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International audience; Several studies in adults having observed the effect of eye movements on postural control provided contradictory results. In the present study, we explored the effect of various oculomotor tasks on postural control and the effect of different postural tasks on eye movements in eleven children (7.8 ± 0.5 years) and nine adults (30.4 ± 6.3 years). To vary the difficulty of the oculomotor task, three conditions were tested: fixation, prosaccades (reactive saccades made toward the target) and antisaccades (voluntary saccades made in the direction opposite to the visual target). To vary the difficulty of postural control, two postural tasks were tested: Standard Romberg (SR) and Tandem Romberg (TR). Postural difficulty did not affect oculomotor behavior, except by lengthening adults' latencies in the prosaccade task. For both groups, postural control was altered in the antisaccade task as compared to fixation and prosaccade tasks. Moreover, a ceiling effect was found in the more complex postural task. This study highlighted a cortical interference between oculomotor and postural control systems.

Patrick Manckoundia1,2, France Mourey1,2, Dominic Pérennou2,3, Pierre Pfitzenmeyer1,21Department of Internal Medicine and Geriatrics, University Hospital, Dijon, France; 2INSERM/ERIT-M 0207 Motricity-Plasticity University of Burgundy, Dijon, France; 3Department of Neurological Rehabilitation, University Hospital, Dijon, FranceAbstract: Backward disequilibrium is observed frequently in daily clinical practice. However, there are no epidemiological data concerning this postural disorder. Defined by a posterior position of the centre of mass with respect to the base of support, backward disequilibrium is abnormal postural behavior, usually characterized by a posterior trunk tilt in standing and sitting positions, which predisposes subjects to backward falls. Many afflictions whether they are somatic (degenerative, ischemic and traumatic brain lesions), psychosomatic (psychomotor disadaptation syndrome, confinement to bed, nonuse situations) or psychological (depression) can cause backward disequilibrium. A vicious circle of falls, and loss of autonomy can arise and this is the main consequence of backward disequilibrium. Thus, in this paper, we review backward disequilibrium in elderly subjects with regard to the causes, consequences, assessment, and management.Keywords: backward disequilibrium, balance, elderly subject, falls, posture

International audience; Impaired postural control has been reported in patients with chronic neck pain of both traumatic and non-traumatic etiologies, but whether painful stimulation of neck muscle per se can affect balance control during quiet standing in humans remains unclear. The purpose of the present experiment was thus to investigate the effect of experimental neck muscle pain on standing balance in young healthy adults. To achieve this goal, 16 male university students were asked to stand upright as still as possible on a force platform with their eyes closed in two conditions of No pain and Pain of the neck muscles elicited by experimental painful electrical stimulation. Postural control and postural performance were assessed by the displacements of the center of foot pressure (CoP) and of the center of mass (CoM), respectively. The results showed increased CoP and CoM displacements variance, range, mean velocity, and mean and median frequencies in the Pain relative to the No pain condition. The present findings emphasize the destabilizing effect of experimental neck muscle pain per se, and more largely stress the importance of intact neck neuromuscular function on standing balance.

International audience; OBJECTIVE: We hypothesised that backward disequilibrium (BD), defined by a posterior position of the centre of mass with respect to the base of support, could be caused by a backward tilt in the perception of verticality. METHODS: The relationship between BD, the perception of verticality, and the history of falls in 25 subjects aged 84.5+/-7.4 years was analysed. An original ordinal scale, the BD scale (BDS), was used to quantify BD. Postural (PV) and haptic verticals (HV) were measured in sagittal plane. RESULTS: BDS scores closely correlated with the number of falls (r = 0.81, p =10(-5)). The more the PV was tilted backward, the greater the BDS scores (r = -0.95, p

ispartof: Annals of Physical and Rehabilitation Medicine vol:58 issue:6 pages:354-356 ispartof: location:Netherlands status: published

The primary goal of curve correction in neuromuscular patients is to restore coronal and sagittal trunk balance, including the pelvis, to maximize sitting balance. For several years, it has been a common practice to inject polymeric cement into osteoporotic bone through specially designed, perforated pedicle screws in an effort to enhance screw stability. Therefore, we started using the association of a spinopelvic fixation with S1 pedicle screw augmentation, using bisphenol-a-glycidyl dimethacrylate composite resin in neuromuscular patients with pelvic obliquity, technique in neuromuscular patients to improve pedicle screw stability of our pelvic construct. Ten patients undergoing spinopelvic fixation for a neuromuscular spinal deformity were enrolled in the study. Clinical and radiographic data were analyzed and presented. Minimal follow-up took place at 6 months to assess early complications. Five patients were diagnosed with spastic quadriplegia secondary to cerebral palsy, four had Duchenne’s muscular dystrophy, and one had a T5-level traumatic flaccid paraplegia. Preoperative PO ranged from 8° to 34° (mean 19.16°). Postoperative PO ranged from 0° to 6.3° (mean 1.6°). After surgery, all patients returned to a full-time sitting position between days 5 and 12 without the need for additional bracing. No mechanical failure of the construct was noted during follow-up. We used sacral pedicle screw augmentation as a reliable tool to strengthen spinopelvic fixation in neuromuscular scoliosis without increasing the intraoperative morbidity. In our practice, sacral screw augmentation can definitely enhance PO correction obtained by a posterior procedure.

International audience; This study investigated whether the tilt of the subjective vertical induced by galvanic vestibular stimulation, demonstrated by asking subjects to set a rod to the vertical, was specific to the visual modality or could be found in two tasks relying on proprioceptive and somatosensory cues. In all cases, settings were significantly deviated in the direction of the anode, but errors were smaller in the somatosensory tasks than in the visual task. We propose that the effects observed in the somatosensory modality reflects only a modification of the central representation of gravity, whereas visual effects are also in part the consequence of unregistered ocular torsion.

Perennou DA, Leblond C, Amblard B, Mi- callef JP, Herisson C, Pelissier JY. Transcutaneous electric nerve stimulation reduces neglect-related postural instability after stroke. Arch Phys Med Rehabil 2001;82:440-8. Objective: To test the existence of a neglect-related com- ponent of postural imbalance in some stroke patients to deter- mine whether neglect patients (1) show worse postural control compared with nonneglect patients and healthy subjects and (2) have latent postural capacities that could be unmasked by an appropriate somatosensory manipulation. Design: Intervention study with and without transcutaneous electric nerve stimulation (TENS). Setting: Rehabilitation center research laboratory. Participants: Twenty-two stroke patients (mean age, 58.3 2.5yr; average days since stroke, 83.2d) and 14 age-matched healthy subjects. Stroke patients were subdivided into 3 groups: 6 with spatial neglect and 16 without (8 with left lesion, 8 with right lesion). Interventions: All participants were subjected to a dynamic balance task, performed while sitting for 8 seconds on a later- ally rocking platform. Seated on this mobile support, they were asked to maintain actively an erect posture, sitting as still as possible. In patients, TENS was applied on the contralesional side of the neck during the postural task. An effective stimu- lation (intensity corresponding to the threshold of perception, TENS) was compared with a placebo stimulation (.01 threshold of perception, TENS). Main Outcome Measures: Postural performance in each trial was monitored by using 2 criteria: the number of aborted trials caused by loss of balance, and the angular dispersion of the support oscillations in roll. The latter criterion, which increased with body instability, was defined as 2 standard deviations of the angular distribution. Results: Patients showing neglect displayed pronounced postural instability compared with other patients and controls. Although dramatic postural instability in the neglect patients was spectacularly and systematically reduced with TENS, no effect was observed in patients without neglect.

Background. For individuals with lateral postural imbalance after stroke, the decision to adopt a cane for walking often is not based on objective findings. Objective. The authors investigated the explanatory value of 2 posturographic criteria for lateral postural imbalance on the walking abilities of poststroke subjects. Methods. Indices of postural asymmetry (percentage of body weight on the less loaded lower limb) and instability (mediolateral variance of center-of-pressure displacements) were measured in 40 healthy individuals and 52 patients (mean 94.2 days after first hemispheric stroke), who stood still on a double force platform. Cut-off values (mean ± 2 standard deviations) were calculated and compared. The predictive value of both postural indices on walking abilities with or without a cane was analyzed. Results. Of the patients, 34.6% were unstable along the mediolateral axis (variance >7 mm2), and 44.2% were asymmetrical (body weight

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.

French version available; International audience; PURPOSE: The perception of verticality results from the integration of vestibular, visual and somatosensory information. Spinal cord injured patients with complete paraplegia have total somatosensory deafferentation below a certain metameric segment. In our study, we were interested in the implication of somatosensory signal in the construction of verticality and in the possible effect of somatosensory loss on spatial representation. METHOD: We analysed haptic and postural aspects of perceived verticality in 14 spinal cord injured patients with complete paraplegia and in an age- and gender-matched group of 13 controls. We also conducted a structured interview on the existence of vertigo or postural instability in daily life. RESULTS: The spinal cord injured patients perceived verticality without any significant directional bias in the orientation of the vertical but with a greater uncertainty than control subjects, both in haptic and postural modalities. If paraplegic did not report vertigo, half described an altered spatial perception without vision. CONCLUSION: The present results confirm the importance of sensory input from the trunk and the lower limbs in the perception of the vertical. However, visual and vestibular information appear to compensate for somatosensory deafferentation.

International audience; In the present study we aimed to determine the attentional cost of postural control during adolescence by studying the influence of a cognitive task on concurrent postural control. 38 teenagers aged 12 to 17 years and 13 young adults (mean age=26.1) stood barefoot on a force platform in a semi-tandem position. A dual-task paradigm consisted of performing a Stroop or a COUNTING BACKWARD task while simultaneously standing quietly on a firm or foam support surface. Different centre of pressure (CoP) measures were calculated (90% confidence ellipse area, mean velocity, root mean square on the antero-posterior (AP) and medio-lateral (ML) axes). The number and percentage of correct responses in the cognitive tasks were also recorded. Our results indicate (1) higher values of surface, ML mean velocity and ML RMS in the COUNTING BACKWARD task in adolescents aged 12 to 15 than in teenagers aged 16 to 17 and in adults, regardless of the complexity of the postural task and, (2) better cognitive performances in the Stroop than in the COUNTING BACKWARD task. The difference in the dual-task performance between the different age groups and particularly the existence of a turning point around 14-15 years of age might be due to 1) difficulties in properly allocating attentional resources to two simultaneous tasks and/or, 2) the inability to manage increased cognitive requests because of a limited information processing capacity in adolescents aged 14-15 years.

International audience; Gait disorders and postural instability, which are commonly observed in elderly patients with Parkinson disease (PD), respond poorly to dopaminergic agents used to treat other parkinsonian symptoms. The brain structures underlying gait disorders and falls in PD and aging remain to be characterized. Using functional MRI in healthy human subjects, we have shown here that activity of the mesencephalic locomotor region (MLR), which is composed of the pedunculopontine nucleus (PPN) and the adjacent cuneiform nucleus, was modulated by the speed of imagined gait, with faster imagined gait activating a discrete cluster within the MLR. Furthermore, the presence of gait disorders in patients with PD and in aged monkeys rendered parkinsonian by MPTP intoxication correlated with loss of PPN cholinergic neurons. Bilateral lesioning of the cholinergic part of the PPN induced gait and postural deficits in nondopaminergic lesioned monkeys. Our data therefore reveal that the cholinergic neurons of the PPN play a central role in controlling gait and posture and represent a possible target for pharmacological treatment of gait disorders in PD.

International audience; The goal of this study was to establish how increased ventilation modifies postural stability, as characterized by body sway and leg muscle activities. Twelve healthy subjects had to perform six 30-second postural tests: one pre-exercise test while breathing gently and then one test every minute for the five minutes immediately following a maximum-intensity, incremental cycling exercise test. Subjects were asked to maintain an upright stance on a force plate for 30 s, with their eyes open. Movement of the centre of pressure in the sagittal plane was monitored in the time and spectral domains. Myoelectric activities of the soleus and tibialis anterior muscles were recorded using surface electromyography. Ventilatory parameters were measured with a portable, telemetric device. Postural changes related to respiratory variations were quantified by coherence analysis. The results showed that hyperventilation induced by exercise was accompanied by a significant increase in postural parameters, indicating a reduction in postural stability following a change in ventilatory drive. Coherence analysis confirmed the ventilatory origin of the postural oscillations. The results suggest that ventilation may be an important factor in postural disturbance during physical activity. The observed increases in leg muscle activities were most likely related to musculo-articular stiffening.

International audience; A postural vertical (PV) tilted backward has been put forward as a reason explaining the backward disequilibrium often observed in elderly fallers. This raises the question of a possible ageing process of the PV involving a backward tilt of verticality perception increasing with age. We have explored this hypothesis by measuring PV in pitch using the wheel paradigm in 87 healthy subjects aged from 20 to 97 years. The possibility that this physiological ageing accelerated in the second part of life was also analysed. Two indices were calculated: the mean orientation (PV-orient) and the dispersion (PV-uncert). The correlation between age and PV-orient was r = -0.2 (p < 0.05). Added to the fact that PV was twice as shifted backward in the 38 seniors over 50 years (-1.15 degrees +/- 1.40 degrees ) as in the 49 young adults under 50 years (-0.45 degrees +/- 0.97 degrees ; t = 2.75, p < 0.01), this indicates the existence of a physiological ageing process on the direction perceived as vertical by the whole body, with a slight backward shift of PV throughout the life span. The correlation between age and PV-uncert was r = 0.35 (p < 0.001) in all subjects and r = 0.59 (p < 0.001) in seniors. This indicates that subjects get less and less accurate in their perception of the postural vertical with age, especially very old subjects who show great uncertainty in determining with their body the direction of the vertical. Taken together, these findings indicate that the internal model of verticality is less robust in elderly people. This may play a part in their postural decline.

International audience; Preventing falls and fall-related fractures in the elderly is an objective yet to be reached. There is increasing evidence that a supplementation of vitamin D and/or of calcium may reduce the fall and fracture rates. A vitamin D-calcium supplement appears to have a high potential due to its simple application and its low cost. However, published studies have shown conflicting results as some studies failed to show any effect, while others reported a significant decrease of falls and fractures. Through a 15-year literature overview, and after a brief reminder on mechanism of falls in older adults, we reported evidences for a vitamin D action on postural adaptations - i.e., muscles and central nervous system - which may explain the decreased fall and bone fracture rates and we underlined the reasons for differences and controversies between published data. Vitamin D supplementation should thus be integrated into primary and secondary fall prevention strategies in older adults.

International audience; In response to repetitive proprioceptive disturbances (vibration) applied to postural muscles, the evoked response has been shown to decrease in amplitude within the first few trials. The present experiment investigated whether this attenuation of the response to vibration stimulation (90Hz, 5s) was muscle specific or would be transferred to the antagonist muscles. Sixteen participants stood upright with eyes closed. One half of the participants practiced 15 tibialis vibrations followed by 15 calf vibrations (TIB-CALF order), while the other half practiced the opposite order (CALF-TIB order). Antero-posterior trunk displacements were measured at the level of C7 and centre of foot pressure (COP). EMG activity of the tibialis anterior (TA) and gastrocnemius lateralis (GL) was also measured. Results showed that evoked postural responses as well as EMG activity decreased with practice when vibration was applied to either calf or tibialis muscles. However, such attenuation of the response appeared muscle specific since it did not generalise when the same vibration stimulus was later applied onto the antagonist muscles.

Objective: To examine the clinimetric properties and clinical applicability of published tools for `quantifying' the degree of lateropulsion or pusher syndrome following stroke. Data sources: Search through electronic databases (MEDLINE, EMBASE, CINAHL, Science Citation Index) with the terms lateropulsion, pushing, pusher syndrome, validity, reliability, internal consistency, responsiveness, sensitivity, specificity, posture and stroke. Databases were searched from their inception to October 2008. Review methods: Abstracts were selected by one author. A panel of experts then determined which should be included in this review. Five abstracts were reviewed and the panel agreed to omit one abstract because those authors did not write a full manuscript. The panel critiqued manuscripts according to predetermined criteria about clinical and clinimetric properties. Results: Four manuscripts referencing three tools for examining lateropulsion were found. Validity and reliability data support the clinical use of the Scale for Contraversive Pushing, the Modified Scale for Contraversive Pushing and the Burke Lateropulsion Scale. The Scale for Contraversive Pushing has the most extensive testing of clinimetric properties. The other tools show promising preliminary evidence of clinical and research utility. More testing is needed with larger, more diverse samples. Reviewers' conclusions: The Scale for Contraversive Pushing, the Modified Scale for Contraversive Pushing and the Burke Lateropulsion Scale are reliable and valid measures with good clinical applicability. Larger, more varied samples should be used to better delineate responsiveness and other clinimetric properties of these examination tools.

International audience; BACKGROUND: Weakness and somatosensory deficits have long been known to be involved in the postural instability of subjects with stroke. Recently, it has been shown that impaired representations of the orientation of the longitudinal axis of the body (LBA, egocentric reference) and of verticality (allocentric reference) may also play a role. The objective of the present study was to determine whether these two references were independently linked to postural asymmetry in standing stroke patients. METHODS: Twenty-two subjects were tested after a first hemispheric stroke (13 +/- 7.5 weeks). The LBA perception was investigated in the supine position by adjusting the orientation of a luminous rod in the frontal plane to correspond to the subjective LBA. The subjective visual vertical (SVV) was assessed by adjusting the orientation of a luminous line in the frontal plane to correspond to the SVV in upright patients. Weight distribution was measured in the standing position for about 2 minutes and 45 seconds by two separate force platforms under the feet. RESULTS: LBA and SVV were strongly associated (r = 0.7; p < 0.001). The estimate of the LBA was a better predictor (r = -0.52: p < 0.02) of weight bearing asymmetry than was SVV (r = -0.41; p = 0.074) when adjusted for motor weakness and hypoesthesia. CONCLUSION: Contralesional rotation of the longitudinal axis of the body could lead to unequal distribution of loading on the feet. This novel interpretation of weight bearing asymmetry underlines the complexity of control of the erect stance following stroke and brings new perspectives for rehabilitation programs.

International audience; The present experiment assessed, in children aged 7-11 and in adults, whether postural control is affected by cognitive processes and vice versa. Using a dual-task, the level of difficulty of a Stroop task and bipedal quiet stance varied alternatively. We hypothesised that the interference between cognitive and postural tasks was non-linear during childhood with a so-called turning point around 8. Twenty-seven children 7- to 11-years-old and nine adults participated in the experiments. The postural task was executed in a semi-tandem Romberg position. Two cognitive conditions (congruent and non-congruent Stroop conditions) and two postural situations (with and without perturbed proprioceptive inputs) were presented simultaneously with the instruction to respond as correctly as possible while remaining as stable as possible. Results showed that, in the Vib condition, CoP mean velocity decreased with the increased cognitive complexity only in children aged 7. Moreover, the data showed a non-linear decrease in postural sway during childhood, whatever the level of complexity of the cognitive and/or postural tasks. CoP mean amplitude and mean velocity decreased between 7 and 8, and again between age 11 and adults. This study (1) confirmed that the interference between mental activity and postural control can be attributed mainly to attentional limitations, (2) showed the existence of a turning point around 8 in the development of this capacity, and (3) suggested that the mature level of attentional resources was not reached until age 11. Further research is needed to assess the development of attention implied in a cognitive/postural dual-task, including probably another so-called turning point during the adolescence.

International audience; PURPOSE: To investigate the effectiveness of a head position-based, tongue-placed biofeedback system in providing sensory supplementation to preserve head stability in space in the absence of visual information. METHODS: Nine healthy young men with normal vision and no history of previous motor problems, neck injury, vertigo, neurologic disease, or vestibular impairment voluntarily participated in the experiment. They were asked to stand, their feet placed in a semitandem position, as immobile as possible in two conditions of No Vision and Vision and two conditions of No Biofeedback and Biofeedback. In the Biofeedback condition, subjects executed the postural task using a biofeedback system whose principle consisted of supplying them with additional information about their head orientation/motion with respect to gravitational vertical through electrotactile stimulation of the tongue. A system for the analysis of movement was used to record the head displacements. RESULTS: Without the provision of the biofeedback (No Biofeedback condition), the No Vision condition yielded increased head displacements along the mediolateral axis compared with the Vision condition. Conversely, when biofeedback was available (Biofeedback condition), no significant difference between the No Vision and Vision conditions was observed. CONCLUSIONS: These results suggest that healthy young subjects were able to efficiently use head position-based, tongue-placed biofeedback to suppress the head instability induced by the suppression of vision. Hence the present findings demonstrate the effectiveness of a head position-based, tongue-placed biofeedback in providing sensory supplementation to preserve head stability in space in conditions of absent visual information.

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, reflecting the mechanical energy expenditure. Contrary to most investigations studying optimality principles of arm movements, this model has the particularity of using a cost function that is not smooth. First, a mathematical theory related to both direct and inverse optimal control approaches is presented. The first theoretical result is the Inactivation Principle, according to which minimizing a term similar to the absolute work implies simultaneous inactivation of agonistic and antagonistic muscles acting on a single joint, near the time of peak velocity. The second theoretical result is that, conversely, the presence of non-smoothness in the cost function is a necessary condition for the existence of such inactivation. Second, during an experimental study, participants were asked to perform fast vertical arm movements with one, two, and three degrees of freedom. Observed trajectories, velocity profiles, and final postures were accurately simulated by the model. In accordance, electromyographic signals showed brief simultaneous inactivation of opposing muscles during movements. Thus, assuming that human movements are optimal with respect to a certain integral cost, the minimization of an absolute-work-like cost is supported by experimental observations. Such types of optimality criteria may be applied to a large range of biological movements., Author Summary When performing reaching and grasping movements, the brain has to choose one trajectory among an infinite set of possibilities. Nevertheless, because human and animal movements provide highly stereotyped features, motor strategies used by the brain were assumed to be optimal according to certain optimality criteria. In this study, we propose a theoretical model for motor planning of arm movements that minimizes a compromise between the absolute work exerted by the muscles and the integral of the squared acceleration. We demonstrate that under these assumptions agonistic and antagonistic muscles are inactivated during overlapping periods of time for quick enough movements. Moreover, it is shown that only this type of criterion can predict these inactivation periods. Finally, experimental evidence is in agreement with the predictions of the model. Indeed, we report the existence of simultaneous inactivation of opposing muscles during fast vertical arm movements. Therefore, this study suggests that biological movements partly optimize the energy expenditure, integrating both inertial and gravitational forces during the motor planning process.

International audience; OBJECTIVE: To compare 2 rehabilitation strategies to improve balance after stroke: (1) a multisensorial approach based on higher intensity of balance tasks and exercise during visual deprivation and (2) a conventional neurodevelopmentaltheory-based treatment (NDT) that used a general approach for sensorimotor rehabilitation. METHODS: This prospective, multicenter, randomized, parallel-group study measured outcomes with blinded assessors. Sixty-eight patients able to walk without human assistance were entered from 3 to 15 months (mean, 7 months) after a first hemispheric stroke. They received 20 sessions in 4 weeks of NDT or multisensorial rehabilitation. On day 0, day 30, and day 90, assessment included the Berg Balance Scale (BBS), posturography, gait (velocity, double stance phase, climbing 10 steps, amount of walking per day), the Functional Independence Measure, and the Nottingham Health Profile. RESULTS: All subjects improved significantly in balance and walking parameters. Regarding the main dependent variable (BBS on day 30), no difference between groups was found. Analysis of secondary outcomes suggested small differences in favor of the experimental group, but the differences are not likely to be clinically relevant. CONCLUSION: No evidence was found for the superiority of a multisensorial rehabilitation program in ambulatory patients with impairments beyond the time of inpatient therapy. Additional studies are recommended.

Background and Purpose— To analyze the postural behavior of standing stroke patients: (1) To differentiate between postural impairment attributable to the neurological condition (deficits attributable to the cerebral lesion) and postural impairment attributable to new mechanical constraints caused by body weight asymmetry; (2) To assess the involvement of each limb in the postural impairment; (3) To better understand which clinical deficits underlie the postural impairment. Methods— The posturographic characteristics of each limb in 41 stroke patients (first hemispheric stroke: 16 left, 25 right cerebral lesions) required to stand in their preferred posture were compared to those in 40 matched healthy individuals required to stand asymmetrically. Results— Compared to normal individuals in a similar asymmetrical posture, stroke patients were more unstable. The weight bearing asymmetry and the lateral postural instability were mainly related to spatial neglect. The paretic limb was unable to bring into play a normal longitudinal pattern of the center of pressure, which reflects an impaired stabilization control. Overall postural instability occurred when the strong limb was unable to compensate for the postural impairment of the paretic limb. Conclusions— The weight bearing asymmetry of standing stroke patients is not the primary cause of their postural imbalance, which is rather the consequence of impaired control of postural stabilization involving both limbs. Weight bearing asymmetry may not be the principle target of rehabilitation programs aiming at restoring standing balance after stroke. Instead it is suggested that more account should be taken of the compensatory role of the strong limb.

International audience; The representation of the vertical can be assessed by measuring the visual, tactile or perception of the postural vertical (PV). It is well accepted that visceral graviceptors and Golgi tendon receptors contribute to perception of the PV, whereas the role of muscular proprioception (Ia muscle spindles) remains to be clarified. The objective of this study was to analyze whether or not muscular proprioception contributes to the representation of verticality. We hypothesized that the modulation of proprioception by appropriate tendinomuscular vibration may tilt the PV. We present two experiments that explore this hypothesis. PV was firstly measured in the pitch plane in twelve healthy subjects in two conditions: baseline and vibration of both Achilles tendons during six minutes, according to a counterbalanced presentation. PV orientation (mean) and dispersion (standard deviation) were calculated on the six measurements per condition. Vibration of the Achilles tendons induced a systematic backward tilt of PV (2.7 degrees +/- 0.8 degrees on average; P < 10(-3)), and no significant changes regarding PV dispersion. A clear post-effect was found for PV orientation in subjects who started the experiment with the condition vibration on. The possibility that PV could also be modulated by a much shorter duration of vibration (less than 8 s of vibration) was analyzed in a second experiment using a similar general procedure but a simplified experimental plane in other subjects. Again a backward PV tilt was induced by the vibration, but with a magnitude lower than that found in the first experiment, and with no post-effect. Since body geometry was unchanged, these two studies mean that proprioception contributes to the representation of the vertical. In conclusion, this study brings new insights to our understanding of the sense of verticality and contributes to the interpretation of backward falls induced by vibration. The induced backward fall is partly due to alignment of the erect posture with a backward-tilted referential of verticality.

International audience; PURPOSE: Although there is currently no epidemiological data on backward disequilibrium, this disturbance of posture does not seem to be rare in frail elderly. ACTUALITIES AND STRONG POINTS: Backward disequilibrium is characterized by the following criteria: the location of buttocks on the anterior side of the seat while the trunk rested at the back of the armchair in the sitting position; an inadequate forward of the trunk and a backward projection of the trunk outside the base of support during sit-to-stand; and a posterior projection of the center of mass outside the base of support in the standing position. Several pathological situations either somatic (degenerative, ischemic and traumatic brain lesions), psycho-somatic (psychomotor disadaptation syndrome, extended bed confining, non-use) or psychological (depression) affections can entail backward disequilibrium. Falls, loss of autonomy and the risk of the vicious circle with its causes are the main consequences of backward disequilibrium. PROSPECTS AND PROJECTS: Although the geriatrician is familiarized with backward disequilibrium, there is no scale to quantify it. In this paper we review causes, consequences and management of backward disequilibrium, and in order to assess it, we propose a semi-quantitative scale, based on some activities of everyday living which are sitting position, sit-to-stand, back-to-sit and standing position. So, a backward disequilibrium score could be determined.

International audience; OBJECTIVES: To describe the incidence, circumstances, and consequences of falls in patients admitted in a rehabilitation ward after a stroke. METHODS: Prospective monitoring of falls over four years in a neurological rehabilitation unit. Use of fall registry. Inclusion criteria: age < 75 years, admission < 45 days after stroke onset, single stroke of 1 cerebral hemisphere (nonlacunar) or of the brain stem. Only falls due to loss of balance were considered; falls caused by a seizure or syncope were not considered. RESULTS: Of 217 consecutive patients with the inclusion criteria, 34 had fallen at least once (15.7%) and 10 twice (4.1%). Fall incidence, defined as the number of falls per patient per day was 2.2 per thousand. Half of the patients fell the first three weeks after admission. Most falls involved getting to or from the wheelchair or the bed; 1 patient had recovered minimal postural abilities at the gym but was not independent. Traumatic lesions were noted in 13 patients: they were minor in nine and severe in four, including three fractures. CONCLUSION: Falls due to loss of balance are a major problem in patients undergoing rehabilitation after a stroke. Getting to and from wheelchairs in the bedroom and bathroom by patients who are not allowed to do so play a key role in many falls. Prevention programs should consider this information.

International audience; OBJECTIVE: To investigate whether pusher behavior (ie, a tendency among stroke patients with spatial deficits to actively push away from the nonparalyzed side and to resist any attempt to hold a more upright posture) affects only the trunk, for which gravitational feedback is given by somesthetic information, or the head as well, whose gravitational information is mainly given by the vestibular system (without vision). DESIGN: Description and measurement of clinical features. SETTING: Rehabilitation center research laboratory. PARTICIPANTS: Eight healthy subjects age matched to 14 patients with left hemiplegia resulting from right-hemisphere stroke (3 pushers showing a severe spatial neglect, 11 without pusher behavior). INTERVENTION: All participants were asked to actively maintain an erect posture while sitting for 8 seconds on a rocking, laterally unstable platform. The task was performed with (in light) and without (in darkness) vision. MAIN OUTCOME MEASURES: The number of trials needed to succeed in the task was monitored. In successful trials, head, shoulders, thoracolumbar spine, and pelvis orientation in roll were measured by means of an automated, optical television image processor. RESULTS: Compared with other patients and healthy subjects, the 3 pushers missed many more trials and displayed a contralesional tilt of the pelvis but kept a correct head orientation. This tilt was especially pronounced without vision. Spatial neglect was a key factor, explaining 56% of patients' misorientation behavior with vision and 61% without vision. CONCLUSION: This pilot kinematic analysis shows that pusher behavior does not result from disrupted processing of vestibular information (eg, caused by a lesion involving the vestibular cortex); rather, it results from a high-order disruption in the processing of somesthetic information originating in the left hemibody, which could be graviceptive neglect (extinction). This disruption leads pushers to actively adjust their body posture to a subjective vertical biased to the side opposite the cerebral lesion.

International audience; In modern literature, internal models are considered as a general neural process for resolving sensory ambiguities, synthesising information from disparate sensory modalities, and combining efferent and afferent information. The polymodal sensory cortex, especially the temporoparietal junction (TPJ), is thought to be a nodal point of the network underlying these properties. According to this view, a pronounced disruption of the TPJ functioning should dramatically impair body balance. Surprisingly, little attention has been paid to this possible relationship, which was the subject of investigation in this study. Twenty-two brain-damaged patients and 14 healthy subjects were subjected to a self-regulated lateral balance task, performed while sitting for 8 s on a rocking platform. Their lateral body balance was analysed both with and without vision (darkness). Support displacements in the frontal plane were recorded by means of an accelerometer. Two criteria were taken into account to evaluate body stability in each trial: the number of aborted trials due to balance loss and the angular dispersion of the supporting surface. Lesions involving the temporoparietal junction were found to markedly increase body instability, both with and without vision. Therefore, the temporoparietal junction plays a pivotal role in lateral body stabilisation, irrespective of the sensory condition in which the task is performed. This suggests that body stability is controlled throughout internal model(s).

International audience; BACKGROUND: This study investigated the effects of obesity on attentional resources allocated to postural control in seating and unipedal standing. METHODS: Ten non obese adults (BMI = 22.4±1.3, age = 42.4±15.1) and 10 obese adult patients (BMI = 35.2±2.8, age = 46.2±19.6) maintained postural stability on a force platform in two postural tasks (seated and unipedal). The two postural tasks were performed (1) alone and (2) in a dual-task paradigm in combination with an auditory reaction time task (RT). Performing the RT task together with the postural one was supposed to require some attentional resources that allowed estimating the attentional cost of postural control. 4 trials were performed in each condition for a total of 16 trials. FINDINGS: (1) Whereas seated non obese and obese patients exhibited similar centre of foot pressure oscillations (CoP), in the unipedal stance only obese patients strongly increased their CoP sway in comparison to controls. (2) Whatever the postural task, the additional RT task did not affect postural stability. (3) Seated, RT did not differ between the two groups. (4) RT strongly increased between the two postural conditions in the obese patients only, suggesting that body schema and the use of internal models was altered with obesity. INTERPRETATION: Obese patients needed more attentional resources to control postural stability during unipedal stance than non obese participants. This was not the case in a more simple posture such as seating. To reduce the risk of fall as indicated by the critical values of CoP displacement, obese patients must dedicate a strong large part of their attentional resources to postural control, to the detriment of non-postural events. Obese patients were not able to easily perform multitasking as healthy adults do, reflecting weakened psycho-motor abilities.

International audience; The purpose of the present study was to explore the lasting effects of a tactile sensitivity enhancement induced by spike insoles on the control of stance in the elderly. Healthy elderly subjects (n = 19, mean age = 68.8) and young adults (n = 17, mean age = 24.3) were instructed to stand or to walk for 5 minutes with sandals equipped with spike insoles. Postural control was evaluated four times during unperturbed stance: (1) before putting on the sandals equipped with spike insoles, (2) 5 minutes after standing or walking with them, (3) immediately after placing thin, smooth, and flexible insoles (no spike insoles) into the sandals to avoid the cutaneous contact with the spikes, and (4) after a sitting rest of 5 minutes with the no spike insoles. Sway parameters such as surface area, mean speed and root mean square were recorded. The present results suggest that (1) whatever the session (i.e. standing or walking) and the population, the artificial sensory message elicited by the spikes improved postural sway and, (2) the elderly were particularly perturbed when the tactile sensitivity enhancement device was removed. Whatever the age, the enriched sensory context provided by this tactile sensitivity enhancement device led to a better postural control; its suppression entailed a reweighting of the plantar cutaneous information. The difficulty that the elderly had to adjust the relative contribution of the different inputs probably reflected their poorer central integrative mechanisms for the reconfiguration of the postural set. A reduced peripheral sensitivity may also explain these postural deficits.