Visual-Somatosensory Integration is Linked to Physical Activity Level in Older Adults

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.

Audio-visual integration is more precise in older adults with a high level of long-term physical activity

It is well established that physical activity leads to numerous health, cognitive, and psychological benefits. However, to date, very few studies have investigated the impact of physical activity on multisensory perception, that is, the brain's capacity to integrate information across sensory modalities. Furthermore, it is unknown what level of long-term physical activity is associated with multisensory integration in adults. We explored the relationship between multisensory integration and a ten-year physical activity trajectory in 2,974 adults aged 50+ from The Irish Longitudinal Study on Ageing by measuring susceptibility to the Sound Induced Flash Illusion (SIFI) at multiple audio-visual temporal asynchronies. Physical activity was measured using the International Physical Activity Questionnaire (IPAQ-SF) at 2 years intervals over ten years. We used latent class trajectory modelling to identify latent growth classes of individuals following a similar trajectory of physical activity over time. We analysed the association of this trajectory with performance accuracy to the illusion trials of the SIFI task with generalized logistic mixed effects regression models, adjusted for several covariates. Results showed that more precise integration (i.e., lower SIFI susceptibility with larger temporal asynchronies) was associated with a higher level of sustained physical activity across ten years. Although the use of self-reported physical activity and a short version of the SIFI task limit our conclusions to some extent, nonetheless, the results suggest that sustained physical activity is associated with more precise multisensory integration, which in turn is linked to better balance and a lower risk of falling in 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.

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.

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.

Multisensory Integration Predicts Balance and Falls in Older Adults

BACKGROUND

Effective integration of concurrent sensory information is crucial for successful locomotion. This study aimed to determine the association of multisensory integration with mobility outcomes in aging.

METHODS

A total of 289 healthy older adults (mean age 76.67 ± 6.37 years; 53% female participants) participated in a visual-somatosensory simple reaction time task. Magnitude of multisensory effects was assessed using probability models, and then categorized into four multisensory integration classifications (superior, good, poor, or deficient). Associations of multisensory integration with falls and balance (unipedal stance) were tested at cross-section and longitudinally using Cox proportional hazards models.

RESULTS

At baseline, the prevalence of falls in the previous year was 24%, and 52% reported an incident fall over a mean follow-up period of 24 ± 17 months. Mean unipedal stance time was 15 ± 11 seconds. Magnitude of multisensory integration was a strong predictor of balance performance at cross-section (β = 0.11; p < .05). Of the cohort, 31% had superior, 26% had good, 28% had poor, and 15% had deficient multisensory effects. Older adults with superior multisensory integration abilities were significantly less likely to report a fall in the past year (17%), compared to the rest of the cohort (28%; χ2 = 4.01; p = .04). Magnitude of multisensory integration was an incremental predictor of incident falls (adjusted hazard ratio = 0.24; p = .01), over and above balance and other known fall risk factors.

CONCLUSIONS

Our study highlights the clinical relevance of multisensory integration in aging; worse visual-somatosensory integration is associated with worse balance and increased risk of incident falls.

A comparison of gait stability between younger and older adults while head turning

Head turning while walking may challenge stability by altering visual and vestibular information. Whether there are age-related changes that affect gait stability while head turning during walking remains unknown. The aim of the current study was to compare gait stability between younger and older adults immediately following a head turn while walking. Ten younger [mean (SD)] [23.4 (3.3) years] and ten older [68.8 (6.0) years] healthy adults walked on a treadmill at their preferred gait velocity and performed head turns by responding to a visual cue. The margin of stability (MoS) in the mediolateral (MoS_ML), anterior (MoS_A) and posterior (MoS_P) directions, foot placement (mean step length and width) and rotation of the head, trunk and pelvis were calculated for the four steps immediately following a cue to head turn and compared to walking only. Older adults increased their MoS_ML and younger adults increased their MoS_P immediately following a head turn. However, older adults had a significantly greater MoS_P than younger adults during this time. Older adults also had greater pelvic rotation velocity and a trend towards smaller head-on-trunk rotation compared to younger adults. Age does not compromise the stability of healthy older compared to younger adults immediately following or when completing a head turn. However, older adults may use a different motor strategy to perform a head turn to limit isolated movement of the head and the effects of a changing sensory frame of reference.

The Effect of Ageing on Optimal Integration of Conflicting and Non-Conflicting Visual–Haptic Stimuli

Multisensory integration typically follows the predictions of a statistically optimal model whereby the contribution of each sensory modality is weighted according to its reliability. Previous research has shown that multisensory integration is affected by ageing, however it is less certain whether older adults follow this statistically optimal model. Additionally, previous studies often present multisensory cues which are conflicting in size, shape or location, yet naturally occurring multisensory cues are usually non-conflicting. Therefore, the mechanisms of integration in older adults might differ depending on whether the multisensory cues are consistent or conflicting. In the current experiment, young () and older () adults were asked to make judgements regarding the height of wooden blocks using visual, haptic or combined visual–haptic information. Dual modality visual–haptic blocks could be presented as equal or conflicting in size. Young and older adults’ size discrimination thresholds (i.e., precision) were not significantly different for visual, haptic or visual–haptic cues. In addition, both young and older adults’ discrimination thresholds and points of subjective equality did not follow model predictions of optimal integration, for both conflicting and non-conflicting cues. Instead, there was considerable between subject variability as to how visual and haptic cues were processed when presented simultaneously. This finding has implications for the development of multisensory therapeutic aids and interventions to assist older adults with everyday activities, where these should be tailored to the needs of each individual.

Temporal Metrics of Multisensory Processing Change in the Elderly

Older adults exhibit greater multisensory response time (RT) facilitation by violating the race model more than young adults; this is commonly interpreted as an enhancement in perception. Older adults typically exhibit wider temporal binding windows (TBWs) and points of subjective simultaneity (PSS) that typically lie farther from true simultaneity as compared to young adults when simultaneity judgment (SJ) and temporal-order judgment (TOJ) tasks are utilized; this is commonly interpreted as an impairment in perception. Here we explore the relation between the three tasks in order to better assess audiovisual multisensory temporal processing in both young and older adults. Our results confirm previous reports showing that audiovisual RT, TBWs and PSSs change with age; however, we show for the first time a significant positive relation between the magnitude of race model violation in young adults as a function of the PSS obtained from the audiovisual TOJ task (r: 0.49, p: 0.007), that is absent in older adults (r: 0.13, p: 0.58). Furthermore, we find no evidence for the relation between race model violation as a function of the PSS obtained from the audiovisual SJ task in both young (r: −0.01, p: 0.94) and older adults (r: 0.1, p: 0.66). Our results confirm previous reports that (i) audiovisual temporal processing changes with age; (ii) distinct processes are likely involved in simultaneity and temporal-order perception; and (iii) common processing between race model violation and temporal-order judgment is impaired in the elderly.

Failure on the Foam Eyes Closed Test of Standing Balance Associated With Reduced Semicircular Canal Function in Healthy Older Adults

OBJECTIVES

Standing on foam with eyes closed (FOEC) has been characterized as a measure of vestibular function; however, the relative contribution of vestibular function and proprioceptive function to the FOEC test has not been well described. In this study, the authors investigate the relationship between peripheral sensory systems (vestibular and proprioception) and performance on the FOEC test in a cohort of healthy adults.

DESIGN

A total of 563 community-dwelling healthy adults (mean age, 72.7 [SD, 12.6] years; range, 27 to 93 years) participating in the Baltimore Longitudinal Study of Aging were tested. Proprioceptive threshold (PROP) was evaluated with passive motion detection at the right ankle. Vestibulo-ocular reflex (VOR) gain was measured using video head impulses. Otolith function was measured with cervical and ocular vestibular-evoked myogenic potentials. Participants stood on FOEC for 40 sec while wearing BalanSens (BioSensics, LLC, Watertown, MA) to quantify center of mass sway area. A mixed-model multiple logistic regression was used to examine the odds of passing the FOEC test based on PROP, VOR, cervical vestibular-evoked myogenic potential, and ocular vestibular-evoked myogenic potential function in a multisensory model while controlling for age and gender.

RESULTS

The odds of passing the FOEC test decreased by 15% (p < 0.001) for each year of increasing age and by 8% with every 0.1 reduction in VOR gain (p = 0.025). Neither PROP nor otolith function was significantly associated with passing the FOEC test.

CONCLUSIONS

Failure to maintain balance during FOEC may serve as a proxy for rotational vestibular contributions to postural control. Semicircular canals are more sensitive to low-frequency motion than otoliths that may explain these relationships because standing sway is dominated by lower frequencies. Lower VOR gain and increased age independently decreased the odds of passing the test.

Visual-Somatosensory Integration and Quantitative Gait Performance in Aging

Background: The ability to integrate information across sensory modalities is an integral aspect of mobility. Yet, the association between visual-somatosensory (VS) integration and gait performance has not been well-established in aging.

Methods: A total of 333 healthy older adults (mean age 76.53 ± 6.22; 53% female) participated in a visual-somatosensory simple reaction time task and underwent quantitative gait assessment using an instrumented walkway. Magnitude of VS integration was assessed using probability models, and then categorized into four integration classifications (superior, good, poor, or deficient). Associations of VS integration with three independent gait factors (Pace, Rhythm, and Variability derived by factor analysis method) were tested at cross-section using linear regression analyses. Given overlaps in neural circuitry necessary for both multisensory integration and goal-directed locomotion, we hypothesized that VS integration would be significantly associated with pace but not rhythm which is a more automatic process controlled mainly through brainstem and spinal networks.

Results: In keeping with our hypothesis, magnitude of VS integration was a strong predictor of pace (β = 0.12, p < 0.05) but not rhythm (β = −0.01, p = 0.83) in fully-adjusted models. While there was a trend for the association of magnitude of VS integration with variability (β = −0.11, p = 0.051), post-hoc testing of individual gait variables that loaded highest on the variability factor revealed that stride length variability (β = −0.13, p = 0.03) and not swing time variability (β = −0.08, p = 0.15) was significantly associated with magnitude of VS integration. Of the cohort, 29% had superior, 26% had good, 29% had poor, and 16% had deficient VS integration effects.

Conclusions: Worse VS integration in aging is associated with worse spatial but not temporal aspects of gait performance.

Visual-Somatosensory Integration in Older Adults: Links to Sensory Functioning

Research investigating multisensory integration (MSI) processes in aging is scarce, but converging evidence for larger behavioral MSI effects in older compared to younger adults exists. The current study employed a three-prong approach to determine whether inherent age-related sensory processing declines were associated with larger (i.e., worse) visual-somatosensory (VS) reaction time (RT) facilitation effects. Non-demented older adults ( n = 156 ; mean age = 77 years; 55% female) without any medical or psychiatric conditions were included. Participants were instructed to make speeded foot-pedal responses as soon as they detected visual, somatosensory, or VS stimulation. Visual acuity was assessed using the Snellen test while somatosensory sensitivity was determined using vibration thresholds. The aims of the current study were to: (1) replicate a reliable MSI effect; (2) investigate the effect of unisensory functioning on VS RT facilitation; and (3) determine whether sensory functioning combination groups manifested differential MSI effects. Results revealed a significant VS RT facilitation effect that was influenced by somatosensory sensitivity but not visual acuity. That is, older adults with poor somatosensory sensitivity demonstrated significantly larger MSI effects than those with intact somatosensory sensitivity. Additionally, a significant interaction between stimulus condition and sensory functioning group suggested that the group with poor visual acuity and poor somatosensory functioning demonstrated the largest MSI effect compared to the other groups. In summary, the current study reveals that worse somatosensory functioning is associated with larger MSI effects in older adults. To our knowledge, this is first study to identify potential mechanisms behind increased RT facilitation in aging.

Using Race Model Violation to Explore Multisensory Responses in Older Adults: Enhanced Multisensory Integration or Slower Unisensory Processing?

Older adults exhibit greater multisensory reaction time (RT) facilitation than young adults. Since older adults exhibit greater violation of the race model (i.e., cumulative distribution functions for multisensory RTs are greater than that of the summed unisensory RTs), this has been attributed to enhanced multisensory integration. Here we explored whether (a) individual differences in RT distributions within each age group might drive this effect, and (b) the race model is more likely to be violated if unisensory RTs are slower. Young () and older adults () made speeded responses to visual, auditory or tactile stimuli, or any combination of these (bi-/tri-modal). The test of the race model suggested greater audiovisual integration for older adults, but only when accounting for individual differences in RT distributions. Moreover, correlations in both age groups showed that slower unisensory RTs were associated with a greater degree of race model violation. Therefore, greater race model violation may be due to greater ‘room for improvement’ from unisensory responses in older adults compared to young adults, and thus could falsely give the impression of enhanced multisensory integration.