Locus coeruleus contrast and diffusivity metrics differentially relate to age and memory performance

Area of Science:

• Neuroimaging
• Neuroscience
• Aging Research

Background:

• The locus coeruleus (LC) is crucial for neuromodulation and degrades with age.
• Standardized magnetic resonance imaging (MRI) metrics are needed to assess LC aging and cognitive function.

Purpose of the Study:

• To identify MRI metrics of LC structure most sensitive to aging and cognitive performance.
• To compare different MRI metrics (magnetization transfer, diffusion tensor imaging, multi-compartment diffusion) for their ability to detect age-related changes in the LC.

Main Methods:

• Acquired magnetization transfer-weighted and diffusion-weighted MRI scans in younger and older adults.
• Administered a free recall memory task to assess cognitive function.
• Analyzed MRI data using metrics such as magnetization transfer contrast (MTC), diffusion tensor imaging (DTI), and Neurite Orientation Dispersion and Density Imaging (NODDI).

Main Results:

• Maximum MTC, axial diffusivity (DTI), and free diffusion (NODDI) showed larger age group differences in the LC.
• Maximum MTC was the strongest predictor of age group; sex modulated age effects for MTC and NODDI.
• Age-related differences varied by LC subdivision and hemisphere; restricted diffusion correlated with lower recall variability in older adults.

Conclusions:

• Specific MRI metrics, particularly maximum MTC, are sensitive to age-related changes in the locus coeruleus.
• Sex and locus coeruleus substructure influence the detection of aging effects using neuroimaging.
• Locus coeruleus integrity, specifically restricted diffusion, is linked to memory recall consistency in older adults.