Specific anatomic associations between white matter integrity and cognitive reserve in normal and cognitively impaired elders

OBJECTIVES: to investigate the associations between white matter (WM) integrity and cognitive reserve (CR) in healthy elders (HE), amnestic mild cognitive impairment (a-MCI), and Alzheimer's disease (AD). The authors studied correlations between CR and WM integrity in regions showing WM age-related effects or pathologic changes and tested the differences of slopes between groups.

METHODS: diffusion tensor images (DTIs) were obtained from 18 young individuals, 15 HE, 16 a-MCI cases, and 15 AD cases. Tract-based spatial statistics was used to process DTI data. Areas showing age-related fractional anisotropy (FA) shrinkages (HE < young) and pathology-related FA network "(AD < HE)" were defined. Correlations between CR and WM integrity were adjusted for age, gender, memory performance and brain volumes.

RESULTS: he presented more negative correlations between CR and WM integrity than patients with a-MCI and AD in age-related areas, such as the genum of the corpus callosum. However, these results were mediated by normal variability in memory function and brain volumes. For patients with a-MCI, negative associations between CR and FA were found in several major tracts, being more robust than in AD group. Although longitudinal results need to be interpreted with caution because of the reduced sample of patients with MCI, after 2 years of follow-up, all patients who progressed to AD had high-CR scores, suggesting a putative link between reduced WM integrity (maximal in patients with high CR) and risk of progression to AD.

CONCLUSIONS: CR correlates are implemented in different anatomic WM areas in HE and patients with a-MCI. Healthy elders with high CR may present better tolerance of typical age-related effects on WM integrity; in patients with a-MCI, the association may reflect increased capacity to cope with incipient cerebral damage.