Cognitive-motor interference refers to dual-tasking (DT) interference (DTi) occurring when the simultaneous performance of a cognitive and a motor task leads to a percentage change in one or both tasks. Several theories exist to explain DTi in humans: the capacity-sharing, the bottleneck and the cross-talk theories.
At first I couldn't walk and talk effectively at the same time.
But nothing here even remotely suggests they wrote a protocol on this. So useless.
Research progress in the application of motor-cognitive dual task training in rehabilitation of walking function in stroke patients
Keywords
1. Introduction
Stroke is a global disease [1]. Its common causes include stenosis, occlusion, or rupture of intracranial and extracranial arteries, which results in impaired cerebral blood flow circulation, brain tissue damage and various functional impairments. Stroke is characterized by high morbidity, mortality, and disability [2]. A survey has shown that 1 in 6 people worldwide has suffered from stroke, and about 90% of these stroke survivors will have varying degrees of functional impairment, of which walking dysfunction is one of the major ones [3]. It not only reduces patients’ ability to perform daily activities but also increases the risk of falls. Therefore, it is crucial to restore walking ability [4]. Walking is a rhythmic movement and is the basis of activity, and its basic motor pattern arises in the spinal cord and is achieved through the control of muscles, while its initiation and fine regulation involves the synergistic action of different brain regions such as the cerebral cortex, cerebellum and brainstem [5]. Current methods to improve walking ability after stroke are mostly based on the plasticity of the central nervous system and promote the improvement of motor ability after brain injury by improving patients’ lower limb muscle strength and walking ability through single-task training including standing, walking, and balancing [6]. However, more and more researchers have seen the importance of cortical function for walking and have placed more emphasis on some methods to improve walking ability by activating cognitive processes in the cortex. Motor-cognitive dual-task training(MCDTT), in which a cognitive task is performed alongside motor training, can more effectively strengthen the functional brain network connections between motor-cognitive brain areas, thereby facilitating the activation of the cerebral cortex and the improvement of walking ability. It facilitates the activation of the cerebral cortex and remodeling of brain function to improve motor dysfunction in stroke patients [7]. The mechanism of MCDTT may involve brain function remodeling, motor relearning and neural facilitation, but the neurophysiological mechanism is not clearly established. Therefore, we searched through the keywords “stroke”, “motor cognitive dual task” and “walking function”. A total of 73 articles related to clinical trials were retrieved from PubMed (https://pubmed.ncbi.nlm.nih.gov/) in the past decade, and 11 articles related to clinical trials were retrieved from CNKI (https://www.cnki.net/). Through reading studies, 58 articles were selected. This paper summarizes the application and research progress of MCDTT in the rehabilitation of walking function after stroke and discusses its possible mechanisms of action, aiming to provide a theoretical basis for promoting the recovery of walking function in stroke patients through motor-cognitive therapy techniques.
2. Overview of MCDTT
2.1. Motor-cognitive dual-task
Dual-task training usually includes motor or balance tasks and secondary tasks that required for distraction, and is divided into two main types: motor-motor dual-task and motor-cognitive dual-task [8]. Motor-motor dual-task refers to the simultaneous execution of motor training and postural control training, such as walking while tapping or kicking a ball. In contrast, MCDTT refers to performing motor training along with cognitive training tasks, such as counting or reciting poetry while walking [9]. In recent years, there has been an increasing recognition of the importance of MCDTT in stroke rehabilitation. Among the many functional walking rehabilitation treatments, the cognitive walking dual task combines motor and cognitive tasks simulating walking in a realistic environment, which can compensate for the current single walking training treatment in stroke rehabilitation and is more relevant to daily life [10, 11].
There are a wide variety of cognitive tasks, and researchers have categorized five main types of cognitive tasks: differentiation and decision-making tasks, information tracking tasks, reaction time tasks, verbal fluency tasks, and working memory tasks [12]. However, different cognitive task types also produce different training effects. Several studies have confirmed that two or more cognitive training tasks performed simultaneously with motor training can effectively improve balance and gait in stroke patients, which in turn can effectively improve walking dysfunction in stroke patients [13, 14].
2.2. The need for cognitive resources for walking
The ability to walk is one of the unique movements that distinguish humans from other organisms. Its control mechanisms involve the brain, cerebellum, and brainstem, and the processing of information through visual, proprioceptive, vestibular, and other sensory perceptions, as well as decision making and control, produces stress feedback control and autonomic conscious control of casual posture [15]. Often people think that the walking process is automatic, in reality, the walking process is in many cases combined with cognition and requires additional cognitive resources, including language, attention, and judgment skills. For example, when walking one will think and talk with people, and will make conscious changes depending on the environment and different scenarios, for example, when encountering an obstacle, one will correct one’s route and gait. The need for cognitive resources during walking varies according to the individual’s age, balance, and postural task, and is influenced by the difficulty of the walking task, the external environment, and one’s own motor ability.
Hyndman et al. [16] found that there is no interaction between standing posture and cognitive tasks when the patients were standing. However, when the stroke patients performed a walking task, both motor task and cognitive task levels decreased: lower memory performance, slower gait speed, and smaller stride length. It suggests that the more complex and difficult the motor task is, the greater the interference with the cognitive task may be, also demonstrates the need for cognitive resources during the walking task in stroke patients. Therefore, it is suggested that the selection of appropriate dual-task training combining exercise and cognition according to the different functional levels of patients may enable patients to reduce the risk of falls and improve walking function more effectively.
2.3. Interference of motor-cognitive dual-task
Motor-cognitive interference is that when an individual performs two or more tasks simultaneously, which may produce a reduction in the performance of one or more of these tasks [13]. Bottlenecking occurs if two tasks require the same mechanism at the same time, which results in behavioral impairment in one or all of the tasks [17]. There are often different patterns of performance, where reduced performance on motor tasks only is referred to as cognitive-related motor interference, and conversely reduced performance on cognitive tasks only is referred to as motor-related cognitive interference, or mutual interference if both motor and cognitive performance are reduced.
Plummer et al. [13] proposed that there are nine patterns of motor-cognitive interference: no interference, cognitive-related motor interference, motor-related cognitive interference, mutual interference, cognitive facilitation, motor facilitation, mutual facilitation, cognitive-first trade-off, and motor-first trade-off. Researchers have found that the degree of difficulty of a cognitive task is closely related to the degree of motor ability and interference, and that as the difficulty or complexity of the task increases, patients devote more attention to it during movement [18]. That is, when stroke patients perform dual-task walking, they devote more attention to the secondary task in order to avoid falling, therefore, the attention to the secondary task is diminished and interference arises. However, it is generally believed that this interference decreases with more practice [19]. The main causes of interference are: capacity sharing theory [20], bottleneck theory [21], and crosstalk model [22]. According to Mitra’s [23] cognitive load theory, interference does not occur when the cognitive load required for a task does not exceed the body’s instinctive cognitive resources, which provides some theoretical basis for the implementation of dual tasks. Therefore, when developing dual-task programs for patients, the difficulty of the task should be investigated in advance, and if there is competition for attention, it is necessary to first prioritize the tasks to select the appropriate level of difficulty and task type [24].
2.4. MCDTT prioritization
When performing MCDTT, flexible arrangement between different tasks and optimal allocation of attentional resources can improve dual-task performance. Dual-task training can be divided into variable-priority dual-task and fixed-priority dual-task according to the type of priority of dual-task training. Studies have shown that variable-priority dual-task training has faster and better completion performance than fixed-priority [25].
Sengar et al. [26] conducted a 4-week fixed-priority cognitive dual-task training and a variable-priority cognitive dual-task in stroke patients separately. The first half of the fixed-priority cognitive dual-task training focused on a walking task and the second half on a cognitive task. The variable priority cognitive dual task focused on both the cognitive task and the walking task. Results indicated that variable-priority cognitive dual-task training was more effective than fixed-priority cognitive dual-task training. A related aspect of dual-task walking is also task priority, which may change as the walking environment becomes more challenging.
Timmermans et al. [27] selected 30 stroke patients and used a repeated measures design to assess task priority. They made the participants walk in three different environments: a flat environment, a physical environment filled with fixations, or a challenging environment with the sudden appearance of a projector-enhanced environment; the participants chose their own walking speed in relation to their situation and simultaneously performed a cognitive task. The results showed that motor skills were prioritized more in the fixed physical environment than in the projector-enhanced environment. Therefore, one should enrich the therapeutic environment according to the situation and should be aware that environmental changes bring about changes in task priorities that could potentially affect patients’ motor performance. In addition, how dual-task training with different priorities adjusts attention allocation in stroke patients is an issue that needs to be further explored in the future.
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