  Introduction: Locus coeruleus (LC) is the primary source of norepinephrine to
the brain and its efferent projections innervate many brain regions, including
the thalamus. 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
(DTI)-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 branch from this tract into the thalamus. The older cohort
exhibited a significant reduction in mean and radial diffusivity within CTT as
compared to 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.
