Information processing speed deficits may be better correlated with the extent of white matter sclerotic lesions in multiple sclerosis than previously suspected.

Despite frequent use of the Paced Auditory Serial Addition Test (PASAT; Gronwall, 1977) for examining information processing speed (IPS) deficits in multiple sclerosis (MS), prior literature on the relationship between PASAT performance and severity of brain disease has been contradictory. In the present study, we found that PASAT performance is moderately well correlated with the total area of sclerotic brain lesions in MS patients only if a modified scoring method (mean "dyad" score; Snyder et al., 1993), but not the standard scoring method, is applied. We conclude that the PASAT remains a useful measure of IPS in MS, if a flaw in the typical scoring technique for this test is corrected. In our sample of 41 MS patients, for every one point decrease in mean dyad score, total lesion area increased by 364.08 mm2 on average, after controlling for age, sex, and education. IPS deficits are more severe for patients with greater brain disease, due to increased disruption of the white matter pathways that likely support the parallel distributed processing of complex information by geographically distant brain regions.