Benefits of postural sway to succeed in goal-directed visual tasks.

When individuals stand, they sway and so have to maintain their balance. It is generally expected that task performance is worse when standing and swaying than when sitting and therefore not swaying. In contrast, we hypothesized that greater sway is associated with better task performance in the absence of external perturbations of posture. Twenty-four healthy, young adults performed two goal-directed, modified Stroop tasks (incongruent and reversed incongruent) in four body position conditions (standing against a vertical surface, and standing freely with a wide, standard or narrow stance). Centre of pressure (COP) sway, head sway, eye movements, visual attention, and task performance were recorded. Partial correlation analyses showed significant positive associations between task performance and some COP and head sway variables, after controlling for the level of visual attention. Analyses of variance with three factors (body position, task difficulty, target distance) also showed significant interaction effects between body position (and therefore postural sway) and the number of accurate target findings. The presence of these interactions showed that narrow stance was both the best body position for performing the incongruent task and the worst body position for performing the reversed incongruent task. Overall, COP sway and head sway can increase task performance. Hence, healthy, young adults in quiet stance appear to use sway to explore their environment more effectively. However, it should be borne in mind that our hypothesis was formulated solely with regard to healthy, young adults standing in quiet stance.

Low-intensity vestibular noise stimulation improves postural symptoms in progressive supranuclear palsy.

BACKGROUND: Postural imbalance and falls are an early disabling symptom in patients with progressive supranuclear palsy (PSP) of multifactorial origin that may involve abnormal vestibulospinal reflexes. Low-intensity noisy galvanic vestibular stimulation (nGVS) is a non-invasive treatment to normalize deficient vestibular function and attenuate imbalance in Parkinson's disease. The presumed therapeutic mode of nGVS is stochastic resonance (SR), a mechanism by which weak sensory noise stimulation can enhance sensory information processing. OBJECTIVE: To examine potential treatment effects of nGVS on postural instability in 16 patients with PSP with a clinically probable and [18F]PI-2620 tau-PET-positive PSP. METHODS: Effects of nGVS of varying intensity (0-0.7 mA) on body sway were examined, while patients were standing with eyes closed on a posturographic force plate. We assumed a bell-shaped response curve with maximal sway reductions at intermediate nGVS intensities to be indicative of SR. An established SR-curve model was fitted on individual patient outcomes and three experienced human raters had to judge whether responses to nGVS were consistent with the exhibition of SR. RESULTS: We found nGVS-induced reductions of body sway compatible with SR in 9 patients (56%) with optimal improvements of 31 ± 10%. In eight patients (50%), nGVS-induced sway reductions exceeded the minimal clinically important difference (improvement: 34 ± 5%), indicative of strong SR. CONCLUSION: nGVS yielded clinically relevant reductions in body sway compatible with the exhibition of SR in vestibular sensorimotor pathways in at least half of the assessed patients. Non-invasive vestibular noise stimulation may be thus a well-tolerated treatment strategy to ameliorate postural symptoms in PSP.

Sound and postural control during stance tasks in abnormal subjective haptic vertical.

BACKGROUND: Patients with vestibular impairment often suffer from postural instability. This could be compensated by other sensory systems such as the auditory system. OBJECTIVE: The aim of this study was to investigate whether auditory input improves postural stability in patients with abnormal subjective haptic vertical (SHV). METHODS: Participants (n = 13) with normal hearing and vision, but abnormal SHV participated. Participants performed standing on firm ground and foam support (eyes open/closed) and Tandem Romberg test (eyes closed) in quiet (reference), noise and with plugged ears. All tasks were conducted in a soundproofed and reverberant room. Postural stability was recorded close to the body's center of gravity. Reference conditions were compared with a control group. RESULTS: In only two tasks sway increased significantly when noise was presented during challenging tasks in the soundproofed room. Sway of the reference conditions did not differ significantly between control and study group. CONCLUSIONS: This study shows no influence of applied auditory stimulation on posture in participants with abnormal SHV in a reverberant room, but an adverse effect on balance during difficult tasks in the soundproofed room. Noise possibly masked auditory information that was helpful in improving posture in the quiet condition. Futhermore, noise might have distracted participants from maintaining balance.

Can I see it in the eyes? An investigation of freezing-like motion patterns in response to avoidable threat.

Freezing is one of the most extensively studied defensive behaviors in rodents. Both reduced body and gaze movements during anticipation of threat also occur in humans and have been discussed as translational indicators of freezing but their relationship remains unclear. We thus set out to elucidate body and eye movements and concomitant autonomic dynamics in anticipation of avoidable threat. Specifically, 50 participants viewed naturalistic pictures that were preceded by a colored fixation cross, signaling them whether to expect an inevitable (shock), no (safety), or a potential shock (flight) that could be avoided by a quick button press. Body sway, eye movements, the heart rate and skin conductance were recorded. We replicated previously described reductions in body sway, gaze dispersion, and the heart rate, and a skin conductance increase in flight trials. Stronger reductions in gaze but not in body sway predicted faster motor reactions on a trial-wise basis, highlighting their functional role in action preparation. We failed to find a trait-like relationship between body and gaze movements across participants, but their temporal profiles were positively related within individuals, suggesting that both metrics partly reflect the same construct. However, future research is desirable to assess these response patterns in naturalistic environments. A more ethological examination of different movement dynamics upon threat would not only warrant better comparability between rodent and human research but also help determine whether and how eye-tracking could be implemented as a proxy for fear-related movements in restricted brain imaging environments.

Instrumented Balance Error Scoring System in Children and Adolescents-A Cross Sectional Study.

Background: The Balance Error Scoring System (BESS) is a commonly used method for clinically evaluating balance after traumatic brain injury. The utilization of force plates, characterized by their cost-effectiveness and portability, facilitates the integration of instrumentation into the BESS protocol. Despite the enhanced precision associated with instrumented measures, there remains a need to determine the clinical significance and feasibility of such measures within pediatric cohorts. Objective: To report a comprehensive set of posturographic measures obtained during instrumented BESS and to examine the concurrent validity, reliability, and feasibility of instrumented BESS in the pediatric point of care setting. Methods: Thirty-seven participants (18 female; aged 13.32 ± 3.31 years) performed BESS while standing on a force plate to simultaneously compute stabilometric measures (instrumented BESS). Ellipse area (EA), path length (PL), and sway velocity (VM) were obtained for each of the six BESS positions and compared with the respective BESS scores. Additionally, the effects of sex and age were explored. A second BESS repetition was performed to evaluate the test-retest reliability. Feedback questionnaires were handed out after testing to evaluate the feasibility of the proposed protocol. Results: The BESS total score was 20.81 ± 6.28. While there was no statistically significant age or sex dependency in the BESS results, instrumented posturography demonstrated an age dependency in EA, VM, and PL. The one-leg stance on a soft surface resulted in the highest BESS score (8.38 ± 1.76), EA (218.78 cm2 ± 168.65), PL (4386.91 mm ± 1859.00), and VM (21.93 mm/s ± 9.29). The Spearman's coefficient displayed moderate to high correlations between the EA (rs = 0.429-0.770, p = 0.001-0.009), PL (rs = 0.451-0.809, p = 0.001-0.006), and VM (rs = 0.451-0.809, p = 0.001-0.006) when compared with the BESS scores for all testing positions, except for the one-leg stance on a soft surface. The BESS total score significantly correlated during the first and second repetition (rs = 0.734, p ≤ 0.001), as did errors during the different testing positions (rs = 0.489-0.799, p ≤ 0.001-0.002), except during the two-legged stance on a soft surface. VM and PL correlated significantly in all testing positions (rs = 0.465-0.675, p ≤ 0.001-0.004; (rs = 0.465-0.675, p ≤ 0.001-0.004), as did EA for all positions except for the two-legged stance on a soft surface (rs = 0.392-0.581, p ≤ 0.001-0.016). A total of 92% of participants stated that the instructions for the testing procedure were very well-explained, while 78% of participants enjoyed the balance testing, and 61% of participants could not decide whether the testing was easy or hard to perform. Conclusions: Instrumented posturography may complement clinical assessment in investigating postural control in children and adolescents. While the BESS score only allows for the consideration of a total score approximating postural control, instrumented posturography offers several parameters representing the responsiveness and magnitude of body sway as well as a more differentiated analysis of movement trajectory. Concise instrumented posturography protocols should be developed to augment neuropediatric assessments in cases where a deficiency in postural control is suspected, potentially stemming from disruptions in the processing of visual, proprioceptive, and/or vestibular information.

Mechanisms underlying treatment effects of vestibular noise stimulation on postural instability in patients with bilateral vestibulopathy.

BACKGROUND: Previous studies indicate that imbalance in patients with bilateral vestibulopathy (BVP) may be reduced by treatment with low-intensity noisy galvanic vestibular stimulation (nGVS). OBJECTIVE: To elucidate the potential mechanisms underlying this therapeutic effect. In particular, we determined whether nGVS-induced balance improvements in patients are compatible with stochastic resonance (SR)-a mechanism by which weak noise stimulation can paradoxically enhance sensory signal processing. METHODS: Effects of nGVS of varying intensities (0-0.7 mA) on body sway were examined in 19 patients with BVP standing with eye closed on a posturographic force plate. We assumed a bell-shaped response curve with maximal sway reductions at intermediate nGVS intensities to be indicative of SR. An established SR curve model was fitted on individual patient outcomes, and three experienced human raters had to judge whether responses to nGVS were consistent with the exhibition of SR. RESULTS: nGVS-induced reductions of body sway compatible with SR were found in 12 patients (63%) with optimal improvements of 31 ± 21%. In 10 patients (53%), nGVS-induced sway reductions exceeded the minimally important clinical difference (optimal improvement: 35 ± 21%), indicative of strong SR. This beneficial effect was more likely in patients with severe vestibular loss (i.e. lower video head impulse test gain; R = 0.663; p = 0.002) and considerable postural imbalance (baseline body sway; R = 0.616; p = 0.005). CONCLUSIONS: More than half of the assessed patients showed robust improvements in postural balance compatible with SR when treated with nGVS. In particular, patients with a higher burden of disease may benefit from the non-invasive and well-tolerated treatment with nGVS.

Fear of heights shapes postural responses to vibration-induced balance perturbation at virtual height.

Introduction: Standing upright at height is a challenging situation involving intense threat of balance loss and fall. The ability to maintain balance in such conditions requires properly resolving sensory conflicts and is influenced by fear. To get more insight on the role of fear in balance control at height, we explored the dynamics of postural behavior in the situation of enhanced threat of potential balance loss. Methods: In 40 young individuals with varying fear of heights, we combined simulated exposure to height in a virtual reality environment with bilateral vibration of tibialis anterior muscles which evokes posture destabilization (the so-called vibration-induced falling). Results: Under such condition of enhanced postural threat, individuals with intense fear of heights showed stronger stiffening of posture compared with individuals with low fear of heights who react more flexibly and adaptively to posture destabilization. This group difference was evident already at ground level but further increased during virtual height exposure. Discussion: Our data show that fear of height significantly affects posture adaptation to balance-destabilizing events. Our findings demonstrate that the assessment of postural behavior during threatening situations in the virtual reality environment provides valuable insights into the mechanisms of balance control and may be used to develop novel strategies aimed at prevention of falls.

The 'Postural Rhythm' of the Ground Reaction Force during Upright Stance and Its Conversion to Body Sway-The Effect of Vision, Support Surface and Adaptation to Repeated Trials.

The ground reaction force (GRF) recorded by a platform when a person stands upright lies at the interface between the neural networks controlling stance and the body sway deduced from centre of pressure (CoP) displacement. It can be decomposed into vertical (VGRF) and horizontal (HGRF) vectors. Few studies have addressed the modulation of the GRFs by the sensory conditions and their relationship with body sway. We reconsidered the features of the GRFs oscillations in healthy young subjects (n = 24) standing for 90 s, with the aim of characterising the possible effects of vision, support surface and adaptation to repeated trials, and the correspondence between HGRF and CoP time-series. We compared the frequency spectra of these variables with eyes open or closed on solid support surface (EOS, ECS) and on foam (EOF, ECF). All stance trials were repeated in a sequence of eight. Conditions were randomised across different days. The oscillations of the VGRF, HGRF and CoP differed between each other, as per the dominant frequency of their spectra (around 4 Hz, 0.8 Hz and <0.4 Hz, respectively) featuring a low-pass filter effect from VGRF to HGRF to CoP. GRF frequencies hardly changed as a function of the experimental conditions, including adaptation. CoP frequencies diminished to <0.2 Hz when vision was available on hard support surface. Amplitudes of both GRFs and CoP oscillations decreased in the order ECF > EOF > ECS ≈ EOS. Adaptation had no effect except in ECF condition. Specific rhythms of the GRFs do not transfer to the CoP frequency, whereas the magnitude of the forces acting on the ground ultimately determines body sway. The discrepancies in the time-series of the HGRF and CoP oscillations confirm that the body's oscillation mode cannot be dictated by the inverted pendulum model in any experimental conditions. The findings emphasise the robustness of the VGRF "postural rhythm" and its correspondence with the cortical theta rhythm, shed new insight on current principles of balance control and on understanding of upright stance in healthy and elderly people as well as on injury prevention and rehabilitation.

Motion analysis of dyadic talk during joint search and decision-making - A replication study.

Human interaction frequently includes decision-making processes during which interactants call on verbal and non-verbal resources to manage the flow of interaction. In 2017, Stevanovic et al. carried out pioneering work, analyzing the unfolding of moment-by-moment dynamics by investigating the behavioral matching during search and decision-making phases. By studying the similarities in the participant's body sway during a conversation task in Finnish, the authors showed higher behavioral matching during decision phases than during search phases. The purpose of this research was to investigate the whole-body sway and its coordination during joint search and decision-making phases as a replication of the study by Stevanovic et al. (2017) but based on a German population. Overall, 12 dyads participated in this study and were asked to decide on 8 adjectives, starting with a pre-defined letter, to describe a fictional character. During this joint-decision task (duration: 206.46 ± 116.08 s), body sway of both interactants was measured using a 3D motion capture system and center of mass (COM) accelerations were computed. Matching of body sway was calculated using a windowed cross correlation (WCC) of the COM accelerations. A total of 101 search and 101 decision phases were identified for the 12 dyads. Significant higher COM accelerations (5.4*10-3 vs. 3.7*10-3 mm/s2, p < 0.001) and WCC coefficients (0.47 vs. 0.45, p = 0.043) were found during decision-making phases than during search phases. The results suggest that body sway is one of the resources humans use to communicate the arrival at a joint decision. These findings contribute to a better understanding of interpersonal coordination from a human movement science perspective.

The relationship between body sway patterns and motor and attentional functions in early childhood.

[Purpose] We focused on the relationship between body sway patterns and motor and attentional functions in early childhood, and classified diagrams of body sway into four patterns. Furthermore, the relationship between physical fitness tests and Interactive Metronome (IM) tasks was used to determine whether the body sway patterns are indicators of motor and attentional functions in early childhood. [Participants and Methods] Participants were 24 male and 26 female children with a mean age of 2,148.1 ± 103.7 days. Participants were evaluated using physical fitness tests, body sway measures, baseline scores on the IM task (the "task average"), and the percentage of perfect hits ("Super Right On") on the IM task (the "Super Right On" score, or SRO%). [Results] The association between the body sway pattern and motor and attentional functions was examined, and results revealed that the body sway pattern was only slightly associated with motor functions. However, participants with an anterior-posterior pattern of body sway had worse timing and attentional functions than participants with other patterns, as indicated by a lower task average and SRO% on the IM task. [Conclusion] These results suggested that anterior-posterior sway may reflect attentional functions when body sway is measured in children such as 6 year-olds.

Effects of passive interpersonal light touch during walking on postural control responses: An exploratory study.

The effects of passive interpersonal light touch (PILT) on postural stability can be observed through improved postural coordination through haptic feedback from the contact provider to the contact receiver while walking. It is unclear, however, whether PILT affects the contact receiver's detailed physical responses, such as muscle activity, body sway, and joint movements. In this study, surface electromyography and an inertial measurement unit were used simultaneously to explore changes in walking speed and control responses induced by PILT. We evaluated fourteen healthy participants for their walking speed and physical responses under two walking conditions: no-touch (NT) and PILT. As a physical response during walking, we measured muscle activity (rectus femoris, semitendinosus, tibialis anterior, and soleus muscles), body sway (pelvis and neck), and joint angles (direction of hip, knee, and ankle joint movements). In PILT condition, fingertip contact force was measured while the contact provider touched the third level of the recipient's lumbar spine. In comparison with the NT condition, PILT condition increased walking speed and decreased body sway on neck position. There were significant correlations between walking speed and neck sway regarding NT and PILT change values. Passive haptic information to the contact receiver may assist in the smooth shift of the center of gravity position during gait through interpersonal postural coordination. These findings suggest that PILT may provide an efficient and stable gait.

How well can we detect cervical driven sensorimotor dysfunction in concussion patients? An observational study comparing patients with idiopathic neck pain, whiplash associated disorders and concussion.

BACKGROUND: Patients with mild traumatic brain injury (mTBI) suffer from sensorimotor impairments. Evidence is emerging that cervical spine plays an important role in mTBI, but it is not known how cervicocephalic kinaesthetic sensibility measured during dynamic unpredictable head movements and measures of position sense, cervical induced postural balance and eye movement control differ between mTBI, whiplash associated disorders (WAD) patients, idiopathic neck pain patients and healthy controls. RESEARCH QUESTION: Are cervical sensorimotor deficits present in mTBI patients and do they differ from sensorimotor deficits found in traumatic and nontraumatic neck pain patients and whether they differ from healthy controls. METHODS: Twenty idiopathic neck pain patients, 18 WAD, 17 mTBI and 20 healthy controls were enroled in the study. Frequency and velocity of centre of pressure movements were measured during parallel stance in the neutral and neck torsion positions, gain and smooth pursuit neck torsion difference of eye movements during smooth pursuit neck torsion test (SPNTT) and cervicocephalic kinaesthesia using Butterfly and head-to-neutral relocation test. RESULTS: Statistically significant differences in postural balance, both tests of cervicocephalic kinaesthesia and SPNTT were observed between healthy controls and all patient groups. No differences were observed between patient groups for SPNTT, Butterfly and head-to-neutral relocation test, but differences were present in postural balance between mTBI and both groups of patients with neck pain disorders. Differences were found in the ML direction for mTBI, but not differences were found for AP direction. SIGNIFICANCE: Results of our study show that mTBI present with similar impairment in cervical driven sensorimotor deficits as patients with neck pain disorders, but they differ from healthy individuals. Clinical practice would benefit from identifying cervical spine related sensorimotor impairments in patients with mTBI. This could enable to design more targeted prevention and rehabilitation programs to minimise cervical spine related disorders in concussion patients.

Reliability and minimal detectable change of body-weight distribution and body sway between right and left brain-damaged patients at a chronic stage.

PURPOSE: To assess the reliability and minimal detectable change (MDC) of weight-bearing asymmetry (WBA) and body sway (BS) during "eyes open" (EO) and "eyes closed" (EC) conditions for those with right brain damage (RBD) and left brain damage (LBD) at a chronic stage. METHODS: Sixteen RBD and 16 LBD patients participated in two sessions within 15 days, composed of two trials of 30 s using a double force platform. Intraclass correlation coefficient (ICC2,1), the standard error of measurement (SEM), and MDC were calculated for WBA and BS (area and velocity of sway). RESULTS: Reliability of WBA was excellent (>0.75) except for EC for LBD patients (low SEM was found). The condition of EC was similar to or less reliable than that of EO. The MDC of WBA was 5.4 and 7.3% for LBD and RBD patients, respectively. Velocity of sway should be favored over the area of sway due to better reliability, with an MDC of 9 and 13 mm/s for RBD and LBD patients, respectively. CONCLUSIONS: Parameters related to WBA and BS were highly reliable, without a difference between RBD and LBD patients, but less so in the condition of EC, and could be used for clinical rehabilitation and/or research.Implications for rehabilitationWeight-bearing asymmetry (WBA) and body sway (BS) are highly reliable posturography parameters.Reliability of WBA/BS is similar among right brain damaged (RBD) and left brain damaged (LBD) patients.A change of 5-7% can be interpreted as significant for WBA for chronic stroke.The minimal detectable change in measures is slightly higher for RBD patients.

Less Vibrotactile Feedback Is Effective to Improve Human Balance Control during Sensory Cues Alteration.

For individuals with altered sensory cues, vibrotactile feedback improves their balance control. However, should vibrotactile feedback be provided every time balance control is compromised, or only one-third of the time their balance is compromised? We hypothesized that vibrotactile feedback would improve balance control more when provided every time their balance is compromised. Healthy young adults were randomly assigned to two groups: group 33% feedback (6 males and 6 females) and group 100% feedback (6 males and 6 females). Vibrotactile feedbacks related to the body's sway angle amplitude and direction were provided, while participants stood upright on a foam surface with their eyes closed. Then, we assessed if balance control improvement lasted when the vibrotactile feedback was removed (i.e., post-vibration condition). Finally, we verified whether or not vibrotactile feedback unrelated to the body's sway angle and direction (sham condition) altered balance control. The results revealed no significant group difference in balance control improvement during vibrotactile feedback. Immediately following vibrotactile feedback, both groups reduced their balance control commands; body sway velocity and the ground reaction forces variability decreased. For both groups, unrelated vibrotactile feedback worsened balance control. These results confirmed that participants processed and implemented vibrotactile feedback to control their body sways. Less vibrotactile feedback was effective in improving balance control.

Differences in body sway can be identified in Huntington's disease using a practical balance assessment device.

INTRODUCTION: Huntington's disease (HD) is a progressive neurodegenerative disorder with motor, cognitive, and psychiatric symptoms that typically manifest in middle adulthood. Balance assessments may be useful for predicting disease onset and progression, but studies are limited. We aimed to enhance estimates of HD onset using an inexpensive and practical body sway assessment device [i.e., Wii Balance Board (WBB)]. METHODS: We assessed total body sway (TBS) on 64 HD gene carriers [Presymptomatic HD (PsHD; n = 16); Prodromal HD (ProHD; n = 16); HD (n = 32)] and 21 demographically similar normal controls (NC) employing a WBB and custom-designed laptop software. Participants completed balance test trials that included combinations of eyes open or closed while standing on a stable versus unstable surface. Non-parametric analyses were conducted to assess group differences in TBS conditions. RESULTS: The HD group had significantly higher TBS in most balance conditions relative to NC, PsHD, and ProHD groups (ps < .05). Importantly, the ProHD group demonstrated higher TBS relative to NC in all balance conditions (ps < .05) with medium to large effect size ranges (r≥ 0.40). No differences in TBS were exhibited between NC and PsHD groups (ps > .05). CONCLUSIONS: Increased body sway, easily evaluated using a brief, objective balance assessment, may serve as an important functional marker in patients with, and during the transition to, HD. Further studies are needed to confirm and extend these findings.

Vertical ground reaction force oscillation during standing on hard and compliant surfaces: The "postural rhythm".

When a person stands upright quietly, the position of the Centre of Mass (CoM), the vertical force acting on the ground and the geometrical configuration of body segments is accurately controlled around to the direction of gravity by multiple feedback mechanisms and by integrative brain centres that coordinate multi-joint movements. This is not always easy and the postural muscles continuously produce appropriate torques, recorded as ground reaction force by a force platform. We studied 23 young adults during a 90 s period, standing at ease on a hard (Solid) and on a compliant support (Foam) with eyes open (EO) and with eyes closed (EC), focusing on the vertical component of the ground reaction force (VGRF). Analysis of VGRF time series gave the amplitude of their rhythmic oscillations (the root mean square, RMS) and of their frequency spectrum. Sway Area and Path Length of the Centre of Pressure (CoP) were also calculated. VGRF RMS (as well as CoP sway measures) increased in the order EO Solid ≈ EC Solid < EO Foam < EC Foam. The VGRF frequency spectra featured prevailing frequencies around 4-5 Hz under all tested conditions, slightly higher on Solid than Foam support. Around that value, the VGRF frequencies varied in a larger range on hard than on compliant support. Sway Area and Path Length were inversely related to the prevailing VGRF frequency. Vision compared to no-vision decreased Sway Area and Path Length and VGRF RMS on Foam support. However, no significant effect of vision was found on VGRF mean frequency for either base of support condition. A description of the VGRF, at the interface between balance control mechanisms and sway of the CoP, can contribute information on how upright balance is maintained. Analysis of the frequency pattern of VGRF oscillations and its role in the maintenance of upright stance should complement the traditional measures of CoP excursions in the horizontal plane.

Aging effects of haptic input on postural control under a dual-task paradigm.

Postural control relies on three principal sensory systems: vision, vestibular and proprioceptive; that are affected by aging. When performing a cognitive task concomitantly with a motor task, those sensory impairments lead to even greater deleterious effects on balance. We aimed to study the effects of a sensory aid (a light touch) on a dual task paradigm and sought to understand the different responses on balance due to aging. Fifty healthy and highly physical active women were divided in two groups: young (N = 25, 24.2 ± 4.0 years) and older adults (N = 25, 67.3 ± 4.2 years). In a random and balanced order, all participants performed five tasks: Stroop test while seated (Seated); Stroop test while standing quiet (ST); Standing quiet (BL); Standing quiet with a haptic input (LT); and Stroop test with a haptic input while standing quiet (SL). In the Stroop test, older women committed more errors (50 vs 11 errors, p < 0.001) and had higher reaction time (1.001 ± 0.191 vs 0.699 ± 0.081 s, p < 0.001). The haptic input (LT) reduced all body sway parameters, in both groups, regardless the condition. This means that postural control under a dual task paradigm (ST) deleterious effect can be mitigated by a haptic input.

Creating a shared musical interpretation: Changes in coordination dynamics while learning unfamiliar music together.

The ability to coordinate with others is fundamental for humans to achieve shared goals. Often, harmonious interpersonal coordination requires learning, such as ensemble musicians rehearing together to synchronize their low-level timing and high-level aesthetic musical expressions. We investigated how the coordination dynamics of a professional string quartet changed as they learned unfamiliar pieces together across eight trials. During all trials, we recorded each musician's body sway motion data, and quantified the group's body sway similarity (cross-correlation) and information flow (Granger causality) on each trial. In line with our hypothesis, group similarity increased, while group information flow decreased significantly across trials. In addition, there was a trend such that group similarity, but not information flow, was related to the quality of the performances. As the ensemble converged on a joint interpretation through rehearsing, their body sways reflected the change from interpersonal information flow for coordinative mutual adaptations and corrections, to synchronous musical coordination made possible by the musicians learning a common internally based expressive interpretation.

Effects of Low-Intensity Vestibular Noise Stimulation on Postural Instability in Patients with Parkinson's Disease.

BACKGROUND: Postural instability is a major disabling factor in patients with advanced Parkinson's disease (PD) and often resistant to treatment. Previous studies indicated that imbalance in PD may be reduced by low-intensity noisy galvanic vestibular stimulation (nGVS). OBJECTIVE: To investigate the potential mode of action of this therapeutic effect. In particular, we examined whether nGVS-induced reductions of body sway in PD are compatible with stochastic resonance (SR), a mechanism by which weak sensory noise stimulation can paradoxically enhance sensory information transfer. METHODS: Effects of nGVS of varying intensities (0-0.7 mA) on body sway were examined in 15 patients with PD standing with eye closed on a posturographic force plate. We assumed a bell-shaped response curve with maximal reductions of sway at intermediate nGVS intensities to be indicative of SR. An established SR-curve model was fitted on individual patient outcomes and three experienced human raters had to judge whether responses to nGVS were consistent with the exhibition of SR. RESULTS: nGVS-induced reductions of body sway compatible with SR were found in 10 patients (67%) with optimal improvements of 23±13%. In 7 patients (47%), nGVS-induced sway reductions exceeded the minimally important clinical difference (optimal improvement: 30±10%), indicative of strong SR. This beneficial effect was more likely in patients with advanced PD (R = 0.45; p = 0.045). CONCLUSIONS: At least half of the assessed patients showed robust improvements in postural balance compatible with SR when treated with low-intensity nGVS. In particular, patients with more advanced disease stages and imbalance may benefit from the non-invasive and well-tolerated treatment with nGVS.

Eye Position Shifts Body Sway Under Foot Dominance Bias in the Absence of Visual Feedback.

Purpose: The purpose of this study was to investigate whether information on extraocular muscle proprioception without visual information affects postural control. Methods: Thirty-five healthy young volunteers participated in the study. Postural control outcomes included the center of pressure (CoP) for static standing, the total length of the sway of the CoP (LNG), and the sway area (SA), as well as the mean CoP in the mediolateral and anteroposterior directions. The following five eye-fixing positions were used: eye-up (E-Up), eye-down (E-Down), eye-right (E-Right), eye-left (E-Left), and eye-center (Center eye position). One-way ANOVA and Bonferroni correction was performed for statistical processing. Electrooculograms were recorded to detect eye orientation errors, measured with the eyes closed. Results: The results of this study showed no significant difference between the LNG and SA results when comparing respective eye positions (E-up, E-down, E-right, E-left) relative to E-Center (control). However, the average CoP was shifted to the right at E-Up, E-Down, and E-Left. Conclusion: These findings indicate that postural control may be affected by eye-body coordination depending on the position of the eyes, even without visual information.