Intellectual enrichment lessens the effect of brain atrophy on learning and memory in multiple sclerosis

Abstract

Objective: Learning and memory impairments are prevalent among persons with multiple sclerosis (MS); however, such deficits are only weakly associated with MS disease severity (brain atrophy). The cognitive reserve hypothesis states that greater lifetime intellectual enrichment lessens the negative impact of brain disease on cognition, thereby helping to explain the incomplete relationship between brain disease and cognitive status in neurologic populations. The literature on cognitive reserve has focused mainly on Alzheimer disease. The current research examines whether greater intellectual enrichment lessens the negative effect of brain atrophy on learning and memory in patients with MS.

Methods: Forty-four persons with MS completed neuropsychological measures of verbal learning and memory, and a vocabulary-based estimate of lifetime intellectual enrichment. Brain atrophy was estimated with third ventricle width measured from 3-T magnetization-prepared rapid gradient echo MRIs. Hierarchical regression was used to predict learning and memory with brain atrophy, intellectual enrichment, and the interaction between brain atrophy and intellectual enrichment.

Results: Brain atrophy predicted worse learning and memory, and intellectual enrichment predicted better learning; however, these effects were moderated by interactions between brain atrophy and intellectual enrichment. Specifically, higher intellectual enrichment lessened the negative impact of brain atrophy on both learning and memory.

Conclusion: These findings help to explain the incomplete relationship between multiple sclerosis disease severity and cognition, as the effect of disease on cognition is attenuated among patients with higher intellectual enrichment. As such, intellectual enrichment is supported as a protective factor against disease-related cognitive impairment in persons with multiple sclerosis.

Figure 1 Interaction between intellectual enrichment and brain atrophy on learning and memory Intellectual enrichment moderates the effect of brain atrophy on (A) verbal learning and (B) verbal memory. The dashed line represents subjects with vocabulary knowledge at the 25th percentile of our sample, which corresponds to approximately the 38th percentile of the WASI normative sample (T = 47). The solid line represents subjects with vocabulary knowledge at the 75th percentile of our sample, which corresponds to approximately the 86th percentile of the WASI normative sample (T = 61). TVW = third ventricle width; WASI = Wechsler Abbreviated Scale of Intelligence.

Figure 2 Interaction between intellectual enrichment and brain atrophy on learning efficiency The negative impact of brain atrophy on learning efficiency is greater among patients with lower intellectual enrichment (A) relative to patients with higher enrichment (B). Subjects with lower and higher brain atrophy are presented in solid and dashed lines.