Information processing deficits in multiple sclerosis: a matter of complexity.

This study examined the relationship between processing speed (PS) and working memory (WM), as measured by performance on an n-back task, in relapsing-remitting multiple sclerosis (RRMS) patients. Simple PS was defined as reaction time (RT) on the 0-back task and complex PS was defined as RT on both the 1-back and 2-back tasks. Participants were administered all three n-back tasks (0-, 1-, and 2-back). Total correct responses, total dyads, and RTs were recorded. As expected, RT for all participants slowed as WM load increased. MS patients had slower RTs than controls across all tasks, and the difference between groups for RT was greatest during the 2-back task. When RT for simple PS (0-back) was parsed from the 1- and 2-back tasks, MS patients still showed impaired complex PS compared to controls. MS patients also made significantly fewer total correct responses and had fewer dyads than controls only on the 2-back task. These findings suggest that both WM and PS deficits are present in RRMS, and that as WM demand increases (from 1- to 2-back) both PS and WM deficits become more prominent.