The contribution of depressive symptoms to slowness of information processing in relapsing remitting multiple sclerosis

Background: Slowness of information processing has been suggested as a fundamental factor modulating cognitive impairment in multiple sclerosis (MS). However, the contribution of depressive symptoms (DS) to slowness remains unclear. One of the most accepted hypotheses on the impact of depression on the general population suggests that depression interferes only with tasks requiring high cognitive demands. However, no studies have investigated if the same pattern occurs in MS. Objective: The aim of this study was to determine the profile of the contribution of DS to slowness. Methods: Four Reaction Time (RT) tasks requiring an increasing level of cognitive demands were administered to 35 relapsing remitting MS patients with DS, 33 MS patients without DS, 17 depressed non-MS patients and 27 controls. Results: MS patients without DS obtained longer RTs than controls in all the tasks. On the contrary, depressed non-MS patients were slower than controls only in the most demanding task. Finally, MS patients with DS were slower than MS patients without DS not only in the most demanding task but also in the task requiring a lower level of cognitive demands. Conclusion: The contribution of DS to slowness depends on the level of cognitive demands. However, its impact on MS is more deleterious than on the general population.