Visuospatial working memory and obstacle crossing in young and older people.

Obstacle crossing requires visuospatial working memory to guide the trailing leg trajectory when vision in unavailable. Visuospatial working memory, as assessed with neuropsychological tests, declines with age, however, this remains to be investigated functionally in obstacle crossing. There is also evidence that visuospatial encoding during a secondary task interferes with balance control during stepping and walking in older people. Here, we studied the interaction effects of age by delay (study 1) and age by secondary visuospatial task (study 2) conditions on obstacle clearance in a visuospatial working memory -guided obstacle crossing task. Healthy young adults aged 19 to 36 years (n = 20 in study 1 and n = 17 in study 2) and healthy older adults aged 66 to 83 years (n = 29 in study 1 and n = 21 in study 2) were instructed to step over an obstacle with their leading leg and straddle it for a delay period before completing the crossing with their trailing leg. In study 1, two obstacle height conditions (12 cm, 18 cm) and two delay durations (20 s, 60 s) were presented in random order. In study 2, participants were required to attend to either no secondary task (control), a visuospatial secondary (star movement) task, or a nonspatial secondary (arithmetic) task, while straddling the obstacle for a delay duration of 20 s, at obstacle heights of 12 cm and 18 cm, randomly presented. Trailing leg kinematics (mean and variability of maximum toe clearance over the obstacle) were determined via motion capture. There were no statistically significant age by delay or age by secondary task interactions. In study 1, toe clearance variability was significantly greater in young adults and increased with increasing delay duration in both groups. In study 2, compared with the control condition, toe clearance variability was significantly greater in the non-spatial secondary task condition but not in the visuospatial condition. Contrary to our hypotheses, these findings suggest that young and older adults alike can store an obstacle representation via visuospatial working memory for durations of at least 60 s and use this information to safely scale their trailing leg over an obstacle. However, the increase in trailing leg toe clearance variability with delay duration suggests that obstacle representation starts to deteriorate even within the first 20 s regardless of age. The finding that undertaking a concurrent arithmetic task impaired visuospatial working memory-guided obstacle clearance suggests a potential increased risk of tripping during obstacle crossing while dual-tasking in both young and older people.

Cortical activation during gait adaptability in people with Parkinson's disease.

BACKGROUND: People with Parkinson's disease (PD) have difficulties adapting their gait. While underlying neural mechanisms involving the prefrontal cortex (PFC) have been studied across various complex walking tasks, less is known about the premotor cortex (PMC) and supplementary motor area (SMA), key cortical regions for motor planning. This study compared frontal cortical regions activation patterns using functional near-infrared spectroscopy (fNIRS), between people with PD and healthy controls (HC) during gait adaptability tasks. METHODS: Forty-nine people with PD (mean (SD) age: 69.5 (7.9) years) and 21 HC (69.0 (5.9) years) completed a simple walk and three randomly presented gait adaptability tasks: (i) stepping on targets, (ii) avoiding obstacles and (iii) negotiating both targets and obstacles. Cortical activity in the dorsolateral PFC (DLPFC), SMA and PMC were recorded using fNIRS. Step length, velocity and accuracy and cortical activity were contrasted between the groups and walking conditions. RESULTS: Compared with the HC, the PD group exhibited greater PMC activation and walked significantly slower and took shorter steps in all conditions. A statistically significant group by condition interaction indicated an increase in DLPFC cortical activation in the HC participants when undertaking the obstacle avoidance task compared with the simple walk but no increase in cortical activation in the PD group when undergoing this more challenging gait task. CONCLUSIONS: Our findings suggest people with PD have little or no DLPFC, SMA and PMC capacity beyond what they need for simple walking and in consequence need to slow their gait velocity to meet the demands of target stepping and obstacle avoidance tasks. Such behavioral and neural patterns appear consistent with concepts of compensatory over-activation and capacity limitation.

Evidence of slow and variable choice-stepping reaction time in cancer survivors with chemotherapy-induced peripheral neuropathy.

BACKGROUND: Chemotherapy-induced peripheral neuropathy (CIPN) is reported to affect up to 70 % of cancer survivors. Despite evidence that CIPN-related impairments often translate into balance and mobility deficits, the effects on stepping and quality of gait, well-documented risk factors for falls, are unclear. AIMS: (i) Establish choice-stepping reaction time (CSRT) performance in survivors with CIPN compared to young and older healthy controls and people with Parkinson's disease; (ii) document walking stability; (iii) investigate relationships between stepping and gait data to objective and patient-reported outcomes. METHODS: 41 cancer survivors with CIPN (mean (SD) age: 60.8 (9.7) years) who were ≥3months post chemotherapy, performed tests of simple and inhibitory CSRT. Walking stability measures were derived from 3-D accelerometry data during the 6-minute walk test. CIPN was assessed using neurological grading and patient-reported outcome measures (European Organization for Research and Treatment of Cancer Quality of Life Questionnaire in CIPN Questionnaire scale EORTC CIPN20). RESULTS: In both stepping tests, CIPN participants performed at the level of adults aged 10 years older and people with mild to moderate Parkinson's disease. Mean (SD) total stepping response times in both CSRT (1160 (190) milliseconds) and inhibitory CSRT (1191 (164) milliseconds) tests were not associated with objective neurological grading but were correlated with increased difficulty feeling the ground. Participants with lower-limb vibration sensation deficit had slower and more variable CSRT times. There were no associations between walking stability and objective measures of CIPN, and limited correlations with the EORTC-CIPN20. CONCLUSIONS: Cancer survivors with CIPN showed deficits in voluntary stepping responses and seemed to compensate for their sensory and motor deficits by walking slower to maintain stability. Objective and patient-reported outcomes of CIPN were correlated with slower and more variable stepping response times. Future studies should aim to identify the causes of the apparent premature decline in cognitive-motor function and develop remediating interventions.

Strength measures are better than muscle mass measures in predicting health-related outcomes in older people: time to abandon the term sarcopenia?

There is no clear consensus on definition, cut-points or standardised assessments of sarcopenia. We found a lower limb strength assessment was at least as effective in predicting balance, mobility and falls in 419 older people as muscle mass-based measures of sarcopenia. INTRODUCTION: There is currently no consensus on the definition, cut-points or standardised assessments of sarcopenia. This study aimed to investigate whether several published definitions of sarcopenia differentiate between older people with respect to important functional and health outcomes. METHODS: Four hundred nineteen community-living older adults (mean age 81.2 ± 4.5, 49 % female) completed assessments of body composition (dual-energy X-ray absorptiometry), strength, balance, mobility and disability. Falls were recorded prospectively for a year using monthly calendars. Sarcopenia was defined according to four skeletal mass-based definitions, two strength-based definitions (handgrip or knee extensor force) and a consensus algorithm (low mass and low strength or slow gait speed). Obesity was defined according to percentage fat mass or waist circumference. RESULTS: The four skeletal mass-based definitions varied considerably with respect to the percentage of participants classified as sarcopenic and their predictive accuracy for functional and health outcomes. The knee extension strength-based definition was equivalent to or better than the mass-based and consensus algorithm definitions; i.e. weaker participants performed poorly in tests of leaning balance, stepping reaction time, gait speed and mobility. They also had higher physiological fall risk scores and were 43 % more likely to fall at home than their stronger counterparts. Adding obesity to sarcopenia definitions identified participants with greater self-reported disability. CONCLUSIONS: A simple lower limb strength assessment was at least as effective in predicting balance, functional mobility and falls in older people as more expensive and time-consuming muscle mass-based measures. These findings imply that functional terms such as muscle weakness or motor impairment are preferable to sarcopenia.

Preliminary evidence of an effect of cerebellar volume on postural sway in FMR1 premutation males.

Recent evidence suggests that early changes in postural control may be discernible among females with premutation expansions (55-200 CGG repeats) of the fragile X mental retardation 1 (FMR1) gene at risk of developing fragile X-associated tremor ataxia syndrome (FXTAS). Cerebellar dysfunction is well described in males and females with FXTAS, yet the interrelationships between cerebellar volume, CGG repeat length, FMR1 messenger RNA (mRNA) levels and changes in postural control remain unknown. This study examined postural sway during standing in a cohort of 22 males with the FMR1 premutation (ages 26-80) and 24 matched controls (ages 26-77). The influence of cerebellar volume, CGG repeat length and FMR1 mRNA levels on postural sway was explored using multiple linear regression. The results provide preliminary evidence that increasing CGG repeat length and decreasing cerebellar volume were associated with greater postural sway among premutation males. The relationship between CGG repeat length and postural sway was mediated by a negative association between CGG repeat size and cerebellar volume. While FMR1 mRNA levels were significantly elevated in the premutation group and correlated with CGG repeat length, FMR1 mRNA levels were not significantly associated with postural sway scores. These findings show for the first time that greater postural sway among males with the FMR1 premutation may reflect CGG repeat-mediated disruption in vulnerable cerebellar circuits implicated in postural control. However, longitudinal studies in larger samples are required to confirm whether the relationships between cerebellar volume, CGG repeat length and postural sway indicate greater risk for neurological decline.

Relationships between serum vitamin D levels, neuromuscular and neuropsychological function and falls in older men and women.

UNLABELLED: Among 463 community dwellers aged 70-90 years, those with vitamin D insufficiency showed reduced neuromuscular function, balance control and stepping ability and performed worse in tests of cognitive function. In men, vitamin D insufficiency was associated with an increased risk of falling. INTRODUCTION: The purpose of this study was to investigate the relationship between serum 25-hydroxy vitamin D (serum 25OHD) levels, physiological and neuropsychological function in older people, and to examine the relationship between serum 25OHD and prospective falls. METHODS: Four hundred sixty-three community-dwelling people aged 70-90 years underwent an assessment of physiological and neuropsychological performance and structured interviews relating to comorbidity and disability. Fall frequency during the 12 months follow-up was monitored with monthly falls diaries. RESULTS: Twenty-one percent of the men and 44% of the women were vitamin D insufficient (serum 25OHD ≤ 50 nmol/L). Participants with vitamin D insufficiency had weaker upper and lower limb strength, slower simple finger press and choice stepping reaction time, poorer leaning balance and slower gait speed, after controlling for age and body mass index, and, poorer executive function and visuospatial ability, after controlling for age and education. Vitamin D insufficiency significantly increased the rate of falls in men (IRR = 1.94, 95% CI = 1.19-3.15, p = 0.008) but not in women. CONCLUSIONS: These findings highlight the associations between vitamin D insufficiency and impairments in physiological and neuropsychological function that predispose older people to fall. The significant relationship between vitamin D insufficiency and falls found in the men may relate to the stronger association found between serum 25OHD levels and dynamic balance measures evident in this male population.