Publications by authors named "On-Yee Lo"

19 Publications

  • Page 1 of 1

Evidence for a Specific Association Between Sustained Attention and Gait Speed in Middle-to-Older-Aged Adults.

Front Aging Neurosci 2021 5;13:703434. Epub 2021 Jul 5.

Boston Attention and Learning Laboratory (BALLAB), VA Boston Healthcare System, Boston, MA, United States.

Although cognitive decline has previously been associated with mobility limitations and frailty, the relationship between sustained attention and gait speed is incompletely characterized. To better quantify the specificity of the sustained attention and gait speed association, we examined the extent to which this relationship is unique rather than accounted for by executive functioning and physical health characteristics. 58 middle-to-older-aged community-dwelling adults without overt evidence of cognitive impairment (45-90 years old; 21 females) participated in the study. Each participant completed a 4-meter gait speed assessment and validated neuropsychological tests to examine various domains of executive functioning including working memory (i.e., Digit Span), inhibitory control (i.e., D-KEFS Color-Word Interference), and task switching (i.e., D-KEFS Number/Letter Switching). Multiple physical and vascular risk factors were also evaluated. Sustained attention was assessed using the gradual onset continuous performance task (gradCPT), a well-validated go/no-go sustained attention task. A series of linear regression models were used to examine how different aspects of cognition, including sustained attention and traditional measures of executive functioning, related to gait speed while controlling for a variety of physical and vascular risk factors. Among all predictors, gradCPT accuracy explained the most variance in gait speed ( = 0.19, < 0.001) and was the only significant predictor (β = 0.35, = 0.01) when accounting for executive functioning and other physical and vascular risk factors. The present results indicate that sustained attention may be uniquely sensitive and mechanistically linked to mobility limitations in middle-to-older adults.
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http://dx.doi.org/10.3389/fnagi.2021.703434DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8289388PMC
July 2021

Gait Variability Is Associated With the Strength of Functional Connectivity Between the Default and Dorsal Attention Brain Networks: Evidence From Multiple Cohorts.

J Gerontol A Biol Sci Med Sci 2021 Sep;76(10):e328-e334

Hinda and Arthur Marcus Institute for Aging Research, Hebrew SeniorLife, Boston, Massachusetts, USA.

Background: In older adults, elevated gait variability when walking has been associated with both cognitive impairment and future falls. This study leveraged 3 existing data sets to determine relationships between gait variability and the strength of functional connectivity within and between large-scale brain networks in healthy older adults, those with mild-to-moderate functional impairment, and those with Parkinson's disease (PD).

Method: Gait and resting-state functional magnetic resonance imaging data were extracted from existing data sets on: (i) 12 older adults without overt disease yet with slow gait and mild executive dysfunction; (ii) 12 older adults with intact cognitive-motor function and age- and sex-matched to the first cohort; and (iii) 15 individuals with PD. Gait variability (%, coefficient of variation of stride time) during preferred walking speed was measured and correlated with the degree of functional connectivity within and between 7 established large-scale functional brain networks.

Results: Regression models adjusted for age and sex revealed that in each cohort, those with less gait variability exhibited greater negative correlation between fluctuations in resting-state brain activity between the default network and the dorsal attention network (functionally limited older: β = 4.38, p = .027; healthy older: β = 1.66, p = .032; PD: β = 1.65, p = .005). No other within- or between-network connectivity outcomes were consistently related to gait variability across all 3 cohorts.

Conclusion: These results provide strong evidence that gait variability is uniquely related to functional connectivity between the default network and the dorsal attention network, and that this relationship may be independent of both functional status and underlying brain disease.
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http://dx.doi.org/10.1093/gerona/glab200DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8436983PMC
September 2021

Targeted tDCS Mitigates Dual-Task Costs to Gait and Balance in Older Adults.

Ann Neurol 2021 Sep 17;90(3):428-439. Epub 2021 Jul 17.

Center for the Study of Movement, Cognition, and Mobility, Neurological Institute, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel.

Objective: Among older adults, the ability to stand or walk while performing cognitive tasks (ie, dual-tasking) requires coordinated activation of several brain networks. In this multicenter, double-blinded, randomized, and sham-controlled study, we examined the effects of modulating the excitability of the left dorsolateral prefrontal cortex (L-DLPFC) and the primary sensorimotor cortex (SM1) on dual-task performance "costs" to standing and walking.

Methods: Fifty-seven older adults without overt illness or disease completed 4 separate study visits during which they received 20 minutes of transcranial direct current stimulation (tDCS) optimized to facilitate the excitability of the L-DLPFC and SM1 simultaneously, or each region separately, or neither region (sham). Before and immediately after stimulation, participants completed a dual-task paradigm in which they were asked to stand and walk with and without concurrent performance of a serial-subtraction task.

Results: tDCS simultaneously targeting the L-DLPFC and SM1, as well as tDCS targeting the L-DLPFC alone, mitigated dual-task costs to standing and walking to a greater extent than tDCS targeting SM1 alone or sham (p < 0.02). Blinding efficacy was excellent and participant subjective belief in the type of stimulation received (real or sham) did not contribute to the observed functional benefits of tDCS.

Interpretation: These results demonstrate that in older adults, dual-task decrements may be amenable to change and implicate L-DPFC excitability as a modifiable component of the control system that enables dual-task standing and walking. tDCS may be used to improve resilience and the ability of older results to walk and stand under challenging conditions, potentially enhancing everyday functioning and reducing fall risks. ANN NEUROL 2021;90:428-439.
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http://dx.doi.org/10.1002/ana.26156DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8434977PMC
September 2021

Recovery from Coronavirus Disease 2019 among Older Adults in Post-Acute Skilled Nursing Facilities.

J Am Med Dir Assoc 2021 06 12;22(6):1138-1141.e1. Epub 2021 Apr 12.

Department of Medicine, Hebrew SeniorLife, Boston, MA, USA; Hinda and Arthur Marcus Institute for Aging Research, Hebrew SeniorLife, Boston, MA, USA; Division of Gerontology, Beth Israel Deaconess Medical Center, Boston, MA, USA.

Objectives: To examine functional outcomes of post-acute care for coronavirus disease 2019 (COVID-19) in skilled nursing facilities (SNFs).

Design: Retrospective cohort.

Setting And Participants: Seventy-three community-dwelling adults ≥65 years of age admitted for post-acute care from 2 SNFs from March 15, 2020, to May 30, 2020.

Measure(s): COVID-19 status was determined from chart review. Frailty was measured with a deficit accumulation frailty index (FI), categorized into nonfrail, mild frailty, and moderate-to-severe frailty. The primary outcome was community discharge. Secondary outcomes included change in functional status from SNF admission to discharge, based on modified Barthel index (mBI) and continuous functional scale scored by physical (PT) and occupational therapists (OT).

Results: Among 73 admissions (31 COVID-19 negative, 42 COVID-19 positive), mean [standard deviation (SD)] age was 83.5 (8.8) and 42 (57.5%) were female, with mean FI of 0.31 (0.01) with no differences by COVID-19 status. The mean length of SNF stay for rehabilitation was 21.2 days (SD 11.1) for COVID-19 negative with 20 (64.5%) patients discharged to community, compared to 23.0 (SD 12.2) and 31 (73.8%) among patients who tested positive for COVID-19. Among those discharged to the community, all groups improved in mBI, PT, and OT score. Those with moderate-to-severe frailty (FI >0.35) had lower mBI scores on discharge [92.0 (6.7) not frail, 81.0 (15.4) mild frailty, 48.6 (20.4) moderate-to-severe frailty; P = .002], lower PT scores on discharge [54.2 (3.9) nonfrail, 51.5 (8.0) mild frailty, 37.1 (9.7) moderate-to-severe frailty; P = .002], and lower OT score on discharge [52.9 (3.2) nonfrail, 45.8 (9.4) mild frailty, 32.4 (7.4) moderate or worse frailty; P = .001].

Conclusions And Implications: Older adults admitted to a SNF for post-acute care with COVID-19 had community discharge rates and functional improvement comparable to a COVID-19 negative group. However, those who are frailer at admission tended to have lower function at discharge.
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http://dx.doi.org/10.1016/j.jamda.2021.04.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8041178PMC
June 2021

The functional implications and modifiability of resting-state brain network complexity in older adults.

Neurosci Lett 2020 02 20;720:134775. Epub 2020 Jan 20.

Hinda and Arthur Marcus Institute for Aging Research, Hebrew SeniorLife, Boston, MA, United States; Harvard Medical School, Boston, MA, United States; Division of Gerontology, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States.

The dynamics of the resting-state activity in brain functional networks are complex, containing meaningful patterns over multiple temporal scales. Such physiologic complexity is often diminished in older adults. Here we aim to examine if the resting-state complexity within functional brain networks is sensitive to functional status in older adults and if repeated exposure to transcranial direct current stimulation (tDCS) would modulate such complexity. Twelve older adults with slow gait and mild-to-moderate executive dysfunction and 12 age- and sex-matched controls completed a baseline resting-state fMRI (rs-fMRI). Ten participants in the functionally-limited group then completed ten 20-minute sessions of real (n = 6) or sham (n = 4) tDCS targeting the left prefrontal cortex over a two-week period as well as a follow-up rs-fMRI. The resting-state complexity associated with seven functional networks was quantified by averaging the multiscale entropy (MSE) of the blood oxygen level-dependent (BOLD) time-series for all voxels within each network. Compared to controls, functionally-limited group exhibited lower complexity in the motor, ventral attention, limbic, executive and default mode networks (F > 6.3, p < 0.02). Within this group, those who received tDCS exhibited greater complexity within the ventral, executive and limbic networks (p < 0.04) post intervention as compared to baseline, while no significant changes in sham group was observed. This study provides preliminary evidence that older adults with functional limitations had diminished complexity of resting-state brain network activity and repeated exposure to tDCS may increase that resting-state complexity, warranting future studies to establish such complexity as a marker of brain health in older adults.
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http://dx.doi.org/10.1016/j.neulet.2020.134775DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7069223PMC
February 2020

Self-Reported Head Trauma Predicts Poor Dual Task Gait in Retired National Football League Players.

Ann Neurol 2020 01 29;87(1):75-83. Epub 2019 Nov 29.

Hinda and Arthur Marcus Institute for Aging Research, Hebrew SeniorLife, Boston, MA.

Objective: Symptomatic head trauma associated with American-style football (ASF) has been linked to brain pathology, along with physical and mental distress in later life. However, the longer-term effects of such trauma on objective metrics of cognitive-motor function remain poorly understood. We hypothesized that ASF-related symptomatic head trauma would predict worse gait performance, particularly during dual task conditions (ie, walking while performing an additional cognitive task), in later life.

Methods: Sixty-six retired professional ASF players aged 29 to 75 years completed a health and wellness questionnaire. They also completed a validated smartphone-based assessment in their own homes, during which gait was monitored while they walked normally and while they performed a verbalized serial-subtraction cognitive task.

Results: Participants who reported more symptomatic head trauma, defined as the total number of impacts to the head or neck followed by concussion-related symptoms, exhibited greater dual task cost (ie, percentage increase) to stride time variability (ie, the coefficient of variation of mean stride time). Those who reported ≥1 hit followed by loss of consciousness, compared to those who did not, also exhibited greater dual task costs to this metric. Relationships between reported trauma and dual task costs were independent of age, body mass index, National Football League career duration, and history of musculoskeletal surgery. Symptomatic head trauma was not correlated with average stride times in either walking condition.

Interpretation: Remote, smartphone-based assessments of dual task walking may be utilized to capture meaningful data sensitive to the long-term impact of symptomatic head trauma in former professional ASF players and other contact sport athletes. ANN NEUROL 2020;87:75-83.
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http://dx.doi.org/10.1002/ana.25638DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6973030PMC
January 2020

Multiscale Dynamics of Spontaneous Brain Activity Is Associated With Walking Speed in Older Adults.

J Gerontol A Biol Sci Med Sci 2020 07;75(8):1566-1571

Hinda and Arthur Marcus Institute for Aging Research, Hebrew SeniorLife, Roslindale, Massachusetts.

Background: In older adults, compromised white matter tract integrity within the brain has been linked to impairments in mobility. We contend that poorer integrity disrupts mobility by altering the processing of sensorimotor and cognitive and attentional resources in neural networks. The richness of information processing in a given network can be quantified by calculating the complexity of resting-state functional MRI time series. We hypothesized that (i) older adults with lower brain complexity, specifically within sensorimotor, executive, and attention networks, would exhibit slower walking speed and greater dual-task costs (ie, dual-task cost) and (ii) such complexity would mediate the effect of white matter integrity on these metrics of mobility.

Methods: Fifty-three older adults completed a walking assessment and a neuroimaging protocol. Brain complexity was quantified by calculating the multiscale entropy of the resting-state functional MRI signal within seven previously defined functional networks. The white matter integrity across structures of the corpus callosum was quantified using fractional anisotropy.

Results: Participants with lower resting-state complexity within the sensorimotor, executive, and attention networks walked more slowly under single- and dual-task (ie, walking while performing a serial-subtraction task) conditions (β > 0.28, p ≤ .01) and had a greater dual-task cost (β < -0.28, p < .04). Complexity in these networks mediated the influence of the corpus callosum genu on both single- (indirect effects > 0.15, 95% confidence intervals = 0.02-0.32) and dual-task walking speeds (indirect effects > 0.13, 95% confidence intervals = 0.02-0.33).

Conclusion: These results suggest that the multiscale dynamics of resting-state brain activity correlate with mobility and mediate the effect of the microstructural integrity in the corpus callosum genu on walking speed in older adults.
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http://dx.doi.org/10.1093/gerona/glz231DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7357585PMC
July 2020

Motor-Cognitive Neural Network Communication Underlies Walking Speed in Community-Dwelling Older Adults.

Front Aging Neurosci 2019 16;11:159. Epub 2019 Jul 16.

Neuroimaging Research for Veterans (NeRVe) Center, VA Boston Healthcare System, Boston, MA, United States.

While walking was once thought to be a highly automated process, it requires higher-level cognition with older age. Like other cognitive tasks, it also becomes further challenged with increased cognitive load (e.g., the addition of an unrelated dual task) and often results in poorer performance (e.g., slower speed). It is not well known, however, how intrinsic neural network communication relates to walking speed, nor to this "cost" to gait performance; i.e., "dual-task cost (DTC)." The current study investigates the relationship between network connectivity, using resting-state functional MRI (rs-fMRI), and individual differences in older adult walking speed. Fifty participants (35 females; 84 ± 4.5 years) from the MOBILIZE Boston Study cohort underwent an MRI protocol and completed a gait assessment during two conditions: walking quietly at a preferred pace and while concurrently performing a serial subtraction task. Within and between neural network connectivity measures were calculated from rs-fMRI and were correlated with walking speeds and the DTC (i.e., the percent change in speed between conditions). Among the rs-fMRI correlates, faster walking was associated with increased connectivity between motor and cognitive networks and decreased connectivity between limbic and cognitive networks. Smaller DTC was associated with increased connectivity within the motor network and increased connectivity between the ventral attention and executive networks. These findings support the importance of both motor network integrity as well as inter-network connectivity amongst higher-level cognitive networks in older adults' ability to maintain mobility, particularly under dual-task (DT) conditions.
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http://dx.doi.org/10.3389/fnagi.2019.00159DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6647911PMC
July 2019

A Cluster Randomized Trial of Tai Chi vs Health Education in Subsidized Housing: The MI-WiSH Study.

J Am Geriatr Soc 2019 09 22;67(9):1812-1819. Epub 2019 May 22.

Harvard Medical School, Boston, Massachusetts.

Objectives: Tai Chi (TC) may benefit older adults with a variety of diseases and disabilities. We tested the hypothesis that TC improves physical function in older adults living in low-income housing facilities.

Design: Cluster randomized controlled trial.

Setting: Subsidized housing facilities in Boston, Massachusetts, and neighboring communities.

Participants: Volunteers were recruited from 15 facilities. The 180 randomized participants were 60 years of age or older, able to understand English and participate in TC, expected to remain in the facility for 1 year, and able to walk independently.

Intervention: TC classes were conducted in the housing facilities twice/week for 1 year and compared with monthly health promotion educational classes and social calls.

Measurements: The primary outcome was physical function measured by the Short Physical Performance Battery (SPPB). Secondary outcomes included other aspects of physical and cognitive function, and falls.

Results: An interim analysis revealed less improvement over 12 months in SPPB scores among TC participants (+.20 units; 95% confidence interval [CI] = -.20 to +.60; P = .69) vs control participants (+.51 units; 95% CI = +.15 to +.87; P = .007), a difference of -.31 units (95% CI = -.66 to .04; P = .082). This met the criterion for futility, and the Data Safety Monitoring Board recommended trial termination. No differences were found in 6- or 12-month changes favoring TC in any secondary outcomes or adverse events.

Conclusion: In older adults with multiple chronic conditions living in subsidized housing facilities, 6 and 12 months of twice/week TC classes were not associated with improvements in functional health. J Am Geriatr Soc 67:1812-1819, 2019.
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http://dx.doi.org/10.1111/jgs.15986DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6732029PMC
September 2019

Effects of transcranial direct current stimulation over right posterior parietal cortex on attention function in healthy young adults.

Eur J Neurosci 2019 06 13;49(12):1623-1631. Epub 2019 Feb 13.

Department of Human Physiology, University of Oregon, Eugene, Oregon.

Attention involves three distinct networks for alerting, orienting, and executive control. Interventions targeting the specific attentional networks remain lacking. Transcranial direct current stimulation (tDCS) has been shown to modulate cortical excitability, which potentially serves as an interventional tool to treat individuals with attention impairment. The purpose of this study was to examine the effects of applying tDCS over the right posterior parietal cortex (PPC) on the performance of the three attentional networks. Twenty-six healthy young adults performed the Attention Network Test before and after anodal or sham tDCS stimulation over the right PPC. The alerting, orienting, and executive effects were assessed before and after the stimulation. The results demonstrated that the orienting effect was significantly improved after real tDCS relative to sham, whereas the alerting and executive control effects remained unaffected. Consistent with previous clinical and functional imaging studies, this suggests that the right PPC is actively engaged with the spatial orienting of attention.
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http://dx.doi.org/10.1111/ejn.14349DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6586514PMC
June 2019

In the Eyes of Those Who Were Randomized: Perceptions of Disadvantaged Older Adults in a Tai Chi Trial.

Gerontologist 2020 05;60(4):672-682

Harvard Medical School, Boston, Massachusetts.

Background And Objectives: Older adults living in subsidized housing have typically been excluded from exercise intervention studies. We conducted a qualitative study to explore the perceived physical, psychological, social, and economic factors that influenced participation in and adherence to a year-long Tai Chi intervention within an ongoing cluster-randomized controlled trial (RCT) for older adults living within subsidized housing facilities.

Research Design And Methods: Focus groups were held with participants of the RCT who were allocated to the trial's Tai Chi intervention. Individual phone interviews were conducted with those allocated to Tai Chi who had low adherence or who had withdrawn their participation from the study. Emergent themes were extracted using grounded-theory methods.

Results: In this qualitative study, we enrolled 41 participants who were allocated to the RCT's Tai Chi intervention: 38 completed and 3 withdrew from the study. Average Tai Chi class attendance was 64.3%. Pragmatic factors that led to higher adherence and retention included: locating classes within each facility; providing programs at no cost; and deployment of a skilled research support team. In addition, the use of an accessible, simplified Tai Chi program improved confidence, social support, self-efficacy, and self-reported improvements in physical and psychological well-being.

Discussion And Implications: Perceived physical, psychological, social benefits, and self-efficacy likely enhance adherence and retention to research-based Tai Chi interventions for older adults. Delivering an on-site, no cost, and supportive program appears critical to overcoming financial and environmental barriers to participation for those living within subsidized housing.
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http://dx.doi.org/10.1093/geront/gny165DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7228436PMC
May 2020

Transcranial Direct Current Stimulation May Improve Cognitive-Motor Function in Functionally Limited Older Adults.

Neurorehabil Neural Repair 2018 09 22;32(9):788-798. Epub 2018 Aug 22.

1 Institute for Aging Research, Hebrew SeniorLife, Roslindale, MA, USA.

Objective: To determine the effects of a transcranial direct current stimulation (tDCS) intervention with the anode placed over the left dorsolateral prefrontal cortex (dlPFC) and cathode over the right supraorbital region, on cognition, mobility, and "dual-task" standing and walking in older adults with mild-to-moderate motor and cognitive impairments.

Methods: A double-blinded, block-randomized, sham-controlled trial was conducted in 18 nondemented, ambulatory adults aged ⩾65 years with slow walking speed (⩽1.0 m/s) and "executive" dysfunction (Trail Making Test B score ⩽25th percentile of age- and education-matched norms). Interventions included ten 20-minute sessions of tDCS or sham stimulation. Cognition, mobility, and dual-task standing and walking were assessed at baseline, postintervention, and 2 weeks thereafter. Dual tasking was also assessed immediately before and after the first tDCS session.

Results: Intervention compliance was high (mean ± SD = 9.5 ± 1.1 sessions) and no unexpected or serious side effects were reported. tDCS, compared with sham, induced improvements in the Montreal Cognitive Assessment total score ( P = .03) and specifically within the executive function subscore of this test ( P = .002), and in several metrics of dual-task standing and walking ( P < .05). Each of these effects persisted for 2 weeks. tDCS had no effect on the Timed Up-and-Go test of mobility or the Geriatric Depression Scale. Those participants who exhibited larger improvements in dual-task standing posture following the first tDCS session exhibited larger cognitive-motor improvements following 2 weeks of tDCS ( P < .04).

Interpretation: tDCS intervention designed to stimulate the left dorsolateral prefrontal cortex may improve executive function and dual tasking in older adults with functional limitations.
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http://dx.doi.org/10.1177/1545968318792616DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6143414PMC
September 2018

Concurrent phone texting alters crossing behavior and induces gait imbalance during obstacle crossing.

Gait Posture 2018 May 6;62:422-425. Epub 2018 Apr 6.

Department of Human Physiology, 122 Esslinger Hall, 1240 University of Oregon, Eugene, OR 97403, USA. Electronic address:

Texting during walking has become a very common daily activity and could alter gait performance, especially during locomotion when additional visual attention is demanded, such as obstacle crossing. The purpose of this study was to examine biomechanical changes in obstructed gait characteristics while engaging in a phone texting activity. Gait analyses were performed on ten young healthy adults under the following two tasks: 1) walking and crossing an obstacle set at a 10% of the subject's height and 2) walking and crossing an obstacle while responding to a text message. Whole body motion data were collected with a 10-camera motion capture system. Our data demonstrated that a conservative gait pattern was adopted while performing texting when approaching and crossing over the obstacle, which was indicated by slower walking speeds and greater toe-obstacle clearances. This gait pattern was, however, accompanied by a greater body sway in the frontal plane during crossing, which could be an indication of perturbed gait balance control. Increased visual-attentional demand from a concurrent phone texting could negatively impact young pedestrians' safety during obstacle crossing.
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http://dx.doi.org/10.1016/j.gaitpost.2018.04.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6360946PMC
May 2018

Smartphone App-Based Assessment of Gait During Normal and Dual-Task Walking: Demonstration of Validity and Reliability.

JMIR Mhealth Uhealth 2018 Jan 30;6(1):e36. Epub 2018 Jan 30.

Hebrew SeniorLife Institute for Aging Research, Harvard Medical School, Roslindale, MA, United States.

Background: Walking is a complex cognitive motor task that is commonly completed while performing another task such as talking or making decisions. Gait assessments performed under normal and "dual-task" walking conditions thus provide important insights into health. Such assessments, however, are limited primarily to laboratory-based settings.

Objective: The objective of our study was to create and test a smartphone-based assessment of normal and dual-task walking for use in nonlaboratory settings.

Methods: We created an iPhone app that used the phone's motion sensors to record movements during walking under normal conditions and while performing a serial-subtraction dual task, with the phone placed in the user's pants pocket. The app provided the user with multimedia instructions before and during the assessment. Acquired data were automatically uploaded to a cloud-based server for offline analyses. A total of 14 healthy adults completed 2 laboratory visits separated by 1 week. On each visit, they used the app to complete three 45-second trials each of normal and dual-task walking. Kinematic data were collected with the app and a gold-standard-instrumented GAITRite mat. Participants also used the app to complete normal and dual-task walking trials within their homes on 3 separate days. Within laboratory-based trials, GAITRite-derived heel strikes and toe-offs of the phone-side leg aligned with smartphone acceleration extrema, following filtering and rotation to the earth coordinate system. We derived stride times-a clinically meaningful metric of locomotor control-from GAITRite and app data, for all strides occurring over the GAITRite mat. We calculated stride times and the dual-task cost to the average stride time (ie, percentage change from normal to dual-task conditions) from both measurement devices. We calculated similar metrics from home-based app data. For these trials, periods of potential turning were identified via custom-developed algorithms and omitted from stride-time analyses.

Results: Across all detected strides in the laboratory, stride times derived from the app and GAITRite mat were highly correlated (P<.001, r=.98). These correlations were independent of walking condition and pocket tightness. App- and GAITRite-derived stride-time dual-task costs were also highly correlated (P<.001, r=.95). The error of app-derived stride times (mean 16.9, SD 9.0 ms) was unaffected by the magnitude of stride time, walking condition, or pocket tightness. For both normal and dual-task trials, average stride times derived from app walking trials demonstrated excellent test-retest reliability within and between both laboratory and home-based assessments (intraclass correlation coefficient range .82-.94).

Conclusions: The iPhone app we created enabled valid and reliable assessment of stride timing-with the smartphone in the pocket-during both normal and dual-task walking and within both laboratory and nonlaboratory environments. Additional work is warranted to expand the functionality of this tool to older adults and other patient populations.
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http://dx.doi.org/10.2196/mhealth.8815DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5811655PMC
January 2018

Transcranial direct current stimulation enhances foot sole somatosensation when standing in older adults.

Exp Brain Res 2018 03 15;236(3):795-802. Epub 2018 Jan 15.

Hebrew SeniorLife Institute for Aging Research, Harvard Medical School, Roslindale, MA, USA.

Foot-sole somatosensation is critical for safe mobility in older adults. Somatosensation arises when afferent input activates a neural network that includes the primary somatosensory cortex. Transcranial direct current stimulation (tDCS), as a strategy to increase somatosensory cortical excitability, may, therefore, enhance foot-sole somatosensation. We hypothesized that a single session of tDCS would improve foot-sole somatosensation, and thus mobility, in older adults. Twenty healthy older adults completed this randomized, double-blinded, cross-over study consisting of two visits separated by one week. On each visit, standing vibratory threshold (SVT) of each foot and the timed-up-and-go test (TUG) of mobility were assessed immediately before and after a 20-min session of tDCS (2.0 mA) or sham stimulation with the anode placed over C3 (according to the 10/20 EEG placement system) and the cathode over the contralateral supraorbital margin. tDCS condition order was randomized. SVT was measured with a shoe insole system. This system automatically ramped up, or down, the amplitude of applied vibrations and the participant stated when they could or could no longer feel the vibration, such that lower SVT reflected better somatosensation. The SVTs of both foot soles were lower following tDCS as compared to sham and both pre-test conditions [F > 3.4, p < 0.03]. A trend towards better TUG performance following tDCS was also observed [F = 2.4, p = 0.07]. Greater improvement in SVT (averaged across feet) moderately correlated with greater improvement in TUG performance (r = 0.48, p = 0.03). These results suggest that tDCS may enhance lower-extremity somatosensory function, and potentially mobility, in healthy older adults.
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http://dx.doi.org/10.1007/s00221-018-5178-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5828881PMC
March 2018

Gait Speed and Gait Variability Are Associated with Different Functional Brain Networks.

Front Aging Neurosci 2017 29;9:390. Epub 2017 Nov 29.

Institute for Aging Research, Hebrew SeniorLife, Boston, MA, United States.

Gait speed and gait variability are clinically meaningful markers of locomotor control that are suspected to be regulated by multiple supraspinal control mechanisms. The purpose of this study was to evaluate the relationships between these gait parameters and the functional connectivity of brain networks in functionally limited older adults. Twelve older adults with mild-to-moderate cognition "executive" dysfunction and relatively slow gait, yet free from neurological diseases, completed a gait assessment and a resting-state fMRI. Gait speed and variability were associated with the strength of functional connectivity of different brain networks. Those with faster gait speed had stronger functional connectivity the frontoparietal control network (). Those with less gait variability (i.e., steadier walking patterns) exhibited stronger functional connectivity the dorsal attention network and the default network (). No other significant relationships between gait metrics and the strength of within- or between- network functional connectivity was observed. Results of this pilot study warrant further investigation to confirm that gait speed and variability are linked to different brain networks in vulnerable older adults.
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http://dx.doi.org/10.3389/fnagi.2017.00390DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5715372PMC
November 2017

Functional implications of muscle co-contraction during gait in advanced age.

Gait Posture 2017 03 20;53:110-114. Epub 2017 Jan 20.

Institute for Aging Research, Hebrew SeniorLife, Boston, MA 02131, USA; Beth Israel Deaconess Medical Center, and Harvard Medical School, Boston, MA 02215, USA. Electronic address:

Older adults often exhibit high levels of lower extremity muscle co-contraction, which may be the cause or effect of age-related impairments in gait and associated falls. Normal gait requires intact executive function and thus can be slowed by challenging executive resources available to the neuromuscular system through the performance of a dual task. We therefore investigated associations between lower limb co-contraction and gait characteristics under normal and dual task conditions in healthy older adults (85.4±5.9years). We hypothesized that greater co-contraction is associated with slower gait speed during dual task conditions that stress executive and attentional abilities. Co-contraction was quantified during different phases of the gait cycle using surface electromyography (EMG) signals obtained from the anterior tibialis and lateral gastrocnemius while walking at preferred speed during normal and dual task conditions. Variables included the time difference to complete the Trail Making Test A and B (ΔTMT) and gait measures during normal or dual task walking. Higher co-contraction levels during the swing phase of both normal and dual task walking were associated with longer ΔTMT (normal: R=0.25, p=0.02; dual task: R=0.27, p=0.01). Co-contraction was associated with gait measures during dual task walking only; greater co-contraction levels during stride and stance were associated with slower gait speed (stride: R=0.38, p=0.04; stance: R=0.38, p=0.04), and greater co-contraction during stride was associated with longer stride time (R=0.16, p=0.03). Our results suggest that relatively high lower limb co-contraction may explain some of the mobility impairments associated with the conduct of executive tasks in older adults.
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http://dx.doi.org/10.1016/j.gaitpost.2017.01.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5346031PMC
March 2017

Distracting visuospatial attention while approaching an obstacle reduces the toe-obstacle clearance.

Exp Brain Res 2015 Apr 8;233(4):1137-44. Epub 2015 Jan 8.

Department of Human Physiology, University of Oregon, Eugene, OR, 97403, USA.

Obstacle crossing during walking requires visuospatial attention to identify the obstacle, so that individuals can integrate visual and somatosensory information for raising the foot with appropriate height and timing without being tripped. However, the interaction between control of foot trajectory and orientation of visuospatial attention during obstacle crossing is complicated and remains unclear. This study probed where attention is directed when approaching and stepping over an obstacle during gait and examined how the presence of the obstacle affects the distribution of attention during walking. Eleven young healthy adults performed a visuospatial attention task while standing (Stand), crossing over an obstacle placed either before (ObsBefore) or after (ObsAfter) the visual target, or crossing without the visual target (ObsOnly). Toe-obstacle clearance was reduced for the trailing leg in the ObsAfter condition but remained the same for the ObsBefore and ObsOnly conditions. In addition, the accuracy rate of the visuospatial attention task tended to be higher at the locations closer to the obstacle. Taken together, these results demonstrate that visuospatial attention and the processes underlying obstacle crossing during locomotion interact in both a spatially and temporally dependent manner.
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http://dx.doi.org/10.1007/s00221-014-4189-1DOI Listing
April 2015

Transcranial magnetic stimulation to the frontal operculum and supramarginal gyrus disrupts planning of outcome-based hand-object interactions.

J Neurosci 2008 Dec;28(53):14422-7

Department of Rehabilitation and Movement Science, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07107, USA.

Behavioral data suggest that goals inform the selection of motor commands during planning. We investigated the neural correlates that mediate planning of goal-oriented actions by asking 10 healthy subjects to prepare either a goal-specific movement toward a common object (a cup), with the intent of grasping-to-pour (liquid into it) or grasping-to-move (to another location) the object, or performing a non-object-oriented stimulus-response task (move a finger). Single-pulse transcranial magnetic stimulation was administered on 50% of trials to the supramarginal gyrus (SMG), anterior intraparietal sulcus, inferior frontal gyrus opercularis (IFGo), and triangularis during motor planning. Stimulation to SMG and IFGo caused a significant delay in planning goal-oriented actions but not responses to an arbitrary stimulus. Despite the delay, movement execution was not affected, suggesting that the motor plan remained intact. Our data implicate the SMG and IFGo in planning goal-oriented hand-object interactions.
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http://dx.doi.org/10.1523/JNEUROSCI.4734-08.2008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5896754PMC
December 2008
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