Structural and diffusion MRI measures of the hippocampus and memory performance.

Area of Science:

• Neuroimaging
• Gerontology
• Cognitive Neuroscience

Background:

• Alzheimer's disease (AD) is associated with hippocampal atrophy and altered diffusion tensor imaging (DTI) measures.
• Understanding early AD markers in non-demented individuals is crucial for timely intervention.

Purpose of the Study:

• To investigate the relationship between hippocampal volume, DTI measures (mean diffusivity [MD] and fractional anisotropy [FA]), and memory performance in non-demented older adults.
• To compare the sensitivity of hippocampal MD and volume as early indicators of cognitive decline.

Main Methods:

• MRI scans were used to segment hippocampal volumes in 892 non-demented participants (age ≥ 55).
• Hippocampal MD and FA were measured by co-registering segmentations to DTI maps.
• Memory performance, including verbal memory and delayed recall, was assessed.

Main Results:

• Higher hippocampal mean diffusivity (MD) was significantly associated with poorer verbal memory performance across all participants (≥ 55 years).
• Hippocampal volume showed a weak positive association with delayed recall only in individuals over 65 years.
• No significant association was found between hippocampal fractional anisotropy (FA) and memory performance.

Conclusions:

• Increased hippocampal MD is a potential early biomarker for cognitive decline and Alzheimer's disease, preceding changes in hippocampal volume.
• DTI measures, particularly MD, may offer earlier detection of AD-related brain changes than traditional volumetric MRI.
• Further longitudinal studies are warranted to confirm MD as an early predictive marker for incident Alzheimer's disease.