Differential effects and discriminative validity of motor and cognitive tasks varying in difficulty on cognitive–motor interference in persons with multiple sclerosis

Abstract

Background: Cognitive-motor interference (CMI) has been well recognized in persons with multiple sclerosis (pwMS); however, there are limited data on effects of task difficulty.Objective: Examine (1) the effects of motor and cognitive tasks varying in difficulty on the magnitude of CMI and (2) the discriminative validity of CMI between pwMS and healthy controls (HC).Methods: Nine cognitive-motor dual-task (DT) conditions (combinations of three cognitive and three walking tasks) were examined. Outcome measures were DT-performance and dual-task cost (DTC) of gait parameters and correct answers. Task differences and overall group-effects were analysed by mixed model analysis, plus the Wilcoxon signed-rank tests or multivariate analysis of variances (MANOVAs), respectively.Results: Task effects were examined in 82 pwMS (Expanded Disability Status Scale (EDSS): 3.3 +/- 1.0) and discriminative validity in a subsample (35 pwMS and 33 HC). Motor-DTC and DT-performance were affected by difficulty of both the cognitive task (p < 0.001) and the walking condition (p <= 0.002), while cognitive-DTC only varied between cognitive tasks with a large difference in difficulty (p <= 0.005) and not between walking conditions (p > 0.125). None of the DTCs differed between groups.Conclusion: CMI, and especially motor performance, is affected by difficulty of the DT. Although pwMS performed worse on the tasks than HC, none of the DT-conditions showed a discriminative DTC.