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The prevention of falls in elderly is a major focus of medical research. Although the mechanisms underlying the effect of aging on the postural control system are varied and complex, impaired sensory function is likely to be an important contributing factor to the deterioration in postural balance and may increase the likelihood of falling. Age-related loss of cutaneous sensation, in particular, is pervasive, and appears to correlate with impaired postural control. As the feet interface directly with the ground, cutaneous cues provide relevant information about the support surface properties, and about the body position in reference to verticality. The purpose of this study was to explore the effects of a mechanical stimulation of the plantar mechanoreceptors, by means of spikes within the footwear insole, on postural stability. Our results provide evidence that applying a mechanical stimulation reduce, to some extent, postural sway in most of the young adults, the elderly and the patients with diabetic neuropathy. The benefits are not correlated with the cutaneous sensitivity or the initial postural performances of the subject. There was also a significant inter-individual variability. The enriched sensory context provided by the spikes is an original method of stimulation that may be appropriated for subjects with balance problems. This stimulation may reproduce, to some extent, the effects of a massage without requiring a systematic therapeutic intervention. Further research is needed to find the best compromise between the duration, the intensity, the frequency of the stimulation and the comfort of the insoles., La prévention des chutes chez les personnes âgées constitue aujourd'hui un objectif prioritaire en matière de santé publique. Bien que les mécanismes associés au vieillissement soient complexes et variables selon les individus, la détérioration des fonctions sensorielles semble être un des facteurs majeurs de la dégradation du contrôle postural. Cette diminution des performances posturales augmente la probabilité de chute. L'altération de la sensibilité cutanée qui apparaît avec l'âge est, en particulier, à l'origine de problèmes d'équilibre. Compte tenu de leur localisation à l'interface du corps et du support podal, les capteurs tactiles plantaires fournissent des informations très pertinentes sur les oscillations du corps par rapport à la verticale. Dans le cadre de ce travail de thèse, nous nous sommes particulièrement intéressés aux effets d'une stimulation mécanique de la sole plantaire par le port de semelles à picots. Nos travaux ont mis en évidence que ce type de stimulation améliore dans certaines conditions la stabilité posturale chez les jeunes, chez les personnes âgées saines ou atteintes d'une neuropathie diabétique. Les bénéfices observés ne sont ni corrélés à la sensibilité cutanée plantaire, ni aux performances posturales initiales du sujet et varient selon les individus. L'enrichissement du contexte sensoriel apporté par les picots pourrait constituer une méthode de stimulation originale et particulièrement appropriée pour les personnes qui présentent des problèmes d'équilibre. Elle permettrait de reproduire dans une certaine mesure les effets bénéfiques d'un massage de la sole plantaire, ce qui éviterait ainsi l'intervention systématique d'un thérapeute. Les perspectives de ce travail sont nombreuses et nous permettront de déterminer le meilleur compromis en termes de durée, d'intensité, de fréquence de stimulation et de confort afin de pouvoir quantifier plus précisément la stimulation optimale.

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L'objectif de cette étude était de savoir si une surface de support à picots pouvait engendrer des modifications de la stabilité posturale et de la sensibilité cutanée plantaire. 21 personnes âgées (âge moyen = 69, 3 ans) et 19 jeunes adultes (âge moyen = 25, 9 ans) ont participé à ce protocole. Ils devaient rester 5 min debout munies de sandales à picots (condition picot). Le contrôle postural était évalué en situation statique (1) immédiatement après avoir mis les sandales à picots et (2) après être resté 5 min debout avec ces sandales L'expérience comprenait aussi une situation contrôle où de fines semelles étaient placées dans les sandales afin d'éviter le contact direct avec les picots (condition sans picot). La sensibilité plantaire cutanée a été évaluée grâce aux monofilaments de Semmes-Weinstein. Les résultats montrent une amélioration de la stabilité posturale dans les deux populations: les effets sont néanmoins plus prononcés chez les personnes âgées.

International audience; Les stratégies de maintien de l'équilibre postural et locomoteur se développent de façon non linéaire au cours de l'enfance et de l'adolescence, et n'atteignent leur maturité qu'à l'âge adulte. Plusieurs périodes charnières sont en effet observées tout au long de cette longue acquisition. De nombreux facteurs peuvent être identifiés comme contribuant de façon déterminante à la bonne (normalité) ou à la mauvaise (pathologie) acquisition de l'ensemble de ces stratégies posturales et locomotrices. Les caractéristiques phylogénétiques et les acquis ontogénétiques, l'utilisation des informations sensorielles, la stabilisation de la tête et du bassin, ainsi que le coût attentionnel sont en effet autant de facteurs à envisager afin de mieux percevoir les contours du développement postural et locomoteur chez l'homme. Il arrive, par ailleurs, que certaines anomalies, telles que la marche digitigrade, la torsion du squelette, l'infirmité motrice cérébrale ou l'autisme, engendrent des troubles de ce développement postural qu'il est important de mieux connaître.

International audience; The present paper tried to provide a review of the different works investigating the attentional cost of postural control. Within the context of a double task, the attentional demand associated to postural control depends on various factors such as (1) the automatic or voluntary focalisation of attention on postural control, (2) the available sensory information, (3) the nature and complexity of the postural task, (4) the subjects' age, and/or (5) the level of subjects' sensory-motor expertise or deficits. Following a brief presentation of the double task paradigm in the context of postural control, the effects of these different factors are analysed more specifically.

The prevention of falls in elderly is a major focus of medical research. Although the mechanisms underlying the effect of aging on the postural control system are varied and complex, impaired sensory function is likely to be an important contributing factor to the deterioration in postural balance and may increase the likelihood of falling. Age-related loss of cutaneous sensation, in particular, is pervasive, and appears to correlate with impaired postural control. As the feet interface directly with the ground, cutaneous cues provide relevant information about the support surface properties, and about the body position in reference to verticality. The purpose of this study was to explore the effects of a mechanical stimulation of the plantar mechanoreceptors, by means of spikes within the footwear insole, on postural stability. Our results provide evidence that applying a mechanical stimulation reduce, to some extent, postural sway in most of the young adults, the elderly and the patients with diabetic neuropathy. The benefits are not correlated with the cutaneous sensitivity or the initial postural performances of the subject. There was also a significant inter-individual variability. The enriched sensory context provided by the spikes is an original method of stimulation that may be appropriated for subjects with balance problems. This stimulation may reproduce, to some extent, the effects of a massage without requiring a systematic therapeutic intervention. Further research is needed to find the best compromise between the duration, the intensity, the frequency of the stimulation and the comfort of the insoles.; La prévention des chutes chez les personnes âgées constitue aujourd'hui un objectif prioritaire en matière de santé publique. Bien que les mécanismes associés au vieillissement soient complexes et variables selon les individus, la détérioration des fonctions sensorielles semble être un des facteurs majeurs de la dégradation du contrôle postural. Cette diminution des performances posturales augmente la probabilité de chute. L'altération de la sensibilité cutanée qui apparaît avec l'âge est, en particulier, à l'origine de problèmes d'équilibre. Compte tenu de leur localisation à l'interface du corps et du support podal, les capteurs tactiles plantaires fournissent des informations très pertinentes sur les oscillations du corps par rapport à la verticale. Dans le cadre de ce travail de thèse, nous nous sommes particulièrement intéressés aux effets d'une stimulation mécanique de la sole plantaire par le port de semelles à picots. Nos travaux ont mis en évidence que ce type de stimulation améliore dans certaines conditions la stabilité posturale chez les jeunes, chez les personnes âgées saines ou atteintes d'une neuropathie diabétique. Les bénéfices observés ne sont ni corrélés à la sensibilité cutanée plantaire, ni aux performances posturales initiales du sujet et varient selon les individus. L'enrichissement du contexte sensoriel apporté par les picots pourrait constituer une méthode de stimulation originale et particulièrement appropriée pour les personnes qui présentent des problèmes d'équilibre. Elle permettrait de reproduire dans une certaine mesure les effets bénéfiques d'un massage de la sole plantaire, ce qui éviterait ainsi l'intervention systématique d'un thérapeute. Les perspectives de ce travail sont nombreuses et nous permettront de déterminer le meilleur compromis en termes de durée, d'intensité, de fréquence de stimulation et de confort afin de pouvoir quantifier plus précisément la stimulation optimale.

International audience

International audience

The aim of the present study was to analyze, in children aged 6, 8 and 11, the developmental trend of the attentional cost related to the programming and execution of pointing movements, using a dual-task paradigm. Our results showed that the attentional cost associated to the programming and the first phase of the pointing movement decreased non linearly with age, in particular a plateau between 8 and 11 was observed. This confirmed that the developmental trend of the control of pointing movements is characterized by a no monotonic evolution in which feedforward processes were predominantly used in the younger children, feedback processes were predominantly used in older children (since age 8), and one-line over feedforward processes were used in adults.

Without visual information, human subjects are not able to maintain displacement in a straight line. This tendency to depart from linearity during locomotion is called veering. The purpose of the present experiment was to investigate the extent to which attention could modulate navigation in the absence of visual information. Blindfolded locomotion on linear pathways was assessed under three different conditions. The Distraction condition was intended to divert participants' attention from the walking task, whereas in the Concentration condition, participants deliberately focused on the task. There was also a Control condition in which no particular instruction was provided. Results showed that subjects veered in all conditions. Furthermore, more accurate performances were observed in the Distraction condition compared to the Control condition, while the Concentration condition led to larger deviations.

Two experiments investigated manual asymmetries in the control of rapid reaching movements according to the movement parameters to be controlled. Single- and double-step reaching movements were performed by right-handed subjects with both hands. Pro and retroactive processes involved in rapid movement control were investigated. Manual performances and kinematic properties of hand movements showed that various forms of hemispheric specialization were involved in sensori-motor information processing. It was shown that the effects of hemispheric specialization were specific to the task constraints, that is, to the various operations involved in movement control.

To examine the interindividual differences in the judgment of the visually perceived eye level (VPEL-upright position) and of the visually perceived apparent zenith (VPAZ-supine position) when the subject is subjected to low gravitational-inertial force (GIF), we independently altered GIF in two different populations: control subjects and spatial experts. Subjects were instructed to set a luminous target to the eye level while they were in total darkness and motionless or undergoing low radial acceleration with respect to the threshold of the otolithic system (0.015-1.67 m/sec2 for the VPEL and 0.55-2.19 m/sec2 for the VPAZ, respectively). Results showed that (1) low GIFs, close to those met during daily life, induced an eye level lowering in the upright and supine positions for the control group, and (2) the spatial expertise modified the influence of low GIF. Whereas an oculogravic illusion was found for the control group, this phenomenon was absent (VPAZ) or weaker (VPEL) for the spatial experts. Thus, the relations that the subjects maintain with their spatial environment and the knowledge acquired through experience modify the processing of sensory information and the perceptive construction resulting from it. The interindividual differences in sensitivity to the oculogravic illusion are discussed in terms of sensory dominance and of a better efficiency in the use of the available sensory information.

International audience; Define the objective of the questionnaire: Discrimination: do you want a questionnaire to enable you to describe the quality of life of patients or to compare the quality of life between groups of patients, for example, to determine who has improved and who has gotten worse? Assessment: do you want a questionnaire to help you measure changes over time (improvement or aggravation) in your patients? Determine the properties of instruments necessary for this objective: If the objective is discrimination, analyze: construct validity, reliability. If the objective is assessment, analyze construct validity, sensitivity to changes. Choose the general category of questionnaire: generic questionnaire, specific questionnaire.

International audience; Human activities often involve sensing body orientation using cues from gravity. Astronauts in microgravity are deprived of those cues and may have difficulty with certain tasks. We theorized that experience in microgravity combined with mechanically induced pressure under the feet (foot pressure) would improve the accuracy of a subject's perception of the body's z-axis as indicated by pointing to the subjective horizon (SH). METHOD: Experiments were conducted during parabolic flights using five experienced subjects and five novices. Subjects were required to raise their arm to point to their SH with eyes closed. Measurements were made on Earth and in microgravity, with or without foot pressure. Both pointing accuracy and the kinetics of the movement were analyzed. RESULTS: Performance by experts was stable under all conditions. However, novices in microgravity pointed to a significantly lower SH (16.5 degrees below the 1-G SH) and slowed their movements (mean angular velocity of movement: 16.8 degrees x s(-1) less than in 1 G). Foot pressure improved the performance of the novices so that it was closer to that observed at 1 G (8.9 degrees below the 1-G SH). DISCUSSION: These results suggest that pressure cues under the feet activated the internal model of gravity in the novices, and thus improved the accuracy of their perception of their z-axis. Subjects with prior experience in microgravity correctly perceived their z-axis without the supplementary input.

International audience

The aim of the present experiment was to study the central control of posture and movement coordination. Subjects' task was voluntarily to raise their arms in response to a visual signal, this movement generating an unloading in which the weight of the load (0 gm, 1500 gm, 3000 gm, or 4500 gm) was known in advance. Thus, subjects could predict the postural perturbation generated by the unloading. Analysis showed an effect of the unloading conditions: in the 0-gm and 1500-gm conditions, reaction time (RT) was longer than in the 3000-gm and 4500-gm conditions. This decrease in RT was exclusively due to a reduction of the premotor time, confirming the posturokinetic coordination in the programming processes. The implications of the decrease in premotor time with the increase of the perturbation for the posture/movement coordination strategies are also discussed.

Without relevant visual cues, the subjective visual vertical (SVV) is biased in roll-tilted subjects toward the body axis (Aubert or A-effect). This study focused on the role of the somatosensory system with respect to the SVV and on whether somesthetic cues act through the estimated body tilt. The body cast technology was used to obtain a diffuse tactile stimulation. An increased A-effect was expected because of a greater underestimation of the body position in the body cast. Sixteen subjects placed in a tilt chair were rolled sideways from 0 degrees to 105 degrees. They were asked to verbally indicate their subjective body position and then to adjust a luminous line to the vertical under strapped and body cast conditions. Results showed a greater A-effect (p < .001) but an overestimation of the body orientation (p < .01) in the body cast condition for the higher tilt values (beyond 60 degrees). Since the otolith organs produced the same gravity response in both conditions, errors were due to a change in somesthetic cues. Visual and postural errors were not directly related (no correlation). However, the angular distance between the apparent body position and the SW remained stable, suggesting that the change in somatosensory pattern inputs has a similar impact on the cognitive processes involved in assessing the perception of external space and the sense of self-position.

The present experiment examined in a visuo-manual task the effects of verbal instructions on the speed/accuracy trade-off across children aged 6, 8 and 10 years and adults. Three different verbal instructions (speed, accuracy and speed-accuracy) had to be respected to perform a pointing task. Analysis of reaction time (RT), movement time (MT) and percentage of targets reach showed that: (1) whatever the age, children were able to comply with the verbal instructions to adapt the velocity and/or the precision of their response (initiation and movement execution); (2) the main age-related difference of the speed-accuracy trade-off concerned the temporal (MT) but not the accuracy (targets reach) characteristics of the pointing movements; and (3) in the older children and even more precisely in adults, a temporal deficit was observed when the accuracy of aiming was required. This deficit increased as accuracy increased. These results were discussed within the theoretical frameworks of the developmental speed processing model proposed by Kail [Psychol. Bull., 109(3) (1991) 490-501] for RT data, and the speed-accuracy trade-off model proposed by Pachella [Pachella, R.G., The interpretation of reaction time in information-processing research, in, Kantowitz, B. (ed) Human Information Processing: Tutorial in Performance and Recognition, Erlbaum, (1974) 41-82] for MT and targets reach data.

Separate studies have demonstrated that vibration and fatigue of ankle muscles alter postural control. The purpose of the present experiment was to investigate the effect of ankle muscle vibration on the regulation of postural sway in bipedal stance following ankle muscle fatigue. Center of foot pressure displacements were recorded using a force platform. Results showed a similar increase in postural sway under muscle fatigue as well as under muscle vibration. Interestingly, under muscle fatigue muscle vibration did not induce a further increase in postural sway. Two hypotheses could, at least, account for this observation: (1). fatigued muscles are less sensitive to muscle vibration and (2). the central nervous system relies less upon proprioceptive information originating from fatigued muscles for regulating postural sway.

The purpose of this experiment was to examine the development of motor preparation across three groups of children aged 6, 8 and 10 years old. The foreperiod duration (500, 1000, 2000 and 4000 ms) and the motor preparation conditions were manipulated using a priming procedure. Two type of primes were provided: (1), a prime carrying no advanced information (neutral condition); and (2), a prime giving advanced information on the nature of the motor response to execute, allowing the participant to prepare for it (selective condition). Reaction time and response errors were analyzed. Results showed that under both conditions, the optimal motor preparation was reached within the same time frame which decreased as age increased. As to the optimal alertness level (neutral preparation), it is maintained longer as age increases, whereas the optimal motor programming level (selective preparation) is reached only for specific foreperiod duration.