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.

Stress and gender effects on prefrontal cortex oxygenation levels assessed during single and dual-task walking conditions.

The ability to walk is critical for functional independence and wellbeing. The pre-frontal cortex (PFC) plays a key role in cognitive control of locomotion, notably under attention-demanding conditions. Factors that influence brain responses to cognitive demands of locomotion, however, are poorly understood. Herein, we evaluated the individual and combined effects of gender and perceived stress on stride velocity and PFC Oxygenated Hemoglobin (HbO2 ) assessed during single and dual-task walking conditions. The experimental paradigm included Normal Walk (NW); Cognitive Interference (Alpha); and Walk-While-Talk (WWT) tasks. An instrumented walkway was used to assess stride velocity in NW and WWT conditions. Functional Near-Infrared-Spectroscopy (fNIRS) was used to quantify PFC HbO2 levels during NW, Alpha and WWT. Perceived task-related stress was evaluated with a single 11-point scale item. Participants were community residing older adults (age = 76.8 ± 6.7 years; %female = 56). Results revealed that higher perceived stress was associated with greater decline in stride velocity from single to dual-task conditions among men. Three-way interactions revealed that gender moderated the effect of perceived stress on changes in HbO2 levels comparing WWT to NW and Alpha. Attenuation in the increase in HbO2 levels, in high compared to low perceived stress levels, from the two single task conditions to WWT was observed only in men. Thus, older men may be more vulnerable to the effect of perceived stress on the change in PFC oxygenation levels across walking conditions that vary in terms of cognitive demands. These findings confer important implications for assessment and treatment of individuals at risk of mobility impairments.

Neurological Gait Abnormalities Moderate the Functional Brain Signature of the Posture First Hypothesis.

The posture first hypothesis suggests that under dual-task walking conditions older adults prioritize gait over cognitive task performance. Functional neural confirmation of this hypothesis, however, is lacking. Herein, we determined the functional neural correlates of the posture first hypothesis and hypothesized that the presence of neurological gait abnormalities (NGA) would moderate associations between brain activations, gait and cognitive performance. Using functional near-infrared spectroscopy we assessed changes in oxygenated hemoglobin levels in the pre-frontal cortex (PFC) during normal walk and walk while talk (WWT) conditions in a large cohort of non-demented older adults (n = 236; age = 75.5 ± 6.49 years; female = 51.7 %). NGA were defined as central (due to brain diseases) or peripheral (neuropathic gait) following a standardized neurological examination protocol. Double dissociations between brain activations and behavior emerged as a function of NGA. Higher oxygenation levels during WWT were related to better cognitive performance (estimate = 0.145; p < 0.001) but slower gait velocity (estimate = -6.336, p < 0.05) among normals. In contrast, higher oxygenation levels during WWT among individuals with peripheral NGA were associated with worse cognitive performance (estimate = -0.355; p < 0.001) but faster gait velocity (estimate = 14.855; p < 0.05). Increased activation in the PFC during locomotion may have a compensatory function that is designed to support gait among individuals with peripheral NGA.

Online fronto-cortical control of simple and attention-demanding locomotion in humans.

Knowledge of online functional brain mechanisms of locomotion is scarce due to technical limitations of traditional neuroimaging methods. Using functional Near Infrared Spectroscopy (fNIRS) we evaluated task-related changes in oxygenated hemoglobin levels (HbO2) in real-time over the pre-frontal-cortex (PFC) regions during simple (Normal Walk; NW) and attention-demanding (Walking While Talking; WWT) locomotion tasks in a large cohort of non-demented older adults. Results revealed that the assessment of task-related changes in HbO2 was internally consistent. Imposing greater demands on the attention system during locomotion resulted in robust bilateral PFC increases in HbO2 levels during WWT compared to NW and the cognitive interference tasks. Elevated PFC oxygenation levels were maintained throughout the course of WWT but not during the NW condition. Increased oxygenation levels in the PFC were related to greater stride length and better cognitive performance but not to faster gait velocity in WWT. These findings elucidate online brain mechanisms of locomotion, and confer significant implications for risk assessment and intervention for major mobility outcomes.

The Association between High Neuroticism-Low Extraversion and Dual-Task Performance during Walking While Talking in Non-demented Older Adults.

The Walking While Talking (WWT) dual-task paradigm is a mobility stress test that predicts major outcomes, including falls, frailty, disability, and mortality in aging. Certain personality traits, such as neuroticism, extraversion, and their combination, have been linked to both cognitive and motor outcomes. We examined whether individual differences in personality dimensions of neuroticism and extraversion predicted dual-task performance decrements (both motor and cognitive) on a WWT task in non-demented older adults. We hypothesized that the combined effect of high neuroticism-low extraversion would be related to greater dual-task costs in gait velocity and cognitive performance in non-demented older adults. Participants (N=295; age range,=65-95 years; female=164) completed the Big Five Inventory and WWT task involving concurrent gait and a serial 7's subtraction task. Gait velocity was obtained using an instrumented walkway. The high neuroticism-low extraversion group incurred greater dual-task costs (i.e., worse performance) in both gait velocity {95% confidence interval (CI) [-17.68 to -3.07]} and cognitive performance (95% CI [-19.34 to -2.44]) compared to the low neuroticism-high extraversion group, suggesting that high neuroticism-low extraversion interferes with the allocation of attentional resources to competing task demands during the WWT task. Older individuals with high neuroticism-low extraversion may be at higher risk for falls, mobility decline and other adverse outcomes in aging.

Visual-somatosensory integration in aging: does stimulus location really matter?

Individuals are constantly bombarded by sensory stimuli across multiple modalities that must be integrated efficiently. Multisensory integration (MSI) is said to be governed by stimulus properties including space, time, and magnitude. While there is a paucity of research detailing MSI in aging, we have demonstrated that older adults reveal the greatest reaction time (RT) benefit when presented with simultaneous visual-somatosensory (VS) stimuli. To our knowledge, the differential RT benefit of visual and somatosensory stimuli presented within and across spatial hemifields has not been investigated in aging. Eighteen older adults (Mean = 74 years; 11 female), who were determined to be non-demented and without medical or psychiatric conditions that may affect their performance, participated in this study. Participants received eight randomly presented stimulus conditions (four unisensory and four multisensory) and were instructed to make speeded foot-pedal responses as soon as they detected any stimulation, regardless of stimulus type and location of unisensory inputs. Results from a linear mixed effect model, adjusted for speed of processing and other covariates, revealed that RTs to all multisensory pairings were significantly faster than those elicited to averaged constituent unisensory conditions (p < 0.01). Similarly, race model violation did not differ based on unisensory spatial location (p = 0.41). In summary, older adults demonstrate significant VS multisensory RT effects to stimuli both within and across spatial hemifields.

Linking Dementia Pathology and Alteration in Brain Activation to Complex Daily Functional Decline During the Preclinical Dementia Stages: Protocol for a Prospective Observational Cohort Study.

BACKGROUND: Progressive difficulty in performing everyday functional activities is a key diagnostic feature of dementia syndromes. However, not much is known about the neural signature of functional decline, particularly during the very early stages of dementia. Early intervention before overt impairment is observed offers the best hope of reducing the burdens of Alzheimer disease (AD) and other dementias. However, to justify early intervention, those at risk need to be detected earlier and more accurately. The decline in complex daily function (CdF) such as managing medications has been reported to precede impairment in basic activities of daily living (eg, eating and dressing). OBJECTIVE: Our goal is to establish the neural signature of decline in CdF during the preclinical dementia period. METHODS: Gait is central to many CdF and community-based activities. Hence, to elucidate the neural signature of CdF, we validated a novel electroencephalographic approach to measuring gait-related brain activation while participants perform complex gait-based functional tasks. We hypothesize that dementia-related pathology during the preclinical period activates a unique gait-related electroencephalographic (grEEG) pattern that predicts a subsequent decline in CdF. RESULTS: We provide preliminary findings showing that older adults reporting CdF limitations can be characterized by a unique gait-related neural signature: weaker sensorimotor and stronger motor control activation. This subsample also had smaller brain volume and white matter hyperintensities in regions affected early by dementia and engaged in less physical exercise. We propose a prospective observational cohort study in cognitively unimpaired older adults with and without subclinical AD (plasma amyloid-ß) and vascular (white matter hyperintensities) pathologies. We aim to (1) establish the unique grEEG activation as the neural signature and predictor of decline in CdF during the preclinical dementia period; (2) determine associations between dementia-related pathologies and incidence of the neural signature of CdF; and (3) establish associations between a dementia risk factor, physical inactivity, and the neural signature of CdF. CONCLUSIONS: By establishing the clinical relevance and biological basis of the neural signature of CdF decline, we aim to improve prediction during the preclinical stages of ADs and other dementias. Our approach has important research and translational implications because grEEG protocols are relatively inexpensive and portable, and predicting CdF decline may have real-world benefits. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/56726.

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.

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.

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.

Brain patterns of pace - but not rhythm - are associated with vascular disease in older adults.

Background: Distinct domains of gait such as pace and rhythm are linked to an increased risk for cognitive decline, falls, and dementia in aging. The brain substrates supporting these domains and underlying diseases, however, remain relatively unknown. The current study aimed to identify patterns of gray matter volume (GMV) associated with pace and rhythm, and whether these patterns vary as a function of vascular and non-vascular comorbidities. Methods: A cross-sectional sample of 297 older adults (M Age = 72.5 years ± 7.2 years, 43% women) without dementia was drawn from the Tasmanian Study of Cognition and Gait (TASCOG). Factor analyses were used to reduce eight quantitative gait variables into two domains. The "pace" domain was primarily composed of gait speed, stride length, and double support time. The "rhythm" domain was composed of swing time, stance time, and cadence. Multivariate covariance-based analyses adjusted for age, sex, education, total intracranial volume, and presence of mild cognitive impairment identified gray matter volume (GMV) patterns associated with pace and rhythm, as well as participant-specific expression (or factor) scores for each pattern. Results: Pace was positively associated with GMV in the right superior temporal sulcus, bilateral supplementary motor areas (SMA), and bilateral cerebellar regions. Rhythm was positively associated with GMV in bilateral SMA, prefrontal, cingulate, and paracingulate cortices. The GMV pattern associated with pace was less expressed in participants with any vascular disease; this association was also found independently with hypertension, diabetes, and myocardial infarction. Conclusion: Both pace and rhythm domains of gait were associated with the volume of brain structures that have been linked to controlled and automatic aspects of gait control, as well as with structures involved in multisensory integration. Only the brain structures associated with pace, however, were associated with vascular disease.

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.

A human intracranial study of long-range oscillatory coherence across a frontal-occipital-hippocampal brain network during visual object processing.

Visual object-recognition is thought to involve activation of a distributed network of cortical regions, nodes of which include the lateral prefrontal cortex, the so-called lateral occipital complex (LOC), and the hippocampal formation. It has been proposed that long-range oscillatory synchronization is a major mode of coordinating such a distributed network. Here, intracranial recordings were made from three humans as they performed a challenging visual object-recognition task that required them to identify barely recognizable fragmented line-drawings of common objects. Subdural electrodes were placed over the prefrontal cortex and LOC, and depth electrodes were placed within the hippocampal formation. Robust beta-band coherence was evident in all subjects during processing of recognizable fragmented images. Significantly lower coherence was evident during processing of unrecognizable scrambled versions of the same. The results indicate that transient beta-band oscillatory coupling between these three distributed cortical regions may reflect a mechanism for effective communication during visual object processing.

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 (ß = -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.

Computerised cognitive remediation to enhance mobility in older adults: a single-blind, single-centre, randomised trial.

BACKGROUND: Decline in executive functions and related cognitive processes is associated with mobility decline, and these functions might be amenable to cognitive remediation. This study aimed to examine whether a computerised cognitive remediation programme would improve walking in adults aged 70 years and older. METHODS: This single-blind, randomised trial at one academic centre in the USA evaluated the efficacy of an 8-week computerised programme (also known as brain games) of progressive intensity and complexity to improve walking in older adults at high-risk for mobility disability. Inclusion criteria included being 70 years or older; ambulatory; and at high-risk for mobility disability, defined using a cutscore of nine or less (frail range) on the Short Physical Performance Battery and a walking speed of 100 cm/s or less. Individuals with dementia, acute or terminal medical illnesses, recent or planned surgery affecting mobility, mobility limitations solely due to musculoskeletal limitation or pain that prevented them from completing mobility tests, and those who were nursing home residents were excluded. Participants were block randomised (1:1; block size 12 and no stratification) to the intervention group or the control group (low complexity computer games and health education classes). Primary outcomes were change in walking speed at normal pace and walking while talking conditions assessed from baseline to 8 weeks post-intervention by investigators who were masked to group assignment. Groups were compared using the intention-to-treat principle with linear mixed models adjusted for confounders. This trial was registered with ClinicalTrails.gov, NCT02567227. FINDINGS: Between March 1, 2016, and March 12, 2020, 383 patients were enrolled and randomly assigned to the intervention or control group. After randomisation, 11 (3%) patients were diagnosed with dementia. 372 (97%; 271 [73%] women) were included in the intention-to-treat analysis. The mean age of participants was 77·0 years [SD 5·6]). 183 (49·2%) participants were Black and 62 (16·7%) were Hispanic. 314 (93%) of the target 338 completers had finished the intervention when the trial was terminated due to the COVID-19 pandemic. Although there were significant within-group improvements in both groups after the 8-week intervention, there was no significant difference in normal walking speed (-1·03 cm/s [SD 1·30]; 95% CI -3·60 to 1·54) and walking while talking conditions (0·59 cm/s [SD 1·61]; 95% CI -2·59 to 3·76) between the intervention and control groups. Similarly, within-group, but no between-group, differences were seen on executive function tests and physical function. There were no severe adverse events related to interventions. INTERPRETATION: Computerised cognitive remediation improved walking in adults aged 70 years and older at high-risk for mobility disability, but improvements were not significantly greater compared with an active control. Although our findings corroborate the within-group improvements on cognition and mobility reported in previous pilot clinical trials, future studies are required to determine the optimal dose, frequency, intensity, and content of computerised cognitive remediation programmes. FUNDING: National Institute on Aging.

Cognitive control in late-life depression: response inhibition deficits and dysfunction of the anterior cingulate cortex.

OBJECTIVES: Geriatric depression is associated with frontolimbic functional deficits, and this frontal dysfunction may underlie the marked executive control deficits often seen in this population. The authors' goal was to assess the integrity of frontal cortical functioning in geriatric depression, while these individuals performed a standard cognitive control task. The N2 component of the event-related potential (ERP), an evoked response generated within the anterior cingulate cortex (ACC), is significantly enhanced when nondepressed individuals successfully inhibit a response, providing an excellent metric of frontal inhibitory function. DESIGN: The authors used a variant of a demanding Go/NoGo task-switching paradigm that required participants to inhibit response execution during NoGo trials by overcoming a potent response tendency established by frequent Go trials. PARTICIPANTS: The authors compared a cohort of depressed geriatric outpatients (N = 11) with a similarly aged group of nondepressed participants (N = 11). MEASUREMENTS: Reaction times, accuracy, and high-density event-related potential recordings from a 64-channel electrode montage were obtained. RESULTS: A significantly enhanced N2 to NoGo trials was observed in nondepressed elderly participants, with generators localized to the ACC. In contrast, this enhancement was strongly reduced in the depressed sample. Source analysis and topographic mapping pointed to a displacement of N2 generators toward more posterior areas of the middle frontal gyrus in depressed subjects. CONCLUSIONS: Findings confirm previous reports of an inhibitory control deficit in depressed elderly who show significantly increased rates of commission errors (i.e., failures to inhibit responses on NoGo trials). Electrophysiologic data suggest underlying dysfunction in ACC as the basis for this deficit.

Alerting, orienting, and executive attention in older adults.

The Attention Network Test (ANT) assesses alerting, orienting, and executive attention. The current study was designed to achieve three main objectives. First, we determined the reliability, effects, and interactions of attention networks in a relatively large cohort of non-demented older adults (n = 184). Second, in the context of this aged cohort, we examined the effect of chronological age on attention networks. Third, the effect of blood pressure on ANT performance was evaluated. Results revealed high-reliability for the ANT as a whole, and for specific cue and flanker types. We found significant main effects for the three attention networks as well as diminished alerting but enhanced orienting effects during conflict resolution trials. Furthermore, increased chronological age and low blood pressure were both associated with significantly worse performance on the executive attention network. These findings are consistent with executive function decline in older adults and the plausible effect of reduced blood flow to the frontal lobes on individual differences in attention demanding tasks.

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 (ß = 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.

Using the Race Model Inequality to Quantify Behavioral Multisensory Integration Effects.

Multisensory integration research investigates how the brain processes simultaneous sensory information. Research on animals (mainly cats and primates) and humans reveal that intact multisensory integration is crucial for functioning in the real world, including both cognitive and physical activities. Much of the research conducted over the past several decades documents multisensory integration effects using diverse psychophysical, electrophysiological, and neuroimaging techniques. While its presence has been reported, the methods used to determine the magnitude of multisensory integration effects varies and typically faces much criticism. In what follows, limitations of previous behavioral studies are outlined and a step-by-step tutorial for calculating the magnitude of multisensory integration effects using robust probability models is provided.

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 (ß = 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.