| Several neuropsychological studies have reported that Multiple Sclerosis (MS) patients exhibit impaired verbal working memory (WM) performance. It is presumed that subcortical demyelination is responsible; however, a mechanism has not been isolated. While total lesion area has been linked to performance deficits in several studies, regional lesion areas have not. We measured regional and whole-brain activity using functional magnetic resonance imaging (FMRI) in MS patients who were concurrently performing a verbal WM task. The aim was to determine if FMRI and regional lesion measures better predict performance than either alone. MS patients demonstrated slow, but otherwise normal verbal WM performance and abnormal brain activity. More extreme activation and deactivation patterns were observed in MS patients compared to age and education matched healthy control (HC) volunteers. Greater cortical intensity was prominent at all difficulty levels. Activation variables accounted for unique variance in performance measures; however, lesion variables did not. The HC group demonstrated an anterior preference for the task, which increased as verbal WM demands increased. Results support the preferential role of anterior systems in verbal WM processing. The HC group data also replicated previous verbal WM studies and extended our knowledge of normal verbal WM processing to include interactions of volume and intensity. Results also suggest that MS patients respond to verbal WM tasks with hyperintense cortical activity, which does not vary with task difficulty. In addition, brain activation measures may be more sensitive predictors of verbal WM performance than lesion load. |
