Valerie E. Kelly

Associations Between Physical Performance and Executive Function in Older Adults With Mild Cognitive Impairment: Gait Speed and the Timed “Up & Go” Test

Background Older adults with amnestic mild cognitive impairment (aMCI) are at higher risk for developing Alzheimer disease. Physical performance decline on gait and mobility tasks in conjunction with executive dysfunction has implications for accelerated functional decline, disability, and institutionalization in sedentary older adults with aMCI. Objectives The purpose of this study was to examine whether performance on 2 tests commonly used by physical therapists (usual gait speed and Timed “Up & Go” Test [TUG]) are associated with performance on 2 neuropsychological tests of executive function (Trail Making Test, part B [TMT-B], and Stroop-Interference, calculated from the Stroop Word Color Test) in sedentary older adults with aMCI. Design The study was a cross-sectional analysis of 201 sedentary older adults with memory impairment participating in a longitudinal intervention study of cognitive function, aging, exercise, and health promotion. Methods Physical performance speed on gait and mobility tasks was measured via usual gait speed and the TUG (at fast pace). Executive function was measured with the TMT-B and Stroop-Interference measures. Results Applying multiple linear regression, usual gait speed was associated with executive function on both the TMT-B (β=−0.215, P=.003) and Stroop-Interference (β=−0.195, P=.01) measures, indicating that slower usual gait speed was associated with lower executive function performance. Timed “Up & Go” Test scores (in logarithmic transformation) also were associated with executive function on both the TMT-B (β=0.256, P<.001) and Stroop-Interference (β=0.228, P=.002) measures, indicating that a longer time on the TUG was associated with lower executive function performance. All associations remained statistically significant after adjusting for age, sex, depressive symptoms, medical comorbidity, and body mass index. Limitations The cross-sectional nature of this study does not allow for inferences of causation. Conclusions Physical performance speed was associated with executive function after adjusting for age, sex, and age-related factors in sedentary older adults with aMCI. Further research is needed to determine mechanisms and early intervention strategies to slow functional decline.

A Review of Dual-Task Walking Deficits in People with Parkinson's Disease: Motor and Cognitive Contributions, Mechanisms, and Clinical Implications

Gait impairments in Parkinsons disease (PD) are exacerbated under dual-task conditions requiring the simultaneous performance of cognitive or motor tasks. Dual-task walking deficits impact functional mobility, which often requires walking while performing concurrent tasks such as talking or carrying an object. The consequences of gait impairments in PD are significant and include increased disability, increased fall risk, and reduced quality of life. However, effective therapeutic interventions for dual-task walking deficits are limited. The goals of this narrative review are to describe dual-task walking deficits in people with PD, to discuss motor and cognitive factors that may contribute to these deficits, to review potential mechanisms underlying dual-task deficits, and to discuss the effect of therapeutic interventions on dual-task walking deficits in persons with PD.

The effects of age on medio-lateral stability during normal and narrow base walking

We examined age-related differences in frontal plane stability during performance of narrow base (NB) walking relative to usual gait. A cross-sectional analysis of participants from the Baltimore Longitudinal Study of Aging (BLSA) was performed on data from the BLSA Motion Analysis Laboratory. Participants were 34 adults aged 54-92 without history of falls. We measured step error rates during NB gait and spatial-temporal parameters, frontal plane stability, and gait variability during usual and NB gait. There was a non-significant age-associated linear increase in step error rate (P=0.12) during NB gait. With increasing age, step width increased (P=0.002) and step length and stride velocity decreased (P<0.001), especially during NB gait. Age-associated increases in medio-lateral (M-L) center of mass (COM) peak velocity (P<0.001) and displacement (P=0.005) were also greater during NB compared to usual gait. With increasing age there was greater variability in stride velocity (P=0.001) and step length (P<0.001) under both conditions. Age-associated differences related to M-L COM stability suggest that the quantification of COM control during NB gait may improve identification of older persons at increased falls risk.

Effects of instructed focus and task difficulty on concurrent walking and cognitive task performance in healthy young adults

Dual task paradigms can be used to examine the interactions between cognition and the control of posture and gait. Measuring and interpreting changes in dual task performance is challenging, however, because many factors can influence performance. This study examined the effects of instructed focus and walking task difficulty, and the interaction between these factors, on dual task performance in healthy young adults. Fifteen participants performed a cognitive task while walking with either a usual base or a narrow base of support. Participants were instructed to focus on either the cognitive task or walking. Trade-offs both within and between tasks were assessed using the modified attention allocation index and the performance operating characteristic. Instructed focus influenced both the cognitive task and walking. Performance on the cognitive task was faster with instructions to focus on the cognitive task, and walking was faster (and more accurate in the narrow-base condition) with instructions to focus on walking. Walking task difficulty did not affect cognitive performance but did affect walking, with faster walking in the usual-base versus narrow-base condition. There was evidence of an interaction, with greater effects of instructed focus on the cognitive task during usual versus narrow-base walking. These results support the idea that the ability to flexibly shift attention allocation and task performance in response to instructions depends on the difficulty of the postural control task. The modified attention allocation index and the performance operating characteristic were instrumental in fully characterizing trade-offs between and within tasks in order to understand dual task performance changes. A clearer understanding of the factors that affect dual task walking and the interactions between these factors has important implications for the assessment of dual task performance in both clinical and research settings.

Association of cognitive domains with postural instability/gait disturbance in Parkinson's disease

INTRODUCTION Research suggests an association between global cognition and postural instability/gait disturbance (PIGD) in Parkinson disease (PD), but the relationship between specific cognitive domains and PIGD symptoms is not clear. This study examined the association of cognition (global and specific cognitive domains) with PIGD symptoms in a large, well-characterized sample of individuals with PD. METHODS Cognitive function was measured with a detailed neuropsychological assessment, including global cognition, executive function, memory, visuospatial function, and language. PIGD symptoms were measured using the Movement Disorder Society Unified Parkinsons Disease Rating Scale (MDS-UPDRS) Part III, Motor Examination subscale. Multiple linear regression analyses were performed to assess the relationship between cognition and PIGD symptoms with models adjusting for age, sex, education, enrollment site, disease duration, and motor symptom severity. RESULTS The analysis included 783 participants, with mean (standard deviation) age of 67.3 (9.7) years and median (interquartile range) MDS-UPDRS Motor Subscale score of 26 (17, 35). Deficits in global cognition, executive function, memory, and phonemic fluency were associated with more severe PIGD symptoms. Deficits in executive function were associated with impairments in gait, freezing, and postural stability, while visuospatial impairments were associated only with more severe freezing, and poorer memory function was associated only with greater postural instability. DISCUSSION While impairments in global cognition and aspects of executive functioning were associated with more severe PIGD symptoms, specific cognitive domains were differentially related to distinct PIGD components, suggesting the presence of multiple neural pathways contributing to associations between cognition and PIGD symptoms in persons with PD.

A systematic review of interventions conducted in clinical or community settings to improve dual-task postural control in older adults

Background Injury due to falls is a major problem among older adults. Decrements in dual-task postural control performance (simultaneously performing two tasks, at least one of which requires postural control) have been associated with an increased risk of falling. Evidence-based interventions that can be used in clinical or community settings to improve dual-task postural control may help to reduce this risk. Purpose The aims of this systematic review are: 1) to identify clinical or community-based interventions that improved dual-task postural control among older adults; and 2) to identify the key elements of those interventions. Data sources Studies were obtained from a search conducted through October 2013 of the following electronic databases: PubMed, CINAHL, PsycINFO, and Web of Science. Study selection Randomized and nonrandomized controlled studies examining the effects of interventions aimed at improving dual-task postural control among community-dwelling older adults were selected. Data extraction All studies were evaluated based on methodological quality. Intervention characteristics including study purpose, study design, and sample size were identified, and effects of dual-task interventions on various postural control and cognitive outcomes were noted. Data synthesis Twenty-two studies fulfilled the selection criteria and were summarized in this review to identify characteristics of successful interventions. Limitations The ability to synthesize data was limited by the heterogeneity in participant characteristics, study designs, and outcome measures. Conclusion Dual-task postural control can be modified by specific training. There was little evidence that single-task training transferred to dual-task postural control performance. Further investigation of dual-task training using standardized outcome measurements is needed.

Interaction of levodopa and cues on voluntary reaching in Parkinson's disease

The bradykinesia associated with Parkinsons disease (PD) can be improved by both levodopa and the use of external cues. We examined the combined effect of levodopa and external cueing on the voluntary reaching movements of individuals with PD. Nine subjects with PD and nine matched controls were studied reaching to a ball target. Subjects with PD were studied after being off levodopa overnight and again on their morning dose. Kinematic data were collected as all subjects made both accurate and fast reaches under two different cue conditions: noncued (self‐initiated) and cued (triggered by a light). Subjects with PD reached more slowly than controls under all conditions. PD subjects increased their reach velocity and decreased movement time after taking levodopa and also when moving to a cue. However, the effects of levodopa and cueing were not additive. Instead, levodopa improved reach velocity to a greater extent in the noncued vs. cued condition. We also found that levodopa improved accurate (self‐paced) reaches more than fast reaches. These data suggest that levodopa may preferentially improve voluntary reaches that are more internally generated.

Factors influencing dynamic prioritization during dual task walking in healthy young adults

Appropriate prioritization during dual-task walking is necessary to achieve task goals and maintain walking stability. We examined the effects of increased walking task difficulty on dual-task walking prioritization in healthy young adults. Walking under simple usual-base conditions was similar between equal-focus and cognitive-focus instructions, but these differed from walking-focus instructions, consistent with cognitive task prioritization. In contrast, narrow-base walking was similar between equal-focus and walking-focus instructions, but these differed from cognitive-focus instructions. This shift in prioritization with increasing walking task difficulty suggests that prioritization is dynamic and flexible.

Staged unilateral versus bilateral subthalamic nucleus stimulator implantation in Parkinson disease.

In 17 consecutive patients with Parkinson disease (PD), bilateral subthalamic nucleus (STN) stimulators were implanted during staged surgeries. The Unified Parkinson Disease Rating Scale (UPDRS) and the Dyskinesia Disability Scale were completed both off and on medication prior to any surgery and also OFF and ON stimulation after each surgery. On‐medication UPDRS activities of daily living (ADL) and motor examination scores changed little with unilateral or bilateral stimulation. Off‐medication UPDRS motor examination scores improved to similar degrees after each staged STN electrode implantation. Most of the improvements in off‐medication ADL scores, dyskinesia scores, complications of therapy, and medication dose reduction occurred after unilateral STN stimulation with smaller improvements after the second operation.

The Effects of Instructions on Dual-Task Walking and Cognitive Task Performance in People with Parkinson's Disease

Gait impairments are prevalent among people with Parkinsons disease (PD). Instructions to focus on walking can improve walking in PD, but the use of such a cognitive strategy may be limited under dual-task walking conditions, when walking is performed simultaneously with concurrent cognitive or motor tasks. This study examined how dual-task performance of walking and a concurrent cognitive task was affected by instructions in people with PD compared to healthy young and older individuals. Dual-task walking and cognitive task performance was characterized under two sets of instructions as follows: (1) focus on walking and (2) focus on the cognitive task. People with PD and healthy adults walked faster when instructed to focus on walking. However, when focused on walking, people with PD and young adults demonstrated declines in the cognitive task. This suggests that dual-task performance is flexible and can be modified by instructions in people with PD, but walking improvements may come at a cost to cognitive task performance. The ability to modify dual-task performance in response to instructions or other task and environmental factors is critical to mobility in daily life. Future research should continue to examine factors that influence dual-task performance among people with PD.