Investigating Long-Term Memory Impairment in MS through the Lens of the Dual-Component Framework of Working Memory

Background: Long-term memory impairment is common in multiple sclerosis (MS) and is associated with lower efficiency within working memory. What aspect of working memory is impaired and contributes to long-term memory impairment in MS remains an open question. 

Objectives: The main aim of the present research is to translate theoretical models of working memory from the cognitive psychology literature in order to better understand working memory related long-term memory impairment in MS. Specifically, we evaluated how the dual-components of working memory (primary memory [capacity] vs. secondary memory [processing]) might differ as a function of long-term memory status in MS participants. 

Methods: MS memory-unimpaired (N=12; delayed recall T-Score=53.67), MS memory-impaired (N=12; delayed recall T-Score=27.75) and healthy control participants (N=15) were recruited to participate in a verbal list learning experiment. Participants read a list of 15 words followed by an immediate and delayed free recall task (this repeated for a total of 4 lists). Immediate free recall output was coded and classified as retrieval from either primary memory or secondary memory to derive estimates of quantitative capacity and processing efficiency for each group, respectively.

Results: The interaction between Memory-Impairment Group and Dual-Component was significant (p = .004). MS memory-impaired participants showed a reduction in their ability to access the secondary memory component of working memory on immediate recall trials compared to MS memory-unimpaired participants (p = <.001, d = 1.63). The MS Groups did not differ in their ability to access the contents of primary memory (p = n.s.).

Conclusions: The present findings corroborate past research that suggest individual differences in working memory efficiency are related to long-term memory impairment in MS. Further, these data support the hypothesis that long-term memory deficits in MS are related to the secondary memory component (processing efficiency) of working memory.