Objective Measurement of Cognitive Fatigue in Multiple Sclerosis

Objective: Objective examination of cognitive fatigue in persons with multiple sclerosis (MS). Participants: Fifty-six individuals with MS and 39 age- and education-matched healthy control subjects. Main Outcome Measures: Cognitive fatigue, operationalized as the failure to sustain effort over the course of a continuous working memory task; performance on the Paced Auditory Serial Addition Test was examined, with number of correct responses generated and responses produced under conditions of sustained central executive load as the dependent variables. Results: Cognitively impaired MS subjects produced significantly fewer correct responses than either nonimpaired MS subjects or healthy control subjects, who performed at a comparable level. Both MS groups, however, showed susceptibility to cognitive fatigue significantly earlier in time than the healthy group. Conclusions: Fatigue can influence performance even in the absence of cognitive impairment.