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Stroke is the leading cause of disability in humans1 and can cause varying degrees of motor, cognitive, emotional, and other functional deficits2. Some stroke patients with better prognosis and only slight functional defects show greater functional autonomy in daily activities, but the functional state of their disability may not be sufficient to support their return to work or previous activities. These patients are referred to as high-functioning stroke patients3,4. Due to their minor functional deficits, it is hard to identify their dysfunctions, especially in terms of cognitive functions, through the general assessment of function scales, such as the Montreal cognitive assessment (MoCA)5 and clinical dementia rating (CDR)6, which have a ceiling effect and poor sensitivity for identifying mild functional defects in high-functioning stroke patients. Therefore, it is necessary to develop objective and simple methods to identify cognitive dysfunction in high-functioning stroke patients.
In recent years, the advantages of the dual-task paradigm in assessment and training have gradually become valued7,8. For example, patients may perform normally on simple cognitive single tasks (e.g., calculation) but show varying degrees of cognitive decline when additional tasks are added9,10 (e.g., walking while counting). Manaf et al. found that stroke patients often use compensatory strategies when performing cognitive-motor dual tasks, such as maintaining stability by sacrificing cognitive task performance11. Therefore, the dual-task assessment may have advantages in identifying cognitive deficits in patients with high-functioning stroke. On the one hand, the content of the dual-task assessment is closer to daily life than a single task, such as walking while observing the surrounding environment or talking and calling. In previous studies, the walking + naming task and walking + crossing obstacles task were designed to simulate walking in real environments12.
On the other hand, the executive ability in dual tasks has a close relationship with divided attention (belonging to the category of advanced cognitive function)13. Divided attention is the ability to handle multiple tasks simultaneously and allocate attention to two or more tasks14. This cognitive skill is of great significance to improve the efficiency of daily activities. Therefore, the results of the dual-task assessment can be used for reflecting the individual's divided attention. Normally, people can deal with two or more simple tasks simultaneously in their daily lives and are not disturbed. However, when brain function is impaired, there may be more dual-task interference when faced with simple dual tasks; that is, when performing dual tasks, the reduced divided attention may be likely to cause the performance of one or two tasks to be impaired15. It is concluded that dual-task execution is more likely to be able to detect advanced cognitive function impairment in patients with high-functioning stroke.
The Stroop paradigm is a classical experimental paradigm to study the Stroop effect (also known as the conflict effect)16, which has been widely used in attention assessment in cognitive function tests, especially in the field of attention inhibition17. The classical Stroop effect refers to the fact that it is difficult for individuals to respond quickly and accurately to non-dominant stimuli due to the interference of the dominant response. This results in a longer response time and lower response accuracy for non-dominant stimuli. The difference in reaction time or accuracy rate between dominant and non-dominant reactions is the Stroop effect18. Therefore, the Stroop requires high levels of attention19. Smaller Stroop effects represent higher attentional inhibition, while larger Stroop effects represent a decline in attentional inhibition18.
The Stroop paradigm may be more suitable for assessing cognitive dysfunction in patients with high-functioning stroke and has higher sensitivity and specificity for attention assessment than the traditional clinical assessment scale20. Therefore, this study designed a dual-task assessment based on the Stroop paradigm to identify cognitive deficits in high-functioning stroke patients. The protocol also includes clinical assessment of cognitive function, lower limb motor function, and balance function in stroke patients to ensure that patients can complete the dual-task assessment. Functional near-infrared spectroscopy (fNIRS) was used as an objective evaluation tool for brain function to detect the activation of brain function in high-functioning stroke patients under the dual task. The effectiveness and feasibility of the dual-task assessment scheme based on the Stroop paradigm were verified from the perspective of neuroimaging, which provides new aspects for clinical practice.