Cognitive performance and cognitive workload in multiple sclerosis: Two different constructs of cognitive functioning?

ABSTRACT

BACKGROUND: Cognitive impairment in individuals with Multiple Sclerosis (iwMS) is traditionally diagnosed using performance measures on cognitive tests. Yet, performance on cognitive tests does not convey the amount of mental effort or cognitive workload it takes to complete the task. The main aim was to evaluate whether cognitive performance and cognitive workload are two different constructs of cognitive functioning in iwMS. METHODS: IwMS were categorized into cognitive impairments (iwMS+, n = 10) and no cognitive impairments (iwMS-, n = 12) using their performance on Brief International Cognitive Assessment for Multiple Sclerosis (BICAMS). Their scores on BICAMS, Stroop, and trail making tests were compared to age- and education-matched controls (n = 22). Cognitive workload was assessed using the self-reported NASA Task Load Index and the Index of Cognitive Activity, derived from pupillary response. RESULTS: IwMS+ performed worse on most cognitive tests compared to iwMS- and controls. However, iwMS+ did not report or exhibit greater cognitive workload compared to the other groups. Potential confounding variables, such as sex, use of antidepressants, and symptoms of depression, fatigue, and dysautonomia did not influence the lack of correlation between cognitive performance and cognitive workload in all three groups. CONCLUSION: Cognitive performance and cognitive workload seem to measure different cognitive constructs of cognitive functioning in MS. Our results suggest that iwMS+ do not show effective allocation of cognitive resources to compensate for deteriorated performance in cognitive tests.