Depression in multiple sclerosis: relationship to working memory capacity.

Recent research has shown that depression in multiple sclerosis (MS) is associated with deficits on cognitively demanding tasks. One explanation for this relationship is that depressed MS patients may have reduced working memory capacity. The present study was designed to test this hypothesis. Depressed MS patients were compared with nondepressed MS patients and nondepressed healthy controls on a task of working memory capacity (reading span) and a short-term memory task not taxing working memory capacity (word span). In support of the capacity-reduction model, compared with the nondepressed groups, depressed MS patients performed significantly worse on reading span (p<.001) but not on word span. Additionally, reading span was significantly correlated with capacity-demanding tasks shown to be impaired in depressed MS patients in previous reports. Results suggest that depressed MS patients are characterized by limited working memory capacity and that the central executive component of the working memory system may be most affected.