Information processing speed and attention in multiple sclerosis

Information processing speed is frequently recognized as the primary cognitive impairment in multiple sclerosis (MS). Recent studies have also reported attention deficits in MS patients compared to healthy controls based on the Attention Network Test (ANT). Performance on the ANT, however, is confounded by group differences in baseline processing speed. This study investigated performance on measures of information processing speed and the ANT in a group of relapsing remitting and secondary progressive MS patients (n = 40) and a group of healthy controls (n=40). Significant group differences were found across all measures of information processing speed, including a simple reaction time task, a choice reaction time task, and the Stroop task. Performance on the Alerting, Orienting, and Executive Control attention networks of the ANT was assessed using both simple difference scores and residualized scores. The residualized scores controlled for group differences in baseline processing speed. MS patients had a significantly weaker Executive Control function than healthy participants when calculated using difference scores. This difference was no longer significant when calculated using residualized scores. A significant group difference was found for the Alerting network when using residualized scores, such that MS patients performed more poorly than controls. The complexity of the task on the Executive Control network may exacerbate group differences in processing speed. When differences in Executive Control were controlled for, no significant differences were found for any attention network using difference or residualized scores. These results are consistent with the hypothesis that group differences in processing speed are the driving factor in apparent differences in attention. The effects of fatigue on information processing speed and attention as well as differences in performance across MS subtypes were also examined