Postural Perturbations Research Articles

Integration of vestibular and hindlimb inputs by vestibular nucleus neurons: multisensory influences on postural control.

We recently demonstrated in decerebrate and conscious cat preparations that hindlimb somatosensory inputs converge with vestibular afferent input onto neurons in multiple central nervous system (CNS) locations that participate in balance control. Although it is known that head position and limb state modulate postural reflexes, presumably through vestibulospinal and reticulospinal pathways, the combined influence of the two inputs on the activity of neurons in these brainstem regions is unknown. In the present study, we evaluated the responses of vestibular nucleus (VN) neurons to vestibular and hindlimb stimuli delivered separately and together in conscious cats. We hypothesized that VN neuronal firing during activation of vestibular and limb proprioceptive inputs would be well fit by an additive model. Extracellular single-unit recordings were obtained from VN neurons. Sinusoidal whole body rotation in the roll plane was used as the search stimulus. Units responding to the search stimulus were tested for their responses to 10° ramp-and-hold roll body rotation, 60° extension hindlimb movement, and both movements delivered simultaneously. Composite response histograms were fit by a model of low- and high-pass filtered limb and body position signals using least squares nonlinear regression. We found that VN neuronal activity during combined vestibular and hindlimb proprioceptive stimulation in the conscious cat is well fit by a simple additive model for signals with similar temporal dynamics. The mean R2 value for goodness of fit across all units was 0.74 ± 0.17. It is likely that VN neurons that exhibit these integrative properties participate in adjusting vestibulospinal outflow in response to limb state.NEW & NOTEWORTHY Vestibular nucleus neurons receive convergent information from hindlimb somatosensory inputs and vestibular inputs. In this study, extracellular single-unit recordings of vestibular nucleus neurons during conditions of passively applied limb movement, passive whole body rotations, and combined stimulation were well fit by an additive model. The integration of hindlimb somatosensory inputs with vestibular inputs at the first stage of vestibular processing suggests that vestibular nucleus neurons account for limb position in determining vestibulospinal responses to postural perturbations.

Effects of a Perturbation-Based Balance Training on Compensatory Postural Responses to Backward Loss of Balance in Patients with Cerebellar Disease: A Case Study

OBJECTIVES The damage to the cerebellum primarily results in balance-related abnormalities that may affect performance of locomotion and postural adjustments, eventually contributing to an increased risk of fall and fear of falling in patients with cerebellar disease. The purpose of the present study was to investigate the effect of a perturbation-based training that induced backward loss of balance on compensatory postural responses in patients with cerebellar disease.METHODS The participant was a 51-year-old female diagnosed with spinocerebellar ataxia and had the disease for 19 years. The perturbation-based backward balance training was performed over 8 weeks (a total of 24 training sessions) in order to facilitate the perception of postural perturbation onset and execution of rapid compensatory responses.RESULTS The patient demonstrated a noticeable reduction in the number of steps required to recover body balance after postural disturbances. The reduction of multi-step reactions in recovering balance could be attributed to improvements in the body center-of-mass displacement and trunk control during the landing of step. Besides, there were also improvements in subjective measures of functional mobility and psychological well-being after the balance training.CONCLUSION Although current research evidence of balance rehabilitation for cerebellar patients is lacking, this study offers the feasibility of adaptive training to improve postural stability through task-specific training intervention.

Electromyographic analysis of ankle muscles in chronic ankle instability during sudden inversion according to visual information provision

Chronic ankle instability is a condition in which the ankle is repetitively giving way, with symptoms such as pain, muscle weakness, and proprioceptive deficits. Therefore, people with chronic ankle instability require complex and systematic interactions between sensory association and the musculoskeletal system. The purpose of this study was to examine changes in ankle muscle activities and reaction times during sudden ankle inversion in chronic ankle instability patients under different visual conditions. Twenty-eight subjects with chronic ankle instability were recruited for the study. All subjects performed a trapdoor platform that was inversion by 25 degrees. This study assessed muscle activity and muscle reaction time during sudden ankle inversion three times with a 60-second rest period between tests with eyes-open and eyes-closed conditions. Muscle activities of tibialis anterior, peroneus longus, and peroneus brevis were significantly diminished with eyes closed, whereas that of gastrocnemius was not significantly different. No significant changes in tibialis anterior, peroneus longus, and peroneus brevis, and gastrocnemius reaction times were observed during sudden ankle inversion in the eyes-open and eyes-closed conditions. Blocking visual information can lower tibialis anterior, peroneus longus, and peroneus brevis muscle activities during postural perturbation in subjects with chronic ankle instability. These results provide insight into the injury mechanism and causes of injury, and thus to improve the existing preventive appliances. Die chronische Instabilität des Sprunggelenks ist eine Erkrankung, die durch wiederholtes Nachgeben des Sprunggelenkes charakterisiert wird, begleitet von Symptomen wie Schmerz, Muskelschwäche und propriozeptiven Defiziten. Menschen mit chronischer Instabilität des Sprunggelenks bedürfen daher komplexer und systematischer Interaktionen von sensorischer Verknüpfung und dem muskuloskelettalen System. Ziel dieser Studie war die Untersuchung der Veränderungen der Muskelaktivitäten im Sprunggelenk sowie der Reaktionszeiten während einer plötzlichen Gelenkkippung bei Patienten mit chronischer Instabilität des Sprunggelenks unter verschiedenen visuellen Bedingungen. 28 Patienten mit chronischer Instabilität des Sprunggelenks nahmen an der Studie teil. Alle Teilnehmer wurden auf einer Kippplattform mit 25 Grad Neigung untersucht. Im Rahmen der Studie wurden während einer plötzlichen Gelenkkippung drei Mal Daten zu Muskelaktivität und Reaktionszeit erhoben, mit jeweils 60 Sekunden Pause zwischen den Tests sowie mit geöffneten und geschlossenen Augen. Bei geschlossenen Augen waren die Muskelaktivitäten im Tibialis anterior, Peroneus longus und Peroneus brevis signifikant vermindert, während im Gastrocnemius hier keine signifikante Veränderung gemessen wurde. Bei der Messung der Reaktionszeiten im Tibialis anterior, Peroneus longus, Peroneus brevis und Gastrocnemius während einer plötzlichen Sprunggelenkkippung mit geöffneten und mit geschlossenen Augen traten keine signifikanten Veränderungen auf. Das Fehlen visueller Informationen bei Stellungsschwankungen kann die Muskelaktivität im Tibialis anterior, Peroneus longus und Peroneus brevis bei Patienten mit chronischer Instabilität des Sprunggelenks verringern. Die vorliegenden Ergebnisse gewähren Einblick in die Natur und die Ursache der Verletzung und unterstützen so die Verbesserung existierender Vorbeugemaßnahmen.

The Effects of Bicycle Simulator Training on Anticipatory and Compensatory Postural Control in Older Adults: Study Protocol for a Single-Blind Randomized Controlled Trial.

Background: Falls are the leading cause of fatal and non-fatal injuries among older adults. Perturbation-Based-Balance Training (PBBT) is a promising approach to reduce fall rates by improving reactive balance responses. PBBT programs are designed for older adults who are able to stand and walk on a motorized treadmill independently. However, frail older adults, whose fall rates are higher, may not have this ability and they cannot participate. Thus, there is a critical need for innovative perturbation exercise programs to improve reactive balance and reduce the fall risks among older adults in a wider range of functioning. Trunk and arms are highly involved in reactive balance reactions. We aim to investigate whether an alternative PBBT program that provides perturbations during hands-free bicycling in a sitting position, geared to improve trunk and arm reactive responses, can be transferred to reduce fall risks and improve balance function among pre-frail older adults.Methods: In a single-blinded randomized-controlled trial, 68 community-dwelling pre-frail older adults are randomly allocated into two intervention groups. The experimental group receives 24-PBBT sessions over 12-weeks that include self-induced internal and machine-induced external unannounced perturbations of balance during hands-free pedaling on a bicycle-simulator system, in combination with cognitive dual-tasks. The control group receives 24 pedaling sessions over 12-weeks by the same bicycle-simulator system under the same cognitive dual-tasks, but without balance perturbations. Participants' reactive and proactive balance functions and gait function are assessed before and after the 12-week intervention period (e.g., balance reactive responses and strategies, voluntary step execution test, postural stability in upright standing, Berg Balance Test, Six-meter walk test, as well as late life function and fear of falling questionnaires).Discussion: This research addresses two key issues in relation to balance re-training: (1) generalization of balance skills acquired through exposure to postural perturbations in a sitting position investigating the ability of pre-frail older adults to improve reactive and proactive balance responses in standing and walking, and (2) the individualization of perturbation training to older adults' neuromotor capacities in order to optimize training responses and their applicability to real-life challenges.Clinical Trial Registration: www.clinicaltrials.gov, NCT03636672 / BARZI0104; Registered: July 22, 2018; Enrolment of the first participant March: 1, 2019. See Supplementary File.

Diabetes and Reactive Balance: Quantifying Stepping Thresholds With a Simple Spring Scale to Measure Fall-Risk in Ambulatory Older Adults.

Fall-risk assessments for patients with diabetes fail to consider reactive responses to balance loss. The purpose of this study was to assess the feasibility of using a simple clinical tool to evaluate the impact of diabetes and fall history on reactive balance in older adults. We recruited 72 older adults with and without diabetes. Postural perturbations were applied by a waist-mounted spring scale. Stepping thresholds (STs) in the anterior and posterior directions were defined as the lowest spring-loads that induced a step. Balance was assessed via the National Institutes of Health Toolbox Standing Balance Test, and lower extremity sensation was assessed using vibratory perception threshold and Semmes-Weinstein monofilaments. Fall history over the past year was self-reported. Cox regressions and analysis of variance were used to compare hazard rates for stepping and observed STs between groups. Anterior STs were elicited in 42 subjects and posterior STs in 65 subjects. Hazard rates for posterior ST were significantly affected by diabetes, with greater hazards for fallers with diabetes versus control fallers and nonfallers, after accounting for balance and sensory loss. For those who stepped, ST was lower in the posterior direction for the diabetes group. Additionally, anterior but not posterior ST was lower in all fallers vs all nonfallers. The waist-mounted spring scale is a clinically implementable device that can assess ST in older adults with diabetes. Using the device, we demonstrated that ST was affected by diabetes and could potentially serve as a fall-risk factor independent of balance or sensory loss.

Comparison of forward and backward postural perturbations in mild-to-moderate Parkinson's disease

BackgroundAssessing postural stability in Parkinson’s disease (PD) often relies on measuring the stepping response to an imposed postural perturbation. The standard clinical technique relies on a brisk backwards pull at the shoulders by the examiner and judgement by a trained rater. In research settings, various quantitative measures and perturbation directions have been tested, but it is unclear which metrics and perturbation direction differ most between people with PD and controls. Objectives(1) Use standardized forward vs. backward perturbations of a support surface to evaluate reactive stepping performance between PD and control participants. (2) Evaluate the utility of using principal components analysis to capture the dynamics of the reactive response and differences between groups. MethodsSixty-two individuals participated (40 mild-to-moderate PD, off medication). Standardized rapid translations of the support surface were applied, requiring at least one step, backward or forward, to restore balance. The number of steps taken and the projection of the first principal component (PC1) of the center of pressure (COP) time series were entered in linear repeated-measures mixed effect models. ResultsForward falls required significantly fewer steps to recover than backward falls. PC1 captured more than half of the variance in the COP trajectory. Analysis of the PC1 projection revealed a significant interaction effect of group (PD vs. controls) by direction, such that there was a group difference in forward stepping, but not backward. SignificanceForward reactive stepping in PD differed from controls more than backward-stepping. PC1 projections of the COP trajectory capture the dynamics of the postural response and differ between PD and controls.

A block randomised controlled trial investigating changes in postural control following a personalised 12-week exercise programme for individuals with lower limb amputation

BackgroundIndividuals with a lower limb amputation (LLA) have an increased risk of falls and often report lower balance confidence. They must compensate for altered mechanics and prosthetic limitations in order to execute appropriate motor responses to postural perturbations. Personalised exercise could be an effective strategy to enhance balance and reduce falls. Research questionIn this study, we investigated whether a personalised exercise programme could improve postural control and self-reported balance confidence in individuals with an LLA. MethodsParticipants were block randomised into two groups (exercise, n = 7; control, n = 7) based on age and level of amputation. The exercise group completed a 12-week personalised exercise programme, including home-based exercise sessions, consisting of balance, endurance, strength, and flexibility training. The control group continued with their normal daily activities. All participants performed the Sensory Organization Test (SOT) and Motor Control Test (MCT) on the NeuroCom SMART Equitest, and completed the Activities-specific Balance Confidence-UK (ABC) self-report questionnaire, at baseline and post-intervention. Results and significanceExercise group equilibrium scores improved significantly when standing on an unstable support surface with no visual input and inaccurate somatosensory feedback (SOT condition 5, P < 0.012, d = 1.45). There were significant group*time interactions for medium (P = 0.029) and large (P = 0.048) support surface forward translations, which were associated with a trend towards increased weight-bearing on the intact limb in the control group (medium: P = 0.055; large: P = 0.087). No significant changes in ABC score were observed. These results indicate reduced reliance on visual input, and/or enhanced interpretation of somatosensory input, following an exercise programme. However, objective improvements in aspects of postural control were not associated with subjective improvements in self-reported balance confidence. More weight-bearing asymmetry in the control group suggests that a lack of targeted exercise training may have detrimental effects, with potential adverse long-term musculoskeletal consequences, that were quantifiable within a short timeframe.

Is it me or the room moving? Recreating the classical “moving room” experiment with virtual reality for postural control adaptation

Postural control is a complex process requiring both sensory and motor responses. Perturbation-based balance training has emerged as an effective fall prevention intervention, which provides physical postural perturbations for postural control training and adaptation. With the advent of technology, virtual reality (VR) has also been used for fall prevention training by providing visual postural perturbations. This article addresses such VR studies, including a recent experiment which involved recreating the classical “moving room” paradigm into a “virtual moving room-wall paradigm” to assess the impact of VR-induced visual postural perturbations on postural stability and control. Evidence of both compensatory and anticipatory postural responses during unexpected and expected visual postural perturbations is presented. The future scope, required virtual environment set-up variations, limitations, and significance of a “virtual moving wall” paradigm in the learning and adaptation of postural control behavior are also discussed.

Relationship between hip abductor strength, rate of torque development scaling factor and medio-lateral stability in older adults

BackgroundRecently, the rate of torque development scaling factor (RTD-SF) has been proposed as a useful tool that could contribute to a more comprehensive insight into muscular capacity. While lower RTD-SF is associated with ageing and certain neuromuscular diseases, it remains unknown whether this novel measure is associated with the postural control in the older adults. Research questionAre hip abductor muscle strength, RTD and RTD-SF associated with responses to external postural perturbations in medio-lateral direction in older adults? MethodsTwenty healthy older adults (14 females, 6 males) were assessed for hip abductor muscle strength, RTD and RTD-SF, using a custom-built dynamometer. Perturbations were applied at waist level (4 perturbation intensities, 15 repetitions each) using a wire-pull paradigm, with centre-of-pressure (CoP) being recorded with force plates. For each condition (i.e. perturbation intensity), medio-lateral displacement and velocity of the CoP were computed. For both parameters, within-individual variation (representing consistency of the responses), expressed by the standard deviation (SD) of CoP parameters was also considered. Pearson correlation coefficients were computed between parameters of hip muscle capacity and CoP responses and SD values of CoP responses. ResultsRTD-SF was moderately positively related to the consistency of the responses of both CoP displacement and velocity (r = 0.53−0.56; p = 0.011−0.016) at the lowest level of the perturbation magnitude (15 N). No other statistically significant relationships were found (all r < 0.35). SignificanceRTD-SF could play a role in preserving postural balance in older adults when low-intensity perturbations are applied. RTD-SF is a novel outcome measure that could represent an important alternative clinical tool to traditional strength assessments. It could represent a supplementary tool to assess the risk of falls, however, several limitations and ambiguities need to be resolved by future research before it can be utilized in practice.

Dopamine-mediated improvements in dynamic balance control in Parkinson’s disease

BackgroundImpaired dynamic balance control increases fall risk and contributes to immobility in individuals with Parkinson’s disease (PD). It is unclear whether higher-level neural processes of the central nervous system contribute to impaired balance control. Research QuestionAre dopamine-mediated neural processes of the higher-level central nervous system important for dynamic balance control in PD? Methods21 individuals with idiopathic PD performed step-threshold assessments before and after self-administered dopaminergic medication. Individuals withstood progressively larger postural perturbations, during which they were explicitly instructed to avoid stepping to recover balance. The perturbation magnitude which elicited stepping responses on four consecutive trials is referred to as the step-threshold. Dynamic balance control was quantified as the minimum margin of stability captured during the largest sub-threshold trial (i.e., the maximum amount of compensated postural instability during the task). We compared dynamic balance between off and on medication states and between individuals who exhibited motor adaptive behavior and those who did not. ResultsDopaminergic medications significantly improved step-thresholds and allowed individuals to withstand greater amounts of instability without stepping, indicating dopamine-mediated improvement in dynamic balance control. Individuals who displayed behavioral evidence for higher-level neural processes (motor adaptation across repeated perturbations) displayed superior dynamic balance control versus those who did not. Anteroposterior ground reaction forces captured during perturbations suggest that individuals alter force profiles to avoid stepping at ∼200 ms after perturbation onset–a latency consistent with a transcortical process. SignificanceCombined, our results indicate that higher-level, dopamine-mediated neural processes are responsible for dynamic balance control in PD. We hypothesize that this process incorporates sensorimotor integration, motor response initiation/inhibition, and goal- and reward-driven behaviors. Interventions targeting these processes may improve dynamic postural control in individuals with PD.

The effects of perturbation type and direction on threat-related changes in anticipatory postural control.

The purpose of this study was to determine whether the type and direction of postural perturbation threat differentially affect anticipatory postural control. Healthy young adults stood on a force plate fixed to a translating platform and completed a series of rise-to-toes movements without (No Threat) and with (Threat) the potential of receiving a postural perturbation to either their feet (15 participants) or torso (16 participants). Each type of perturbation threat was presented along the anteroposterior (A-P) or mediolateral (M-L) axis. For each condition, the A-P center of pressure (COP) signal and tibialis anterior (TA) and soleus (SOL) electromyographical (EMG) recordings were used to quantify the anticipatory postural adjustment (APA). Results indicated that across both threat types and directions, postural threat induced a 40.2% greater TA activation (p<0.001), a 18.5% greater backward COP displacement (p<0.001) and a 23.9% greater backward COP velocity (p<0.001), leading to larger and faster APAs than the No Threat condition. Subsequently, a 7.7% larger forward COP displacement (p=0.001), a 20.4% greater forward COP velocity (p<0.001) and 43.2% greater SOL activation (p=0.009) were observed during the execution phase of the rise-to-toes for the Threat compared to the No Threat condition. Despite these threat effects, there were no differences in the magnitude or velocity of APAs between the threat directsion conditions. Since the type and direction of perturbation-induced postural threat had minimal differential effects on anticipatory postural control, these factors are unlikely to explain the discrepancy of previous findings.

Postural control and perturbation response in aging populations: fall risk implications.

Falls are an increasing cause of mortality in an ever-growing aging population. The main factors to consider in reducing mortality rates due to falls are postural control, consisting of the vestibular, visual, and proprioceptive system, and perturbation response. This Neuro Forum article reviews recent literature highlighting the developmental changes that occur in aging populations and the possible avenues for interventions and training to mitigate fall risk.

Maintained Representations of the Ipsilateral and Contralateral Limbs during Bimanual Control in Primary Motor Cortex.

Primary motor cortex (M1) almost exclusively controls the contralateral side of the body. However, M1 activity is also modulated during ipsilateral body movements. Previous work has shown that M1 activity related to the ipsilateral arm is independent of the M1 activity related to the contralateral arm. How do these patterns of activity interact when both arms move simultaneously? We explored this problem by training 2 monkeys (male, Macaca mulatta) in a postural perturbation task while recording from M1. Loads were applied to one arm at a time (unimanual) or both arms simultaneously (bimanual). We found 83% of neurons (n = 236) were responsive to both the unimanual and bimanual loads. We also observed a small reduction in activity magnitude during the bimanual loads for both limbs (25%). Across the unimanual and bimanual loads, neurons largely maintained their preferred load directions. However, there was a larger change in the preferred loads for the ipsilateral limb (∼25%) than the contralateral limb (∼9%). Lastly, we identified the contralateral and ipsilateral subspaces during the unimanual loads and found they captured a significant amount of the variance during the bimanual loads. However, the subspace captured more of the bimanual variance related to the contralateral limb (97%) than the ipsilateral limb (66%). Our results highlight that, even during bimanual motor actions, M1 largely retains its representations of the contralateral and ipsilateral limbs.SIGNIFICANCE STATEMENT Previous work has shown that primary motor cortex (M1) represents information related to the contralateral limb, its downstream target, but also reflects information related to the ipsilateral limb. Can M1 still represent both sources of information when performing simultaneous movements of the limbs? Here we record from M1 during a postural perturbation task. We show that activity related to the contralateral limb is maintained between unimanual and bimanual motor actions, whereas the activity related to the ipsilateral limb undergoes a small change between unimanual and bimanual motor actions. Our results indicate that two independent representations can be maintained and expressed simultaneously in M1.

Alteration of muscle synergy structure while walking under increased postural constraints

It is hypothesised that specific groups of muscles aka muscle synergies (MSs) are combined by the central nervous system to control a wide repertoire of movements and also simplify motor control. Therefore, studying MSs during human locomotion is of significance, as it may reveal neuromuscular strategies for postural stability. In this study, the authors aimed to use the hypothesis of MSs to identify specific muscle co-activations during overground walking and slacklining where postural perturbations were generated by the participants rather than being externally controlled. Nine participants were asked to walk overground and on a slackline while they recorded myoelectric activity of their leg muscles. They extracted synergies from the electromyography signals in the two tasks using factor analysis. The results showed adaptation in the shared MSs structure during walking on the slackline and these shared MSs across participants were recruited flexibly to meet the demand for stability. The modulation of synergies suggests adaptive neuromuscular strategies for stability while walking on a slackline. Specifically, higher activation of quadriceps during slacklining suggests a crouched gait to facilitate balance. During overground walking, lower leg muscles revealed higher activation compared to slacklining to support a more consistent toe-off during the stance phase.

Postural stability after treadmill and overground walking in young and elderly

BackgroundAgeing commonly disrupts the balance control and compensatory postural responses that contribute to maintaining balance and preventing falls during perturbation of posture. Improvement of compensatory postural responses during walking is one of the main goals in fall prevention programs which often include treadmill walking training. However, during treadmill walking, there is a sensory (visualsomatosensory and vestibular-somatosensory) conflict that can evoke aftereffects of self-motion sensation and could alter postural stability after training. Research questionThe aim of this study was to compare the effect of overground and treadmill walking on postural stability in healthy young and elderly subjects. Methods: Postural responses of 31 Young and 19 healthy Elderly before and after overground and treadmill walking were assessed by a force platform in four stance conditions: firm and foam surface with eyes open and eyes closed. ResultsIn Elderly group, velocity parameters significantly increased after treadmill walking but not after overground walking. This increase was found particularly in the conditions with eyes open in both types of surfaces (firm, foam). The velocity parameters values (expect Vx) were significantly increased in Elderly compared to Young almost in all four conditions after treadmill and overground walking. Significance: Our study suggests that Elderly become more unstable after treadmill walking and have greater difficulties to adapt to new balance circumstances caused by sensory conflict associated with treadmill walking. It seems that during treadmill walking and subsequent stance, vision is the major factor contributing to posture stabilization. Thus, the suitability of treadmill walking as a part of training programs for elderly adults with higher fall risk should be seriously considered.

Impact of pain on reactive balance and falls in community-dwelling older adults: a prospective cohort study

pain is associated with increased postural sway and falls in older adults. However, the impact of pain on reactive balance induced by postural perturbations and how this might predispose older adults to falls is not known. to investigate whether any pain, back/neck pain and lower limb pain are associated with poor reactive balance and prospective fall outcomes in older adults. 12-month prospective cohort study. community. 242 community-dwelling older adults aged 70+ years. participants completed a questionnaire on the presence of pain and underwent force-controlled waist-pull postural perturbations while standing. Force thresholds for stepping, step initiation time, step velocity and step length were quantified. Falls were monitored with monthly falls calendars for 12-months. participants with lower limb pain had significantly lower force thresholds for stepping. Those with any pain or pain in the back/neck had longer step initiation time, slower step velocity and shorter step length. The three pain measures (any pain, back/neck pain, lower limb pain) were significantly associated with multiple falls when adjusted for age, sex, body mass index, use of polypharmacy, strength and walking speed. In mediation analyses, there was a significant indirect effect of reactive balance for the relationship between back/neck pain and falls with fractures. older people with pain have impaired reactive balance and an increased risk of falls. Reactive balance partially mediated the association between pain and fall-related fractures. Further research is required to confirm the findings of this study.

Postural Control Adaptation and Habituation During Vibratory Proprioceptive Stimulation: An HD-EEG Investigation of Cortical Recruitment and Kinematics.

The objective of the present work is to measure postural kinematics and power spectral variation from HD-EEG to assess changes in cortical activity during adaptation and habituation to postural perturbation. To evoke proprioceptive postural perturbation, vibratory stimulation at 85 Hz was applied to the calf muscles of 33 subjects over four 75-second stimulation periods. Stimulation was performed according to a pseudorandom binary sequence. Vibratory impulses were synchronized to high-density electroencephalography (HD-EEG, 256 channels). Changes in absolute spectral power (ASP) were analyzed over four frequency bands ( ∆ : 0.5-3.5 Hz; θ : 3.5-7.5 Hz; α : 7.5-12.5 Hz; β : 12.5-30 Hz). A force platform recorded torque actuated by the feet, and normalized sway path length (SPL) was computed as a construct for postural performance during each period. SPL values indicated improvement in postural performance over the trial periods. Significant variation in absolute power values (ASP) was found in assessing postural adaptation: an increase in θ band ASP in the frontal-central region for closed-eyes trials, an increase in θ and β band ASP in the parietal region for open-eyes trials. In habituation, no significant variations in ASP were observed during closed-eyes trials, whereas an increase in θ , α , and β band ASP was observed with open eyes. Furthermore, open-eyed trials generally yielded a greater number of significant ASP differences across all bands during both adaptation and habituation, suggesting that following cortical activity during postural perturbation may be up-regulated with the availability of visual feedback. These results altogether provide deeper insight into pathological postural control failure by exploring the dynamic changes in both cortical activity and postural kinematics during adaptation and habituation to proprioceptive postural perturbation.

Investigation of Adaptation to Successive Postural Perturbations in Patients with Multiple Sclerosis

Investigation of Adaptation to Successive Postural Perturbations in Patients with Multiple Sclerosis

A Modified Lean and Release Technique to Emphasize Response Inhibition and Action Selection in Reactive Balance.

Assessment of reactive balance traditionally imposes some type of perturbation to upright stance or gait followed by measurement of the resultant corrective behavior. These measures include muscle responses, limb movements, ground reaction forces, and even direct neurophysiological measures such as electroencephalography. Using this approach, researchers and clinicians can infer some basic principles regarding how the nervous system controls balance to avoid a fall. One limitation with the way in which these assessments are currently used is that they heavily emphasize reflexive actions without any need to revise automatic postural reactions. Such an exclusive focus on these highly stereotypical reactions would fail to adequately address how we can modify these reactions should the need arise (e.g., avoiding an obstacle with a recovery step). This would appear to be a glaring omission when one considers the enormous complexity of the environments we face daily. Overall, the status quo when evaluating the neural control of balance fails to truly expose how higher brain resources contribute to preventing falls in complex settings. The present protocol offers a way to require suppression of automatic, but inappropriate corrective balance reactions, and force a selection among alternative action choices to successfully recover balance following postural perturbation.

Decreased respiratory-related postural perturbations at the cervical level under cognitive load.

In healthy humans, postural and respiratory dynamics are intimately linked and a breathing-related postural perturbation is evident in joint kinematics. A cognitive dual-task paradigm that is known to induce both postural and ventilatory disturbances can be used to modulate this multijoint posturo-ventilatory (PV) interaction, particularly in the cervical spine, which supports the head. The objective of this study was to assess this modulation. With the use of optoelectronic sensors, the breathing profile, articular joint motions of the cervical spine, hip, knees and ankles, and centre of pressure (CoP) displacement were measured in 20 healthy subjects (37years old [29; 49], 10 females) during natural breathing (NB), a cognitive dual task (COG), and eyes-closed and increased-tidal-volume conditions. The PV interaction in the CoP and joint motions were evaluated by calculating the respiratory emergence (REm). Only the COG condition induced a decrease in the cervical REm (NB: 17.2% [7.8; 37.2]; COG: 4.2% [1.8; 10.0] p = 0.0020) concurrent with no changes in the cervical motion. The CoP REm (NB: 6.2% [3.8; 10.3]; COG: 12.9% [5.8; 20.7] p = 0.0696) and breathing frequency (NB: 16.6min-1 [13.3; 18.7]; COG: 18.6min-1 [16.3; 19.4] p = 0.0731) tended to increase, while the CoP (p = 0.0072) and lower joint motion displacements (p < 0.05) increased. This study shows stable cervical spine motion during a cognitive dual task, as well as increased postural perturbations globally and in other joints. The concurrent reduction in the PV interaction at the cervical spine suggests that this "stabilization strategy" is centrally controlled and is achieved by a reduction in the breathing-related postural perturbations at this level. Whether this strategy is a goal for maintaining balance remains to be studied.