Motivation in multiple sclerosis cognitive fatigue: An experimental approach

Introduction: Cognitive fatigue is a common symptom in multiple sclerosis (MS). Recent research has implicated dopaminergic pathways originating in the basal ganglia as neurological correlates of cognitive fatigue in MS. This same system has long been associated with goal-directed behavior and reward-based motivation. While researchers have demonstrated that reward has a reliable impact on performance in tasks of sustained attention in healthy individuals, the effect of reward on fatigue is less clear, as prior research has not adequately controlled for desensitization to reward in a sustained attention task. The primary aims of this study were to examine the effect of reward on attention in MS patients, and to examine the effect of reward on objective cognitive fatigue. Method: The study employed a 3 × 3 repeated measures design to evaluate performance of N = 64 patients with definite MS on a measure of cognitive fatigue across several reward conditions. The study utilized a novel delayed-reward paradigm to better control the measured effect of reward on fatigue. Results: Reward (main effect) displayed a significant effect on overall performance (F = 3.050, p < .05). Reward was also shown to affect fatigue trajectory (Reward × Interval, F = 2.433, p < .05). However, this effect was dependent on the method of reward administration. Conclusions: Study findings support the role of motivation in MS cognitive performance, particularly in objective cognitive fatigue, a behavioral finding that is consistent with current neuropsychological theory. Study findings support the delayed-reward paradigm as an effective method for measuring reward effect on tasks of sustained attention.