Multisensory reweighting of vision and touch is intact in healthy and fall-prone older adults

Sensorimotor and proprioceptive exercise programs to improve balance in older adults: a systematic review with meta-analysis

The primary aim of this study was to systematically review and meta-analyze the impact of sensorimotor and proprioceptive exercises on balance in older adults. We also sought to define how researchers describe proprioceptive and sensory-motor training and their respective protocols. The review was conducted following the PRISMA guidelines, with searches performed in March 2023. Both authors carried out independent searches using the PubMed and PEDro databases. From a total of 320 identified records, 12 studies were deemed eligible for meta-analysis after screening and removal of duplicates. The average PEDro score was 5.11 ± 1.11 indicating overall fair quality of studies.  Common outcome measures included the Berg balance scale, Timed up and go test, Tinetti balance scale, Functional reach test and various single-leg stance tests. All outcomes were significantly improved by the interventions (standard mean difference = 0.65 - 1.29), with little difference between proprioceptive and sensorimotor training. However, the quality of evidence ranged from "very low" to "low" based on GRADE guidelines, suggesting further high-quality studies are needed. This review underscores the potential benefits of sensorimotor and proprioceptive exercises for enhancing balance in older adults, while also highlighting the ambiguity and inconsistency regarding the usage of the terms proprioceptive and sensorimotor training.

Age-Related Changes in Inter-Joint Interactions for Global and Local Kinematics While Standing

Inter-joint interactions are involved in human standing. These interactions work not only for global kinematics that control the center of mass (COM) of the entire body, but also for local kinematics that control joint angular movements. Age-related changes in these interactions are thought to cause unstable standing postures in older people. Interactions of global kinematics are known to be deficient owing to aging. However, it is unclear whether the interaction of local kinematics is affected by aging. We investigated the age-related changes in inter-joint interactions, especially local kinematics, during standing. Differences were investigated in these two inter-joint interactions between older and younger adults in three different postures: normal, eyes-closed, and foam-surface standings. The inter-joint interaction for local kinematics was computed using the induced-acceleration analysis with a double-inverted pendulum model and quantified using an uncontrolled manifold approach. Consistent with previous studies, the inter-joint interaction for COM acceleration (global kinematics) deteriorated in older adults. In contrast, the interactions for angular accelerations in the ankle and hip joints (local kinematics) were slightly better in the older adults. Moreover, the individual components of angular acceleration which were induced by net torques from homonymous and remote joints were significantly increased in older adults. Thus, global and local inter-joint interactions are driven by distinct neural mechanisms and the interaction of local kinematics can compensate for the increment of each component of joint angular acceleration in older adults.

Adaptation in motor strategies for postural control associated with sensory reweighting

The purpose of this study was to identify and differentiate the motor strategies associated with sensory reweighting adapted during specific sensory integration tasks by healthy young adults. Thirty-six subjects (age range: 21-33 years) performed standing computerized dynamic posturography balance tasks across progressively increasing amplitudes of visual (VIS), somatosensory (SOM) and both (VIS+SOM) systems perturbation conditions. Adaptation in the motor strategy was measured as changes in electromyographic (EMG) activities and joint angles. The contribution of the perturbed sensory input in maintaining postural stability was calculated to determine the sensory reweighting. A multivariate design was used to model a linear combination of motor adaptation variables that discriminates specific sensory integration tasks. Results showed a significant progressive decrease in postural sway per unit amplitude of sensory perturbation in each condition, indicating dynamic sensory reweighting. Linear discriminant function analysis indicated that the adaptation in motor strategy during the VIS condition was associated with increased activity of EMG and joint angles in the upper body compared to the lower body. Conversely, during the SOM and VIS+SOM conditions, the adaptation in motor strategy was associated with decreased activity of EMG and joint angles in the lower body compared to the upper body. Therefore, the adaptation in motor strategies associated with sensory reweighting were different for different sensory integration tasks.

Impact of Sensory Afferences in Postural Control Quantified by Force Platform: A Protocol for Systematic Review

Older adults’ postural balance is a critical domain of research as balance deficit is an important risk factor for falls that can lead to severe injuries and death. Considering the effects of ageing on sensory systems, we propose that posturographic evaluation with a force platform exploring the effect of sensory deprivation or perturbation on balance could help understand postural control alterations in the elderly. The aim of the future systematic review and meta-analysis described in this protocol is to explore the capacity of older adults to maintain their balance during sensory perturbations, and compare the effect of perturbation between the sensory channels contributing to balance. Seven databases will be searched for studies evaluating older adults’ balance under various sensory conditions. After evaluating the studies’ risk of bias, results from similar studies (i.e., similar experimental conditions and posturographic markers) will be aggregated. This protocol describes a future review that is expected to provide a better understanding of changes in sensory systems of balance due to ageing, and therefore perspectives on fall assessment, prevention, and rehabilitation.

Association Between Sensory Loss and Falls Among Middle-Aged and Older Chinese Population: Cross-Sectional and Longitudinal Analyses

Introduction: Previous studies have suggested that sensory loss is linked to falls. However, most of these studies were cross-sectional designed, focused on single sensory loss, and were conducted in developed countries with mixed results. The current study aims to investigate the longitudinal relationship between hearing loss (HL), vision loss (VL) and dual sensory loss (DSL) with falls among middle-aged and older Chinese population over 7 years. Methods: The data was obtained from the China Health and Retirement Longitudinal Survey (CHARLS). In total, 7,623 Chinese older adults aged over 45 were included at baseline 2011 in this study. Self-reported falls and HL/VL/DSL were accepted. Other confounding variables included age, sex, BMI, educational level, marital status, various physical disorders and lifestyles. The impact of baseline sensory status on baseline prevalence of falls and incident falls over 7 years were assessed using logistic regression analyses. A logistic mixed model was used to assess the association between time-varying sensory loss with incident falls over 7 years after adjusted with multi-confounding factors. Results: Single and dual sensory loss groups had significantly higher prevalence of falls compared to no sensory loss (NSL) group (DSL: 22.4%, HL: 17.4%, VL: 15.7%, NSL: 12.3%). Baseline HL (OR: 1.503, 95% CI: 1.240-1.820), VL (OR: 1.330, 95% CI: 1.075-1.646) and DSL (OR: 2.061, 95% CI: 1.768-2.404) were significantly associated with prevalence of falls. For longitudinal observation over 7 years, baseline HL/DSL and persistence of all types of sensory loss were associated with incidence of falls. Time-varying HL (OR: 1.203, 95% CI: 1.070-1.354) and DSL (OR: 1.479, 95% CI: 1.343-1.629) were associated with incident falls after adjusted with multi-confounders, while VL was not. Conclusion: HL and DSL are significantly associated with both onset and increased incidence of falls over 7 year's observation in middle-aged and elderly Chinese population. Persistence or amelioration of sensory loss status could exert divergent influences on incidence of falls, which should be considered in the development of falls-prevention public health policies for aging population.

Saccadic eye movement performance reduces visual manipulation influence and center of pressure displacements in older fallers

This study examined changes in postural control and gaze performance of faller and non-faller older adults under conditions of visual tasks and optical flow manipulations. Fifteen older non-fallers (69.8 years, ± 3.2) and fifteen older fallers (71.1 years, ± 6.4) stood on a force platform inside a moving room wearing an eye tracker. Four tasks were performed: gaze fixation; predictable saccades; unpredictable saccades; and free-viewing. The stimuli appeared at a frequency of 1.1 Hz during conditions of predictable and unpredictable saccades. Sixteen trials were divided into two blocks. In the first block, the room remained stationary. In the second block, the room oscillated, without the participant's awareness, with a 0.6 cm amplitude and 0.2 Hz frequency. Results showed postural sway attenuation in older fallers during the saccadic tasks compared to gaze fixation and free-viewing tasks, in both stationary and moving room conditions. Both groups showed increased center of pressure (CoP) magnitude during the moving room condition and CoP displacements strongly coupled to the room's movement. The influence of the moving room on the postural sway was reduced during the saccadic tasks for both older groups. Older fallers exhibited higher variability compared to older non-fallers. Gaze behavior differences between groups were dependent on the goals of the visual tasks. Therefore, CoP displacements of older adults are reduced during saccadic tasks regardless of their falling history. However, postural and gaze performance of older fallers suggests increased deterioration of postural and oculomotor control which may be used as a predictor of fall risk.

The Effects of Exergaming on Sensory Reweighting and Mediolateral Stability of Women Aged Over 60: Usability Study

Background

Older adults tend to experience difficulties in switching quickly between various reliable sensory inputs, which ultimately may contribute to an increased risk of falls and injuries. Sideward falls are the most frequent cause of hip fractures among older adults. Recently, exergame programs have been confirmed as beneficial tools for enhancing postural control, which can reduce the risk of falls. However, studies to explore more precisely which mechanism of exergaming directly influences older women’s ability to balance are still needed.

Objective

Our aim was to evaluate, in a single-group pretest/posttest/follow-up usability study, whether Kinect exergame balance training might have a beneficial impact on the sensory reweighting in women aged over 60.

Methods

A total of 14 healthy women (mean age 69.57 [SD 4.66] years, mean body mass index 26.21 [SD 2.6] kg/m²) participated in the study. The volunteers trained with the commercially available games of Kinect for Xbox 360 console 3 times (30 minutes/session) a week over a 6-week period (total of 18 visits). Participants’ postural sway in both the anteroposterior (AP) and mediolateral (ML) directions was recorded with NeuroCom Balance Master 6.0. To assess and measure postural sensory reweighting, the Modified Clinical Test of Sensory Interaction in Balance was used, where volunteers were exposed to various changes in visual (eyes open or eyes closed) and surface conditions (firm or foam surface).

Results

In the ML direction, the Kinect exergame training caused a significant decrease in the sway path on the firm surface with the eyes open (P<.001) and eyes closed (P=.001), and on the foam surface with the eyes open (P=.001) and eyes closed (P<.001) conditions compared with baseline data. The follow-up measurements when compared with the baseline data showed a significant change in the sway path on the firm surface with the eyes open (P<.001) and eyes closed (P<.001) conditions, as well as on the foam surface with the eyes open (P=.003) and eyes closed (P<.001) conditions. Besides, on the firm surface, there were no significant differences in sway path values in the AP direction between the baseline and the posttraining measurements (eyes open: P=.49; eyes closed: P=.18). Likewise, on the foam surface, there were no significant differences in sway path values in the AP direction under both eyes open (P=.24) and eyes closed (P=.84) conditions.

Conclusions

The improved posturography measurements of the sway path in the ML direction might suggest that the Kinect exergame balance training may have effects on sensory reweighting, and thus on the balance of women aged over 60. Based on these results, Kinect exergaming may provide a safe and potentially useful tool for improving postural stability in the crucial ML direction, and thus it may help reduce the risk of falling.

Perceptual-motor styles

Even for a stereotyped task, sensorimotor behavior is generally variable due to noise, redundancy, adaptability, learning or plasticity. The sources and significance of different kinds of behavioral variability have attracted considerable attention in recent years. However, the idea that part of this variability depends on unique individual strategies has been explored to a lesser extent. In particular, the notion of style recurs infrequently in the literature on sensorimotor behavior. In general use, style refers to a distinctive manner or custom of behaving oneself or of doing something, especially one that is typical of a person, group of people, place, context, or period. The application of the term to the domain of perceptual and motor phenomenology opens new perspectives on the nature of behavioral variability, perspectives that are complementary to those typically considered in the studies of sensorimotor variability. In particular, the concept of style may help toward the development of personalised physiology and medicine by providing markers of individual behaviour and response to different stimuli or treatments. Here, we cover some potential applications of the concept of perceptual-motor style to different areas of neuroscience, both in the healthy and the diseased. We prefer to be as general as possible in the types of applications we consider, even at the expense of running the risk of encompassing loosely related studies, given the relative novelty of the introduction of the term perceptual-motor style in neurosciences.

Medical aromatherapy in geriatric syndrome

Geriatric syndromes are symptoms and signs, such as falls, incontinence, delirium, pressure ulcers, dysphagia and so on, that often threaten the independence of older adults, rather than the disease itself. Although the syndromes are very common in older people, it is difficult to treat those by modern medicine due to their complexity. To mitigate the intractable geriatric symptoms, we review the efficacy of aromatherapy, especially for dysphagia, dyspnea, cognitive dysfunction and falls in geriatric syndrome. Olfactory stimulation using a volatile black pepper oil on institutional residents improved the swallowing reflex, which is a crucial risk factor of aspiration pneumonia. Brain imaging study showed that olfactory stimulation using volatile black pepper oil activated cerebral regions of the anterior cingulate and the insular cortex, which play a role in controlling appetite and swallowing. Also, aromatherapy with volatile l-menthol decreased the sense of dyspnea and improved the efficacy of exercise therapy. The fragrance of the combination of rosemary and lemon oils in the morning, and the combination of lavender and orange oils in the night-time were reported to improve cognition and behavioural and psychological symptoms of dementia, respectively. Also, the combination of lavender and lemon balm oils was reported to be effective for irritability-related agitation in older adults. Furthermore, aromatherapy with lavender fragrance could improve both static and dynamic balance, resulting in a reduction in the number of fallers and the incidence rate in older people. Thus, aromatherapy is a promising remedy for geriatric syndrome. Geriatr Gerontol Int 2021; 21: 377-385.

Sensory reweighting in frail aged adults: Are the balance deficiencies mainly compensated by visual or podal dependences?

BACKGROUND

Postural control is based on the integration of different sensory inputs. The process of scaling the relative importance of these sensory cues (visual, vestibular and proprioceptive) depends on individuals and creates sensory preferences, leading to sensory dependences when one particular source is preponderant. In this context, the literature showed a frequent visual dependence (visual inputs weighting) in aged adults. However, the somaesthetic inputs can also be prioritised in a podal-dependent profile. In the frail aged adults, none study has shown the distribution of these two dependences.

RESEARCH QUESTION

Which sensory orientation profile is preferentially adopted by frail aged males and females?

METHODS

In this cross-sectional study, we compared 33 frail aged adults to 16 non frail aged adults during a static postural control task in three conditions on a force platform: i) a standard condition, ii) a no-vision condition and iii) a foam condition. An analysis with the factor sex was also performed in each group of participants.

RESULTS

The analysis of stabilometric parameters (mean velocity and mean velocity variance) highlighted a significant difference in no-vision or foam conditions when compared to the standard condition in frail aged males and only in the foam condition when compared to the standard condition for females in the frail group. No significant difference was observed between conditions in the control group.

SIGNIFICANCE

Our study showed the predominance of both visual and podal information in frail aged adults when controlling their posture. Considering the sex factor, frail males were more dependents to their visual cues than frail females. This result should be used when designing the rehabilitation programs in this population.

Discrimination of standing postures between young and elderly people based on center of pressure

Posturography is utilized to assess the influence of aging on postural control. Although this measurement is advantageous for finding group-level differences between the young and the elderly, it is unclear whether it has the potential to differentiate elderly individuals who are affected by various impacts of aging. The purpose of this study was to determine the utility of posturography to discriminate elderly individuals from young adults. We investigated the performances of the random forest classifiers constructed from center of pressure (COP) indices for discriminating standing postures between healthy elderly and young people. Postural sways in 19 young and 31 community-dwelling elderly participants were measured using force plates in 4 standing conditions: bipedal standing, standing on a narrow base, standing on foam rubber, and standing with eyes closed. We further verified the informative predictors that contributed to the prediction model. As the results, the classifier based on the COP indices for standing on foam rubber showed the best performance (accuracy: 93.4%, sensitivity: 94.4%, specificity: 93.6%, area under the curve of receiving operator characteristics: 0.95), followed by the classifier for standing with eyes closed. The informative predictors varied depending on the postural conditions. Our findings demonstrated the potential of posturography for identifying elderly postures. The evaluation of sensory re-weighting using the appropriate COP indices would be a useful clinical tool for detecting the progress of aging on postural control.

Impaired Multisensory Integration Predisposes the Elderly People to Fall: A Systematic Review

Background: This systematic review pooled all the latest data and reviewed all the relevant studies to look into the effect of multisensory integration on the balance function in the elderly.

Methods: PubMed, Web of Science and Scopus were searched to find eligible studies published prior to May 2019. The studies were limited to those published in Chinese and English language. The quality of the included studies was assessed against the Newcastle-Ottawa Scale or an 11-item checklist, as recommended by Agency for Healthcare Research and Quality (AHRQ). Any disagreement among reviewers was resolved by comparing notes and reaching a consensus.

Results: Eight hundred thirty-nine records were identified and 17 of them were included for systematic review. The result supported our assumption that multisensory integration works on balance function in the elderly. All the 17 studies were believed to be of high or moderate quality.

Conclusions: The systematic review found that the impairment of multisensory integration could predispose elderly people to fall. Accurate assessment of multisensory integration can help the elderly identify the impaired balance function and minimize the risk of fall. And our results provide a new basis for further understanding of balance maintenance mechanism. Further research is warranted to explore the change in brain areas related to multisensory integration in the elderly.

Effect of Visual Information on Postural Control in Adults with Autism Spectrum Disorder

Sensory processing difficulties affect the development of sensorimotor skills in individuals with autism spectrum disorder (ASD). However, the effect of sensory information on postural control is unclear in the ASD adult population. The present study examined the effect of visual information on postural control as well as the attentional demands associated with postural control in fourteen adults with ASD and seventeen typically developed adults. The results showed that postural sway and attention demands of postural control were larger in adults with ASD than in typically developed adults. These findings indicate that visual processing used for postural control may be different in adults with ASD. Further research in visual field processing and visual motion processing may elucidate these sensorimotor differences.

Weighting and reweighting of visual input via head mounted display given unilateral peripheral vestibular dysfunction

We translated a well-established laboratory paradigm to study sensory integration into a Head-Mounted-Display (HMD). In the current study, a group of 23 individuals with unilateral vestibular dysfunction and 16 age-matched controls observed moving spheres projected from the Oculus Rift. We confirmed increased visual weighting with an unstable surface and decreased visual weighting (i.e., reweighting) with increased visual amplitude. We did not observe significant differences in gains and phases between individuals with vestibular dysfunction and age-matched controls. The vestibular group increased sway in mid and high frequencies significantly more than controls with the change in surface or visual amplitude. Mild visual perturbations within HMDs carry the potential to become a useful portable assessment of postural control in individuals with vestibular disorders.

Sensory-Challenge Balance Exercises Improve Multisensory Reweighting in Fall-Prone Older Adults

BACKGROUND AND PURPOSE

Multisensory reweighting (MSR) deficits in older adults contribute to fall risk. Sensory-challenge balance exercises may have value for addressing the MSR deficits in fall-prone older adults. The purpose of this study was to examine the effect of sensory-challenge balance exercises on MSR and clinical balance measures in fall-prone older adults.

METHODS

We used a quasi-experimental, repeated-measures, within-subjects design. Older adults with a history of falls underwent an 8-week baseline (control) period. This was followed by an 8-week intervention period that included 16 sensory-challenge balance exercise sessions performed with computerized balance training equipment. Measurements, taken twice before and once after intervention, included laboratory measures of MSR (center of mass gain and phase, position, and velocity variability) and clinical tests (Activities-specific Balance Confidence Scale, Berg Balance Scale, Sensory Organization Test, Limits of Stability test, and lower extremity strength and range of motion).

RESULTS

Twenty adults 70 years of age and older with a history of falls completed all 16 sessions. Significant improvements were observed in laboratory-based MSR measures of touch gain (P = 0.006) and phase (P = 0.05), Berg Balance Scale (P = 0.002), Sensory Organization Test (P = 0.002), Limits of Stability Test (P = 0.001), and lower extremity strength scores (P = 0.005). Mean values of vision gain increased more than those for touch gain, but did not reach significance.

DISCUSSION AND CONCLUSIONS

A balance exercise program specifically targeting multisensory integration mechanisms improved MSR, balance, and lower extremity strength in this mechanistic study. These valuable findings provide the scientific rationale for sensory-challenge balance exercise to improve perception of body position and motion in space and potential reduction in fall risk.

From One to Two: Can Visual Feedback Improve the Light Touch Effects on Postural Sway?

The postural control is improved by implicit somatosensory information from lightly touching a rigid bar or explicit visual information about the postural sway. Whether these two additional sources provided at the same time further reduce the postural sway is still unknown. Participants stood on a force plate as quiet as possible lightly touching the bar while received or not visual feedback of the center of pressure position on a monitor screen. Postural sway reduced similarly with the light touch regardless of the additional visual feedback. The findings suggested that providing explicit visual feedback of the center of pressure does not increase the light touch effects on the postural sway. The importance of the implicit somatosensory information on postural control is discussed.

Center of Pressure Trace and Sensory Components of the Limits of Stability Test in Older Adults With Vertebral Compression Fractures

BACKGROUND AND PURPOSE

Patients with vertebral compression fracture (VCF) usually exhibit impaired postural control and consequently are at an increased risk of falling. This study aimed to assess the sensory and kinematic components of the limits of stability (LOS) test in patients with VCF.

METHODS

This study enrolled 13 adults with VCF (VCF group), 13 older adults without spinal deformity (NE group), and 13 young adults (NY group). The Biodex balance system was employed to calculate the balance score and the LOS of participants. An inertia motion system was used to record kinematic data. The center of pressure signals of postural stability and LOS were used to calculate the frequency power spectrum for interpreting the sensory component.

RESULTS

Compared with the NY group, the VCF group exhibited a longer reaction time and lower balance scores and used a higher median frequency in the medial-lateral and anterior-posterior direction of body acceleration to perform the LOS test. The required ranges of hip rotation and pelvic pitch were significantly higher in the older adult group than in the NY group. In the postural stability test, the VCF group exhibited significantly higher frequency power in the 0.01- to 0.5-Hz band (visual and vestibular) under both the eyes-closed and eyes-open conditions than the other groups. In the LOS test, the VCF group also exhibited lower sensory component activity than the other groups, particularly in vestibular function (0.1-0.5 Hz).

CONCLUSIONS

Both musculoskeletal degeneration and sensory integration impairment may contribute to poor direction control and a longer reaction time in patients with VCF.

Does local dynamic stability during unperturbed walking predict the response to balance perturbations? An examination across age and falls history

BACKGROUND

Older adults are at an exceptionally high risk of falls, and most falls occur during locomotor activities such as walking. Reduced local dynamic stability in old age is often interpreted to suggest a lessened capacity to respond to more significant balance challenges encountered during walking and future falls risk. However, it remains unclear whether local dynamic stability during normal, unperturbed walking predicts the response to larger external balance disturbances.

RESEARCH QUESTION

We tested the hypothesis that larger values of local dynamic instability during unperturbed walking would positively correlate with larger changes thereof due to optical flow balance perturbations.

METHODS

We used trunk kinematics collected in subjects across a spectrum of walking balance integrity - young adults, older non-fallers, and older fallers - during walking with and without mediolateral optical flow perturbations of four different amplitudes.

RESULTS

We first found evidence that optical flow perturbations of sufficient amplitude appear capable of revealing independent effects of aging and falls history that are not otherwise apparent during normal, unperturbed walking. We also reject our primary hypothesis; a significant negative correlation only in young adults indicated that individuals with more local dynamic instability during normal, unperturbed walking exhibited smaller responses to optical flow perturbations. In contrast, most prominently in older fallers, the response to optical flow perturbations appeared independent of their baseline level of dynamic instability.

SIGNIFICANCE

We propose that predicting the response to balance perturbations in older fallers, at least that measured using local dynamic stability, likely requires measuring that response directly.

Trunk motion visual feedback during walking improves dynamic balance in older adults: Assessor blinded randomized controlled trial

BACKGROUND

Virtual reality and augmented feedback have become more prevalent as training methods to improve balance. Few reports exist on the benefits of providing trunk motion visual feedback (VFB) during treadmill walking, and most of those reports only describe within session changes.

RESEARCH QUESTION

To determine whether trunk motion VFB treadmill walking would improve over-ground balance for older adults with self-reported balance problems.

METHODS

40 adults (75.8 years (SD 6.5)) with self-reported balance difficulties or a history of falling were randomized to a control or experimental group. Everyone walked on a treadmill at a comfortable speed 3×/week for 4 weeks in 2 min bouts separated by a seated rest. The control group was instructed to look at a stationary bulls-eye target while the experimental group also saw a moving cursor superimposed on the stationary bulls-eye that represented VFB of their walking trunk motion. The experimental group was instructed to keep the cursor in the center of the bulls-eye. Somatosensory (monofilaments and joint position testing) and vestibular function (canal specific clinical head impulses) was evaluated prior to intervention. Balance and mobility were tested before and after the intervention using Berg Balance Test, BESTest, mini-BESTest, and Six Minute Walk.

RESULTS

There were no significant differences between groups before the intervention. The experimental group significantly improved on the BESTest (p = 0.031) and the mini-BEST (p = 0.019). The control group did not improve significantly on any measure. Individuals with more profound sensory impairments had a larger improvement on dynamic balance subtests of the BESTest.

SIGNIFICANCE

Older adults with self-reported balance problems improve their dynamic balance after training using trunk motion VFB treadmill walking. Individuals with worse sensory function may benefit more from trunk motion VFB during walking than individuals with intact sensory function.

Changes in Regional Brain Grey-Matter Volume Following Successful Completion of a Sensori-Motor Intervention Targeted at Healthy and Fall-Prone Older Adults

Previous studies have suggested that discrete cross-sensory events could be incorrectly combined in the brain of older adults with a history of falls, possibly undermining motor and balance control. Based on previous findings that multisensory integration is modifiable with practice, even in an ageing population, we designed a serious game, named CityQuest, to train typical, everyday multisensory processes including sensori-motor control, spatial navigation, obstacle avoidance and balance control. Played over several sessions, this game was shown to improve these functions in older adults with and without a history of falls, depending on the specific condition of the game on which they were trained. Here, using voxel-based morphometry analysis of anatomical magnetic resonance imaging (MRI) data, we investigated structural changes in the brain of a smaller group of older adults from those who successfully completed this five-week intervention. A grey-matter (GM) volume increase in the precentral gyrus, and GM volume reduction in the inferior temporal and orbitofrontal gyri, was found for all participants. Changes in GM volume within regions of the cerebellum were differentially associated with fall-prone and healthy older adults. Furthermore, a greater GM volume increase in the precentral gyrus was observed in participants who performed the full CityQuest intervention relative to those required to avoid obstacles only. Our results support previous evidence that multisensory training can affect structural changes in the older brain and have implications for programmes designed for the successful rehabilitation of perceptual and cognitive functions.

Effects of the availability of accurate proprioceptive information on older adults' postural sway and muscle co-contraction

During conditions of increased postural instability, older adults exhibit greater lower limb muscle co-contraction. This response has been interpreted as a compensatory postural strategy, which may be used to increase proprioceptive information from muscle spindles or to stiffen the lower limb as a general response to minimise postural sway. The current study aimed to test these two hypotheses by investigating use of muscle co-contraction during sensory transitions that manipulated proprioceptive input. Surface EMG was recorded from the bilateral tibialis anterior and gastrocnemius medialis muscles, in young (aged 18-30) and older adults (aged 68-80) during blind-folded postural assessment. This commenced on a fixed platform (baseline: 2 min), followed by 3 min on a sway-referenced platform (adaptation) and a final 3 min on a fixed platform again (reintegration). Sensory reweighting was slower in older adults, as shown by a significantly larger and longer postural sway after-effect once a stable platform was restored. Muscle co-contraction showed similar after-effects, whereby older adults showed a larger increase in co-contraction once the stable platform had been restored, compared to young adults. This co-contraction after-effect did not return to baseline until after 1 min. Our evidence for high muscle co-contraction during the reintroduction of veridical proprioceptive input suggests that increased co-contraction in older adults is not dependent on contemporaneous proprioceptive input. Rather, it is more likely that co-contraction is a general postural strategy used to minimise postural sway, which is increased during this sensory transition. Future research should examine whether muscle co-contraction is typically a reactive or anticipatory response.

Adaptation of postural recovery responses to a vestibular sensory illusion in individuals with Parkinson disease and healthy controls

BACKGROUND

The ability to adapt postural responses to sensory illusions diminishes with age and is further impaired by Parkinson disease. However, limited information exists regarding training-related adaptions of sensory reweighting in these populations.

METHODS

This study sought to determine whether Parkinson disease or age would differentially affect acute postural recovery or adaptive postural responses to novel or repeated exposure to sensory illusions using galvanic vestibular stimulation during quiet stance.

FINDINGS

Acutely, individuals with Parkinson disease demonstrated larger center of pressure coefficient of variation compared to controls. Unlike individuals with Parkinson disease and asymptomatic older adults, healthy young adults acutely demonstrated a reduction in Sample Entropy to the sensory illusion. Following a period of consolidation Sample Entropy increased in the healthy young group, which coincided with a decreased center of pressure coefficient of variation. Similar changes were not observed in the Parkinson disease or older adult groups.

INTERPRETATION

Taken together, these results suggest that young adults learn to adapt to vestibular illusion in a more robust manner than older adults or those with Parkinson disease. Further investigation into the nature of this adaptive difference is warranted.

Assessment via the Oculus of Visual "Weighting" and "Reweighting" in Young Adults

Substantial advances in virtual reality technology open an exciting window toward better understanding of subdomains of balance control. Here, we studied whether a portable virtual reality headset can be used to test sensory integration for balance. Twenty young adults stood on a both-sides-up ball or floor. Moving spheres were projected from an Oculus Development Kit 2 at various amplitudes and frequencies. Participants' gains indicated visual "weighting" when standing on both-sides-up but not on the floor and "reweighting" with increased visual amplitude. Intraclass correlations showed acceptable to good reliability for all floor conditions and for some of the both-sides-up conditions when we repeated the protocol a week later. Future steps to further develop our paradigm into a clinical assessment of sensory integration for postural control are discussed.

Balance Training Enhances Vestibular Function and Reduces Overactive Proprioceptive Feedback in Elderly

Objectives: Postural control in elderly people is impaired by degradations of sensory, motor, and higher-level adaptive mechanisms. Here, we characterize the effects of a progressive balance training program on these postural control impairments using a brain network model based on system identification techniques. Methods and Material: We analyzed postural control of 35 healthy elderly subjects and compared findings to data from 35 healthy young volunteers. Eighteen elderly subjects performed a 10 week balance training conducted twice per week. Balance training was carried out in static and dynamic movement states, on support surfaces with different elastic compliances, under different visual conditions and motor tasks. Postural control was characterized by spontaneous sway and postural reactions to pseudorandom anterior-posterior tilts of the support surface. Data were interpreted using a parameter identification procedure based on a brain network model. Results: With balance training, the elderly subjects significantly reduced their overly large postural reactions and approximated those of younger subjects. Less significant differences between elderly and young subjects' postural control, namely larger spontaneous sway amplitudes, velocities, and frequencies, larger overall time delays and a weaker motor feedback compared to young subjects were not significantly affected by the balance training. Conclusion: Balance training reduced overactive proprioceptive feedback and restored vestibular orientation in elderly. Based on the assumption of a linear deterioration of postural control across the life span, the training effect can be extrapolated as a juvenescence of 10 years. This study points to a considerable benefit of a continuous balance training in elderly, even without any sensorimotor deficits.

Relationship of visual dependence to age, balance, attention, and vertigo

[Purpose] The aim of this study was to investigate the relationship of increased visual dependence to age, balance, attention, and vertigo. [Subjects and Methods] Twelve younger, 12 visually independent (VI) older and 12 visually dependent (VD) older adults were assessed for levels of visual dependence using Subjective Visual Vertical (SVV) tilt values, balance ability using the Clinical Test of Sensory Integration for Balance (CTSIB), and attentional requirements through the dual-task paradigm and experience of vertigo by completing the Situational Vertigo Questionnaire (SVQ). [Results] VD older adults had higher SVV tilt values, greater postural sway in a scenario where visual and proprioceptive inputs were simultaneously altered, similar dual-task cost and lower SVQ scores compared with younger and VI older adults. No difference was observed between the latter two. [Conclusion] Visual dependence may not necessarily increase with age but affect balance in a sensory condition involving visual-proprioceptive conflict. There is a non-significant trend for elevated visual dependence with increased attentional demands. Greater visual dependence is not accompanied by more frequent symptoms of vertigo in visually complex environments.

Smooth pursuits decrease balance control during locomotion in young and older healthy females

Dynamic balance control-characterised as movement of the trunk and lower limbs-was assessed during fixation of a fixed target, smooth pursuits and saccadic eye movements in ten young (22.9 ± 1.5 years) and ten older (72.1 ± 8.2 years) healthy females walking overground. Participants were presented with visual stimuli to initiate eye movements, and posture and gaze were assessed with motion analysis and eye tracking equipment. The results showed an increase in medial/lateral (ML) trunk movement (C7: p = 0.012; sacrum: p = 0.009) and step-width variability (p = 0.052) during smooth pursuits compared to a fixed target, with no changes for saccades compared to a fixed target. The elders demonstrated greater ML trunk movement (sacrum: p = 0.037) and step-width variability (p = 0.037) than the younger adults throughout, although this did not interact with the eye movements. The findings showed that smooth pursuits decreased balance control in young and older adults similarly, which was likely a consequence of more complicated retinal flow. Since healthy elders are typically already at a postural disadvantage, further decreases in balance caused by smooth pursuits are undesirable.

Effects of Aging in Multisensory Integration: A Systematic Review

Multisensory integration (MSI) is the integration by the brain of environmental information acquired through more than one sense. Accurate MSI has been shown to be a key component of successful aging and to be crucial for processes underlying activities of daily living (ADLs). Problems in MSI could prevent older adults (OA) to age in place and live independently. However, there is a need to know how to assess changes in MSI in individuals. This systematic review provides an overview of tests assessing the effect of age on MSI in the healthy elderly population (aged 60 years and older). A literature search was done in Scopus. Articles from the earliest records available to January 20, 2016, were eligible for inclusion if assessing effects of aging on MSI in the healthy elderly population compared to younger adults (YA). These articles were rated for risk of bias with the Newcastle-Ottawa quality assessment. Out of 307 identified research articles, 49 articles were included for final review, describing 69 tests. The review indicated that OA maximize the use of multiple sources of information in comparison to YA (20 studies). In tasks that require more cognitive function, or when participants need to adapt rapidly to a situation, or when a dual task is added to the experiment, OA have problems selecting and integrating information properly as compared to YA (19 studies). Additionally, irrelevant or wrong information (i.e., distractors) has a greater impact on OA than on YA (21 studies). OA failing to weigh sensory information properly, has not been described in previous reviews. Anatomical changes (i.e., reduction of brain volume and differences of brain areas' recruitment) and information processing changes (i.e., general cognitive slowing, inverse effectiveness, larger time window of integration, deficits in attentional control and increased noise at baseline) can only partly explain the differences between OA and YA regarding MSI. Since we have an interest in successful aging and early detection of MSI issues in the elderly population, the identified tests form a good starting point to develop a clinically useful toolkit to assess MSI in healthy OA.

The relationship between sensory-processing patterns and occupational engagement among older persons

BACKGROUND

Meaningful occupational engagement is essential for successful aging. Sensory-processing abilities that are known to deteriorate with age may reduce occupational engagement. However, the relationship between sensory-processing abilities and occupational engagement among older persons in daily life is unknown.

PURPOSE

This study examined the relationship between sensory-processing patterns and occupational engagement among older persons.

METHOD

Participants were 180 people, ages 50 to 73 years, in good health, who lived in their homes. All participants completed the Adolescent/Adult Sensory Profile and the Activity Card Sort.

FINDINGS

Better registration of sensory input and greater sensory seeking were related to greater occupational engagement.

IMPLICATIONS

Sensory-processing abilities among older persons and their relation to occupational engagement in various life settings should receive attention in research and practice. Occupational therapists should encourage older people to seek sensory input and provide them with rich sensory environments for enhancing meaningful engagement in real life.

A central processing sensory deficit with Parkinson's disease

Parkinson's disease (PD) is a progressive degenerative disease manifested by tremor, rigidity, bradykinesia, and postural instability. Deficits in proprioceptive integration are prevalent in individuals with PD, even at early stages of the disease. These deficits have been demonstrated primarily during investigations of reaching. Here, we investigated how PD affects sensory fusion of multiple modalities during upright standing. We simultaneously perturbed upright stance with visual, vestibular, and proprioceptive stimulation, to understand how these modalities are reweighted so that overall feedback remains suited to stabilizing upright stance in individuals with PD. Eight individuals with PD stood in a visual cave with a moving visual scene at 0.2 Hz while an 80-Hz vibratory stimulus was applied bilaterally to their Achilles tendons (stimulus turns on-off at 0.28 Hz) and a ±1 mA bilateral monopolar galvanic stimulus was applied at 0.36 Hz. The visual stimulus was presented at different amplitudes (0.2°, 0.8° rotation about ankle axis) to measure: the change in gain (weighting) to vision, an intramodal effect; and a simultaneous change in gain to vibration and galvanic stimulation, both intermodal effects. Trunk/leg gain relative to vision decreased when visual amplitude was increased, reflecting an intramodal visual effect. In contrast, when vibration was turned on/off, leg gain relative to vision was equivalent in individuals with PD, indicating no reweighting of visual information when proprioception was disrupted through vibration (i.e., no intermodal effect). Trunk and leg angle gain relative to GVS also showed no reweighting in individuals with PD. These results are in contrast to previous results with healthy adults, who showed clear intermodal effects in the same paradigm, suggesting that individuals with PD not only have a proprioceptive deficit during standing, but also have a cross-modal sensory fusion deficit that is crucial for upright stance control.

Human upright posture control models based on multisensory inputs; in fast and slow dynamics

Posture control to maintain an upright stance is one of the most important and basic requirements in the daily life of humans. The sensory inputs involved in posture control include visual and vestibular inputs, as well as proprioceptive and tactile somatosensory inputs. These multisensory inputs are integrated to represent the body state (body schema); this is then utilized in the brain to generate the motion. Changes in the multisensory inputs result in postural alterations (fast dynamics), as well as long-term alterations in multisensory integration and posture control itself (slow dynamics). In this review, we discuss the fast and slow dynamics, with a focus on multisensory integration including an introduction of our study to investigate "internal force control" with multisensory integration-evoked posture alteration. We found that the study of the slow dynamics is lagging compared to that of fast dynamics, such that our understanding of long-term alterations is insufficient to reveal the underlying mechanisms and to propose suitable models. Additional studies investigating slow dynamics are required to expand our knowledge of this area, which would support the physical training and rehabilitation of elderly and impaired persons.

Changes in sensory reweighting of proprioceptive information during standing balance with age and disease

With sensory reweighting, reliable sensory information is selected over unreliable information during balance by dynamically combining this information. We used system identification techniques to show the weight and the adaptive process of weight change of proprioceptive information during standing balance with age and specific diseases. Ten healthy young subjects (aged between 20 and 30 yr) and 44 elderly subjects (aged above 65 yr) encompassing 10 healthy elderly, 10 with cataract, 10 with polyneuropathy, and 14 with impaired balance, participated in the study. During stance, proprioceptive information of the ankles was disturbed by rotation of the support surface with specific frequency content where disturbance amplitude increased over trials. Body sway and reactive ankle torque were measured to determine sensitivity functions of these responses to the disturbance amplitude. Model fits resulted in a proprioceptive weight (changing over trials), time delay, force feedback, reflexive stiffness, and damping. The proprioceptive weight was higher in healthy elderly compared with young subjects and higher in elderly subjects with cataract and with impaired balance compared with healthy elderly subjects. Proprioceptive weight decreased with increasing disturbance amplitude; decrease was similar in all groups. In all groups, the time delay was higher and the reflexive stiffness was lower compared with young or healthy elderly subjects. In conclusion, proprioceptive information is weighted more with age and in patients with cataract and impaired balance. With age and specific diseases the time delay was higher and reflexive stiffness was lower. These results illustrate the opportunity to detect the underlying cause of impaired balance in the elderly with system identification.

Elderly Use Proprioception Rather than Visual and Vestibular Cues for Postural Motor Control

Multiple factors have been proposed to contribute to the deficits of postural control in the elderly. They were summarized as sensory, motor, and higher-level adaptation deficits. Using a model-based approach, we aimed to identify which of these deficits mainly determine age-related changes in postural control. We analyzed postural control of 20 healthy elderly people with a mean age of 74 years. The findings were compared to data from 19 healthy young volunteers (mean age 28 years) and 16 healthy middle-aged volunteers (mean age 48 years). Postural control was characterized by spontaneous sway measures and measures of perturbed stance. Perturbations were induced by pseudorandom anterior-posterior tilts of the body support surface. We found that spontaneous sway amplitude and velocity were significantly larger, and sway frequencies were higher in elderly compared to young people. Body excursions as a function of tilt stimuli were clearly different in elderly compared to young people. Based on simple feedback model simulations, we found that elderly favor proprioceptive over visual and vestibular cues, other than younger subjects do. Moreover, we identified an increase in overall time delay challenging the feedback systems stability, and a decline in the amplitude of the motor feedback, probably representing weakness of the motor system. In general, these parameter differences between young and old may result from both deficits and compensation strategies in the elderly. Our model-based findings correlate well with deficits measured with clinical balance scores, which are widely used in clinical practice.

Impact of altered lower limb proprioception produced by tendon vibration on adaptation to split-belt treadmill walking

It has been proposed that proprioceptive input is essential to the development of a locomotor body schema that is used to guide the assembly of successful walking. Proprioceptive information is used to signal the need for, and promotion of, locomotor adaptation in response to environmental or internal modifications. The purpose of this investigation was to determine if tendon vibration applied to either the hamstrings or quadriceps of participants experiencing split-belt treadmill walking modified lower limb kinematics during the early adaptation period. Modifications in the adaptive process in response to vibration would suggest that the sensory-motor system had been unsuccessful in down weighting the disruptive proprioceptive input resulting from vibration. Ten participants experienced split-belt walking, with and without vibration, while gait kinematics were obtained with a 12-camera collection system. Bilateral hip, knee, and ankle joint angles were calculated and the first five strides after the split were averaged for each subject to create joint angle waveforms for each of the assessed joints, for each experimental condition. The intralimb variables of stride length, percent stance time, and relative timing between various combinations of peak joint angles were assessed using repeated measures MANOVA. Results indicate that vibration had very little impact on the split-belt walking adaptive process, although quadriceps vibration did significantly reduce percent stance time by 1.78% relative to the no vibration condition. The data suggest that the perceptual-motor system was able to down weight the disrupted proprioceptive input such that the locomotor body schema was able to effectively manage the lower limb patterns of motion necessary to adapt to the changing belt speed. Complementary explanations for the current findings are also discussed.

Effect of haptic supplementation on postural control of younger and older adults in an unstable sitting task

Standing postural control is known to be altered during aging, but age-related changes in sitting postural control have scarcely been explored. The present experiment studied the roles of visual and haptic information in a sitting task in both young and older adults. Fifteen young and fifteen older adults participated in this study. Six experimental conditions were performed with eyes open and eyes closed: quiet sitting, rocker-board sitting, and 4 conditions of haptic supplementation, provided by a hand-held pen, during rocker-board sitting. Classical variables were extracted from the center of pressure (COP) and pen trajectories, and the stabilogram diffusion analysis was performed on the COP data. Three-way ANOVAs (Group×Vision×Condition) were carried out. Postural instability was strongly attenuated by haptic supplementation in both age groups. Furthermore, instability due to visual deprivation was compensated by haptic supplementation. Long- and short-term diffusion coefficients were smaller in conditions of haptic supplementation. The present study confirmed the effect of haptic supplementation on both open-loop and closed-loop mechanisms of postural control and extended it to unstable sitting in young and older adults despite the complex biomechanical systems involved in sitting postural tasks.

Stance width changes how sensory feedback is used for multisegmental balance control

A multilink sensorimotor integration model of frontal plane balance control was developed to determine how stance width influences the use of sensory feedback in healthy adults. Data used to estimate model parameters came from seven human participants who stood on a continuously rotating surface with three different stimulus amplitudes, with eyes open and closed, and at four different stance widths. Dependent variables included lower body (LB) and upper body (UB) sway quantified by frequency-response functions. Results showed that stance width had a major influence on how parameters varied across stimulus amplitude and between visual conditions. Active mechanisms dominated LB control. At narrower stances, with increasing stimulus amplitude, subjects used sensory reweighting to shift reliance from proprioceptive cues to vestibular and/or visual cues that oriented the LB more toward upright. When vision was available, subjects reduced reliance on proprioception and increased reliance on vision. At wider stances, LB control did not exhibit sensory reweighting. In the UB system, both active and passive mechanisms contributed and were dependent on stance width. UB control changed across stimulus amplitude most in wide stance (opposite of the pattern found in LB control). The strong influence of stance width on sensory integration and neural feedback control implies that rehabilitative therapies for balance disorders can target different aspects of balance control by using different stance widths. Rehabilitative strategies designed to assess or modify sensory reweighting will be most effective with the use of narrower stances, whereas wider stances present greater challenges to UB control.

Visual reliance for balance control in older adults persists when visual information is disrupted by artificial feedback delays

Sensory information from our eyes, skin and muscles helps guide and correct balance. Less appreciated, however, is that delays in the transmission of sensory information between our eyes, limbs and central nervous system can exceed several 10s of milliseconds. Investigating how these time-delayed sensory signals influence balance control is central to understanding the postural system. Here, we investigate how delayed visual feedback and cognitive performance influence postural control in healthy young and older adults. The task required that participants position their center of pressure (COP) in a fixed target as accurately as possible without visual feedback about their COP location (eyes-open balance), or with artificial time delays imposed on visual COP feedback. On selected trials, the participants also performed a silent arithmetic task (cognitive dual task). We separated COP time series into distinct frequency components using low and high-pass filtering routines. Visual feedback delays affected low frequency postural corrections in young and older adults, with larger increases in postural sway noted for the group of older adults. In comparison, cognitive performance reduced the variability of rapid center of pressure displacements in young adults, but did not alter postural sway in the group of older adults. Our results demonstrate that older adults prioritize vision to control posture. This visual reliance persists even when feedback about the task is delayed by several hundreds of milliseconds.

Sensory reweighting dynamics in human postural control

Healthy humans control balance during stance by using an active feedback mechanism that generates corrective torque based on a combination of movement and orientation cues from visual, vestibular, and proprioceptive systems. Previous studies found that the contribution of each of these sensory systems changes depending on perturbations applied during stance and on environmental conditions. The process of adjusting the sensory contributions to balance control is referred to as sensory reweighting. To investigate the dynamics of reweighting for the sensory modalities of vision and proprioception, 14 healthy young subjects were exposed to six different combinations of continuous visual scene and platform tilt stimuli while sway responses were recorded. Stimuli consisted of two components: 1) a pseudorandom component whose amplitude periodically switched between low and high amplitudes and 2) a low-amplitude sinusoidal component whose amplitude remained constant throughout a trial. These two stimuli were mathematically independent of one another and, thus, permitted separate analyses of sway responses to the two components. For all six stimulus combinations, the sway responses to the constant-amplitude sine were influenced by the changing amplitude of the pseudorandom component in a manner consistent with sensory reweighting. Results show clear evidence of intra- and intermodality reweighting. Reweighting dynamics were asymmetric, with slower reweighting dynamics following a high-to-low transition in the pseudorandom stimulus amplitude compared with low-to-high amplitude shifts, and were also slower for inter- compared with intramodality reweighting.

Drawing on related knowledge to advance multiple sclerosis falls-prevention research

There is much to be learned from falls-related research outside the field of multiple sclerosis (MS), as well as from work within the MS field but not specific to falls or falls prevention. This article describes three examples of such bodies of work that have potential to broaden approaches to falls-prevention research: 1) sensory components of postural control among older adults, 2) lessons learned from physical activity promotion among people with spinal cord injury (SCI), and 3) aging among people with MS. Age-related deterioration in visual, vestibular, and somatosensory systems or in sensory integration can adversely affect postural control and can contribute to falls in older people. Sensory-specific interventions designed for improving balance in older people could be adapted for preventing falls in individuals with MS. Spinal Cord Injury (SCI) Action Canada's strategy for disseminating physical activity promotion interventions for adults with SCI has been successful and widely accepted by community partners. Many of the peer-based interventions developed by SCI Action Canada are potentially relevant and could be adapted to the MS population for both physical activity promotion and falls prevention. Considering that older people with MS constitute a growing proportion of the MS population and over 70% of older people with MS report moderate to extreme balance problems, falls prevention should be one of the key components, particularly for MS management in older or more disabled groups. Overall, given people's different ages, symptoms, strengths, and barriers, a tailored MS falls-prevention intervention that includes peer/caregiver support is critical.

Adaptive visual re-weighting in children's postural control

This study investigated how children's postural control adapts to changes in the visual environment and whether they use previous experience to adjust postural responses to following expositions. Four-, eight-, and twelve-year-old children (10 in each group) and 10 young adults stood upright inside of a moving room during eight trials each lasting one-minute. In the first trial, the room was stationary. In the following seven trials, the room oscillated at 0.2 Hz, amplitude of 0.5 cm, with the exception of the fifth trial, in which the room oscillated with amplitude of 3.2 cm. Body sway responses of young adults and older children down-weighted more to the increased visual stimulus amplitude when compared to younger children. In addition, four- and eight-year-old children quickly up-weighted body responses to visual stimulus in the subsequent two trials after the high amplitude trial. Sway variability decreased with age and was greatest during the high-amplitude trial. These results indicate that four year olds have already developed the adaptive capability to quickly down-weight visual influences. However, the increased gain values and residual variability observed for the younger children suggest that they have not fully calibrated their adaptive response to that of the young adults tested. Moreover, younger children do not carry over their previous experience from the sensorial environment to adapt to future changes.

Age effects on sensory-processing abilities and their impact on handwriting

Background.

Sensory-processing abilities are known to deteriorate in the elderly. As a result, daily activities such as handwriting may be impaired. Yet, knowledge about sensory-processing involvement in handwriting characteristics among older persons is limited.

Purpose

To examine how age influences sensory-processing abilities and the impact on handwriting as a daily performance.

Method.

The study participants were 118 healthy, independently functioning adults divided into four age groups: 31–45, 46–60, 61–75 and 76+ years. All participants completed the Adolescent/Adult Sensory Profile (AASP). Handwriting process was documented using the Computerized Handwriting Penmanship Evaluation Tool (ComPET).

Findings.

Age significantly affects sensory processing and handwriting pressure as well as temporal and spatial measures. Both handwriting time and spatial organization of the written product were predicted by sensory seeking. When examining age contribution to the prediction of handwriting by sensory processing, sensory seeking showed a tendency for predicting handwriting pressure (p = .06), while sensory sensitivity significantly predicted handwriting velocity.

Implications.

Age appears to influence sensory-processing abilities and affect daily performance tasks, such as handwriting, for which sensitivity and seeking for sensations are essential. Awareness of clinicians to sensory-processing deficits among older adults and examining their impact on broader daily activities are essential to improve daily performance and quality of life.

Age-dependent modulation of sensory reweighting for controlling posture in a dynamic virtual environment

Older adults require more time to reweight sensory information for maintaining balance that could potentially lead to increased incidence of falling in rapidly changing or cognitively demanding environments. In this study, we manipulated the visual surround information during a collision avoidance task in order to investigate how young and elderly adults engage in sensory reweighting under conditions of visual anticipation. Sixteen healthy elderly (age: 71.5 ± 4.9 years; height: 159.3 ± 6.6 cm; mass: 73.3 ± 3.3 kg) and 20 young (age: 22.8 ± 3.3 years; height: 174.4 ± 10.7 cm; mass: 70.1 ± 13.9 kg) participants stood for 240 s on a force platform under two experimental conditions: quiet standing and standing while anticipating randomly approaching virtual objects to be avoided. During both tasks, the visual surround changed every 60 s from a stationary virtual scene (room) to either a moving room or darkness and then back to a stationary scene to evoke sensory reweighting processes. In quiet standing, elderly showed greater sway variability and were more severely affected by the removal or degradation of visual surround information when compared to young participants. During visual anticipation, sway variability was not different between the age groups. In addition, both young and elderly participants were similarly affected by the degradation or removal of the visual surround. These findings suggest that sensory reweighting in a dynamic virtual environment that evokes visual anticipation interacts with postural state anxiety regardless of age. Elderly show less efficient sensory reweighting in quiet standing due to greater visual field dependence possibly associated with fear of falling.

Dynamics of inter-modality re-weighting during human postural control

Flexible and stable postural control requires adaptation to changing environmental conditions, a process which requires re-weighting of multisensory stimuli. Recent studies, as well as predictions from a computational model, have indicated a reciprocal re-weighting relationship between modalities when a sensory stimulus changes amplitude. As one modality is down-weighted, another is up-weighted to compensate (and vice versa). The purpose of this study was to investigate the dynamics of intra- and inter-modality re-weighting process by examining postural responses to manipulation of proprioception and visual modalities simultaneously. Twenty-two young adults were placed in a visual cave and stood on a variable-pitch platform for thirteen trials of 250 s apiece. The platform was rotated at constant frequency of 0.4 Hz and amplitudes of 0.3 (low) or 1.5 (high) degrees. Platform amplitude was manipulated in two conditions: low-to-high or high-to-low. The visual stimulus was displayed at constant frequency of 0.35 Hz and amplitude of 0.08 degrees. The results showed both fast and slow changes in center of mass (CoM) response to the switch in platform amplitude. On both timescales, CoM response changed in a reciprocal manner relative to platform amplitude. When the platform amplitude increased (low-to-high condition), CoM response decreased relative to the platform and increased relative to the visual stimulus, indicating both intra-modality and inter-modality sensory re-weighting. In the high-to-low condition, however, there was no change in CoM response relative to visual stimulus, indicating that re-weighting may also be dependent on the absolute level of gain. Sway variability at frequencies other than the stimulus frequency also showed a reciprocal relationship with CoM gain relative to platform. Overall, these results indicate that dynamics of multisensory re-weighting is clearly more complicated than the schemes proposed by current adaptive models of human postural control.

Development of multisensory reweighting is impaired for quiet stance control in children with developmental coordination disorder (DCD)

Background

Developmental Coordination Disorder (DCD) is a leading movement disorder in children that commonly involves poor postural control. Multisensory integration deficit, especially the inability to adaptively reweight to changing sensory conditions, has been proposed as a possible mechanism but with insufficient characterization. Empirical quantification of reweighting significantly advances our understanding of its developmental onset and improves the characterization of its difference in children with DCD compared to their typically developing (TD) peers.

Methodology/Principal Findings

Twenty children with DCD (6.6 to 11.8 years) were tested with a protocol in which visual scene and touch bar simultaneously oscillateded medio-laterally at different frequencies and various amplitudes. Their data were compared to data on TD children (4.2 to 10.8 years) from a previous study. Gains and phases were calculated for medio-lateral responses of the head and center of mass to both sensory stimuli. Gains and phases were simultaneously fitted by linear functions of age for each amplitude condition, segment, modality and group. Fitted gains and phases at two comparison ages (6.6 and 10.8 years) were tested for reweighting within each group and for group differences. Children with DCD reweight touch and vision at a later age (10.8 years) than their TD peers (4.2 years). Children with DCD demonstrate a weak visual reweighting, no advanced multisensory fusion and phase lags larger than those of TD children in response to both touch and vision.

Conclusions/Significance

Two developmental perspectives, postural body scheme and dorsal stream development, are provided to explain the weak vision reweighting. The lack of multisensory fusion supports the notion that optimal multisensory integration is a slow developmental process and is vulnerable in children with DCD.