Working Memory Mediates the Relationship Between Intellectual Enrichment and Long-Term Memory in MS: An Exploratory Analysis of Cognitive Reserve

Background: Roughly half of the individuals suffering from Multiple Sclerosis (MS) show signs of memory impairment, including decline in long-term memory. The cognitive reserve hypothesis states that persons with greater lifetime intellectual enrichment (frequently estimated using indices of pre-morbid verbal intelligence) are protected against disease-related memory decline. It is unknown, however, how intellectual enrichment affords this benefit. Herein we investigate whether working memory capacity (WMC) is the mechanism through which higher intellectual enrichment helps to preserve memory. Working memory is the system involved in the control, regulation, and maintenance of only a limited amount of information and WMC is a useful individual difference metric that is highly correlated with intelligence. Objectives: The aim of the present study was to investigate whether WMC can explain the relationship between intellectual enrichment and long-term memory, thereby helping to explain mechanisms of cognitive reserve. Methods: The sample consisted of 75 (65 female) patients diagnosed with MS. The average age was 49.45 (+/- 9.76) with 15.33 years of education. Intellectual enrichment, long-term memory, and WMC were estimated using the standardized scores of the WTAR, delayed recall of the HVLT-R, and Digit Span Total from the WAIS– IV, respectively. We investigated this hypothesis using a mediation analysis by conducting a series of simple and multiple hierarchical linear regressions and testing for mediation with a Sobel Test. Results: Intellectual enrichment significantly predicted long-term memory, b = .300, p = .009, and the mediator, WMC, b = .148, p < .001. WMC significantly predicted long-term memory, b = 1.57, p < .001. In the final step, WMC fully mediated the relationship between intellectual enrichment [b = .122, p = .37] and long-term memory [b = .1.27, p = .03], the Sobel test of mediation was significant, Z = 2.99, p = .003. Conclusions: Through an exploratory mediation analysis, the present findings suggest that WMC fully mediates the relationship between intellectual enrichment and long-term memory in MS. Future research will be necessary to explicate any type of a causal relationship between these variables. The present findings are an initial step in understanding the relationship between intellectual enrichment, working memory, and long-term memory.