Impact of Locus Coeruleus and Its Projections on Memory and Aging

Introduction: Locus coeruleus (LC) is the primary source of norepinephrine to the brain and its efferent projections innervate many brain regions, including the thalamus. The LC degrades with normal aging, but not much is known regarding whether its structural connectivity evolves with age or predicts aspects of cognition.Methods: Here, we use high-resolution diffusion tensor imaging-based tractography to examine structural connectivity between LC and the thalamus in younger and older adults.Results: We found LC projections to be bundled in a fiber tract anatomically consistent with the central tegmental tract (CTT) and branched from this tract into the thalamus. The older cohort exhibited a significant reduction in mean and radial diffusivity within CTT, as compared with the young cohort. We also observed a significant correlation between CTT mean, axial, and radial diffusivities and memory performance (delayed recall) in the older adult cohort.Discussion: These observations suggest that although LC projections degrade with age, the degree of degradation is associated with cognitive abilities in older adults. Impact statementLocus coeruleus (LC) modulates several cognitive processes, including modulating arousal, attention modulation, and memory. Sustaining the integrity of LC neurons is hypothesized to play a key role in staving off age-related cognitive decline. However, less is known about how efferent projections of LC change with age or cognition. Here, we examine how age affects the microstructure of the central tegmental tract, a fiber tract in which LC efferent projections are bundled, and whether age-related changes in the microstructure of this tract are associated with cognitive decline.