the step length and velocity, and the amplitude of the horizontal ground reaction forces during each phase. Compared to CS, the PP showed a lengthening of the postural phase, a decrease in the step length and velocity and a reduction of the horizontal forces. The comparisons between the performances obtained in the WR versus those obtained the RO show in CS that the performances remained unchanged, whereas in PP the performances were significantly more altered in the RO. It illustrates the specific deficit occurring in PP while performing complex tasks where coordination between several components has to be achieved simultaneously.

Essential tremor is the most common movement disorder in adults. It is characterized by a postural and kinetic tremor affecting the arms, but it can also affect other body parts. It evolves gradually and can be responsible for a functional impairment in activities of daily living. Its pathophysiology remains poorly understood and effective therapeutic options are limited. There are significant semiological variations between patients, and the term "essential tremor" seems to encompass a wide range of heterogeneous clinical phenotypes. The diagnostic criteria presented in 1998 are now challenged. Furthermore, there is a current debate concerning the etiology of this affection, as to whether essential tremor is a complex degenerative disorder or a functional reversible disorder of neuronal oscillation. In this review, we summarize some aspects of clinical, etiologic and therapeutic news, to better address the questioning on unravelling the clinical presentation and examine the current pathophysiological controversy in this disorder.

International audience; Objectives Both stabilization and orientation components of postural control are affected in Parkinson's disease (PD). These deficits are partly due to proprioceptive impairments, which frequently coexist with a visual dependence. This study aimed to evaluate if a visual biofeedback -- i.e. real time anteroposterior trunk and head orientations indicated with a simplified avatar and represented in a head-mounted display -- could improve the postural control of PD patients in response to a postural disturbance. The influence of focusing on one specific component of the postural control (stabilization or orientation) was also examined. Methods Seventeen medicated PD patients performed sequences of pull-tests, either with eyes open, eyes closed or visual biofeedback, crossed with the verbal instruction to focus either on the stabilization or on the vertical body orientation. Kinematics data were collected. Results Backward trunk tilts consequent to the pulls were unchanged across the different conditions. With eyes open and eyes closed, patients did not recover their initial vertical orientation by adopting a slightly tilted backward position. This bias disappeared with the visual biofeedback. Moreover, falls consecutive to the test were significantly less frequent with the visual biofeedback than in the two other visual conditions. These different orientation and stabilization parameters were not affected by the instruction. Conclusion Unlike a verbal instruction, visualizing in real time their own body's geometry improved both components of postural control of PD patients. This provides evidences in PD about links between impaired vertical orientation, deficits in balance control, and contribution of supplementary sensory cues.

International audience; In order to perceive and act in its environment, the individual's body and its interactions with the sensory and social environment are represented in the brain. This internal representation of the moving body segments is labeled the body schema. Throughout life, body schema develops based on the sensory information used by the moving body and by its interactions with the environment including other people. Internal representations including body schema and representations of the outside world develop with learning and actions throughout ontogenesis and are constantly updated based on different sensory inputs. The aim of this review is to present some concepts and experimental data about body schema, internal representations and updating process during childhood and adolescence, as obtained using a neurosensory approach. From our developmental studies, it was possible to explore the slow maturation of the sensorimotor representations by examining the anticipatory control. By manipulating proprioceptive and visual information, which are at the heart of the construction of body schema, we wished to highlight notable differences between adolescents and young adults on both a postural and perceptual level, which confirms the late maturation of multisensory integration for central motor control.

The feeling of illusory movement is considered important in the study of human behavior because it is deeply related to motor consciousness. However, the neural basis underlying the illusion of movement remains to be understood. Following optimal vibratory stimulation of muscle tendon, certain subjects experience illusory movements while others do not. In the present fMRI study, we sought to uncover the neural basis of illusory movement awareness by contrasting a posteriori these two types of subjects. Examining fMRI data using leave‐one‐subject‐out general linear models and region of interest analyses, we found that a non‐limb‐specific associative network, including the opercular part of the right inferior frontal gyrus and the right inferior parietal lobule, was more active in subjects with illusions. On the other hand, levels of activation in other brain areas involved in kinaesthetic processing were rather similar between the two subsamples of subjects. These results suggest that activation of the right inferior frontoparietal areas, once passed a certain threshold, forms the basis of illusory movements. This is consistent with the global neuronal workspace hypothesis that associates conscious processing with surges of frontoparietal activity. Hum Brain Mapp 35:5166–5178, 2014. © 2014 Wiley Periodicals, Inc.

Introduction Agir avec l’environnement necessite d’etre conscient de son corps. Cette conscience corporelle est basee sur le schema corporel (SC) qui correspond a la representation interne du corps en action. Le SC se construit lentement au cours de l’ontogenese, sous-tendu par une lente maturation de la proprioception. L’objectif de cette etude est d’evaluer le developpement du SC, en particulier les modifications du reseau cerebral en charge des representations du corps en action. A cette fin, nous avons utilise une approche correlationnelle cerveau-comportement. Materiel et methodes Vingt jeunes adultes (28,2 ± 4,8 ans) et vingt enfants âges de 8 a 12 ans (10,0 ± 0,9 ans) ont effectue : –une tâche d’acuite proprioceptive ; –une tâche de delestage bimanuelle, toutes deux impliquant les representations du corps en action. Un enregistrement en IRMf de repos a egalement ete realise. L’erreur et la variabilite de position, ainsi que la stabilisation de l’avant-bras ont ete mesurees, respectivement dans chacune des deux tâches comportementales. Les correlations unissant connectivite fonctionnelle (CF) et scores comportementaux ont ensuite ete evaluees. Resultats Chez l’adulte comme chez l’enfant, nous avons pu etablir une correlation negative entre la CF impliquant les regions frontales, parietales et sous-corticales et les performances comportementales dans chacune des deux tâches. Autrement dit, plus la CF est forte entre ces regions, meilleures sont la precision de position et la stabilisation de l’avant-bras. Seule l’anticipation signe une difference developpementale avec une correlation entre la CF impliquant les regions frontales et parietales inferieures. Discussion–conclusion Le reseau des representations du corps en action connaitrait deux phases de maturation : l’une precoce relative a la composante motrice qui serait deja etabli des la fin de l’enfance, et une autre plus tardive, relative a la composante frontoparietale qui presenterait une maturation au-dela de l’adolescence.

The objective of this study was to investigate the updating process of internal models of action in children and young adults, through the postural and motor strategies adopted in simple tasks, namely sit-to-stand (STS) and back-to-sit (BTS). To this end, 11 healthy children from 7 to 10 years (latest stage of childhood) and 12 healthy adults participated in the experiment. The STS and BTS tasks were performed with horizontal support surface and support surface tilted 10° to the right or forward in order to investigate the immediate adaptation of the internal representations of the movement. Movement variables that included the durations of STS and BTS and the amplitudes of the trunk movement were computed. Postural characteristics were also considered during the transition from STS to BTS, including the trunk orientation and the head stabilization strategies. Despite certain similarities with adults, especially in terms of the asymmetry of the performance times for the two tasks (STS vs. BTS) and the partial movement adaptations, the children were less able than adults to adapt both postural and movement controls to the new support conditions. Thus, it appears that the updating of internal models of action is a process that matures slowly throughout ontogenesis.

International audience; The aim of this study was to explore, during adolescence, alterations in the use of a sensori-motor representation as unveiled by the measurement of anticipatory postural control in a bimanual load-lifting task. We hypothesised that adolescence constitutes a period of refinement of anticipatory postural control due to on-going updates of the body schema and sensori-motor representations. The anticipatory postural control was assessed using a bimanual load-lifting paradigm in which subjects stabilise their left postural forearm, which is supporting an object, while they use their right hand to lift up the object. Kinematics and electromyographic data were recorded in two groups of adolescents (11-13 and 14-16 years of age) and a group of adults. Age and gender effects were tested. During voluntary unloading, the postural forearm stabilisation in adolescents was still different from the adult one, suggesting that further improvement of the postural forearm stabilisation must take place after the age of 16. No differences occur in the two adolescent groups. Moreover, girls presented a better stabilisation of the postural forearm than boys, indicating an earlier refinement of anticipatory postural control. The decrease of activity over postural flexors, which ensure postural stabilisation, appeared later in adolescents with respect to adults. Delayed timing adjustments and increased variability could reflect intense developmental processes underlain by an intense period of CNS maturation during adolescence. We discuss the role of brain maturation in the refinement of sensori-motor representations and the update of body schema.

International audience; IntroductionIt has been reported that AIS rely much more on ankle proprioception to control the amplitude of the balance control commands as compared to age-matched healthy adolescents. Our hypothesis was that AIS do not neglect proprioceptive information to control posture probably because of their vestibular deficits. We investigated the proprioceptive contribution to postural control in AIS which expresses spinal deformity during a crucial transitional period of ontogenesis.Methods10 adolescents with idiopathic scoliosis (AIS) with moderate spinal deformity (10° < Cobb Angle >35°) and 10 control adolescents (CA) had to maintain vertical stance while very slow oscillations in the frontal plane (below the detection threshold of the semicircular canal system) were applied to the support with the eyes open and closed. Postural orientation and segmental stabilisation were analysed at head, shoulder, trunk and pelvis levels.ResultsScoliosis did not affect vertical orientation control and segmental stabilization strategies. Vision improves postural control in both CA and AIS, which seem more dependent on visual cues than adults.ConclusionsAIS as CA were unable to control efficiently their postural orientation on the basis of the proprioceptive cues, the only sensory information available in the EC situation, whereas in the same condition healthy young adults present no difficulty to achieve the postural control. This suggests that AIS as CA transitory neglect proprioceptive information to control their posture. These results and previous studies suggest the existence of different afferent pathways for proprioceptive information subserving different parts in sensory integration of postural control. We conclude that the static proprioceptive system is not affected by the idiopathic scoliosis, while the dynamic proprioceptive system would be mainly affected.

According to the simulation theory, the internal simulation of a movement (imagined movement, IM) and its execution (actual movement, AM) are based on the same motor representations. The brain uses these representations for controlling action. The specific objective of this study was to investigate the updating process of internal models of action in adults, through massive environmental changes involved by microgravity (0G). 0G has multiple effects on motor control, including short-term adaptations with respect to the planification and performance of actions. However, the effects of 0G on internal representations of action are still largely unknown. To address this issue, thirteen subjects performed first sit-to-stand (STS) and back-to-sit (BTS) tasks, and subsequently had to imagine movement performance in these tasks. The tasks were performed under normogravity (1G) and 0G conditions. Based on durations of actual and IMs, two main results emerged from this study. In 1G, actual and IM's durations were similar. However, in 0G, AM durations were significantly longer than IM durations. Furthermore, IM durations in 0G were similar to the 1G value. These results show that although the planification and execution of action were immediately adapted to the 0G condition, the storage of afferent information was inadequate to recalibrate the predictive model. These results suggest that sudden change in gravity was not considered for updating internal models of action, and that forward model probably required more practice in order to integrate the modification of the sensorial feedback generated by the new environmental constraints.

Introduction Si le tremblement essentiel (TE) est frequent, sa physiopathologie reste mal connue et peu de donnees sont disponibles quant a l’existence de troubles de la marche dans cette affection. Le TE pourrait englober differents phenotypes et les patients presentant un tremblement du chef (TEC) associe au tremblement des membres superieurs (TEMS) pourraient representer un sous-groupe phenotypique de TE. L’objectif etait de caracteriser ces differents phenotypes, en comparant les performances locomotrices et les donnees d’imagerie cerebrale anatomique et metabolique de patients avec un TEC et de patients avec un TEMS isole. Materiel et methode La marche de 54 patients TE (dont 30 TEC) (âge moyen = 72 ± 7 ans) a ete analysee par un systeme multiparametrique d’analyse du mouvement. Une etude de la densite de matiere grise du cortex cerebral par VBM et du metabolisme cerebral en TEP-scan 18-FDG a aussi ete realisee dans ces deux sous-groupes de patients. Resultats En comparaison a des sujets controles, les TE ont une diminution de la vitesse de marche. Les TEC n’avaient pas de difference de la vitesse de marche naturelle compares aux TEMS. En comparaison intergroupes, deux regions cerebrales presentaient une augmentation de densite de matiere grise (hemisphere cerebelleux et BA6 droits) et quatre regions presentaient une augmentation du metabolisme cerebral (lobe cerebelleux posterieur, BA6, gyrus post-central, lobule paracentral droits) dans le sous-groupe TEC en comparaison aux TEMS. Discussion–conclusion Cette etude confirme l’existence de troubles de la marche dans le TE. L’existence de differences cerebrales morphologiques et metaboliques entre les patients avec TEC et TEMS suggere que les TEC appartiendraient a un sous-groupe phenotypique different au sein d’une affection heterogene.

Introduction La construction du schema corporel (SC) au cours de l’ontogenese repose sur les entrees sensorielles (visuelles, proprioceptives, vestibulaires) et leurs interactions avec un repertoire moteur qui s’enrichit. Le but de cette etude etait de : – tester l’influence du couplage perception-action sur la perception de postures humaines ; – valider un nouvel outil d’evaluation de la construction du SC. Materiel et methodes Vingt adultes et 20 enfants ont effectue une tâche de discrimination visuelle de photos d’individus adoptant des postures diverses impliquant les membres superieurs et inferieurs. Les sujets devaient rapporter si les postures presentees etaient identiques ou differentes. Cette tâche a ete realisee en executant des mouvements aleatoires ou specifiques de la posture observee. Une condition controle, sans mouvement, a aussi ete realisee, ainsi que les memes tests perceptifs avec des assemblages de Lego. Resultats Le pourcentage de bonnes reponses est plus important pour les items de posture que pour les items de Lego dans les deux groupes. Un effet developpemental etait observe dans la capacite a reconnaitre les postures. Effectuer des mouvements lors de la discrimination d’item avait une incidence uniquement sur les performances des enfants. Discussion–conclusion Notre test semble specifique de la perception corporelle et se revele sensible a l’âge sur la base des temps de reaction. Augmenter les effectifs et differencier les tranches d’âge devraient nous permettre d’en faire un nouvel outil simple et efficace d’evaluation de la construction du SC chez l’enfant sain et pathologique, a partir du couplage perception-action.

International audience; How sensory organization for postural control matures in children is not clear at this time. The present study examined, in children aged 7 to 11 and in adults, the postural control modifications in quiet standing when somatosensory inputs from the ankle were disturbed. Since the reweighting of sensory inputs is not mature before 10, we hypothesized that postural stability was more affected in children than in adults when somatosensory inputs were altered and that this postural instability decreased as age increased during childhood. 37 children aged 7 to 11 years and 9 adults participated in the experiments. The postural task was a semi-tandem position with the right foot in front of the left one. Postural performance was measured by means of a force platform. Two experimental conditions were presented to the participants to maintain quiet standing: With or without altered somatosensory inputs (i.e., with or without ankles vibration). Results showed that postural stability--and thus how the reweighting process of the visual/somatosensory inputs matured--increased non-monotonically between 7 years of age and adult age: There was a linear improvement of postural stability from 7 to 10, followed by a more steady behaviour between 10 and 11 and then postural stability increased to reach the adults' level of performance.

International audience; OBJECTIVES:Whispered voice is investigated from the energetic point of view. Our hypothese is that whispered voice, and mainly the forced whispers are very similar to vocal effort, for non acoustic vocal parameters, and body movements.DESIGN:Two experiments are combined. The first experiment focused on the laryngeal aspects, mainly the subglottal pressure, and also the electroglottography. The second experiment analyzed the body movements associated with loud whispered voice.RESULTS:No electroglottograhic wave was observed during the two experiments. The vocal intensity was always lower during whispered voice than during comfortable voice (p < 0.001). In experiment 1, subglottal pressure was significantly higher during forced whisper than during the other conditions (p < 0.001). In experiment 2, the amplitude of the trunk movements in the sagittal plane were greater during loud whisper than during comfortable voice (p < 0.001).CONCLUSION:Whispered voice can be close to vocal loading, especially the loud whispered voice.; Etudes expérimentales préliminaires de la voix chuchotée : pression sous-glottique et étude posturale 1 Preliminary experimental studies of whispered voice: subglottal pressure and postural aspects Résumé Objectifs : cette étude propose de décrire les aspects éner-gétiques de la voix chuchotée, en la mettant en relation avec les éléments qui caractérisent l'effort vocal. L'hypothèse de travail est qu'il existe des similitudes entre la voix chuchotée, en parti-culier la voix chuchotée forte et l'effort vocal. Méthodes : Deux expérimentations sont combinées pour répondre à l'hypothèse de travail. L'une, centrée sur le niveau laryngé, étudiait l'électroglottographie et la pression sous-glottique réelle (expérience 1) ; l'autre analysait les modifications posturales associées à la voix chuchotée (expérience 2). Résultats : dans les deux expériences, aucune onde électroglottographique n'a été mise en évidence au cours de la production de voix chucho-tée. L'intensité de la voix chuchotée était plus faible que celle de la voix parlée (p < 0.0001). Dans l'expérience 1, la pression sous-glottique était significativement supérieure en voix chuchotée forcée que dans les autres productions (p < 0.0001). Dans l'expérience 2, les mouvements du tronc dans le plan sagittal (flexion vers l'avant) étaient significativement plus importants au cours de la production de voix chuchotée qu'au cours de la voix parlée (p < 0.001). Conclusion : la voix chuchotée dite forcée présente de nombreuses similitudes avec l'effort vocal, à l'inverse de la voix chuchotée «silencieuse». Summary Objectives: Whispered voice is investigated from the energetic point of view. Our hypothese is that whispered voice, and mainly the forced whispers are very similar to vocal effort, for non acoustic vocal parameters, and body movements. Design: Two experiments are combined. The first experiment focused on the laryngeal aspects, mainly the subglottal pressure, and also the electroglottography. The second experiment analyzed the body movement associated with loud whispered voice. Results: No electroglottograhic wave was observed during the two experiments. The vocal intensity was always lower during whispered voice than during comfortable voice (p< 0.001). In experiment 1, subglottal pressure was significantly higher during forced whisper than during the other conditions (p< 0.001). The amplitude of the trunk movements in the sagittal plane were greater during loud whisper than during comfortable voice (p< 0.001). Conclusion: Whispered voice can be close to vocal loading, especially the loud whispered voice.

International audience; Introduction: Postural aspects of vocal effort are unusually described in the literature whereas they are extensively managed in speech therapy. Objectives: This study aims to determine whether body movement is a side-effect of vocal effort or an integrant part of global communication effort behaviour. The answer to this question is mainly based on the correlations between the movement and the phonation.Design: This experimental study involved healthy subjects. They had to communicate to a listener during exposure to three situations where the environmental obstacles were increasing.Results: Vocal parameters such as sound pressure level, fundamental frequency, closed quotient and words duration all increased with increasing difficulty of communication (ie. increasing vocal effort). All body segments movement increased their amplitude and duration with increasing vocal effort. Vocal and kinematic characteristics were significantly correlated.Conclusion: The close correlation of movement and vocal production during vocal effort definitely excludes that the movement is a consequence of the latter. Posture and voice are coordinated in the action of communication and each body segment seems to play a different role in the vocal effort behaviour.

Gait disorders are important because of their prevalence, particularly among the elderly, and the associated risk of falls and injury. The main physiological characteristics of locomotion and neural networks that organize locomotion and maintain balance are briefly reviewed. A simplified classification designed clinical practice and based upon clinical characteristics and more recent data obtained from quantified gait analysis is proposed.

Clinical findings and experimental studies both in parkinsonian patients and on animal provide evidence that the control of the axial orientation is markedly impaired in Parkinson's disease (stooped posture, Camptocormia, Pisa syndrome). Nevertheless the postural orientation component in Parkinson's disease has been poorly investigated. One study reports that Parkinsonian patients present a major impairment of the postural orientation component in relation with a proprioceptive impairment. On the basis of these results, the visual dependence observed in Parkinsonian patients is re-defined as an adaptive strategy partly compensating for the impaired proprioception.

BACKGROUND: In order to test how gravitational information would affect the choice of stable reference frame used to control posture and voluntary movement, we have analysed the forearm stabilisation during sit to stand movement under microgravity condition obtained during parabolic flights. In this study, we hypothesised that in response to the transient loss of graviceptive information, the postural adaptation might involve the use of several strategies of segmental stabilisation, depending on the subject's perceptual typology (dependence--independence with respect to the visual field). More precisely, we expected a continuum of postural strategies across subjects with 1) at one extreme the maintaining of an egocentric reference frame and 2) at the other the re-activation of childhood strategies consisting in adopting an egocentric reference frame. METHODOLOGY/PRINCIPAL FINDINGS: To check this point, a forearm stabilisation task combined with a sit to stand movement was performed with eyes closed by 11 subjects during parabolic flight campaigns. Kinematic data were collected during 1-g and 0-g periods. The postural adaptation to microgravity's constraint may be described as a continuum of strategies ranging from the use of an exo- to an egocentric reference frame for segmental stabilisation. At one extremity, the subjects used systematically an exocentric frame to control each of their body segments independently, as under normogravity conditions. At the other, the segmental stabilisation strategies consist in systematically adopting an egocentric reference frame to control their forearm's stabilisation. A strong correlation between the mode of segmental stabilisation used and the perceptual typology (dependence--independence with respect to the visual field) of the subjects was reported. CONCLUSION: The results of this study show different subjects' typologies from those that use the forearm orientation in a mainly exocentric reference frame to those that use the forearm orientation in a mainly egocentric reference frame.