Background: Multiple sclerosis (MS) starts with clinically isolated syndrome (CIS), which in approximately 25 % represents optic neuritis (ON). Balance and cognitive problems including working memory deficits can be detected in majority of CIS patients. Dual-task paradigm is often used to study cognitive-motor interference (CMI). Due to the lack of consistent data about the effect of demyelinating disease in its earliest stages on balance and CMI, we aimed to study interactions between working memory and three different aspects of balance in highly selected patients with ON without significant neurological impairment. Such data are important in order to identify and further study possible prognostic biomarkers to better predict the course of the disease. Additionally, new information could be used for counselling and establishing better rehabilitation strategies.
Methods: Twenty patients with ON (CIS) and good visual acuity and 20 healthy subjects underwent assessments of three aspects of balance (standing, gait initiation and gait). The assessments were performed with and without concurrent verbal and visuospatial working memory tasks. Balance was assessed using centre of pressure measures. Patients underwent neuropsychological assessment to estimate baseline cognitive functioning.
Results: Neuropsychological testing did not reveal important deficits of working memory in patients. In majority impairment of attention and executive functions was noted. Static balance (while standing) was impaired in patients. We observed a higher effect of concurrent visuospatial cognitive task on balance performance compared to verbal working memory task in patients. Dynamic balance while initiating gait was not different between the groups. Performance on both cognitive tasks was lower in patients while dual-tasking compared to cognitive task alone. Additionally, CMI was higher in patients compared to healthy subjects. We observed higher CMI between verbal working memory task and gait initiation compared to visuospatial working memory task in both groups. Patients walked significantly slower compared to healthy controls. Both groups lowered gait speed while dual-tasking regardless of the nature of the concurrent cognitive task.
Conclusions: Our results and the data from the literature suggest that interference between working memory and static balance largely occurs at the level of parietal cortex, which is involved in afferent signal processing and perception of the body in space as well as visual working memory and attention. On the other hand, interference between working memory and gait initiation occurs mainly in the frontal cortex (prefrontal area), since these regions are involved in generation of anticipatory postural adjustments and verbal working memory. Additionally, impaired performance on both cognitive tasks while initiating gait suggests CMI is happening at the level of central executive. Similar responses to cognitive tasks while walking in patients and healthy subjects suggest slower gait to be an appropriate response to dual-tasking. Similarly, we consider lower baseline gait speed observed in patients to be an appropriate response from prefrontal areas responsible for gait speed control.
Baseline working memory performance of the patients was normal. Taking this into account, all our findings can be explained by impaired quality of afferent and efferent signals to the brain resulting in higher need for cognitive involvement while balancing. Attention deficits and impairment of executive functions might lower the threshold for the observed interactions in some instances and become especially important when demanding motor tasks such as gait initiation are involved.
New data from our study represents foundation for further prospective research to identify possible biomarkers for the disease prognosis. The observation of executive functions and attention deficits becoming important only while performed along with demanding motor tasks allows us to counsel the patients properly and suggest health-care workers to focus on these cognitive domains while planning rehabilitation programmes for the patients.
Methods: Twenty patients with ON (CIS) and good visual acuity and 20 healthy subjects underwent assessments of three aspects of balance (standing, gait initiation and gait). The assessments were performed with and without concurrent verbal and visuospatial working memory tasks. Balance was assessed using centre of pressure measures. Patients underwent neuropsychological assessment to estimate baseline cognitive functioning.
Results: Neuropsychological testing did not reveal important deficits of working memory in patients. In majority impairment of attention and executive functions was noted. Static balance (while standing) was impaired in patients. We observed a higher effect of concurrent visuospatial cognitive task on balance performance compared to verbal working memory task in patients. Dynamic balance while initiating gait was not different between the groups. Performance on both cognitive tasks was lower in patients while dual-tasking compared to cognitive task alone. Additionally CMI was higher in patients compared to healthy subjects. We observed higher CMI between verbal working memory task and gait initiation compared to visuospatial working memory task in both groups. Patients walked significantly slower compared to healthy controls. Both groups lowered gait speed while dual-tasking regardless of the nature of the concurrent cognitive task.
Conclusions: Our results and the data from the literature suggest that interference between working memory and static balance largely occurs at the level of parietal cortex, which is involved in afferent signal processing and perception of the body in space as well as visual working memory. On the other hand interference between working memory and gait initiation occurs mainly in the frontal cortex (prefrontal area), since these regions are involved in generation of anticipatory postural adjustments and verbal working memory. Additionally, impaired performance on both cognitive tasks while initiating gait suggests CMI is happening at the level of central executive. Similar responses to cognitive tasks while walking in patients and healthy subjects suggest slower gait to be an appropriate response to dual-tasking. Similarly we consider lower baseline gait speed observed in patients to be an appropriate response from prefrontal areas responsible for gait speed control.
Baseline working memory performance of the patients was normal. Taking this into account, all our findings can only be explained by impaired quality of afferent and efferent signals to the brain resulting in higher need for cognitive involvement while balancing. Attention deficits and impairment of executive functions become important only when demanding motor tasks such as gait initiation are involved.
New data from our study represents foundation for further prospective research to identify possible biomarkers for the disease prognosis. The observation of executive functions and attention deficits becoming important only while performed along with demanding motor tasks allows us to counsel the patients properly and suggest health-care workers to focus on these cognitive domains while planning rehabilitation programmes for the patients.
|
