|Tsang, Sau Lan
|Cognitive-motor interference during walking after stroke : relationship to type and complexity of cognitive and mobility tasks, and underlying neural mechanisms
|Pang, Marco (RS)
|FHSS Faculty Distinguished Thesis Award (2019/20)
|Cerebrovascular disease -- Patients
Cerebrovascular disease -- Patients -- Rehabilitation
Hong Kong Polytechnic University -- Dissertations
|Department of Rehabilitation Sciences
|xxix, 371 pages : illustrations
|Overall background: Dual-task walking, which involves the concurrent performance of a secondary task when walking, is hardly avoidable in community ambulation. Dual-task interference, or denoted as cognitive-motor interference when a cognitive task was performed simultaneously with a manual or mobility task, may occur during the performance of dual-task walking. The dual-task interference or cognitive-motor interference is considered as a deterioration in either or both of the component task performances when the tasks are performed simultaneously compared to the performances when the component tasks are completed separately. A deteriorated walking performance during dual-task walking may adversely affect the walking stability and hence increase the risk of falling. Gait-related dual-task interference is thus considered to be a major concern in the community dwelling individuals post-stroke. A number of factors such as the prioritization of task during the performance of dual-task walking and the type and complexity of the component tasks adopted may influence the degree and pattern of dual-task interference. The overall objectives of this thesis are to consolidate the existing knowledge on the gait-related dual-task interference, identify the knowledge gap in this field, and provide new insights into the assessment of dual-task walking performance, the factors that affect the degree and pattern of gait-related dual-task interference, the association of gait-related dual-task interference with the risk of falling and the underlying mechanisms of gait-related dual-task interference. These objectives were achieved through a series of six interrelated studies. Abstracts of the individual studies are shown as follows. Study 1 (Chapter 2): Degree and pattern of dual-task Interference during walking varied with component task type and complexity in people post-stroke: a systematic review and meta-analysis. Questions: What are the degree and pattern of dual-task interference (DTI) during walking in people post-stroke? How do these vary with disease chronicity and component task type and complexity in individuals post-stroke? How do these differ between people with and without stroke? Design: Systematic review with meta-analysis of studies reported dual-task interference during walking. Participants: People post-stroke and able-bodied controls. Intervention: Not applicable. Outcome measures: Walking and secondary cognitive/manual task performances under dual-task conditions relative to those under single-task conditions. Results: Seventy-four studies (2,324 people with stroke and 482 able-bodied adults) were included. Manual and mental tracking tasks imposed the greatest DTI (-0.12 to 0.13 m/s, 95%CI -0.17 to -0.07) on gait speed. Among mental tracking tasks, the apparently least complex task (serial-1-subtractions) induced the greatest DTI (0.17m/s, 95%CI -0.25 to -0.10) on gait speed. Mutual interference (decrement in both the walking and secondary component task performances during dual-tasking) was the most common DTI pattern. Sensitivity analyses of studies involving only people with chronic stroke yielded largely similar results as the primary analyses. Individuals post-stroke tended to show more substantial DTI (-0.08m/s, 95%CI=0.17 to 0.01) than those without stroke in walking while performing a manual task, but not in walking while performing a mental tracking task. Conclusions: The degree and pattern of DTI depend on the choice of component task type and complexity. Different dual-task combinations with standardized procedures are required to comprehensively capture the dual-task mobility function post-stroke. PROSPERO registration: 59004. Study 2 (Chapter 3): Cognitive-Motor Interference in Walking After Stroke: Test-Retest Reliability and Validity of Dual-Task Walking Assessments. Objective: To explore the reliability and validity of a series of dual-task mobility assessments among individuals post-stroke. Design: Observational study with repeated measures. Setting: University laboratory. Participants: Thirty community-dwelling individuals with chronic stroke. Interventions: Not applicable. Main Measures: Each of the two mobility tasks (1-minute level-ground walking with and without obstacle-negotiation) was performed concurrently with each of the eight cognitive tasks (auditory Stroop test, serial subtraction, shopping list recall and category naming at two difficulty levels). Walking distance and obstacle hitting rate (OHR) indicated dual-task mobility performance. Number of correct responses (NCR) indicated cognitive performance. Reaction time (RT) was additionally measured for the auditory Stroop test. Construct validity was examined by correlations between the dual-task assessments. The dual-task assessments were repeated within 7-14 days for test-retest reliability. Results: Excellent test-retest reliability in walking distance and OHR (ICC(3,1) = 0.891-0.984, p < 0.05) was found. Moderate to excellent reliability was found in NCR and RT (ICC(3,1) = 0.480-0.911, p < 0.01). Correlations between walking distance were excellent (rs = 0.840-0.985, p < 0.01). Correlations of NCR and RT between low-and high-level cognitive tasks were mosty moderate to excellent (rs= 0.515-0.793, p < 0.01). Generally no significant correlations were found in NCR between the dual-task assessments with different cognitive domains. Conclusions: The dual-task walking assessments are reliable and valid for evaluating cognitive-motor interference in community-dwelling individuals post-stroke. The lack of correlations between the tasks of different cognitive domains indicates the need of using different cognitive domains in dual-task walking assessment post-stroke. Study 3 (Chapter 4): The effects of component task type and complexity on dual-task interference during walking after stroke. Objective: To examine interaction between cognitive task type and component task complexity on the dual-task performances in people post-stroke. Design: Observational study with repeated measures. Setting: University laboratory. Participants: Community-dwelling individuals with mild to moderate chronic stroke. Interventions: Not applicable. Main outcome measures: A mobility task (levelground walking/obstacle-crossing) was performed concurrently with a cognitive task of high/low complexity level. Five cognitive task types covering distinct cognitive domains were used. Dual-task costs (DTCs, i.e., difference between the single-task and dual-task performances divided by the single-task performance) of walking distance and number of correct responses. Results: Ninety-three individuals [mean (SD) age: 62.4 (6.7) years; mean post-stroke duration: 67.7 (53.5)] participated. Cognitive DTC varied with the cognitive task type and the cognitive and mobility task complexities (F=4.6, p=0.001, ηp2=0.05). Overall, walking while completing serial-subtractions showed the greatest interference effect on the cognitive performance in virtually all dual-task combinations. Facilitation on the cognitive performance (i.e., positive cognitive DTC) was shown in a number of dual-task combinations. For the mobility performance, there was virtually no facilitation. Interference generally increased as the cognitive task complexity increased and decreased as the mobility task complexity increased (F=7.2, p<0.001, ηp2=0.07). Mutual interference and no interference were the most common dual-task interference patterns observed. Conclusion: Cognitive task type and component task complexity levels interact to influence the degree and pattern of dual-task interference. Standardized dual-task testing protocols including various cognitive domains are necessary to obtain a comprehensive profile of dual-task interference during walking among individuals with stroke. Study 4 (Chapter 5): Association of subsequent falls with evidence of dual task interference whilst walking in community dwelling individuals after stroke. Objective: To examine fall predictive value of single-task walking tests and extent of interference observed in dual-task walking tests in ambulatory individuals post-stroke. Design: Observational study with prospective cohort. Setting: University laboratory. Participants: Ninety-one community-dwelling individuals with chronic stroke. Interventions: Not applicable. Main outcome measures: Time required to complete 10-meter walk test with and without obstacle negotiation was measured in isolation and in conjunction with performance of a verbal fluency task (category naming). Fall incidence, circumstances and related injuries were recorded by monthly telephone calls for 12 months. Results: Ninety-one individuals [mean (SD) age: 62.7 (8.3) years; mean post-stroke duration: 8.8 (5.3) years] participated. Twenty-nine (32%) of them reported at least one fall during the follow-up period, with a total of 71 fall episodes. There was a significant difference in obstacle-crossing time under single-task (mean difference: 8.3 sec) and dual-task conditions (mean difference: 7.4 sec), and also the degree of interference in mobility performance (increased dual-task obstacle-crossing time relative to the single-task obstacle-crossing time) (mean difference: 3.3%) between the fallers and non-fallers (p<0.05). After adjusting for the effects of other relevant factors, a greater degree of interference in mobility performance remained significantly associated with a decreased risk of falling (adjusted odds ratio=0.951, 95%CI=0.907-0.997, p=0.037). Conclusions: The degree of mobility interference during dual-task obstacle-crossing was the most effective in predicting falls amongst all the single-task and dual-task walking measure parameters tested. This simple dual-task walking assessment has potential clinical utility in identifying people post-stroke at high risk of future falls.
Study 5 (Chapter 6): Association of single-task and dual-task walking performances with falls in community-dwelling individuals with chronic stroke: A prospective cohort study. Objectives: Falling is common among individuals with chronic stroke and often occurs during dual-tasking. This study compared the ability of dual-task walking tests and the corresponding single-task tests in predicting falls in individuals with chronic stroke. Methods: Ninety-three individuals post-stroke (mean age: 62.4 ± 6.7 years; mean post-stroke years: 5.6 ± 4.5) participated in this prospective cohort study. Each of the two mobility tasks (level-ground walking and obstacle-crossing) was performed in isolation and in conjunction with five individual cognitive tasks (category naming, serial-subtraction, shopping list recall, auditory clock task, and auditory Stroop task). Participants were asked not to prioritize either component task while dual-tasking. Data on demographics and other clinical characteristics including depressive symptoms and functional abilities were also collected. Monthly telephone interviews were conducted to collect data on fall incidence, and the related circumstances and injuries during a 12-month follow-up period. Multivariate logistic regression analysis was performed to identify factors that predicted future fall status. Results: Thirty-six participants (39%) reported one or more falls during the follow-up period. The regression model including reaction time (milliseconds) during performance of the auditory clock task while walking over obstacles correctly classified the fall status of 80% participants (72% future fallers and 84% non-fallers, adjusted OR = 0.999, 95% CI = 0.998, 1.000, p = 0.044). Performance did not differ between fallers and non-fallers on any of the other measures. Conclusions: The dual-task obstacle-crossing test has potential clinical utility for identifying people with chronic stroke who have a high risk of future falls. Study 6 (Chapter 7): Cognitive-motor interference during walking in individuals with stroke: A functional near infrared spectroscopy study. Objectives: To compare the brain activity during single-task and dual-task walking between ambulatory community-dwelling individuals with cortical stroke, those with subcortical (basal ganglia) stroke and those with no stroke, and between people who showed dual-task interference and those did not among these three groups with use of functional near infrared spectroscopy (fNIRS). Methods: An observational study with repeated measures in 25 non-demented community-dwelling right-handed individuals (9 able-bodied individuals, 8 individuals with cortical stroke and 8 individuals with subcortical stroke) was conducted in a university laboratory. Participants walked on a motorized treadmill for 1 minute at 75% of their fastest level ground speed while counting back by 7s. Brain activation at bilateral dorsolateral prefrontal cortices (DLPFC), primary motor cortices (M1), supplementary motor areas (SMA), primary somatosensory cortices (SS1) and posterior parietal cortices (PPC) was deduced with fNIRS measures. Between-and within-group differences of brain activation level during single and dual-task conditions were compared. For between-group comparisons, the ipsilesional hemisphere of stroke patients was compared with the non-dominant (right) hemisphere of the controls whereas the contralesional hemisphere of the stroke group was compared with the dominant (left) hemisphere of the controls. Results: The ipsilesional/non-dominant DLPFC demonstrated a higher level of activation during dual-task walking (MD=0.203 μmol/L, 95%CI=0.119-0.395, p=0.038) than during single-task walking. The control group showed an overall higher activation level in the ipsilesional/non-dominant DLPFC than the cortical stroke (MD=0.376 μmol/L, 95%CI=0.142-611, p=0.001) and the subcortical stroke groups (MD=0.275 μmol/L, 95%CI=0.407-0.510, p=0.018). In the control group, people who showed dual-task interference (i.e., decrement in performance of the serial-7-subtraction task during walking) showed a lower activation in the dominant SMA during serial-subtraction under single-task condition than those who did not (MD=0.882 μmol/L, 95% CI=0.396-1.367, p=0.004). In the cortical stroke group, people who showed dual-task interference showed a lower activation in the contralesional M1 during single-task walking than those who did not (MD=0.326 μmol/L, 95% CI=0.263-1.861, p=0.017). In the subcortical stroke group, people who showed dual-task interference showed a lower activation in the contralesional DLPFC (MD=1.010, 95% CI=0.310-1.710, p=0.012) during single-task walking than those who did not. Conclusion: Activation in the ipsilesional/non-dominant DLPFC is higher during dual-task walking than during single-task walking. The control group has an overall higher activation level in the ipsilesional/non-dominant DLPFC than people with cortical stroke and those with subcortical stroke. The presence of dual-task interference is associated with lower activation of the contralesional/dominant motor cortex and DLPFC when performing the cognitive (for control group) and mobility component task (for participants with stroke) under single-task condition. Overall conclusions: Taken together, the studies presented in this thesis were designed to systematically evaluate the effects of DTI in individuals with stroke. The series of studies highlighted the need to assess different dual-task combinations among people with stroke for obtaining a more comprehensive picture of the dual-task mobility function. Our systematic review (study 1, Chapter 2) showed that the DTI degree and pattern changed with the choice of component task type and complexity. Individuals with stroke tended to show a more substantial DTI than their counterparts without stroke in certain, but not all, dual-task conditions. It highlighted the need to assess different dual-task combinations with a standardized paradigm for a more comprehensive picture of the dual-task mobility function within and between individuals, groups, and across time. Results from Study 2 (Chapter 3) showed that the battery of dual-task walking assessments we assessed are reliable and valid for evaluating cognitive-motor interference in community-dwelling individuals post-stroke. The lack of correlations between the tasks of different cognitive domains indicated the need to use different cognitive domains in dual-task walking assessment post-stroke. The findings of this study provide clinicians and researchers with a series of validated dual-task walking assessments that can be used in their future clinical practice and research studies. The interplays between the component task complexity and the cognitive task type found in Study 3 (Chapter 4) reinforced the importance of addressing the performance of both component tasks in dual-task mobility testing after stroke. Findings from the two prospective cohort studies (Chapters 5 and 6) showed that the dual-task obstacle crossing tests were more effective in identifying potential fallers than the single task measures. Thus, the dual-task obstacle crossing tests have potential clinical utility for identifying people with stroke who have a high risk of future falls. Our last study (Chapter 7) showed that performance of the component tasks was associated with the presence of dual-task interference. In able-bodied older adults, the presence of dual-task interference was associated with a decreased brain activation during performance of the cognitive component task. In older adults with stroke, a decreased activation during performance of the mobility component task was more associated with the presence of interference during dual-tasking. These findings provide insights into future studies in investigating the effect of specific exercise training on reducing dual-task interference and the associated neuroplastic changes in people with stroke. Overall, our findings might have important implications for clinical assessment and management in stroke rehabilitation, and form a good basis of future research studies on methods to improve dual-task gait performance and decipher the related neural mechanisms.
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