Multiple Sclerosis cognitive fatigue and motivation: Decreasing cognitive fatigue in MS using a novel delayed-reward paradigm
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Cognitive fatigue is a common subjective complaint in multiple sclerosis (MS) among other medical populations. Recent advances in research have leant credible evidence to MS cognitive fatigue as an objective phenomenon of neurocognitive performance which is a parallel phenomenon to the objective functional weakness identified in non-clinical populations as "sustained attention decrement." Consensus among contemporary neuroscientists points to observed weaknesses in dopaminergic circuitry in the basal ganglia as a likely neural correlate of MS cognitive fatigue. This same system has long been associated with goal-directed behavior and reward-based motivation, while research in neurocognition points to dopamine as an integral component in attention and sustained attention, as well. While researchers have demonstrated that reward has a reliable impact on performance in tasks of sustained attention in healthy individuals, reward's effect on fatigue is less clear, particularly, as prior research has not adequately controlled for desensitization to reward, a phenomenon which presents a strong operational confound to fatigue. Furthermore, to our knowledge, no research has been done to consider the effect of reward on cognitive performance in an MS population. The primary aims of this study are to examine the effect of reward on sustained attention in MS patients, and to examine the effect of reward on objective cognitive fatigue. The study employed a novel targeted reward paradigm which introduced reward part-way through the task administration at a point definitely judged to be after fatigue onset so as to ensure that the full strength of reward motivation was present at a time of fatigue. In addition to strong main effects for learning (F = 40.550, p < .001) and fatigue (F = 132.891,p < .001), study results revealed that while the main effect of reward on performance was not significant, (F = 1.651, p = .193), the interaction of Reward x Interval (i.e., the effect of reward on fatigue) was significant (F = 4.552, p = .001) and its effect contributed significantly to the study model (Delta-2LL = 17.791, d = 4,p = .001). Additional analyses of covariate terms showed that, in addition to the primary measures, the covariates of age, (F = 12.801,p = .001), intelligence (F = 4.962,p < .05), disease duration (F = 9.619,p < .01), disability (F = 11.846,p < .01) and depression (F = 7.216,p < .05) all contributed significantly to the study model. Overall, this study gives evidence for the role of motivation in MS cognitive performance, particularly in objective cognitive fatigue, a behavioral finding which is consistent with current neuropsychological theory.