Multisensory Integration Predicts Balance and Falls in Older Adults

Multisensory mechanisms of gait and balance in Parkinson's disease: an integrative review

Understanding the neural underpinning of human gait and balance is one of the most pertinent challenges for 21st-century translational neuroscience due to the profound impact that falls and mobility disturbances have on our aging population. Posture and gait control does not happen automatically, as previously believed, but rather requires continuous involvement of central nervous mechanisms. To effectively exert control over the body, the brain must integrate multiple streams of sensory information, including visual, vestibular, and somatosensory signals. The mechanisms which underpin the integration of these multisensory signals are the principal topic of the present work. Existing multisensory integration theories focus on how failure of cognitive processes thought to be involved in multisensory integration leads to falls in older adults. Insufficient emphasis, however, has been placed on specific contributions of individual sensory modalities to multisensory integration processes and cross-modal interactions that occur between the sensory modalities in relation to gait and balance. In the present work, we review the contributions of somatosensory, visual, and vestibular modalities, along with their multisensory intersections to gait and balance in older adults and patients with Parkinson's disease. We also review evidence of vestibular contributions to multisensory temporal binding windows, previously shown to be highly pertinent to fall risk in older adults. Lastly, we relate multisensory vestibular mechanisms to potential neural substrates, both at the level of neurobiology (concerning positron emission tomography imaging) and at the level of electrophysiology (concerning electroencephalography). We hope that this integrative review, drawing influence across multiple subdisciplines of neuroscience, paves the way for novel research directions and therapeutic neuromodulatory approaches, to improve the lives of older adults and patients with neurodegenerative diseases.

A systematic review of exergame usability as home-based balance training tool for older adults usability of exergames as home-based balance training

BACKGROUND

Exergames are a fun, viable, attractive, and safe way to engage in physical exercise for most patient populations, including older adults. Their use in the home environment enables an expanded understanding about its applicability and its impact on clinical outcomes that can contribute to improved functionality and quality of life in this population. This systematic review aimed to synthesize the evidence on the usability of exergames as a tool for home-based balance training in older adults.

METHODS

The search was realized in 6 electronic databases and were included 1) randomized controlled trials with exergames home-based training as intervention, 2) studies involving older adults (aged 60 years or older) described as having impaired static or dynamic balance, 3) that compared the effects of exergames to usual care, health education or no intervention, and 4) reported usability and balance outcomes. The Cochrane Risk of Bias tool for randomized trials version 2 and the Grading of Recommendations Assessment, Development, and Evaluation were used to evaluate the methodological quality of studies and levels of evidence for outcomes.

RESULTS

After screening 1107 records, we identified 4 trials were included. The usability score of exergames was classified as an acceptable, good, and feasible tool. The pooled effect indicated improvements in favor of the exergame group for functional balance by TUG test (MD = -5.90; 95%CI = -10.29 to -1.51) with low-certainty evidence and Tinetti scale (MD = 4.80; 95%CI = 3.36 to 6.24) with very low-certainty evidence. Analyzing the different immersion level, it was observed a significant difference in the experimental group for the immersive exergames (MD = -9.14; 95%CI = -15.51 to -2.77) with very low-certainty evidence.

CONCLUSION

Exergames applied at home showed good usability and had significant effects on functional balance compared to usual care or no intervention, especially in the immersive modality.

TRIAL REGISTRATION

PROSPERO registration number: CRD42022343290.

[Interpretation of a concept for functional movement disorders from the perspective of older patients]

A recently published concept considers a significant proportion of the occurrence and persistence of functional movement disorders (FMD) to be explained by increased/incorrect weighting of the expected movement (feedforward signal) in the presence of decreased/altered actual feedback of the movement. In the context of aging and age-associated diseases, there is an increased likelihood that these prerequisites will occur, also in combination. For example, the feedforward signal can be enhanced by accumulation of a wealth of experience but can for example become prone to error due to changes in attention and (fear of) falling. Conversely, the actual feedback is subject to age-related changes, such as reduction of sensory functions. This could explain why FMDs also occur in old age and offer treatment approaches for this so far poorly studied disorder. It follows that a specific focus on (the correction of) feedforward signals and strengthening as well as training of the actual feedback are potentially promising therapeutic approaches for older people with FMD.

Multisensory Calibration: A Variety of Slow and Fast Brain Processes Throughout the Lifespan

From before we are born, throughout development, adulthood, and aging, we are immersed in a multisensory world. At each of these stages, our sensory cues are constantly changing, due to body, brain, and environmental changes. While integration of information from our different sensory cues improves precision, this only improves accuracy if the underlying cues are unbiased. Thus, multisensory calibration is a vital and ongoing process. To meet this grand challenge, our brains have evolved a variety of mechanisms. First, in response to a systematic discrepancy between sensory cues (without external feedback) the cues calibrate one another (unsupervised calibration). Second, multisensory function is calibrated to external feedback (supervised calibration). These two mechanisms superimpose. While the former likely reflects a lower level mechanism, the latter likely reflects a higher level cognitive mechanism. Indeed, neural correlates of supervised multisensory calibration in monkeys were found in higher level multisensory cortical area VIP, but not in the relatively lower level multisensory area MSTd. In addition, even without a cue discrepancy (e.g., when experiencing stimuli from different sensory cues in series) the brain monitors supra-modal statistics of events in the environment and adapts perception cross-modally. This too comprises a variety of mechanisms, including confirmation bias to prior choices, and lower level cross-sensory adaptation. Further research into the neuronal underpinnings of the broad and diverse functions of multisensory calibration, with improved synthesis of theories is needed to attain a more comprehensive understanding of multisensory brain function.

Virtual reality as a tool to explore multisensory processing before and after engagement in physical activity

Introduction

This pilot study employed a non-randomized control trial design to explore the impact of physical activity within a virtual reality (VR) environment on multisensory processing among community-dwelling older adults.

Methods

The investigation compared both chronic (over 6 weeks) and acute effects of VR-based physical activity to a reading control group. The evaluation metrics for multisensory processing included audiovisual response time (RT), simultaneity judgments (SJ), sound-induced flash illusion (SIFI), and temporal order judgments (TOJ). A total of 13 older adults were provided with VR headsets featuring custom-designed games, while another 14 older adults were assigned to a reading-based control group.

Results

Results indicated that acute engagement in physical activity led to higher accuracy in the SIFI task (experimental group: 85.6%; control group: 78.2%; p = 0.037). Additionally, both chronic and acute physical activity resulted in quicker response times (chronic: experimental group = 336.92; control group = 381.31; p = 0.012; acute: experimental group = 333.38; control group = 383.09; p = 0.006). Although the reading group showed a non-significant trend for greater improvement in mean RT, covariate analyses revealed that this discrepancy was due to the older age of the reading group.

Discussion

The findings suggest that immersive VR has potential utility for enhancing multisensory processing in older adults. However, future studies must rigorously control for participant variables like age and sex to ensure more accurate comparisons between experimental and control conditions.

Age-related changes to the attentional modulation of temporal binding

During multisensory integration, the time range within which visual and auditory information can be perceived as synchronous and bound together is known as the temporal binding window (TBW). With increasing age, the TBW becomes wider, such that older adults erroneously, and often dangerously, integrate sensory inputs that are asynchronous. Recent research suggests that attentional cues can narrow the width of the TBW in younger adults, sharpening temporal perception and increasing the accuracy of integration. However, due to their age-related declines in attentional control, it is not yet known whether older adults can deploy attentional resources to narrow the TBW in the same way as younger adults. This study investigated the age-related changes to the attentional modulation of the TBW. Thirty younger and 30 older adults completed a cued-spatial-attention version of the stream-bounce illusion, assessing the extent to which the visual and auditory stimuli were integrated when presented at three different stimulus-onset asynchronies, and when attending to a validly cued or invalidly cued location. A 2 × 2 × 3 mixed ANOVA revealed that when participants attended to the validly cued location (i.e., when attention was present), susceptibility to the stream-bounce illusion decreased. However, crucially, this attentional manipulation significantly affected audiovisual integration in younger adults, but not in older adults. These findings suggest that older adults have multisensory integration-related attentional deficits. Directions for future research and practical applications surrounding treatments to improve the safety of older adults' perception and navigation through the environment are discussed.

Age-Related Changes to Multisensory Integration and Audiovisual Speech Perception

Multisensory integration is essential for the quick and accurate perception of our environment, particularly in everyday tasks like speech perception. Research has highlighted the importance of investigating bottom-up and top-down contributions to multisensory integration and how these change as a function of ageing. Specifically, perceptual factors like the temporal binding window and cognitive factors like attention and inhibition appear to be fundamental in the integration of visual and auditory information-integration that may become less efficient as we age. These factors have been linked to brain areas like the superior temporal sulcus, with neural oscillations in the alpha-band frequency also being implicated in multisensory processing. Age-related changes in multisensory integration may have significant consequences for the well-being of our increasingly ageing population, affecting their ability to communicate with others and safely move through their environment; it is crucial that the evidence surrounding this subject continues to be carefully investigated. This review will discuss research into age-related changes in the perceptual and cognitive mechanisms of multisensory integration and the impact that these changes have on speech perception and fall risk. The role of oscillatory alpha activity is of particular interest, as it may be key in the modulation of multisensory integration.

Older adults with slow sit to stand times show reduced temporal precision of audio-visual integration

Sustained integration of sensory inputs over increased temporal delays is associated with reduced cognitive and physical functioning in older adults and adverse outcomes such as falls. Here, we explored the relationship between multisensory integration and a clinically relevant measure of balance/postural control; Sit-to-Stand Time, the efficiency with which an older adult can transition between a seated and a standing posture. We investigated whether temporal multisensory integration was associated with performance on the Five-Times Sit-to-Stand Test (FTSST) in a large sample of 2556 older adults (mean age = 63.62 years, SD = 7.50; 55% female) drawn from The Irish Longitudinal Study on Ageing (TILDA). K-means clustering was applied to FTSST data, yielding three clusters characterised by fast (mean = 10.88 s; n = 1122), medium (mean = 14.34 s; n = 1133) and slow (mean = 18.97 s; n = 301) sit-to-stand times. At wave 3 of TILDA, older adults participated in the Sound Induced Flash Illusion (SIFI), a measure of the precision of temporal audio-visual integration, which included three audio-visual stimulus onset asynchronies (SOAs): 70, 150 and 230 ms. Older adults with the slowest sit-to-stand times were more susceptible to the SIFI at the longest SOA (230 ms) compared to the shortest SOA (70 ms) relative to those with the fastest times (p = 0.02). Older adults who take longer to repeatedly transition from a seated to a standing posture exhibit an expanded temporal binding window for audio-visual events, supporting a link between multisensory perception and balance/postural control in ageing.

Effectiveness of Different Training Modalities on Static Balance in Older Adults: A Systematic Review and Meta-Analysis

(1) Background: aging is associated with functional changes such as balance, which plays a critical role in older adults. Physical exercise has been established as a factor capable of modulating these age-related alterations. (2) Methods: a meta-analysis of randomized clinical trials (RCTs) was conducted. The systematic search was performed in the PubMed/MEDLINE, Web of Science, the SPORTDiscus and Cochrane Library databases. Articles were included if participants were 65 years or older, healthy and performing resistance training, aerobic training, balance training or multicomponent training. Studies were excluded if there was a combination of training with other types of intervention. The protocol of this systematic review was published in the International Prospective Register of Systematic Reviews (PROSPERO) with the code CRD42021233252 (3) Results: the search strategy found a total of 1103 studies. After removing duplicates and the inclusion and exclusion criteria, eight articles were included in the meta-analysis, with a total of 335 healthy older adults analyzed. The results showed no significant differences between the intervention groups and the control groups after the exercise programs. (4) Conclusions: interventions based on different types of exercise improved static balance in elderly population, but without statistically significant difference in comparison with the control groups.

The temporal precision of audiovisual integration is associated with longitudinal fall incidents but not sensorimotor fall risk in older adults

Sustained multisensory integration over long inter-stimulus time delays is typically found in older adults, particularly those with a history of falls. However, the extent to which the temporal precision of audio-visual integration is associated with longitudinal fall or fall risk trajectories is unknown. A large sample of older adults (N = 2319) were grouped into longitudinal trajectories of self-reported fall incidents (i.e., decrease, stable, or increase in number) and, separately, their performance on a standard, objective measure of fall risk, Timed Up and Go (TUG; stable, moderate decline, severe decline). Multisensory integration was measured once as susceptibility to the Sound-Induced Flash Illusion (SIFI) across three stimulus onset asynchronies (SOAs): 70 ms, 150 ms and 230 ms. Older adults with an increasing fall number showed a significantly different pattern of performance on the SIFI than non-fallers, depending on age: For adults with increasing incidents of falls, those aged 53-59 years showed a much smaller difference in illusion susceptibility at 70 ms versus 150 ms than those aged 70 + years. In contrast, non-fallers showed a more comparable difference between these SOA conditions across age groups. There was no association between TUG performance trajectories and SIFI susceptibility. These findings suggests that a fall event is associated with distinct temporal patterns of multisensory integration in ageing and have implications for our understanding of the mechanisms underpinning brain health in older age.

The order of attentional focus instructions affects how postural control processes compensate for multisensory mismatch: a crossover study

Directing attention during balance training can have an immediate and lasting impact on a patient's balance and ultimately decrease the risk of future falls. However, it is unclear how attention can best be utilized to improve postural control. The current study uses a 2 × 2 crossover design to investigate the potential impact of receiving multiple verbal instructions during a single session of sensorimotor control testing for balance. Twenty-eight healthy adults were tasked to balance on a rocker board while immersed in virtual reality (VR). The VR created a multisensory mismatch between visual VR motion and body motion. The strength of the relationship between visual motion and body motion was measured to assess visual dependence. Alpha and theta frequency bands in electroencephalography (EEG) recordings were also analyzed to identify potential neural correlates of visual dependence and postural stability. Participants were randomized into two groups: one group was first instructed to keep the board leveled (external focus) and then instructed to keep both feet leveled (internal focus) to help maintain stability. The other group was given these two instructions in reverse order. Analyses focused on time, instruction, and group effects from receiving multiple instructions. Results revealed that when participants are given external focus first, and internal focus second, they are more likely to demonstrate lower visual dependence and better postural stability throughout the entire session than participants given internal focus first and external focus second. However, channel-level EEG analyses did not reveal differences between the groups. Current findings suggest that the order of attentional focus instructions may influence how the postural control system resolves sensory incongruence during a single testing session.

Visual-somatosensory integration (VSI) as a novel marker of Alzheimer’s disease: A comprehensive overview of the VSI study

Identification of novel, non-invasive, non-cognitive based markers of Alzheimer’s disease (AD) and related dementias are a global priority. Growing evidence suggests that Alzheimer’s pathology manifests in sensory association areas well before appearing in neural regions involved in higher-order cognitive functions, such as memory. Previous investigations have not comprehensively examined the interplay of sensory, cognitive, and motor dysfunction with relation to AD progression. The ability to successfully integrate multisensory information across multiple sensory modalities is a vital aspect of everyday functioning and mobility. Our research suggests that multisensory integration, specifically visual-somatosensory integration (VSI), could be used as a novel marker for preclinical AD given previously reported associations with important motor (balance, gait, and falls) and cognitive (attention) outcomes in aging. While the adverse effect of dementia and cognitive impairment on the relationship between multisensory functioning and motor outcomes has been highlighted, the underlying functional and neuroanatomical networks are still unknown. In what follows we detail the protocol for our study, named The VSI Study, which is strategically designed to determine whether preclinical AD is associated with neural disruptions in subcortical and cortical areas that concurrently modulate multisensory, cognitive, and motor functions resulting in mobility decline. In this longitudinal observational study, a total of 208 community-dwelling older adults with and without preclinical AD will be recruited and monitored yearly. Our experimental design affords assessment of multisensory integration as a new behavioral marker for preclinical AD; identification of functional neural networks involved in the intersection of sensory, motor, and cognitive functioning; and determination of the impact of early AD on future mobility declines, including incident falls. Results of The VSI Study will guide future development of innovative multisensory-based interventions aimed at preventing disability and optimizing independence in pathological aging.

Effects of visual restoration on gait performance and kinematics of lower extremities in patients with age-related cataract

BACKGROUND

Visual inputs are critical for locomotor navigation and sensorimotor integration in the elderly; however, the mechanism needs to be explored intensively. The present study assessed the gait pattern after cataract surgery to investigate the effects of visual restoration on locomotion.

METHODS

The prospective study recruited 32 patients (70.1 ± 5.2 years) with bilateral age-related cataracts in the Department of Ophthalmology at Peking University Third Hospital from October 2016 to December 2019. The temporal-spatial gait parameters and kinematic parameters were measured by the Footscan system and inertial measurement units. Paired t -test was employed to compare data normally distributed and Wilcoxon rank-sum test for non-normally distributed.

RESULTS

After visual restoration, the walking speed increased by 9.3% (1.19 ± 0.40 m/s vs. 1.09 ± 0.34 m/s, P =0.008) and exhibited an efficient gait pattern with significant decrease in gait cycle (1.02 ± 0.08 s vs. 1.04 ± 0.07 s, P =0.012), stance time (0.66 ± 0.06 s vs. 0.68 ± 0.06 s, P =0.045), and single support time (0.36 ± 0.03 s vs. 0.37 ± 0.02 s, P =0.011). High amplitude of joint motion was detected in the sagittal plane in the left hip (37.6° ± 5.3° vs. 35.5° ± 6.2°, P =0.014), left thigh (38.0° ± 5.2° vs. 36.4° ± 5.8°, P =0.026), left shank (71.9° ± 5.7° vs. 70.1° ± 5.6°, P =0.031), and right knee (59.1° ± 4.8° vs. 56.4° ± 4.8°, P =0.001). The motor symmetry of thigh improved from 8.35 ± 5.30% to 6.30 ± 4.73% ( P =0.042).

CONCLUSIONS

The accelerated gait in response to visual restoration is characterized by decreased stance time and increased range of joint motion. Training programs for improving muscle strength of lower extremities might be helpful to facilitate the adaptation to these changes in gait.

Longitudinal Associations Between Falls and Risk of Gait Decline: Results From the Central Control of Mobility and Aging Study

OBJECTIVE

To examine whether falls are associated with longitudinal changes in different gait domains and onset of clinical gait abnormalities.

DESIGN

Longitudinal study.

SETTING

General community.

PARTICIPANTS

Ambulatory older adults free of dementia (N=428; mean age, 77.8±6.4 years).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Gait was assessed with a computerized walkway. Pace, rhythm, and variability (outcome measures) were derived from individual gait measures, using principal component analysis. Clinical gait abnormalities (neurologic, nonneurologic, mixed) were visually assessed by clinicians. Linear mixed-effects models were used to examine the associations between falls (the exposure variable coded as none, single, and multiple) and changes in gait domains. Multinomial logistic regression was used to examine associations between falls and the onset of clinical gait abnormalities. Models were adjusted for sex, education, age, body mass index, number of comorbidities, gait speed at the first follow-up, and time between the last fall and the first follow-up gait assessment.

RESULTS

Pace declined while rhythm and variability increased at a faster rate (P<.05) among 32 participants with multiple falls in the first year of follow-up compared with 299 participants with no falls. Risk for clinical gait abnormalities between those with no falls, a single fall, or multiple falls was not different.

CONCLUSIONS

Multiple falls predict future gait decline in multiple domains in aging. Interventions to prevent gait decline after multiple falls should be investigated.

Increases in sensory noise predict attentional disruptions to audiovisual speech perception

We receive information about the world around us from multiple senses which combine in a process known as multisensory integration. Multisensory integration has been shown to be dependent on attention; however, the neural mechanisms underlying this effect are poorly understood. The current study investigates whether changes in sensory noise explain the effect of attention on multisensory integration and whether attentional modulations to multisensory integration occur via modality-specific mechanisms. A task based on the McGurk Illusion was used to measure multisensory integration while attention was manipulated via a concurrent auditory or visual task. Sensory noise was measured within modality based on variability in unisensory performance and was used to predict attentional changes to McGurk perception. Consistent with previous studies, reports of the McGurk illusion decreased when accompanied with a secondary task; however, this effect was stronger for the secondary visual (as opposed to auditory) task. While auditory noise was not influenced by either secondary task, visual noise increased with the addition of the secondary visual task specifically. Interestingly, visual noise accounted for significant variability in attentional disruptions to the McGurk illusion. Overall, these results strongly suggest that sensory noise may underlie attentional alterations to multisensory integration in a modality-specific manner. Future studies are needed to determine whether this finding generalizes to other types of multisensory integration and attentional manipulations. This line of research may inform future studies of attentional alterations to sensory processing in neurological disorders, such as Schizophrenia, Autism, and ADHD.

Motion Analysis of Balance Pre and Post Sensorimotor Exercises to Enhance Elderly Mobility: A Case Study

Quantitative assessment of movement using motion capture provides insights on mobility which are not evident from clinical evaluation. Here, in older individuals that were healthy or had suffered a stroke, we aimed to investigate their balance in terms of changes in body kinematics and muscle activity. Our research question involved determining the effects on post- compared to pre-sensorimotor training exercises on maintaining or improving balance. Our research hypothesis was that training would improve the gait and balance by increasing joint angles and extensor muscle activities in lower extremities and spatiotemporal measures of stroke and elderly people. This manuscript describes a motion capture-based evaluation protocol to assess joint angles and spatiotemporal parameters (cadence, step length and walking speed), as well as major extensor and flexor muscle activities. We also conducted a case study on a healthy older participant (male, age, 65) and an older participant with chronic stroke (female, age, 55). Both participants performed a walking task along a path with a rectangular shape which included tandem walking forward, right side stepping, tandem walking backward, left side stepping to the starting location. For the stroke participant, the training improved the task completion time by 19 s. Her impaired left leg had improved step length (by 0.197 m) and cadence (by 10 steps/min) when walking forward, and cadence (by 12 steps/min) when walking backward. The non-impaired right leg improved cadence when walking forward (by 15 steps/min) and backward (by 27 steps/min). The joint range of motion (ROM) did not change in most cases. However, the ROM of the hip joint increased significantly by 5.8 degrees (p = 0.019) on the left leg side whereas the ROMs of hip joint and knee joint increased significantly by 4.1 degrees (p = 0.046) and 8.1 degrees (p = 0.007) on the right leg side during backward walking. For the healthy participant, the significant changes were only found in his right knee joint ROM having increased by 4.2 degrees (p = 0.031) and in his left ankle joint ROM having increased by 5.5 degrees (p = 0.006) during the left side stepping.

Falls caused by balance disorders in the elderly with multiple systems involved: Pathogenic mechanisms and treatment strategies

Falls are the main contributor to both fatal and nonfatal injuries in elderly individuals as well as significant sources of morbidity and mortality, which are mostly induced by impaired balance control. The ability to keep balance is a remarkably complex process that allows for rapid and precise changes to prevent falls with multiple systems involved, such as musculoskeletal system, the central nervous system and sensory system. However, the exact pathogenesis of falls caused by balance disorders in the elderly has eluded researchers to date. In consideration of aging phenomenon aggravation and fall risks in the elderly, there is an urgent need to explore the pathogenesis and treatments of falls caused by balance disorders in the elderly. The present review discusses the epidemiology of falls in the elderly, potential pathogenic mechanisms underlying multiple systems involved in falls caused by balance disorders, including musculoskeletal system, the central nervous system and sensory system. Meanwhile, some common treatment strategies, such as physical exercise, new equipment based on artificial intelligence, pharmacologic treatments and fall prevention education are also reviewed. To fully understand the pathogenesis and treatment of falls caused by balance disorders, a need remains for future large-scale multi-center randomized controlled trials and in-depth mechanism studies.

Risk factors for decline in gait speed during walking while talking in older adults

BACKGROUND & AIMS

Slow gait speed during Walking While Talking (walking while reciting alternate letters of the alphabet; WWT) is associated with an increased risk of developing dementia and falls. The aim of this study was to examine longitudinal changes in WWT-speed and to identify risk factors that may modify the rate of change in WWT-speed.

METHODS

A total of 431 older participants (55.7% female; M Age=76.8 ± 6.4 years; mean follow up 2.1 ± 1.8 years) enrolled in the Central Control of Mobility in Aging study were examined. WWT-speed (cm/s) was measured with a computerized walkway. The following baseline measures were examined as risk factors: demographics [age, sex, education], medical illnesses [hypertension, diabetes, cardiac arrhythmias, history of stroke, Parkinson's disease, kidney disease, arthritis], cognitive functions [global cognition, executive function, processing speed], physical and sensory functions [unipedal stance time, gait speed during single task walking, visual acuity], psychological variables [depression, anxiety] and falls. Linear mixed effect models were used to examine 1) change in WWT-speed over time, and 2) risk factors associated with change in WWT-speed over time.

RESULTS

WWT-speed declined in an accelerating non-linear fashion over time after adjusting for baseline age, sex and education. The rate of decline in WWT-speed was modified by older age (b -0.16 95%CI -0.22, -0.09), poorer balance (b -1.73 95%CI -2.57, -0.90), and faster gait speed during single task walking (b -0.06 95%CI -0.08, -0.04).

SIGNIFICANCE

This study identified fixed and modifiable risk factors of faster decline in WWT-speed over time in community-residing older adults.

Does Cognitive Training Improve Mobility, Enhance Cognition, and Promote Neural Activation?

A close inter-relationship between mobility and cognition is reported in older adults, with improvements in gait performance noticeable after cognitive remediation in frail individuals. The aim of this study was to evaluate the efficacy of computerized cognitive training (CCT) on mobility in healthy, independently living older adults, and to determine whether CCT is associated with changes in neural activation for mobility-related brain processes. Using a randomized single-blind control design, sixty-three non-demented adults age 60 y and older (mean age = 67 y; 76% female, mean Montreal Cognitive Assessment [MoCA] score = 27) were recruited from a local Senior Activity Center. Participants were randomly assigned to either a 2-month CCT program (8 weeks, 3x/week, 40 min/session) or a wait-list control group. Primary outcome was self-selected gait speed during single- and dual-task walking. Secondary outcome was executive function on Trail Making Test (TMT), Part B. Neural activity was assessed via electroencephalography/event-related potentials (EEG/ERPs) targeting lower-limb performance. Results from a linear mixed effect model, adjusted for baseline MoCA score, age, gender, and study completion revealed that compared to controls, CCT improved gait speed during the dual-task (p = 0.008) but not during the single-task walking condition (p = 0.057). CCT also improved executive function (p = 0.024). Further, shorter foot reaction time responses (p = 0.019) were found with enhanced neural activation over sensorimotor areas, with shorter ERP latencies during the P2 component (p = 0.008) and enhanced motor responses (p = 0.009) also evident in the CCT group after the intervention. Overall, the electrophysiological findings suggest possible neural adaptations that could explain improvements in mobility and executive functions associated with CCT in healthy older adults.

Age-related changes to vestibular heave and pitch perception and associations with postural control

Falls are a common cause of injury in older adults (OAs), and age-related declines across the sensory systems are associated with increased falls risk. The vestibular system is particularly important for maintaining balance and supporting safe mobility, and aging has been associated with declines in vestibular end-organ functioning. However, few studies have examined potential age-related differences in vestibular perceptual sensitivities or their association with postural stability. Here we used an adaptive-staircase procedure to measure detection and discrimination thresholds in 19 healthy OAs and 18 healthy younger adults (YAs), by presenting participants with passive heave (linear up-and-down translations) and pitch (forward-backward tilt rotations) movements on a motion-platform in the dark. We also examined participants' postural stability under various standing-balance conditions. Associations among these postural measures and vestibular perceptual thresholds were further examined. Ultimately, OAs showed larger heave and pitch detection thresholds compared to YAs, and larger perceptual thresholds were associated with greater postural sway, but only in OAs. Overall, these results suggest that vestibular perceptual sensitivity declines with older age and that such declines are associated with poorer postural stability. Future studies could consider the potential applicability of these results in the development of screening tools for falls prevention in OAs.

Postural Sway in Parkinson's Disease and Multiple Sclerosis Patients During Tasks With Different Complexity

Neurological diseases are associated with static postural instability. Differences in postural sway between neurological diseases could include "conceptual" information about how certain symptoms affect static postural stability. This information might have the potential to become a helpful aid during the process of finding the most appropriate treatment and training program. Therefore, this study investigated static postural sway performance of Parkinson's disease (PD) and multiple sclerosis (MS) patients, as well as of a cohort of healthy adults. Three increasingly difficult static postural tasks were performed, in order to determine whether the postural strategies of the two disease groups differ in response to the increased complexity of the balance task. Participants had to perform three stance tasks (side-by-side, semi-tandem and tandem stance) and maintain these positions for 10 s. Seven static sway parameters were extracted from an inertial measurement unit that participants wore on the lower back. Data of 47 healthy adults, 14 PD patients and 8 MS patients were analyzed. Both healthy adults and MS patients showed a substantial increase in several static sway parameters with increasingly complex stance tasks, whereas PD patients did not. In the MS patients, the observed substantial change was driven by large increases from semi-tandem and tandem stance. This study revealed differences in static sway adaptations between PD and MS patients to increasingly complex stance tasks. Therefore, PD and MS patients might require different training programs to improve their static postural stability. Moreover, this study indicates, at least indirectly, that rigidity/bradykinesia and spasticity lead to different adaptive processes in static sway.

Effect of Treadmill Training Interventions on Spatiotemporal Gait Parameters in Older Adults with Neurological Disorders: Systematic Review and Meta-Analysis of Randomized Controlled Trials

Objective: Treadmill interventions have been shown to promote ‘normal’ walking patterns, as they facilitate the proper movement and timing of the lower limbs. However, prior reviews have not examined which intervention provides the most effective treatment of specific gait impairments in neurological populations. The objective of this systematic review was to review and quantify the changes in gait after treadmill interventions in adults with neurological disorders. Data Sources: A keyword search was performed in four databases: PubMed, CINAHL, Scopus, and Web of Science (January 2000−December 2021). We performed the search algorithm including all possible combinations of keywords. Full-text articles were examined further using forward/backward search methods. Study Selection: Studies were thoroughly screened using the following inclusion criteria: study design: Randomized Controlled Trial (RCT); adults ≥55 years old with a neurological disorder; treadmill intervention; spatiotemporal gait characteristics; and language: English. Data Extraction: A standardized data extraction form was used to collect the following methodological outcome variables from each of the included studies: author, year, population, age, sample size, and spatiotemporal gait parameters including stride length, stride time, step length, step width, step time, stance time, swing time, single support time, double support time, or cadence. Data Synthesis: We found a total of 32 studies to be included in our systematic review through keyword search, out of which 19 studies included adults with stroke and 13 studies included adults with PD. We included 22 out of 32 studies in our meta-analysis that examined gait in adults with neurological disorders, which only yielded studies including Parkinson’s disease (PD) and stroke patients. A meta-analysis was performed among trials presenting with similar characteristics, including study population and outcome measure. If heterogeneity was >50% (denoted by I2), random plot analysis was used, otherwise, a fixed plot analysis was performed. All analyses used effect sizes and standard errors and a p < 0.05 threshold was considered statistically significant (denoted by *). Overall, the effect of treadmill intervention on cadence (z = 6.24 *, I2 = 11.5%) and step length (z = 2.25 *, I2 = 74.3%) in adults with stroke was significant. We also found a significant effect of treadmill intervention on paretic step length (z = 2.34 *, I2 = 0%) and stride length (z = 6.09 *, I2 = 45.5%). For the active control group, including adults with PD, we found that overground physical therapy training had the largest effect on step width (z = −3.75 *, I2 = 0%). Additionally, for PD adults in treadmill intervention studies, we found the largest significant effect was on step length (z = 2.73 *, I2 = 74.2%) and stride length (z = −2.54 *, I2 = 96.8%). Conclusion: Treadmill intervention with sensory stimulation and body weight support treadmill training were shown to have the largest effect on step length in adults with PD and stroke.

Which Exercise Interventions Can Most Effectively Improve Reactive Balance in Older Adults? A Systematic Review and Network Meta-Analysis

BACKGROUND

Reactive balance is the last line of defense to prevent a fall when the body loses stability, and beneficial effects of various exercise-based interventions on reactive balance in older adults have been reported. However, their pooled evidence on the relative effects has yet to be described.

OBJECTIVE

To review and evaluate the comparative effectiveness of various exercise-based interventions on reactive balance in older adults.

METHODS

Nine electronic databases and reference lists were searched from inception to August 2021. Eligibility criteria according to PICOS criteria were as follows: (1) population: older adults with the mean age of 65 years or above; (2) intervention and comparison: at least two distinct exercise interventions or one exercise intervention with a no-exercise controlled intervention (NE) compared in each trial; (3) outcome: at least one measure of reactive balance; (4) study: randomized controlled trial. The main network meta-analysis was performed on data from the entire older adult population, involving all clinical conditions as well as healthy older adults. Subgroup analyses stratified by characteristics of participants (healthy only) and reactive balance outcomes (simulated slip or trip while walking, simulated forward falls, being pushed or pulled, and movable platform) were also conducted.

RESULTS

Thirty-nine RCTs (n = 1388) investigating 17 different types of exercise interventions were included in the network meta-analysis. Reactive balance training as a single intervention presented the highest probability (surface under the cumulative ranking (SUCRA) score) of being the best intervention for improving reactive balance and the greatest relative effects vs. NE in the entire sample involving all clinical conditions [SUCRA = 0.9; mean difference (95% Credible Interval): 2.7 (1.0 to 4.3)]. The results were not affected by characteristics of participants (i.e., healthy older adults only) or reactive balance outcomes.

SUMMARY/CONCLUSION

The findings from the NMA suggest that a task-specific reactive balance exercise could be the optimal intervention for improving reactive balance in older adults, and power training can be considered as a secondary training exercise.

The Role of Altered Sensory Processing and Its Association with Participation in Daily Activities and Quality of Life among Older Adults in the Community

To identify variables that contribute to fall risk in older adults, this study examined the relationship between fall risk, sensory processing, participation in daily activities, and quality of life (QoL). Of the 123 participants, those at high-risk were significantly less able to register sensory input and had increased sensory sensitivity, restricted participation and overall lower QoL. Altered sensory processing was related with risk of falling. Additionally, both sensory process and fall risk were subsequently related with lower daily participation and, together, were related with lower QoL. Thus, sensory processing, participation and QoL assessments need to be included in occupational therapy evaluations and interventions for fall risk among older adults.

Introducing CatchU™: A Novel Multisensory Tool for Assessing Patients' Risk of Falling

To date, only a few studies have investigated the clinical translational value of multisensory integration. Our previous research has linked the magnitude of visual-somatosensory integration (measured behaviorally using simple reaction time tasks) to important cognitive (attention) and motor (balance, gait, and falls) outcomes in healthy older adults. While multisensory integration effects have been measured across a wide array of populations using various sensory combinations and different neuroscience research approaches, multisensory integration tests have not been systematically implemented in clinical settings. We recently developed a step-by-step protocol for administering and calculating multisensory integration effects to facilitate innovative and novel translational research across diverse clinical populations and age-ranges. In recognizing that patients with severe medical conditions and/or mobility limitations often experience difficulty traveling to research facilities or joining time-demanding research protocols, we deemed it necessary for patients to be able to benefit from multisensory testing. Using an established protocol and methodology, we developed a multisensory falls-screening tool called CatchU ^™ (an iPhone app) to quantify multisensory integration performance in clinical practice that is currently undergoing validation studies. Our goal is to facilitate the identification of patients who are at increased risk of falls and promote physician-initiated falls counseling during clinical visits (e.g., annual wellness, sick, or follow-up visits). This will thereby raise falls-awareness and foster physician efforts to alleviate disability, promote independence, and increase quality of life for our older adults. This conceptual overview highlights the potential of multisensory integration in predicting clinical outcomes from a research perspective, while also showcasing the practical application of a multisensory screening tool in routine clinical practice.

Changes in postural balance associated with a woman's aging process

CONTEXT

Aging causes a progressive worsening in postural balance, affecting functional independence and increasing the risk of falls.

OBJECTIVE

The aim of the study was to evaluate the effect of aging on the static balance in women from 50-years to 89-years of age.

DESIGN

This was a cross-sectional study, with 400 irregularly active women were evaluated and grouped by age: Group 6^th decade (age 50 to 59) ‒ 58 participants; Group 7^th decade (age 60 to 69) ‒ 214 participants; Group 8^th decade (age 70 to 79) ‒ 92 participants; Group 9^th decade (age 80 to 89) ‒ 36 participants. Postural balance was evaluated using a portable force platform in a standard standing position, with Eyes Open (EO) and Eyes Closed (EC).

RESULTS

In the two measurement conditions, the elderly women in Group 9^th decade presented mediolateral displacement and range, and mean velocity greater than the women's values in Groups 6^th and 7^th decade. In the EO e EC situation, the displacement was higher in the elderly Group 9^th decade compared to younger groups. Group 8^th has a mean velocity greater than Group 6^th decade in the EO situation.

CONCLUSIONS

Posturography showed a decline in postural balance with advancing age, suggesting that the 9^th decade of life is a borderline age to this detriment due to an increase in postural instability.

A systematic review of one-legged balance performance and falls risk in community-dwelling adults

OBJECTIVE

The aim of this systematic review was to synthesise all published evidence on associations between one-legged balance performance and falls.

METHODS

Medline, EMBASE, CINAHL and Web of Science were systematically searched (to January 2021) to identify peer-reviewed, English language journal articles examining the association between one-legged balance performance and falls in community-dwelling adults.

RESULTS

Of 4310 records screened, 55 papers were included (n = 36954 participants). There was considerable heterogeneity between studies including differences in study characteristics, ascertainment of balance and falls, and analytical approaches. A meta-analysis of the time that individuals could maintain the one-legged balance position indicated that fallers had worse balance times than non-fallers (standardised mean difference: -0.29 (95%CI:-0.38,-0.20) in cross-sectional analyses; -0.19 (-0.28, -0.09) in longitudinal analyses), although there was no difference in the pooled median difference. Due to between-study heterogeneity, regression estimates between balance and fall outcomes could not be synthesised. Where assessed, prognostic accuracy indicators suggested that one-legged balance was a poor discriminator of fall risk; for example, 5 of 7 studies demonstrated poor prognostic accuracy (Area Under the Curve <0.6), with most studies demonstrating poor sensitivity.

CONCLUSIONS

This systematic review identified 55 papers that examined associations between balance and fall risk, the majority in older aged adults. However, the evidence was commonly of low quality and results were inconsistent. This contradicts previous perceptions of one-legged balance as a useful fall risk tool and highlights crucial gaps that must be addressed in order to translate such assessments to clinical settings.

Participation in cognitive activities is associated with foot reaction time and gait speed in older adults

BACKGROUND

Given the evidence of the links between cognition and mobility, participation in cognitive activities may benefit neuromotor performance and mobility in older adults.

AIMS

To examine the association between participation in cognitive activities and foot reaction time (RT) and gait speed in community-dwelling older adults.

METHODS

The MOBILIZE Boston Study II (MBSII) re-enrolled 354 community-dwelling older adults aged ≥ 70 years from the original MBS cohort. Of these, 310 completed the performance testing and we excluded three participants who had Parkinson's disease. Cognitive Activities Scale (CAS) assessed participation in 17 cognitive activities. Simple and Choice foot RT (SRT, CRT, msec) and gait speed (m/s) were measured using a sensored GAITRite® gait mat.

RESULTS

The average age of the 307 participants was 84 years; 79% were white and 65% were women. The average CAS score was 25.5 ± 11.7, indicating participation in approximately 26 activities per week on average. The average foot SRT was 245 ± 57msec and average CRT was 323 ± 85msec. Usual-paced gait speed was 0.9 ± 0.3 m/s on average. More frequent participation in cognitive activities was associated with shorter SRT (β = - 0.759, p = 0.015) and CRT (β = - 1.125, p = 0.013), and faster gait speed (β = 0.003, p = 0.026), after adjusting for potential confounders.

DISCUSSION

Participation in cognitively stimulating activities may be beneficial for neuromotor performance and mobility in older adults.

CONCLUSIONS

Prospective and intervention studies are needed to determine whether participation in cognitive activities may prevent mobility decline over time, and thus reduce fall risk.

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.

Comparison of Gait Speed Reserve, Usual Gait Speed, and Maximum Gait Speed of Adults Aged 50+ in Ireland Using Explainable Machine Learning

Gait speed is a measure of general fitness. Changing from usual (UGS) to maximum (MGS) gait speed requires coordinated action of many body systems. Gait speed reserve (GSR) is defined as MGS-UGS. From a shortlist of 88 features across five categories including sociodemographic, cognitive, and physiological, we aimed to find and compare the sets of predictors that best describe UGS, MGS, and GSR. For this, we leveraged data from 3,925 adults aged 50+ from Wave 3 of The Irish Longitudinal Study on Ageing (TILDA). Features were selected by a histogram gradient boosting regression-based stepwise feature selection pipeline. Each model's feature importance and input-output relationships were explored using TreeExplainer from the Shapely Additive Explanations explainable machine learning package. The meanR a d j 2 (SD) from fivefold cross-validation on training data and theR a d j 2   score on test data were 0.38 (0.04) and 0.41 for UGS, 0.45 (0.04) and 0.46 for MGS, and 0.19 (0.02) and 0.21 for GSR. Each model selected features across all categories. Features common to all models were age, grip strength, chair stands time, mean motor reaction time, and height. Exclusive to UGS and MGS were educational attainment, fear of falling, Montreal cognitive assessment errors, and orthostatic intolerance. Exclusive to MGS and GSR were body mass index (BMI), and number of medications. No features were selected exclusively for UGS and GSR. Features unique to UGS were resting-state pulse interval, Center for Epidemiologic Studies Depression Scale (CESD) depression, sit-to-stand difference in diastolic blood pressure, and left visual acuity. Unique to MGS were standard deviation in sustained attention to response task times, resting-state heart rate, smoking status, total heartbeat power during paced breathing, and visual acuity. Unique to GSR were accuracy proportion in a sound-induced flash illusion test, Mini-mental State Examination errors, and number of cardiovascular conditions. No interactions were present in the GSR model. The four features that overall gave the most impactful interactions in the UGS and MGS models were age, chair stands time, grip strength, and BMI. These findings may help provide new insights into the multisystem predictors of gait speed and gait speed reserve in older adults and support a network physiology approach to their study.

[How the brain perceives the world in old age with all senses]

BACKGROUND

Aging is a multidimensional process that may lead to physical, psychological and social changes. This is predominantly due to a decline of sensory functions and their central processing.

MATERIAL AND METHODS

Selective literature search in Medline and the Cochrane Library.

RESULTS

In addition to specific disorders of the sensory organs, unspecific age-related degenerative processes are responsible for the high prevalence of sensory limitations in older people. This can lead to a significant reduction in the quality of life. Balance impairment, decreasing function of hearing, vision, smell and the somatosensory system are associated with an increased risk of falling and an increased mortality in older people. Furthermore, there is evidence for a link between hearing loss and cognitive decline. In addition to the functional ability of every sense on its own, the integration of multiple sensory perceptions plays an increasing role in age-related sensory limitations.

CONCLUSION

Sensory impairments have to be considered when working with older people. Early detection and an interdisciplinary therapeutic approach can reduce the negative consequences. Multimodal stimulation appears to stimulate brain plasticity which helps to compensate age-related changes.

Sensory Dysfunction in Old Age

BACKGROUND

The senses serve as the crucial interface between the individual and the environment. They are subject to aging and disease processes.

METHODS

This review is based on pertinent publications retrieved by a selective search in the Medline and Cochrane Library databases.

RESULTS

Approximately 40% of persons aged 70 to 79 manifest dysfunction in at least one, and more than 25% in multiple senses. Sensory changes are accompanied by diverse comorbidities which depend on the particular sense(s) affected. The presence of sensory deficits is associated with an increased risk of developing dementia (OR: 1.49 [95% confidence interval: 1.12; 1.98] for dysfunction in a single sensory modality, 2.85 [1.88; 4.30] for dysfunction in three or more sensory modalities). The risk of developing depressive symptoms is elevated as well (OR 3.36 [2.28; 4.96]). The individual's ability to cope with the demands of everyday life is largely determined by the ability to carry out multisensory integration, in which the perceptions of the different senses are bound together. This function itself is subject to age-related changes that can be either adaptive or maladaptive; it can, therefore, serve as an indicator for pathological aging processes.

CONCLUSION

Sensory dysfunction in old age should be detected as early as possible. This implies the need for close collaboration of all of the involved disciplines. It would be desirable to develop sensory screening tests as well as a procedure for testing multisensory integration in routine clinical practice.

Measuring threshold and latency of motion perception on a swinging bed

INTRODUCTION

Our objective was to develop and to evaluate a system to measure latency and threshold of pendular motion perception based on a swinging bed.

MATERIALS AND METHODS

This prospective study included 30 healthy adults (age: 32 ± 12 years). All subjects were tested twice with a 10 min. interval. A second trial was conducted 2 to 15 days after. A rehabilitation swinging bed was connected to an electronic device emitting a beep at the beginning of each oscillation phase with an adjustable time lag. Subjects were blindfolded and auditory cues other than the beep were minimized. The acceleration threshold was measured by letting the bed oscillate freely until a natural break and asking the patient when he did not perceive any motion. The perception latency was determined by asking the patient to indicate whether the beep and the peak of each oscillation were synchronous. The time lag between sound and peak of the head position was swept from -750 to +750 ms by 50 ms increments.

RESULTS

The mean acceleration threshold was 9.2±4.60 cm/s2. The range width of the synchronous perception interval was estimated as 535±190 ms. The point of subjective synchronicity defined as the center of this interval was -195±106 ms (n = 30). The test-retest evaluation in the same trial showed an acceptable reproducibility for the acceleration threshold and good to excellent for all parameters related to sound-movement latency.

CONCLUSION

Swinging bed combined to sound stimulation can provide reproducible information on movement perception in a simple and non-invasive manner with highly reproducible results.

Narrative review of the multisensory integration tasks used with older adults: inclusion of multisensory integration tasks into neuropsychological assessment

Introduction: Age-related changes in sensory functioning impact the activities of daily living and interact with cognitive decline. Given the interactions between sensory and cognitive functioning, combining multisensory integration (MI) assessment with the neuropsychological assessment of older adults seems promising. This review aims to examine the characteristics and utility of MI tasks in functional and cognitive assessment of older adults, with or without neurocognitive impairment.Areas covered: A literature search was conducted following the quality assessment of narrative review criteria. Results focused on tasks of detection, discrimination, sensory illusion, temporal judgment, and sensory conflict. Studies were not consensual regarding the enhancement of MI with age, but most studies showed that older adults had an expanded time window of integration. In older adults with mild cognitive impairment or major neurocognitive disorder it was a mediating role of the magnitude of visual-somatosensory integration between neurocognitive impairment and spatial aspects of gait.Expert opinion: Recently, some concerns have been raised about how to maximize the ecological validity of the neuropsychological assessment. Since most of our activities of daily living are multisensory and older adults benefit from multisensory information, MI assessment has the potential to improve the ecological validity of the neuropsychological assessment.

The Influence of Diabetes on Multisensory Integration and Mobility in Aging

(1) Background: one out of every four adults over the age of 65 are living with diabetes, and this alarming rate continues to increase with age. Diabetes in older adults is associated with many adverse health outcomes, including sensory and motor impairments. The objective of this exploratory study was to determine whether diabetes influences the interplay between multisensory integration processes and mobility in aging. (2) Methods: in this cross-sectional observational study, we recruited 339 non-demented older adults (76.59 ± 6.21 years; 52% female, 18% with diabetes). Participants completed a simple reaction time test in response to visual, somatosensory, and combined visual-somatosensory stimulation. Magnitude of visual-somatosensory integration was computed and served as the independent variable. (3) Results: logistic regression revealed that presence of diabetes was inversely associated with the magnitude of visual-somatosensory integration (β = −3.21; p < 0.01). Further, mediation models revealed that presence of diabetes negatively influenced the relationship of visual–somatosensory integration magnitude with balance (95% CI −0.16, −0.01) and gait (95% CI −0.09, −0.01). Participants with diabetes and taking insulin (n = 14) failed to integrate sensory information entirely; (4) conclusions: taken together, results from this exploration provide compelling evidence to support the adverse effect of diabetes on both multisensory and motor functioning in older adults.

Ageing and multisensory integration: A review of the evidence, and a computational perspective

The processing of multisensory signals is crucial for effective interaction with the environment, but our ability to perform this vital function changes as we age. In the first part of this review, we summarise existing research into the effects of healthy ageing on multisensory integration. We note that age differences vary substantially with the paradigms and stimuli used: older adults often receive at least as much benefit (to both accuracy and response times) as younger controls from congruent multisensory stimuli, but are also consistently more negatively impacted by the presence of intersensory conflict. In the second part, we outline a normative Bayesian framework that provides a principled and computationally informed perspective on the key ingredients involved in multisensory perception, and how these are affected by ageing. Applying this framework to the existing literature, we conclude that changes to sensory reliability, prior expectations (together with attentional control), and decisional strategies all contribute to the age differences observed. However, we find no compelling evidence of any age-related changes to the basic inference mechanisms involved in multisensory perception.

Postural Control in Childhood: Investigating the Neurodevelopmental Gradient Hypothesis

Neurodevelopmental disorders (NDDs) have been suggested to lie on a gradient continuum, all resulting from common brain disturbances, but with different degrees of impairment severity. This case-control study aimed to assess postural stability against such hypothesis in 104 children/adolescents aged 5–17, of whom 81 had NDDs and 23 were healthy controls. Compared to healthy controls, Autism Spectrum Disorder (ASD) resulted in the most severely impaired neurodevelopmental condition, followed by Attention Deficit Hyperactive Disorder (ADHD) and Tourette Syndrome (TS). In particular, while ASD children/adolescents performed worse than healthy controls in a number of sensory conditions across all parameters, ADHD children/adolescents performed worse than healthy controls only in the sway area for the most complex sensory conditions, when their vision and somatosensory functions were both compromised, and performance in Tourette Syndrome (TS) was roughly indistinguishable from that of healthy controls. Finally, differences were also observed between clinical groups, with ASD children/adolescents, and to a much lesser extent ADHD children/adolescents, performing worse than TS children/adolescents, especially when sensory systems were not operationally accurate. Evidence from this study indicates that poor postural control may be a useful biomarker for risk assessment during neurodevelopment, in line with predictions from the gradient hypothesis.

When Will My Patient Fall? Sensor-Based In-Home Walking Speed Identifies Future Falls in Older Adults

BACKGROUND

Although there are known clinical measures that may be associated with risk of future falls in older adults, we are still unable to predict when the fall will happen. Our objective was to determine whether unobtrusive in-home assessment of walking speed can detect a future fall.

METHOD

In both ISAAC and ORCATECH Living Laboratory studies, a sensor-based monitoring system has been deployed in the homes of older adults. Longitudinal mixed-effects regression models were used to explore trajectories of sensor-based walking speed metrics in those destined to fall versus controls over time. Falls were captured during a 3-year period.

RESULTS

We observed no major differences between those destined to fall (n = 55) and controls (n = 70) at baseline in clinical functional tests. There was a longitudinal decline in median daily walking speed over the 3 months before a fall in those destined to fall when compared with controls, p < .01 (ie, mean walking speed declined 0.1 cm s-1 per week). We also found prefall differences in sensor-based walking speed metrics in individuals who experienced a fall: walking speed variability was lower the month and the week just before the fall compared with 3 months before the fall, both p < .01.

CONCLUSIONS

While basic clinical tests were not able to differentiate who will prospectively fall, we found that significant variations in walking speed metrics before a fall were measurable. These results provide evidence of a potential sensor-based risk biomarker of prospective falls in community living older adults.

Multisensory integration involved in the body perception of community-dwelling older adults

This study investigates how the multisensory integration in body perception changes with increasing age, and whether it is associated with older adults’ risk of falling. For this, the rubber hand illusion (RHI) and rubber foot illusion (RFI) were used. Twenty-eight community-dwelling older adults and 25 university students were recruited. They viewed a rubber hand or foot that was stimulated in synchrony or asynchrony with their own hidden hand or foot. The illusion was assessed by using a questionnaire, and measuring the proprioceptive drift and latency. The Timed Up and Go Test was used to classify the older adults into lower and higher fall-risk groups. No difference was observed in the RHI between the younger and older adults. However, several differences were observed in the RFI. Specifically, the older adults with a lower fall-risk hardly experienced the illusion, whereas those with a higher fall-risk experienced it with a shorter latency and no weaker than the younger adults. These results suggest that in older adults, the mechanism of multisensory integration for constructing body perception can change depending on the stimulated body parts, and that the risk of falling is associated with multisensory integration.

Audio-Visual Training in Older Adults: 2-Interval-Forced Choice Task Improves Performance

A growing interest in ameliorating multisensory perception deficits in older adults arises from recent evidence showing that impaired multisensory processing, particularly in the temporal domain, may be associated with cognitive and functional impairments. Perceptual training has proved successful in improving multisensory temporal processing in young adults, but few studies have investigated this training approach in older adults. In the present study we used a simultaneity (or synchronicity) judgement task with feedback, to train the audio-visual abilities of community-dwelling, cognitively healthy older adults. We recruited 23 older adults (M = 74.17, SD = 6.23) and a group of 20 young adults (M = 24.20, SD = 4.23) who served as a comparison. Participants were tested before and after perceptual training using a 2-Interval Forced Choice Task (2-IFC); and the Sound-Induced Flash Illusion (SIFI). After 3 days of training, participants improved on the 2-IFC task, with a significant narrowing of the temporal window of integration (TWI) found for both groups. Generalization of training effects was not found, with no post-training differences in perceptual sensitivity to the SIFI for either group. These findings provide evidence perceptual narrowing can be achieved in older as well as younger adults after 3 days of perceptual training. These results provide useful information for future studies attempting to improve audio-visual temporal discrimination abilities in older people.

Gait and balance disturbances are common in young urbanites and associated with cognitive impairment. Air pollution and the historical development of Alzheimer's disease in the young

To determine whether gait and balance dysfunction are present in young urbanites exposed to fine particular matter PM2.5 ≥ annual USEPA standard, we tested gait and balance with Tinetti and Berg tests in 575 clinically healthy subjects, age 21.0 ± 5.7 y who were residents in Metropolitan Mexico City, Villahermosa and Reynosa. The Montreal Cognitive Assessment was also applied to an independent cohort n:76, age 23.3 ± 9.1 y. In the 575 cohort, 75.4% and 34.4% had abnormal total Tinetti and Berg scores and high risk of falls in 17.2% and 5.7% respectively. BMI impacted negatively Tinetti and Berg performance. Gait dysfunction worsen with age and males performed worse than females. Gait and balance dysfunction were associated with mild cognitive impairment MCI (19.73%) and dementia (55.26%) in 57/76 and 19 cognitively intact subjects had gait and balance dysfunction. Seventy-five percent of urbanites exposed to PM2.5 had gait and balance dysfunction. For MMC residents-with historical documented Alzheimer disease (AD) and CSF abnormalities, these findings suggest Alzheimer Continuum is in progress. Early development of a Motoric Cognitive Risk Syndrome ought to be considered in city dwellers with normal cognition and gait dysfunction. The AD research frame in PM2.5 exposed young urbanites should include gait and balance measurements. Multicity teens and young adult cohorts are warranted for quantitative gait and balance measurements and neuropsychological and brain imaging studies in high vs low PM2.5 exposures. Early identification of gait and balance impairment in young air pollution-exposed urbanites would facilitate multidisciplinary prevention efforts for modifying the course of AD.

Does Cognitive Impairment Influence Visual-Somatosensory Integration and Mobility in Older Adults?

BACKGROUND

Deficits in visual-somatosensory (VS) integration are linked to poor mobility. Given that sensory, motor, and cognitive processes rely on overlapping neural circuitry that are compromised in dementia and pre-dementia stages like mild cognitive impairment (MCI), we hypothesize that cognitive impairment will be associated with reduced VS integration, which will, in turn, impact the relation between VS integration and mobility.

METHODS

A total of 345 older adults (mean age 76.88 ± 6.45 years; 52% female) participated in the current study. Cognitive impairment was defined as presence of MCI or dementia. Magnitude of VS integration was quantified using probability models. All participants completed assessments of general cognition (Repeatable Battery for the Assessment of Neuropsychological Status; RBANS), quantitative gait, and balance (unipedal stance).

RESULTS

The magnitude of VS integration was lower in the 40 individuals with MCI (p = .02) and 12 with dementia (p = .04), relative to the 293 individuals without cognitive impairment. In fully adjusted models, magnitude of VS integration was only a strong predictor of performance on attention-based tests of the RBANS (β = 0.161; p < .01), regardless of cognitive status. Results from mediation analyses, however, reveal that cognitive impairment causes variation in magnitude of VS integration, which in turn causes variation in unipedal stance 95% confidence interval (CI) (-0.265, -0.002) and spatial aspects of gait 95% CI (-0.087, -0.001).

CONCLUSIONS

Cognitive impairment influences multisensory integration, which adversely impacts balance and gait performance in aging. Future studies should aim to uncover the precise neural circuitry involved in multisensory, cognitive, and mobility processes.

Aging, Vestibular Function, and Balance: Proceedings of a National Institute on Aging/National Institute on Deafness and Other Communication Disorders Workshop

Balance impairment and falls are among the most prevalent and morbid conditions affecting older adults. A critical contributor to balance and gait function is the vestibular system; however, there remain substantial knowledge gaps regarding age-related vestibular loss and its contribution to balance impairment and falls in older adults. Given these knowledge gaps, the National Institute on Aging and the National Institute on Deafness and Other Communication Disorders convened a multidisciplinary workshop in April 2019 that brought together experts from a wide array of disciplines, such as vestibular physiology, neuroscience, movement science, rehabilitation, and geriatrics. The goal of the workshop was to identify key knowledge gaps on vestibular function and balance control in older adults and develop a research agenda to make substantial advancements in the field. This article provides a report of the proceedings of this workshop. Three key questions emerged from the workshop, specifically: (i) How does aging impact vestibular function?; (ii) How do we know what is the contribution of age-related vestibular impairment to an older adult's balance problem?; and more broadly, (iii) Can we develop a nosology of balance impairments in older adults that can guide clinical practice? For each of these key questions, the current knowledge is reviewed, and the critical knowledge gaps and research strategies to address them are discussed. This document outlines an ambitious 5- to 10-year research agenda for increasing knowledge related to vestibular impairment and balance control in older adults, with the ultimate goal of linking this knowledge to more effective treatment.

Aging-related changes in cortical mechanisms supporting postural control during base of support and optic flow manipulations

Behavioral findings suggest that aging alters the involvement of cortical sensorimotor mechanisms in postural control. However, corresponding accounts of the underlying neural mechanisms remain sparse, especially the extent to which these mechanisms are affected during more demanding tasks. Here, we set out to elucidate cortical correlates of altered postural stability in younger and older adults. 3D body motion tracking and high-density electroencephalography (EEG) were measured while 14 young adults (mean age = 24 years, 43% women) and 14 older adults (mean age = 77 years, 50% women) performed a continuous balance task under four different conditions. Manipulations were applied to the base of support (either regular or tandem (heel-to-toe) stance) and visual input (either static visual field or dynamic optic flow). Standing in tandem, the more challenging position, resulted in increased sway for both age groups, but for the older adults, only this effect was exacerbated when combined with optic flow compared to the static visual display. These changes in stability were accompanied by neuro-oscillatory modulations localized to midfrontal and parietal regions. A cluster of electro-cortical sources localized to the supplementary motor area showed a large increase in theta spectral power (4-7 Hz) during tandem stance, and this modulation was much more pronounced for the younger group. Additionally, the older group displayed widespread mu (8-12 Hz) and beta (13-30 Hz) suppression as balance tasks placed more demands on postural control, especially during tandem stance. These findings may have substantial utility in identifying early cortical correlates of balance impairments in otherwise healthy older adults.

A new perspective on transient characteristics of quiet stance postural control

Postural control provides insight into health concerns such as fall risk but remains relatively untapped as a vital sign of health. One understudied aspect of postural control involves transient responses within center of pressure (CoP) data to events such as vision occlusion. Such responses are masked by common whole-trial analyses. We hypothesized that the transient behavior of postural control would yield unique and clinically-relevant information for quiet stance compared to traditionally calculated whole-trial CoP estimates. Three experiments were conducted to test different aspects of this central hypothesis. To test whether transient, epoch-based characteristics of CoP estimates provide different information than traditional whole-trial estimates, we investigated correlations between these estimates for a population of young adults performing three 60-second trials of quiet stance with eyes closed. Next, to test if transient behavior is a result of sensory reweighting after eye closure, we compared transient characteristics between eyes closed and eyes open conditions. Finally, to test if there was an effect of age on transient behavior, we compared transient characteristics during eyes closed stance between populations of young and older adults. Negligible correlations were found between transient characteristics and whole-trial estimates (p>0.08), demonstrating limited overlap in information between them. Additionally, transient behavior was exaggerated during eyes closed stance relative to eyes open (p<0.044). Lastly, we found that transient characteristics were able to distinguish between younger and older adults, supporting their clinical relevance (p<0.029). An epoch-based approach captured unique and potentially clinically-relevant postural control information compared to whole-trial estimates. While longer trials may improve the reliability of whole-trial estimates, including a complementary assessment of the initial transient characteristics may provide a more comprehensive characterization of postural control.