Postural control system

The internal representation of head orientation differs for conscious perception and balance control

KEY POINTS

We tested perceived head-on-feet orientation and the direction of vestibular-evoked balance responses in passively and actively held head-turned postures. The direction of vestibular-evoked balance responses was not aligned with perceived head-on-feet orientation while maintaining prolonged passively held head-turned postures. Furthermore, static visual cues of head-on-feet orientation did not update the estimate of head posture for the balance controller. A prolonged actively held head-turned posture did not elicit a rotation in the direction of the vestibular-evoked balance response despite a significant rotation in perceived angular head posture. It is proposed that conscious perception of head posture and the transformation of vestibular signals for standing balance relying on this head posture are not dependent on the same internal representation. Rather, the balance system may operate under its own sensorimotor principles, which are partly independent from perception.

ABSTRACT

Vestibular signals used for balance control must be integrated with other sensorimotor cues to allow transformation of descending signals according to an internal representation of body configuration. We explored two alternative models of sensorimotor integration that propose (1) a single internal representation of head-on-feet orientation is responsible for perceived postural orientation and standing balance or (2) conscious perception and balance control are driven by separate internal representations. During three experiments, participants stood quietly while passively or actively maintaining a prolonged head-turned posture (>10 min). Throughout the trials, participants intermittently reported their perceived head angular position, and subsequently electrical vestibular stimuli were delivered to elicit whole-body balance responses. Visual recalibration of head-on-feet posture was used to determine whether static visual cues are used to update the internal representation of body configuration for perceived orientation and standing balance. All three experiments involved situations in which the vestibular-evoked balance response was not orthogonal to perceived head-on-feet orientation, regardless of the visual information provided. For prolonged head-turned postures, balance responses consistent with actual head-on-feet posture occurred only during the active condition. Our results indicate that conscious perception of head-on-feet posture and vestibular control of balance do not rely on the same internal representation, but instead treat sensorimotor cues in parallel and may arrive at different conclusions regarding head-on-feet posture. The balance system appears to bypass static visual cues of postural orientation and mainly use other sensorimotor signals of head-on-feet position to transform vestibular signals of head motion, a mechanism appropriate for most daily activities.

Effects of visual motion consistent or inconsistent with gravity on postural sway

Vision plays an important role in postural control, and visual perception of the gravity-defined vertical helps maintaining upright stance. In addition, the influence of the gravity field on objects' motion is known to provide a reference for motor and non-motor behavior. However, the role of dynamic visual cues related to gravity in the control of postural balance has been little investigated. In order to understand whether visual cues about gravitational acceleration are relevant for postural control, we assessed the relation between postural sway and visual motion congruent or incongruent with gravity acceleration. Postural sway of 44 healthy volunteers was recorded by means of force platforms while they watched virtual targets moving in different directions and with different accelerations. Small but significant differences emerged in sway parameters with respect to the characteristics of target motion. Namely, for vertically accelerated targets, gravitational motion (GM) was associated with smaller oscillations of the center of pressure than anti-GM. The present findings support the hypothesis that not only static, but also dynamic visual cues about direction and magnitude of the gravitational field are relevant for balance control during upright stance.

Change in the natural head-neck orientation momentarily altered sensorimotor control during sensory transition

Achilles tendon vibration generates proprioceptive information that is incongruent with the actual body position; it alters the perception of body orientation leading to a vibration-induced postural response. When a person is standing freely, vibration of the Achilles tendon shifts the internal representation of the verticality backward thus the vibration-induced postural response realigned the whole body orientation with the shifted subjective vertical. Because utricular otoliths information participates in the creation of the internal representation of the verticality, changing the natural orientation of the head-neck system during Achilles tendon vibration could alter the internal representation of the earth vertical to a greater extent. Consequently, it was hypothesized that compared to neutral head-neck orientation, alteration in the head-neck orientation should impair balance control immediately after Achilles tendon vibration onset or offset (i.e., sensory transition) as accurate perception of the earth vertical is required. Results revealed that balance control impairment was observed only immediately following Achilles tendon vibration offset; both groups with the head-neck either extended or flexed showed larger body sway (i.e., larger root mean square scalar distance between the center of pressure and center of gravity) compared to the group with the neutral head-neck orientation. The fact that balance control was uninfluenced by head-neck orientation immediately following vibration onset suggests the error signal needs to accumulate to a certain threshold before the internal representation of the earth vertical becomes incorrect.

The effect of combined mechanism ankle support on postural control of patients with chronic ankle instability

BACKGROUND

Chronic ankle instability is associated with neuromechanical changes and poor postural stability. Despite variety of mechanisms of foot and ankle orthoses, almost none apply comprehensive mechanisms to improve postural control in all subgroups of chronic ankle instability patients.

OBJECTIVES

The purpose of this study was to investigate the effect of an ankle support implementing combined mechanisms to improve postural control in chronic ankle instability patients.

STUDY DESIGN

Cross-sectional study.

METHODS

An ankle support with combined mechanism was designed based on most effective action mechanisms of foot and ankle orthoses. The effect of this orthosis on postural control was evaluated in 20 participants with chronic ankle instability and 20 matched healthy participants. The single-limb stance balance test was measured in both groups with and without the new orthosis using a force platform.

RESULTS

The results showed that application of combined mechanism ankle support significantly improved all postural sway parameters in chronic ankle instability patients. There were no differences in means of investigated parameters with and without the orthosis in the healthy group. No statistically significant differences were found in postural sway between chronic ankle instability patients and healthy participants after applying the combined mechanism ankle support.

CONCLUSION

The combined mechanism ankle support is effective in improving static postural control of chronic ankle instability patients to close to the postural sway of healthy individual. the orthosis had no adverse effects on balance performance of healthy individuals. Clinical relevance Application of the combined mechanism ankle support for patients with chronic ankle instability is effective in improving static balance. This may be helpful in reduction of recurrence of ankle sprain although further research about dynamic conditions is needed.

Targeted rehabilitation reduces visual dependency and improves balance in severe traumatic brain injury: a case study

PURPOSE

To further understand the mechanisms underlying gait impairment following traumatic brain injury.

CASE REPORT

A 58-year-old man presented with marked unsteadiness and motion sensitivity following a severe traumatic brain injury. He underwent a 6-week inpatient rehabilitation program focused on re-weighting and subsequently re-integrating ascending interoceptive information, by gradual reduction of maladaptive visual fixation techniques. We report clinical neurological outcomes and measures of functional outcome, as well as an objective assessment of visual dependency (the rod and disk test) at baseline and after the rehabilitation.

RESULTS

Clinically, the patient had gait unsteadiness exacerbated by visual motion. A significant reduction in visual dependency occurred with tailored multi-disciplinary rehabilitation via gradual removal of visual fixation strategies that the patient had developed to maintain balance (t-test; p < 0.01), as well as clinical improvements in gait, balance, and functional outcome.

CONCLUSIONS

We highlight the importance of visual dependency in the generation of maladaptive gait strategies following brain injury. Our data suggest assessing and treating visual dependency to be an important component of gait rehabilitation after traumatic brain injury. Implications for rehabilitation Whilst gait disturbance in TBI is multifactorial, abnormal visual dependency may be important but under-recognised component of the disorder. Visual dependency can be easily and objectively assessed by the bedside in patients using a dynamic rod and disc test. Tailored rehabilitation with gradual reduction of maladaptive visual fixation can reduce visual dependency and contribute to improved gait and balance following TBI.

Transitions of postural coordination as a function of frequency of the moving support platform

This study was set-up to investigate the multi-segmental organization of human postural control in a dynamic balance task. The focus was on the coupling between the center of mass (CoM) and center of pressure (CoP) as a candidate collective variable that supports maintaining balance on a sinusoidal oscillating platform in the medial-lateral (ML) plane and was continuously scaled up and then down across a frequency range from 0.2Hz to 1.2Hz. The CoM-CoP coordination changed from in-phase to anti-phase and anti-phase to in-phase at a critical frequency (∼0.4Hz to 0.6Hz, respectively) in the scaling up or down of the support surface frequency, showed hysteresis as a function of the direction of frequency change and critical fluctuations at the transition region. There was evidence of head motion independent of CoM motion at the higher platform frequencies and a learning effect on several of the dynamic indices over 2days of practice. The findings are consistent with the hypothesis of CoM-CoP acting as an emergent collective variable that is supported by the faster time scale motions of the joints and their synergies in postural control.

Head orientation of walking blowflies is controlled by visual and mechanical cues

During locomotion animals employ visual and mechanical cues in order to establish the orientation of their head, which reflects the orientation of the visual coordinate system. However, in certain situations, contradictory cues may suggest different orientations relative to the environment. We recorded blowflies walking on a horizontal or tilted surface surrounded by visual cues suggesting a variety of orientations. We found that the different orientations relative to gravity of visual cues and walking surface were integrated, with the orientation of the surface being the major contributor to head orientation, while visual cues and gravity also play an important role. In contrast, visual cues did not affect body orientation much. Cue integration was modeled as the weighted sum of orientations suggested by the different cues. Our model suggests that in case of lacking visual cues more weight is given to gravity.

Postural orientation and equilibrium processes associated with increased postural sway in autism spectrum disorder (ASD)

Background

Increased postural sway has been repeatedly documented in children with autism spectrum disorder (ASD). Characterizing the control processes underlying this deficit, including postural orientation and equilibrium, may provide key insights into neurophysiological mechanisms associated with ASD. Postural orientation refers to children’s ability to actively align their trunk and head with respect to their base of support, while postural equilibrium is an active process whereby children coordinate ankle dorsi-/plantar-flexion and hip abduction/adduction movements to stabilize their upper body. Dynamic engagement of each of these control processes is important for maintaining postural stability, though neither postural orientation nor equilibrium has been studied in ASD.

Methods

Twenty-two children with ASD and 21 age and performance IQ-matched typically developing (TD) controls completed three standing tests. During static stance, participants were instructed to stand as still as possible. During dynamic stances, participants swayed at a comfortable speed and magnitude in either anterior-posterior (AP) or mediolateral (ML) directions. The center of pressure (COP) standard deviation and trajectory length were examined to determine if children with ASD showed increased postural sway. Postural orientation was assessed using a novel virtual time-to-contact (VTC) approach that characterized spatiotemporal dimensions of children’s postural sway (i.e., body alignment) relative to their postural limitation boundary, defined as the maximum extent to which each child could sway in each direction. Postural equilibrium was quantified by evaluating the amount of shared or mutual information of COP time series measured along the AP and ML directions.

Results

Consistent with prior studies, children with ASD showed increased postural sway during both static and dynamic stances relative to TD children. In regard to postural orientation processes, children with ASD demonstrated reduced spatial perception of their postural limitation boundary towards target directions and reduced time to correct this error during dynamic postural sways but not during static stance. Regarding postural equilibrium, they showed a compromised ability to decouple ankle dorsi-/plantar-flexion and hip abduction/adduction processes during dynamic stances.

Conclusions

These results suggest that deficits in both postural orientation and equilibrium processes contribute to reduced postural stability in ASD. Specifically, increased postural sway in ASD appears to reflect patients’ impaired perception of their body movement relative to their own postural limitation boundary as well as a reduced ability to decouple distinct ankle and hip movements to align their body during standing. Our findings that deficits in postural orientation and equilibrium are more pronounced during dynamic compared to static stances suggests that the increased demands of everyday activities in which children must dynamically shift their COP involve more severe postural control deficits in ASD relative to static stance conditions that often are studied. Systematic assessment of dynamic postural control processes in ASD may provide important insights into new treatment targets and neurodevelopmental mechanisms.

Electronic supplementary material

The online version of this article (doi:10.1186/s11689-016-9178-1) contains supplementary material, which is available to authorized users.

Decreased postural control in adult survivors of childhood cancer treated with chemotherapy

The objective of cancer treatment is to secure survival. However, as chemotherapeutic agents can affect the central and peripheral nervous systems, patients must undergo a process of central compensation. We explored the effectiveness of this compensation process by measuring postural behaviour in adult survivors of childhood cancer treated with chemotherapy (CTS). We recruited sixteen adults treated with chemotherapy in childhood for malignant solid (non-CNS) tumours and 25 healthy age-matched controls. Subjects performed posturography with eyes open and closed during quiet and perturbed standing. Repeated balance perturbations through calf vibrations were used to study postural adaptation. Subjects were stratified into two groups (treatment before or from 12 years of age) to determine age at treatment effects. Both quiet (p = 0.040) and perturbed standing (p ≤ 0.009) were significantly poorer in CTS compared to controls, particularly with eyes open and among those treated younger. Moreover, CTS had reduced levels of adaptation compared to controls, both with eyes closed and open. Hence, adults treated with chemotherapy for childhood cancer may suffer late effects of poorer postural control manifested as reduced contribution of vision and as reduced adaptation skills. These findings advocate development of chemotherapeutic agents that cause fewer long-term side effects when used for treating children.

Grasp and index finger reach zone during one-handed smartphone rear interaction: effects of task type, phone width and hand length

Recently, some smartphones have introduced index finger interaction functions on the rear surface. The current study investigated the effects of task type, phone width, and hand length on grasp, index finger reach zone, discomfort, and muscle activation during such interaction. We considered five interaction tasks (neutral, comfortable, maximum, vertical, and horizontal strokes), two device widths (60 and 90 mm) and three hand lengths. Horizontal (vertical) strokes deviated from the horizontal axis in the range from -10.8° to -13.5° (81.6-88.4°). Maximum strokes appeared to be excessive as these caused 43.8% greater discomfort than did neutral strokes. The 90-mm width also appeared to be excessive as it resulted in 12.3% increased discomfort relative to the 60-mm width. The small-hand group reported 11.9-18.2% higher discomfort ratings, and the percent maximum voluntary exertion of their flexor digitorum superficialis muscle, pertaining to index finger flexion, was also 6.4% higher. These findings should be considered to make smartphone rear interaction more comfortable. Practitioner Summary: Among neutral, comfortable, maximum, horizontal, and vertical index finger strokes on smartphone rear surfaces, maximum vs. neutral strokes caused 43.8% greater discomfort. Horizontal (vertical) strokes deviated from the horizontal (vertical) axis. Discomfort increased by 12.3% with 90-mm- vs. 60-mm-wide devices. Rear interaction regions of five commercialised smartphones should be lowered 20 to 30 mm for more comfortable rear interaction.

Electrocortical Sources Related to Whole-Body Surface Translations during a Single- and Dual-Task Paradigm

Appropriate reactive motor responses are essential in maintaining upright balance. However, little is known regarding the potential location of cortical sources that are related to the onset of a perturbation during single- and dual-task paradigms. The purpose of this study was to estimate the location of cortical sources in response to a whole-body surface translation and whether diverted attention decreases the N1 event-related potential (ERP) amplitude related to a postural perturbation. This study utilized high-resolution electroencephalography in conjunction with measure projection analysis from ERPs time-locked to backwards surface translation onsets to determine which cortical sources were related to whole-body postural perturbations. Subjects (n = 15) either reacted to whole-body surface translations with (dual task) or without (single task) performing a visual working memory task. For the single task, four domains were identified that were mainly localized within the frontal and parietal lobes and included sources from the prefrontal, premotor, primary and supplementary motor, somatosensory and anterior cingulate cortex. Five domains were estimated for the dual task and also included sources within the frontal and parietal lobes, but the sources also shifted to other locations that included areas within the temporal and occipital lobes. Additionally, mean absolute N1 ERP amplitudes representing the activity from similar locations in both tasks were greater for the single than dual task. The present localization results highlight the importance of frontal, parietal and anterior cingulate cortical areas in reactive postural control and suggest a re-allocation or shift of cortical sources related to reactive balance control in the presence of a secondary task. Thus, this study provides novel insight into the underlying neurophysiology and contribution of cortical sources in relation to the neural control of reactive balance.

Postural Effects of Vestibular Manipulation Depend on the Physical Activity Status

The purpose of this study was to compare the effects of galvanic vestibular stimulation (GVS) on postural control for participants of different physical activity status (i.e. active and non-active). Two groups of participants were recruited: one group of participants who regularly practised sports activities (active group, n = 17), and one group of participants who did not practise physical and/or sports activities (non-active group, n = 17). They were compared in a reference condition (i.e bipedal stance with eyes open) and four vestibular manipulation condition (i.e. GVS at 0.5 mA and 3 mA, in accordance with two designs) lasting 20 seconds. The centre of foot pressure displacement velocities were compared between the two groups. The main results indicate that the regular practice of sports activities counteracts postural control disruption caused by GVS. The active group demonstrated better postural control than the non-active group when subjected to higher vestibular manipulation. The active group may have developed their ability to reduce the influence of inaccurate vestibular signals. The active participants could identify the relevant sensory input, thought a better central integration, which enables them to switch faster between sensory inputs.

Influence of the Plantar Cutaneous Information in Postural Regulation Depending on the Age and the Physical Activity Status

The aim was to compare the balance control adaptation to different supporting surfaces depending on the age and the physical activity status. The balance control of two groups of young (n = 17) and old (n = 17) participants who practiced regular physical activity (active groups) and two groups of young (n = 17) and old (n = 17) participants who did not practice physical activity (non-active groups) was compared on a firm surface and on a foam surface. The parameters of the center of foot pressure (COP) displacement were compared between the groups. The two older groups were more disturbed than the two younger groups when they stood on a foam surface and there was no difference between active and non-active groups. This result may be linked to the structural and functional involutions of the plantar cutaneous sole and foot that occur with age advancement. The participants' physical activity practice might be not specific enough to generate a more efficient postural adaption to the foam condition for the active groups than the non-active groups within their respective age groups.

Implicit Timing as the Missing Link between Neurobiological and Self Disorders in Schizophrenia?

Disorders of consciousness and the self are at the forefront of schizophrenia symptomatology. Patients are impaired in feeling themselves as the authors of their thoughts and actions. In addition, their flow of consciousness is disrupted, and thought fragmentation has been suggested to be involved in the patients' difficulties in feeling as being one unique, unchanging self across time. Both impairments are related to self disorders, and both have been investigated at the experimental level. Here we review evidence that both mechanisms of motor control and the temporal structure of signal processing are impaired in schizophrenia patients. Based on this review, we propose that the sequencing of action and perception plays a key role in the patients' impairments. Furthermore, the millisecond time scale of the disorders, as well as the impaired sequencing, highlights the cooperation between brain networks including the cerebellum, as proposed by Andreasen (1999). We examine this possibility in the light of recent knowledge on the anatomical and physiological properties of the cerebellum, its role in timing, and its involvement in known physiological impairments in patients with schizophrenia, e.g., resting states and brain dynamics. A disruption in communication between networks involving the cerebellum, related to known impairments in dopamine, glutamate and GABA transmission, may help to better explain why patients experience reduced attunement with the external world and possibly with themselves.

Techniques and Methods for Testing the Postural Function in Healthy and Pathological Subjects

The different techniques and methods employed as well as the different quantitative and qualitative variables measured in order to objectify postural control are often chosen without taking into account the population studied, the objective of the postural test, and the environmental conditions. For these reasons, the aim of this review was to present and justify the different testing techniques and methods with their different quantitative and qualitative variables to make it possible to precisely evaluate each sensory, central, and motor component of the postural function according to the experiment protocol under consideration. The main practical and technological methods and techniques used in evaluating postural control were explained and justified according to the experimental protocol defined. The main postural conditions (postural stance, visual condition, balance condition, and test duration) were also analyzed. Moreover, the mechanistic exploration of the postural function often requires implementing disturbing postural conditions by using motor disturbance (mechanical disturbance), sensory stimulation (sensory manipulation), and/or cognitive disturbance (cognitive task associated with maintaining postural balance) protocols. Each type of disturbance was tackled in order to facilitate understanding of subtle postural control mechanisms and the means to explore them.

Novel plasticity rule can explain the development of sensorimotor intelligence

Grounding autonomous behavior in the nervous system is a fundamental challenge for neuroscience. In particular, self-organized behavioral development provides more questions than answers. Are there special functional units for curiosity, motivation, and creativity? This paper argues that these features can be grounded in synaptic plasticity itself, without requiring any higher-level constructs. We propose differential extrinsic plasticity (DEP) as a new synaptic rule for self-learning systems and apply it to a number of complex robotic systems as a test case. Without specifying any purpose or goal, seemingly purposeful and adaptive rhythmic behavior is developed, displaying a certain level of sensorimotor intelligence. These surprising results require no system-specific modifications of the DEP rule. They rather arise from the underlying mechanism of spontaneous symmetry breaking, which is due to the tight brain body environment coupling. The new synaptic rule is biologically plausible and would be an interesting target for neurobiological investigation. We also argue that this neuronal mechanism may have been a catalyst in natural evolution.

Bioceramic fabrics improve quiet standing posture and handstand stability in expert gymnasts

Bioceramic fabrics have been claimed to improve blood circulation, thermoregulation and muscle relaxation, thereby also improving muscular activity. Here we tested whether bioceramic fabrics have an effect on postural control and contribute to improve postural stability. In Experiment 1, we tested whether bioceramic fabrics contribute to reduce body-sway when maintaining standard standing posture. In Experiment 2, we measured the effect of bioceramic fabrics on body-sway when maintaining a more instable posture, namely a handstand hold. For both experiments, postural oscillations were measured using a force platform with four strain gauges that recorded the displacements of the center of pressure (CoP) in the horizontal plane. In half of the trials, the participants wore a full-body second skin suit containing a bioceramic layer. In the other half of the trials, they wore a 'placebo' second skin suit that had the same cut, appearance and elasticity as the bioceramic suit but did not contain the bioceramic layer. In both experiments, the surface of displacement of the CoP was significantly smaller when participants were wearing the bioceramic suit than when they were wearing the placebo suit. The results suggest that bioceramic fabrics do have an effect on postural control and improve postural stability.

Effects of cold water immersion on variables of balance in healthy subjects with open and closed eyes

AbstractIntroduction Cryotherapy is the use of cold as therapeutic approach. Although often used, its impact on the postural balance is not well-known.Objectives To analyze the effects of cold water immersion in the postural balance on single-leg balance in healthy subjects through the variables of center-of-pressure, velocity anteroposterior and medial-lateral oscillations, comparing conditions open and closed eyes in the moments before, immediately, 20 and 40 minutes after cold water immersion.Material and methods Cross-sectional study with 30 male subjects, cold water immersion at 5 °C during 15 minutes assessed in a force platform, protocol of 3 trials of 30 seconds each with 10 seconds of rest, the average of the 3 trials was used for analysis. The software GraphPad Prisma 5.0 was used for statistical analysis, with the ANOVA test for repeated measures and comparisons with test of Friedman and post-test of Dunn.Results It was observed improvement of the balance by the results of the following variables: in the condition Open Eyes (OE) it was observed significant difference only in the velocity anteroposterior (AP) in the moment before immersion when compared to the 40-minute moment. Significant differences were observed in the condition Closed Eyes (CE) in the following comparisons: in the Center-of-Pressure (COP) only at the immediate moment when compared to the 40-minute moment; in the velocity AP in the moment before when compared to the 40-minute moment, in the immediate moment when compared to the 20-minute and 40-minute moments; and in the medial-lateral velocity (Vel-ML) in two comparisons: in the moment before immersion when compared to the 20-minute and 40-minute moments after cryotherapy. Results show safety in performing activities after cryotherapy.Conclusion Improvement of the postural balance after cold water immersion on the predetermined conditions of this study.

The role of cerebellar circuitry alterations in the pathophysiology of autism spectrum disorders

The cerebellum has been repeatedly implicated in gene expression, rodent model and post-mortem studies of autism spectrum disorder (ASD). How cellular and molecular anomalies of the cerebellum relate to clinical manifestations of ASD remains unclear. Separate circuits of the cerebellum control different sensorimotor behaviors, such as maintaining balance, walking, making eye movements, reaching, and grasping. Each of these behaviors has been found to be impaired in ASD, suggesting that multiple distinct circuits of the cerebellum may be involved in the pathogenesis of patients' sensorimotor impairments. We will review evidence that the development of these circuits is disrupted in individuals with ASD and that their study may help elucidate the pathophysiology of sensorimotor deficits and core symptoms of the disorder. Preclinical studies of monogenetic conditions associated with ASD also have identified selective defects of the cerebellum and documented behavioral rescues when the cerebellum is targeted. Based on these findings, we propose that cerebellar circuits may prove to be promising targets for therapeutic development aimed at rescuing sensorimotor and other clinical symptoms of different forms of ASD.

Effects of microvascular decompression surgery on posture control: A case report in an elderly patient

AIMS OF THE STUDY

We report the case of an 84-year-old woman with neurovascular conflict of the left cochleovestibular nerve. Prior to surgery, the patient complained of positional vertigo and dizziness for the past two years, and marked instability. Hearing loss and tinnitus were reported on the left side. The aim of this study was to investigate the effects of microvascular decompression of the cochleovestibular nerve on posture control.

MATERIALS AND METHODS

Evaluation of cochleovestibular function and posture control was performed before and after surgery. Postural performance was analyzed in static and dynamic conditions, with and without vision, and with optokinetic stimulation. Perception of the static visual vertical (SVV) was recorded in darkness.

RESULTS

Positional vertigo and tinnitus disappeared immediately after the decompression. The SVV remained unchanged one week after the surgery. Speech intelligibility of the left ear was improved (30 dB), and the vestibular deficit on this side was also significantly reduced (54% versus 18%). However, the more spectacular result was the effect on postural control. This elderly patient improved her postural balance in both static and dynamic conditions, and became able to maintain her equilibrium in the more challenging dynamic conditions, with and without vision, as early as one week after the surgery, a postural performance that she had been unable to do preoperatively.

CONCLUSION

This work is the first to show that the postural deficits resulting from neurovascular conflict of the cochleovestibular nerve are strongly improved after microvascular decompression.

Spatial and temporal analyses of posture in strabismic children

PURPOSE

To analyse postural performances of strabismic children, both in the spatial and the temporal domains, by wavelet transformation, comparing both stable and unstable situations.

METHODS

Twenty-six strabismic children aged from 4 to 11 years old and 26 age-matched normal children participated in the study. Postural performances were evaluated using the Framiral® platform. Posture was recorded in the following conditions: eyes open fixating a target and eyes closed on stable and unstable platforms.

RESULTS

For both strabismic and non-strabismic children, the surface and the mean velocity of the center of pressure (CoP) were significantly larger in the eyes closed on unstable platform condition, but this was much more pronounced in case of strabismus. Spectral power index and cancelling time were also found to be altered in strabismic children compared to non-strabismic children.

CONCLUSIONS

This data demonstrates poor postural stability for both groups on an unstable platform with the eyes closed. However, strabismic children had significantly worse performance than non-strabismic children. Strabismic children also engage more energy to stabilize their posture by using visuo-vestibular sensory inputs to compensate their altered vision due to strabismus, in comparison to non-strabismic children.

The efficacy of plantar stimulation on human balance control

AIM

The aim of this study was to evaluate the body sway using firm, foam, and firm textured surfaces on 17 young adults.

METHOD

Displacement of center of pressure (CoP), anteroposterior velocity (VA/P), and mediolateral velocity (VM/L) were measured.

DATA

The data showed a significant decrease of CoP, VA/P, and VM/L between support surfaces and vision.

RESULTS

The results showed that, differently from the firm and foam, the textured surface is able to increase the plantar feedback to maintaining postural control.

Evaluation of a Smartphone-based audio-biofeedback system for improving balance in older adults--a pilot study

This study was designed to assess the effectiveness of a Smartphone-based audio-biofeedback (ABF) system for improving balance in older adults. This so-called "iBalance-ABF" system that we recetly developed is "all-inclusive" in the sense that its three main components of a balance prosthesis, (i) the sensory input unit, (ii) the processing unit, and (iii) the sensory output unit, are entirely embedded into the Smartphone. The underlying principle of this system is to supply the user with supplementary information about the medial-lateral (ML) trunk tilt relative to a predetermined adjustable "dead zone" through sound generation in earphones. Six healthy older adults voluntarily participated in this pilot study. Eyes closed, they were asked to stand upright and to sway as little as possible in two (parallel and tandem) stance conditions executed without and with the use of the iBalance-ABF system. Results showed that, without any visual information, the use of the Smartphone-based ABF allowed the older healthy adults to significantly decrease their ML trunk sway in the tandem stance posture and to mitigate the destabilizing effect induced by this particular stance. Although an extended study including a larger number of participants is needed to confirm these data, the present results are encouraging. They do suggest that Smartphone-based ABF system could be used for balance training and rehabilitation therapy in older adults.

Ashtanga-Based Yoga Therapy Increases the Sensory Contribution to Postural Stability in Visually-Impaired Persons at Risk for Falls as Measured by the Wii Balance Board: A Pilot Randomized Controlled Trial

Objective

Persons with visual impairment (VI) are at greater risk for falls due to irreparable damage to visual sensory input contributing to balance. Targeted training may significantly improve postural stability by strengthening the remaining sensory systems. Here, we evaluate the Ashtanga-based Yoga Therapy (AYT) program as a multi-sensory behavioral intervention to develop postural stability in VI.

Design

A randomized, waitlist-controlled, single-blind clinical trial

Methods

The trial was conducted between October 2012 and December 2013. Twenty-one legally blind participants were randomized to an 8-week AYT program (n = 11, mean (SD) age = 55(17)) or waitlist control (n=10, mean (SD) age = 55(10)). AYT subjects convened for one group session at a local yoga studio with an instructor and two individual home-based practice sessions per week for a total of 8 weeks. Subjects completed outcome measures at baseline and post-8 weeks of AYT. The primary outcome, absolute Center of Pressure (COP), was derived from the Wii Balance Board (WBB), a standalone posturography device, in 4 sensory conditions: firm surface, eyes open (EO); firm surface, eyes closed (EC); foam surface, EO; and foam surface, EC. Stabilization Indices (SI) were computed from COP measures to determine the relative visual (SI_firm, SI_foam), somatosensory (SI_EO, SI_EC) and vestibular (SI_V, i.e., Foam_EC vs. Firm_EO) contributions to balance. This study was not powered to detect between group differences, so significance of pre-post changes was assessed by paired samples t-tests within each group.

Results

Groups were equivalent at baseline (all p > 0.05). In the AYT group, absolute COP significantly increased in the Foam_EO (t(8) = -3.66, p = 0.01) and Foam_EC (t(8) = -3.90, p = 0.01) conditions. Relative somatosensory SI_EO (t(8) = -2.42, p = 0.04) and SI_EC (t(8) = -3.96, p = 0.01), and vestibular SI_V (t(8) = -2.47, p = 0.04) contributions to balance increased significantly. As expected, no significant changes from EO to EC conditions were found indicating an absence of visual dependency in VI. No significant pre-post changes were observed in the control group (all p > 0.05).

Conclusions

These preliminary results establish the potential for AYT training to develop the remaining somatosensory and vestibular responses used to optimize postural stability in a VI population.

Trial Registration

www.ClinicalTrials.govNCT01366677

Exercise interventions improve postural control in children with cerebral palsy: a systematic review

AIM

The aim of this study was to evaluate the efficacy and effectiveness of exercise interventions that may improve postural control in children with cerebral palsy (CP).

METHOD

A systematic review was performed using American Academy of Cerebral Palsy and Developmental Medicine (AACPDM) and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology. Six databases were searched using the following keywords: ('cerebral palsy' OR 'brain injury'); AND ('postur*' OR 'balance' OR 'postural balance' [MeSH]); AND ('intervention' OR 'therapy' OR 'exercise' OR 'treatment'). Articles were evaluated based on their level of evidence and conduct.

RESULTS

Searches yielded 45 studies reporting 13 exercise interventions with postural control outcomes for children with CP. Five interventions were supported by a moderate level of evidence: gross motor task training, hippotherapy, treadmill training with no body weight support (no-BWS), trunk-targeted training, and reactive balance training. Six of the interventions had weak or conflicting evidence: functional electrical stimulation (FES), hippotherapy simulators, neurodevelopmental therapy (NDT), treadmill training with body weight support, virtual reality, and visual biofeedback. Progressive resistance exercise was an ineffective intervention, and upper limb interventions lacked high-level evidence.

INTERPRETATION

The use of exercise-based treatments to improve postural control in children with CP has increased significantly in the last decade. Improved study design provides more clarity regarding broad treatment efficacy. Research is required to establish links between postural control impairments, treatment options, and outcome measures. Low-burden, low-cost, child-engaging, and mainstream interventions also need to be explored.

Diurnal variation on balance control in patients with symptomatic knee osteoarthritis

OBJECTIVE

Increasing evidence supports balance control impairment in older adult patients with knee osteoarthritis (OA). However, there is limited data on diurnal variation of balance control in these patients. This study aimed to investigate postural stability in older adult patients with symptomatic knee OA during different periods in a daytime.

METHODS

Two-hundred and forty-one patients with OA knee (median age=65 ± 12 years; 82 males) were enrolled in this study. Static posturography was performed under four standing conditions: eyes open and eyes closed, without and with foam support. To assess diurnal postural variations, testing sessions were defined as follows: 8-10 am, 10-12 am, 1 pm-3 pm, 3 pm-5 pm. Influence of sex, age, height, weight, and body mass index on postural stability was evaluated. Knee pain was also assessed in these four testing sessions.

RESULTS

Postural control was in particular less efficient in the late morning than in the early afternoon (p<0.05). Diurnal variation of balance control was more noticeable in older, heavier, and male patients (p<0.05). Patients' knee pain was more pronounced in the morning than in the afternoon (p<0.001).

CONCLUSION

Balance stability of patients with OA knee was different during a daytime. Altered postural performance in the morning could be explained by joint pain. This diurnal variation should be taken into account in the daily management of knee OA.

The preparatory set: a novel approach to understanding stress, trauma, and the bodymind therapies

Basic to all motile life is a differential approach/avoid response to perceived features of environment. The stages of response are initial reflexive noticing and orienting to the stimulus, preparation, and execution of response. Preparation involves a coordination of many aspects of the organism: muscle tone, posture, breathing, autonomic functions, motivational/emotional state, attentional orientation, and expectations. The organism organizes itself in relation to the challenge. We propose to call this the "preparatory set" (PS). We suggest that the concept of the PS can offer a more nuanced and flexible perspective on the stress response than do current theories. We also hypothesize that the mechanisms of body-mind therapeutic and educational systems (BTES) can be understood through the PS framework. We suggest that the BTES, including meditative movement, meditation, somatic education, and the body-oriented psychotherapies, are approaches that use interventions on the PS to remedy stress and trauma. We discuss how the PS can be adaptive or maladaptive, how BTES interventions may restore adaptive PS, and how these concepts offer a broader and more flexible view of the phenomena of stress and trauma. We offer supportive evidence for our hypotheses, and suggest directions for future research. We believe that the PS framework will point to ways of improving the management of stress and trauma, and that it will suggest directions of research into the mechanisms of action of BTES.

Ankylosing spondylitis and posture control: the role of visual input

Objectives. To assess the motor control during quiet stance in patients with established ankylosing spondylitis (AS) and to evaluate the effect of visual input on the maintenance of a quiet posture. Methods. 12 male AS patients (mean age 50.1 ± 13.2 years) and 12 matched healthy subjects performed 2 sessions of 3 trials in quiet stance, with eyes open (EO) and with eyes closed (EC) on a baropodometric platform. The oscillation of the centre of feet pressure (CoP) was acquired. Indices of stability and balance control were assessed by the sway path (SP) of the CoP, the frequency bandwidth (FB1) that includes the 80% of the area under the amplitude spectrum, the mean amplitude of the peaks (MP) of the sway density curve (SDC), and the mean distance (MD) between 2 peaks of the SDC. Results. In severe AS patients, the MD between two peaks of the SDC and the SP of the center of feet pressure were significantly higher than controls during both EO and EC conditions. The MP was significantly reduced just on EC. Conclusions. Ankylosing spondylitis exerts negative effect on postural stability, not compensable by visual inputs. Our findings may be useful in the rehabilitative management of the increased risk of falling in AS.

Managing haemophilia for life: 4th Haemophilia Global Summit

The 4th Haemophilia Global Summit was held in Potsdam, Germany, in September 2013 and brought together an international faculty of haemophilia experts and delegates from multidisciplinary backgrounds. The programme was designed by an independent Scientific Steering Committee of haemophilia experts and explored global perspectives in haemophilia care, discussing practical approaches to the optimal management of haemophilia now and in the future. The topics outlined in this supplement were selected by the Scientific Steering Committee for their relevance and potential to influence haemophilia care globally. In this supplement from the meeting, Jan Astermark reviews current understanding of risk factors for the development of inhibitory antibodies and discusses whether this risk can be modulated and minimized. Factors key to the improvement of joint health in people with haemophilia are explored, with Carlo Martinoli and Víctor Jiménez-Yuste discussing the utility of ultrasound for the early detection of haemophilic arthropathy. Other aspects of care necessary for the prevention and management of joint disease in people with haemophilia are outlined by Thomas Hilberg and Sébastian Lobet, who highlight the therapeutic benefits of physiotherapy and sports therapy. Riitta Lassila and Carlo-Federico Perno describe current knowledge surrounding the risk of transmission of infectious agents via clotting factor concentrates. Finally, different types of extended half-life technology are evaluated by Mike Laffan, with a focus on the practicalities and challenges associated with these products.

Effect of a spinal brace on postural control in different sensory conditions in adolescent idiopathic scoliosis: a preliminary analysis

BACKGROUND

Despite the positive effects of spinal braces on postural stability, they may constrain movement, resulting in poor balance control in patients with adolescent idiopathic scoliosis (AIS). Therefore, assessment of postural dynamics may aid in designing new less-constraining braces.

OBJECTIVES

The effects of a spinal brace on postural stability and Cobb angle were investigated in this study.

METHODS

Thirteen pediatric patients (10 females, three males) with AIS were recruited to participate in the study. Cobb angle was assessed by X-ray analyses, and postural stability was tested by computerized dynamic posturography in braced and unbraced conditions. A polyethylene underarm corrective spinal brace was fabricated for the subjects.

RESULTS

Thoracic and lumbar curvature decreased to 18.88 ± 11.73° and 17.70 ± 10.58°, respectively, after bracing (p < 0.05). Lower equilibrium scores were observed in the "eyes closed" condition and higher scores in the "eyes closed with a swaying support" condition; higher composite equilibrium scores were also observed for the sensory organization test (p < 0.05) in the braced condition. Lower scores were observed for the "toes-up adaptation test" in the braced condition (p < 0.05). In the braced condition, the reaction time was slower in the right-backward direction and movement velocity was higher in the right-front direction on the limits of stability test (p < 0.05). Furthermore, lower on-axis velocity during forward/backward dynamic balance control was observed in the braced condition (p < 0.05).

CONCLUSIONS

Wearing a spinal brace improved postural stability in terms of increased proprioception, equilibrium performance, and rhythmic movement ability in patients with AIS.

Long-term effects from bacterial meningitis in childhood and adolescence on postural control

Bacterial meningitis in childhood is associated with cognitive deficiencies, sensorimotor impairments and motor dysfunction later in life. However, the long-term effects on postural control is largely unknown, e.g., whether meningitis subjects as adults fully can utilize visual information and adaptation to enhance stability. Thirty-six subjects (20 women, mean age 19.3 years) treated in childhood or adolescence for bacterial meningitis, and 25 controls (13 women, mean age 25.1 years) performed posturography with eyes open and closed under unperturbed and perturbed standing. The meningitis subjects were screened for subjective vertigo symptoms using a questionnaire, clinically tested with headshake and head thrust test, as well as their hearing was evaluated. Meningitis subjects were significantly more unstable than controls during unperturbed (p≤0.014) and perturbed standing, though while perturbed only with eyes open in anteroposterior direction (p = 0.034) whereas in lateral direction both with eyes open and closed (p<0.001). Meningitis subjects had poorer adaption ability to balance perturbations especially with eyes open, and they frequently reported symptoms of unsteadiness (88% of the subjects) and dizziness (81%), which was found significantly correlated to objectively decreased stability. Out of the 36 subjects only 3 had unilateral hearing impairment. Hence, survivors of childhood bacterial meningitis may suffer long-term disorders affecting postural control, and would greatly benefit if these common late effects became generally known so treatments can be developed and applied.

Postural instability detection: aging and the complexity of spatial-temporal distributional patterns for virtually contacting the stability boundary in human stance

Falls among the older population can severely restrict their functional mobility and even cause death. Therefore, it is crucial to understand the mechanisms and conditions that cause falls, for which it is important to develop a predictive model of falls. One critical quantity for postural instability detection and prediction is the instantaneous stability of quiet upright stance based on motion data. However, well-established measures in the field of motor control that quantify overall postural stability using center-of-pressure (COP) or center-of-mass (COM) fluctuations are inadequate predictors of instantaneous stability. For this reason, 2D COP/COM virtual-time-to-contact (VTC) is investigated to detect the postural stability deficits of healthy older people compared to young adults. VTC predicts the temporal safety margin to the functional stability boundary ( =  limits of the region of feasible COP or COM displacement) and, therefore, provides an index of the risk of losing postural stability. The spatial directions with increased instability were also determined using quantities of VTC that have not previously been considered. Further, Lempel-Ziv-Complexity (LZC), a measure suitable for on-line monitoring of stability/instability, was applied to explore the temporal structure or complexity of VTC and the predictability of future postural instability based on previous behavior. These features were examined as a function of age, vision and different load weighting on the legs. The primary findings showed that for old adults the stability boundary was contracted and VTC reduced. Furthermore, the complexity decreased with aging and the direction with highest postural instability also changed in aging compared to the young adults. The findings reveal the sensitivity of the time dependent properties of 2D VTC to the detection of postural instability in aging, availability of visual information and postural stance and potential applicability as a predictive model of postural instability during upright stance.

Time-interval for integration of stabilizing haptic and visual information in subjects balancing under static and dynamic conditions

Maintaining equilibrium is basically a sensorimotor integration task. The central nervous system (CNS) continually and selectively weights and rapidly integrates sensory inputs from multiple sources, and coordinates multiple outputs. The weighting process is based on the availability and accuracy of afferent signals at a given instant, on the time-period required to process each input, and possibly on the plasticity of the relevant pathways. The likelihood that sensory inflow changes while balancing under static or dynamic conditions is high, because subjects can pass from a dark to a well-lit environment or from a tactile-guided stabilization to loss of haptic inflow. This review article presents recent data on the temporal events accompanying sensory transition, on which basic information is fragmentary. The processing time from sensory shift to reaching a new steady state includes the time to (a) subtract or integrate sensory inputs; (b) move from allocentric to egocentric reference or vice versa; and (c) adjust the calibration of motor activity in time and amplitude to the new sensory set. We present examples of processes of integration of posture-stabilizing information, and of the respective sensorimotor time-intervals while allowing or occluding vision or adding or subtracting tactile information. These intervals are short, in the order of 1–2 s for different postural conditions, modalities and deliberate or passive shift. They are just longer for haptic than visual shift, just shorter on withdrawal than on addition of stabilizing input, and on deliberate than unexpected mode. The delays are the shortest (for haptic shift) in blind subjects. Since automatic balance stabilization may be vulnerable to sensory-integration delays and to interference from concurrent cognitive tasks in patients with sensorimotor problems, insight into the processing time for balance control represents a critical step in the design of new balance- and locomotion training devices.