The Attentional Cost of Movement in Individuals with MS

Background: Individuals with MS have difficulty performing cognitive and motor tasks simultaneously. This phenomenon, termed cognitive-motor interference, has been theorized to be due the increase in attentional demands of movement in individuals with MS. To date, this theory has not been expressly tested in individuals with MS.

Objectives: To investigate the association between the attentional costs of movement and dual task performance in individuals with MS.

Methods: Twenty individuals with MS (Age: 56.4yr±11.0yr, EDSS: median (IQR)=3.5(2.5) and 26 healthy controls (Age: 61.0yr±8.7yr) participated in the investigation. Participants completed a probe reaction test during five conditions with varying levels of stability and mobility (sitting, standing, leaning to the limits of stability, stationary cycling and walking).  During each condition participants responded to 20 auditory tones – which were presented randomly. All participants were instructed to respond to each cue as quickly as possible with an emphasis on not altering their performance on the motor tasks. In addition to the probe reaction time task, participants also completed a complex dual task scenario that included walking while subtracting by 7s from a given number. The primary outcomes were average probe reaction times (PRT) for each motor task and changes in walking and cognitive performance for the dual task. Group and task differences were analyzed with a 2 x 5 repeated measures ANOVA and comparisons between attentional costs (i.e. PRTs of walking) and complex dual task performance was analyzed with Spearman correlations.

Results: Overall, individuals with MS displayed significantly higher PRTs across all tasks (p=.01).  There was an overall significant effect of task (p<.01) with conditions including movement and dynamic balance control elicited greater PRTs than static conditions. Overall, no significant correlations were observed between attentional costs and complex dual task performance.

Conclusions: The findings suggest that individuals with MS have increased attentional costs of movement across a range of movement tasks compared to healthy controls.  The lack of correlation between PRT and complex dual task performance outcomes, however, points to an inadequacy of simple attentional capacity models alone explaining deficits observed during dual tasking.