Cooperative contributions of structural and functional connectivity to successful memory in aging

Simon W Davis,Roberto Cabeza,Thomas Fink,Amanda Szymanski,Homa Boms

doi:10.1162/netn_a_00064

Abstract

Understanding the precise relation between functional connectivity and structural (white matter) connectivity and how these relationships account for cognitive changes in older adults are major challenges for neuroscience. We investigate these issues using an approach in which structural equation modeling (SEM) is employed to integrate functional and structural connectivity data from younger and older adults (n = 62), analyzed with a common framework based on regions connected by canonical tract groups (CTGs). CTGs (e.g., uncinate fasciculus) serve as a common currency between functional and structural connectivity matrices, and ensure equivalent sparsity in connectome information. We used this approach to investigate the neural mechanisms supporting memory for items and memory for associations, and how they are affected by healthy aging. We found that different structural and functional CTGs made independent contributions to source and item memory performance, suggesting that both forms of connectivity underlie age-related differences in specific forms of memory. Furthermore, the relationship between functional and structural connectivity was best explained by a general relationship between latent constructs—a relationship absent in any specific CTG group. These results provide insights into the relationship between structural and functional connectivity patterns, and elucidate their relative contribution to age-related differences in source memory performance.

Highlights

One of the most consistent patterns in the literature on episodic memory and aging is that older adults tend to be more impaired in episodic memory for associations than in episodic memory for individual items
During the last three decades, cognitive neuroimaging has gradually moved from an emphasis on individual brain regions to a focus on the interactions among brain regions, or connectivity, which can be examined at the functional level using functional MRI and at the structural level using diffusion-weighted imaging (DWI)
The present analysis seeks to address these gaps by using task-based functional connectivity and whole-brain structural connectivity informed by classical white matter anatomy to ask a specific question: Do functional and structural connectivity make independent contributions to memory in older adults? we explore the possibility that function-structure relationships are best characterized by either specific linkages between modalities for a given tract, or instead reflect a general relationship shared by task-relevant tract groups

Summary

Introduction

One of the most consistent patterns in the literature on episodic memory and aging is that older adults tend to be more impaired in episodic memory for associations than in episodic memory for individual items. The second challenge is the problem of the granularity of mapping; while a large array of techniques have attempted to delineate structural-functional connectivity relationships at the level of wholebrain parcellations (Betzel et al, 2014; Zimmermann et al, 2016), between discrete pairs of regions (Andrews-Hanna et al, 2007; Davis, Kragel, Madden, & Cabeza, 2012; Dennis et al, 2008), or at the level of voxels (Horn, Ostwald, Reisert, & Blankenburg, 2014), each technique tends to form a unique claim about how the structure-function relationship changes with age Both of these problems preclude any lasting or satisfying conclusions about how these modalities relate to one another, and have issues unique to datasets that include older adults

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Discussion

Conclusion