Abstract
Episodic memory is particularly sensitive to normative aging; however, studies investigating the structure-function relationships that support episodic memory have primarily been limited to gross volumetric measures of brain tissue health. Magnetic resonance elastography (MRE) is an emerging non-invasive, high-resolution imaging technique that uniquely quantifies brain viscoelasticity, and as such, provides a more specific measure of neural microstructural integrity. Recently, a significant double dissociation between orbitofrontal cortex-fluid intelligence and hippocampal-relational memory structure-function relationships was observed in young adults, highlighting the potential of sensitive MRE measures for studying brain health and its relation to cognitive function. However, the structure-function relationship observed by MRE has not yet been explored in healthy older adults. In this study, we examined the relationship between hippocampal (HC) viscoelasticity and episodic memory in cognitively healthy adults aged 66–73 years (N = 11), as measured with the verbal-paired associates (VPA) subtest from the Wechsler Memory Scale (WMS-R). Given the particular dependence of verbal memory tasks on the left HC, unilateral HC MRE measurements were considered for the first time. A significant negative correlation was found between left HC damping ratio, ξ and VPA recall score (rs = −0.77, p = 0.009), which is consistent with previous findings of a relationship between HC ξ and memory performance in young adults. Conversely, correlations between right HC ξ with VPA recall score were not significant. These results highlight the utility of MRE to study cognitive decline and brain aging and suggest its possible use as a sensitive imaging biomarker for memory-related impairments.
Highlights
Age-related cognitive decline affects an estimated 40% of an otherwise healthy population over the age of 60 and reduces both quality of life and independent living (Small 2002)
By adopting a processing pipeline that examined unilateral HC Magnetic resonance elastography (MRE) measures and excluded voxels containing cerebrospinal fluid (CSF), we have demonstrated that the relative viscous-to-elastic behavior of the left HC is associated with explicit episodic memory, such that individuals with lower HC ξ performed better on the memory task
It is conceivable to propose that a combination of imaging modalities that may include MRE could prove useful in the identification of healthy individuals at greatest risk for cognitive decline. This is the first report of a significant structure-function relationship between hippocampal viscoelasticity and episodic memory performance in a sample of cognitively intact older adults
Summary
Age-related cognitive decline affects an estimated 40% of an otherwise healthy population over the age of 60 and reduces both quality of life and independent living (Small 2002). Episodic memory has long been recognised as being dependent on the function of an intact hippocampus (HC), a medial temporal lobe structure essential for encoding and consolidating new memories (Aggleton and Brown 1999; Eichenbaum et al 2007); Vargha-Khadem et al 1997). To study this relationship, many researchers typically rely on. Understanding how changes in hippocampal microstructure impact cognition in the context of aging may prove important for identifying critical neural underpinnings of the cognitive aging process and intervention targets for combating cognitive decline
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