Memory dysfunction in multiple sclerosis: Its relation to working memory, semantic encoding, and implicit learning.

Memory disturbance is common in patients with multiple sclerosis (MS), as previously demonstrated on clinical memory tests of explicit learning using effortful retrieval paradigms. To better understand the mechanisms underlying memory failure, the authors compared the performance of 46 MS patients and 47 demographically matched normal controls on experimental tests of working memory, semantic encoding, and implicit memory. On the working memory task, MS patients demonstrated an exaggerated word length effect, which indicates a deficit in the control process of articulatory rehearsal. In contrast, MS patients demonstrated a normal buildup and release from proactive inhibition, which suggests intact semantic encoding. Finally, on priming and procedural memory tasks, MS patients performed without difficulty. The MS patients' test performance was not correlated with illness duration or course, severity of physical disability, or psychoactive medication use.