Structural correlates of memory performance with diffusion tensor imaging.

Aging is associated with a variety of structural and pathological brain changes. Memory, or the ability to store and retrieve information, declines significantly during aging. In order to characterize the brain micro-structural correlates of memory performance, 52 healthy subjects, age 25-82 years, completed a computerized non-verbal memory test and were scanned using magnetic resonance diffusion tensor imaging. Partial correlation was conducted between DTI parameters and memory performance (accuracy and reaction time (RT) for different learning stages) controlling for age. A similar correlation pattern was found for apparent diffusion coefficient (ADC), FA, and radial and axial diffusivities, but correlations between ADC and memory performance were the most informative and are therefore reported here. While ADC was correlated with accuracy mainly in temporal and frontal cortical regions, it was correlated with RT in temporal and frontal white matter pathways, including the inferior longitudinal fasciculus and uncinate fasciculus. The task was repeated four times, performance in the first repetition was correlated with ADC in frontal white matter and in the fourth repetition with ADC in temporal gray matter structures mainly the parahippocapus and in the middle temporal gyrus. The localization of the correlations of ADC with the different task parameters is in line with previous studies. Thus, inter-subject variability in memory performance and tissue morphology, as expressed by diffusion tensor magnetic resonance imaging, can be used to relate tissue microstructures with cognitive performance, and to provide information to corroborate other functional localization techniques.