The contribution of closed loop tracking control of motion platform on laterally induced postural instability of the drivers at SAAM dynamic simulator

This paper explains the effect of a motion platform closed loop control comparing to the static condition for driving simulators on postural instability. The postural instabilities of the participants (N=18, 15 male and 3 female subjects) were measured as lateral displacements of subject body centre of pressure (YCP ) just before and after each driving session via a balance platform. After having completed the experiments, the two-tailed Mann-Whitney U test was applied to analyze the objective data for merely the post-exposure cases. The objective data analysis revealed that the YCP for the dynamic case indicated a significant lower value than the static situation (U(18), p < 0,0001). It can be concluded that the closed loop tracking control of the hexapod platform of the driving simulator (dynamic platform condition) decreased significantly the lateral postural stability compared to the static operation condition. However the two-tailed Mann-Whitney U test showed that no significant difference was obtained between the two conditions in terms of psychophysical perception

Information decomposition of multichannel EMG to map functional interactions in the distributed motor system

The central nervous system needs to coordinate multiple muscles during postural control. Functional coordination is established through the neural circuitry that interconnects different muscles. Here we used multivariate information decomposition of multichannel EMG acquired from 14 healthy participants during postural tasks to investigate the neural interactions between muscles. A set of information measures were estimated from an instantaneous linear regression model and a time-lagged VAR model fitted to the EMG envelopes of 36 muscles. We used network analysis to quantify the structure of functional interactions between muscles and compared them across experimental conditions. Conditional mutual information and transfer entropy revealed sparse networks dominated by local connections between muscles. We observed significant changes in muscle networks across postural tasks localized to the muscles involved in performing those tasks. Information decomposition revealed distinct patterns in task-related changes: unimanual and bimanual pointing were associated with reduced transfer to the pectoralis major muscles, but an increase in total information compared to no pointing, while postural instability resulted in increased information, information transfer and information storage in the abductor longus muscles compared to normal stability. These findings show robust patterns of directed interactions between muscles that are task-dependent and can be assessed from surface EMG recorded during static postural tasks. We discuss directed muscle networks in terms of the neural circuitry involved in generating muscle activity and suggest that task-related effects may reflect gain modulations of spinal reflex pathways

A validation of mobile sensing actigraphy devices for generating a biomechanical model of posture

Mobile sensing actigraphy was tested and validated as a modality for computing dynamic posturography. Twelve healthy volunteer subjects (6 male) were administered risperidone and assessed for postural stability using a NeuroCom® Balance Master system and BioSensics® mobile sensors at baseline, 2 hours, 6 hours, and 24 hours post-dose. A strong positive correlation was shown between BioSensics and Balance Master systems in a modified Sensory Organization Task, with Pearson’s r = 0.76, p < 0.001 on composite equilibrium scores. Strong to moderate correlations during the same task showed r = 0.48, p < 0.001 to r = 0.74, p < 0.001. Mobile sensing actigraphy may be a viable alternative to force plate posturography in assessing drug-induced postural instability

The Relationship between Force Platform Measures and Total Body Center of Mass

The ability of a person to maintain stable posture is essential for activities of daily living. Research in this field has evolved to include sensitive assessment technology including force platforms and 3-dimensional kinematic motion analysis systems. Although many studies have investigated postural stability under the auspice of posturography and the use of force platforms, relatively few have incorporated kinematic motion analysis techniques. Furthermore, of the studies that have utilized a multivariate research model, none have sought to identify the relationship between force platform measures including both the variation of movement of the x- and y-coordinates of the center of pressure (COP), and the 3-dimensional coordinates of the total body center of mass (COM). This study used a descriptive design to evaluate the relationship between force platform measures and the kinematic measures dealing with the total body COM in 14 healthy participants (height = 1.70 ± 0.09 m, mass = 67.7 ± 9.9 kg; age = 24.9 ± 3.8 yrs). Intraclass correlations (ICC) and standard error of measurements (SEM) were determined for common variables of interest used in standard posturography models. The results suggest that the variation of the excursion of the COP coordinates best represent the variation of the total body COM in the x- and y-directions. There was a force platform measure that correlated significantly with the vertical component of total body COM in only 3 of the 8 conditions. The ICC values obtained when analyzing individual conditions revealed that the variation in the force measurements were much more reliable than those representing the variation in movement of the COP, suggesting a need for the development of higher order methods of modeling 3-dimensional COM information from force platforms

Interference between postural control and mental task performance in patients with vestibular disorder and healthy controls

OBJECTIVES - To determine whether interference between postural control and mental task performance in patients with balance system impairment and healthy subjects is due to general capacity limitations, motor control interference, competition for spatial processing resources, or a combination of these.METHOD - Postural stability was assessed in 48 patients with vestibular disorder and 24 healthy controls while they were standing with eyes closed on (a) a stable and (b) a moving platform. Mental task performance was measured by accuracy and reaction time on mental tasks, comprising high and low load, spatial and non-spatial tasks. Interference between balancing and performing mental tasks was assessed by comparing baseline (single task) levels of sway and mental task performance with levels while concurrently balancing and carrying out mental tasks.RESULTS - As the balancing task increased in difficulty, reaction times on both low load mental tasks grew progressively longer and accuracy on both high load tasks declined in patients and controls. Postural sway was essentially unaffected by mental activity in patients and controls.CONCLUSIONS - It is unlikely that dual task interference between balancing and mental activity is due to competition for spatial processing resources, as levels of interference were similar in patients with vestibular disorder and healthy controls, and were also similar for spatial and non-spatial tasks. Moreover, the finding that accuracy declined on the high load tasks when balancing cannot be attributed to motor control interference, as no motor control processing is involved in maintaining accuracy of responses. Therefore, interference between mental activity and postural control can be attributed principally to general capacity limitations, and is hence proportional to the attentional demands of both tasks

'SO STONED' : common sense approach of the dizzy patient

The history taking of a dizzy patient is of utmost importance in order to differentiate the possible etiologies of vertigo. The key factors that allow a first approximation of diagnosis identification are based on the time profile, symptom profile, and trigger profile of the disease. Here, the proposed mnemonic "SO STONED" comprises eight different dimensions that characterize the vertigo-related complaints of the patient and guide the clinician in his or her decision scheme. All the letters "SO STONED" have a specific meaning: Symptoms, Often (Frequency), Since, Trigger, Otology, Neurology, Evolution, and Duration. Since the most common vestibular diseases have different fingerprints when all dimensions are considered, this tool can facilitate the identification of the appropriate vestibular diagnosis

Impaired scaling of responses to vestibular stimulation in incomplete SCI

Patients with incomplete spinal cord injury (iSCI) have impaired postural control leading to a high danger of falling. Clinically, it is impossible to assess the extent to which postural instability due to sensorimotor deficit is influenced by a disturbance in the vestibulospinal pathways. Galvanic vestibular stimulation (GVS) was applied to investigate changes in the vestibular spinal responses and their potential influence on postural stability in iSCI patients. Six chronic iSCI patients and age-matched controls were stimulated with a bipolar binaural stimulus. The centre of pressure (CoP) and soleus EMG responses during free standing with closed eyes on firm and compliant ground were measured. The impairment in postural stability was assessed by the mean amplitude of CoP deflections during two minutes undisturbed standing. Although iSCI patients were significantly less stable than controls, direct GVS responses of the soleus EMG and postural sways tended to be increased on firm ground. The GVS responses increased when changing from firm to compliant ground, showing a close correlation between the extent of postural instability and the response amplitudes. Therefore, challenging proprioceptive feedback induced a significant up-modulation of the GVS responses. However, when we took the postural instability in iSCI patients into account, the EMG and CoP responses to GVS were reduced compared to controls. The combined assessment of EMG and CoP responses to GVS complements the clinical examination and permits evaluation of the preservation and modulation of vestibulospinal responses in iSC