University Honors

Older adults have shown well-documented declines in memory for relationships between items, especially as the number of items that must be bound together increases. Less is known about the neural mechanisms that support this type of associative memory, particularly the hippocampus and its neuromodulatory input from the Locus Coeruleus (LC). In the current study, cognitively healthy older adults completed the QuadMax associative memory task during fMRI scanning. They studied word pairs, triplets, and quadruplets and were subsequently tested on their ability to remember repeated, recombined, and novel word sets. Diffusion-weighted MRI measures were also collected to assess LC microstructural integrity. Results revealed that associative memory, recognition, and hit rates declined significantly as associative load increased from pairs to triplets to quadruplets. These effects were no longer significant when age and sex were included as covariates. At the neural level, associative memory encoding led to greater hippocampal BOLD activity for pairs relative to quadruplets in the left hippocampus, with a similar trend in the right hippocampus. Increase hippocampal activity for the pairs > quadruplets contrast was significantly associated with worse associative memory and recognition performance for quadruplets. Finally, LC mean diffusivity was significantly associated with poorer recognition performance for pairs, but not to hippocampal associative memoryñrelated activity. These findings suggest that age-related variability in hippocampal engagement, but not LC integrity, contributes to individual differences in associative memory performance in older adults. Our study highlights the importance of examining both neural activity and neuromodulatory structure when studying associative memory in aging.