Imagine your brain as a giant jigsaw puzzle, with each piece representing a different aspect of memory. In this study, scientists investigated how the connections between these puzzle pieces – the structural and functional connectivity in the brain – influence episodic memory in older adults. They focused on factors like the diffusion tensor imaging (DTI) measure of radial diffusivity (RD) to examine structural connectivity, and resting state functional magnetic resonance imaging (rsfMRI) to analyze functional connectivity within different brain networks. The results were fascinating! They found that specific markers of structural and functional connectivity, such as the fornix and hippocampal cingulum RD, along with salience network functional connectivity, were strong independent predictors of memory performance. Surprisingly, cerebrospinal fluid markers and gray matter volumes didn’t show the same predictive power. By combining both types of connectivity markers, researchers were able to create an even more accurate model for understanding individual variability in episodic memory function in older adults. So put on your researcher hat and dive into this exciting study to uncover the secrets of memory and aging!

In this study, we examined the independent contributions of structural and functional connectivity markers to individual differences in episodic memory performance in 107 cognitively normal older adults from the BIOCARD study. Structural connectivity, defined by the diffusion tensor imaging (DTI) measure of radial diffusivity (RD), was obtained from two medial temporal lobe white matter tracts: the fornix and hippocampal cingulum, while functional connectivity markers were derived from network-based resting state functional magnetic resonance imaging (rsfMRI) of five large-scale brain networks: the control, default, limbic, dorsal attention, and salience/ventral attention networks. Hierarchical and stepwise linear regression methods were utilized to directly compare the relative contributions of the connectivity modalities to individual variability in a composite delayed episodic memory score, while also accounting for age, sex, cerebrospinal fluid (CSF) biomarkers of amyloid and tau pathology (i.e., Aβ42/Aβ40 and p-tau181), and gray matter volumes of the entorhinal cortex and hippocampus. Results revealed that fornix RD, hippocampal cingulum RD, and salience network functional connectivity were each significant independent predictors of memory performance, while CSF markers and gray matter volumes were not. Moreover, in the stepwise model, the addition of sex, fornix RD, hippocampal cingulum RD, and salience network functional connectivity each significantly improved the overall predictive value of the model. These findings demonstrate that both DTI and rsfMRI connectivity measures uniquely contributed to the model and that the combination of structural and functional connectivity markers best accounted for individual variability in episodic memory function in cognitively normal older adults.

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