Episodic memory loss is one of the hallmarks of aging and is an important risk factor for dementia. Given the rapid rise in the aging population and the increased prevalence of Alzheimer's disease (AD), understanding the neural basis of age-related memory decline is of the utmost importance. The formation of memories is known to depend critically on brain regions within the medial temporal lobes (MTL). Prior aging research has focused on age-related changes in the hippocampus, but changes in extrahippocampal MTL cortices have garnered less attention. These cortices appear to be functionally segregated such that the perirhinal cortex (PRC) is primarily engaged by memory for items or objects, whereas the parahippocampal cortex (PHC) is engaged by memory for spatial configurations or contexts. Animal studies have further demonstrated that that this division of labor extends into the entorhinal cortex (EC), with the lateral portion (LEC) supporting object memory and the medial portion (MEC) supporting spatial memory. We designed a discrimination task taxing both object and spatial memory and used high-resolution functional MRI to not only replicate the dissociation between PRC and PHC, but also critically demonstrated key evidence of a similar object/spatial dissociation between LEC and MEC in humans. Related to these advancements, recent rodent models of neurocognitive aging have identified a selective vulnerability in the PRC/LEC pathway to pathology associated with cognitive decline. The LEC/PRC (transentorhinal) region is also the first to deposit tangle pathology in AD mouse models, which is also clear from postmortem tissue from AD patients (i.e. Braak Stage I). Building on our highly innovative approach to functionally segregate the human PRC/LEC and PHC/MEC networks, we propose a novel series of experiments to characterize the earliest behavioral deficits and functional aberrations in the PRC and LEC in older adults. Furthermore, we intend to probe for specific disruptions in structural connectivity between the hippocampal dentate (DG)/CA3 and upstream PRC/LEC, which project to the DG/CA3 via the lateral perforant path. We have previously reported perforant path degradation in older adults using cutting-edge ultrahigh- resolution diffusion imaging. Here, we will use novel techniques to segment the perforant path into medial and lateral portions and will test the hypothesis that this degradation is more severe in the lateral portion. The proposed project builds on the last five years of work from our lab, which successfully translates decades of animal and computational models to the human aging condition. We have identified aberrant conditions in the DG/CA3 associated with age-related memory loss using multimodal high-resolution MRI techniques. Our proposal here extends this work in an innovative direction both in terms of approach and hypothesis. This project is expected to significantly improve our understanding of the neurobiological bases of memory deficits in aging, and may yield highly selective neural targets for treatments and interventions.

Public Health Relevance

The population over 65 is projected to grow to 72.1 million by 2030. The risk for dementia increases dramatically with age, leading to serious public health challenges. Episodic memory loss in older adults confers additional risk for Alzheimer's disease (AD) and is one of the earliest reported manifestations of the disease. The goals of this project are aimed at comprehensively advancing our understanding of the neural basis of episodic memory decline in older adults, and developing early mechanistic biomarkers for age-related memory decline such that the diagnosis of age-related pathological conditions and early interventions are more viable and maximally effective.

Agency
National Institute of Health (NIH)
Institute
National Institute on Aging (NIA)
Type
Exploratory/Developmental Grants (R21)
Project #
5R21AG049220-02
Application #
9143635
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Wagster, Molly V
Project Start
2015-09-15
Project End
2017-05-31
Budget Start
2016-06-01
Budget End
2017-05-31
Support Year
2
Fiscal Year
2016
Total Cost
Indirect Cost
Name
University of California Irvine
Department
Other Basic Sciences
Type
Schools of Arts and Sciences
DUNS #
046705849
City
Irvine
State
CA
Country
United States
Zip Code
92617
Sinha, Neha; Reagh, Zachariah M; Tustison, Nicholas J et al. (2018) ABCA7 risk variant in healthy older African Americans is associated with a functionally isolated entorhinal cortex mediating deficient generalization of prior discrimination training. Hippocampus :
Suwabe, Kazuya; Byun, Kyeongho; Hyodo, Kazuki et al. (2018) Rapid stimulation of human dentate gyrus function with acute mild exercise. Proc Natl Acad Sci U S A 115:10487-10492
Stevenson, Rebecca F; Zheng, Jie; Mnatsakanyan, Lilit et al. (2018) Hippocampal CA1 gamma power predicts the precision of spatial memory judgments. Proc Natl Acad Sci U S A 115:10148-10153
Reagh, Zachariah M; Noche, Jessica A; Tustison, Nicholas J et al. (2018) Functional Imbalance of Anterolateral Entorhinal Cortex and Hippocampal Dentate/CA3 Underlies Age-Related Object Pattern Separation Deficits. Neuron 97:1187-1198.e4
Stark, Shauna M; Reagh, Zachariah M; Yassa, Michael A et al. (2018) What's in a context? Cautions, limitations, and potential paths forward. Neurosci Lett 680:77-87
Leal, Stephanie L; Noche, Jessica A; Murray, Elizabeth A et al. (2017) Age-related individual variability in memory performance is associated with amygdala-hippocampal circuit function and emotional pattern separation. Neurobiol Aging 49:9-19
Snigdha, Shikha; Yassa, Michael A; deRivera, Christina et al. (2017) Pattern separation and goal-directed behavior in the aged canine. Learn Mem 24:123-131
Suwabe, Kazuya; Hyodo, Kazuki; Byun, Kyeongho et al. (2017) Acute moderate exercise improves mnemonic discrimination in young adults. Hippocampus 27:229-234
Reagh, Zachariah M; Murray, Elizabeth A; Yassa, Michael A (2017) Repetition reveals ups and downs of hippocampal, thalamic, and neocortical engagement during mnemonic decisions. Hippocampus 27:169-183
Wisse, Laura E M; Daugherty, Ana M; Olsen, Rosanna K et al. (2017) A harmonized segmentation protocol for hippocampal and parahippocampal subregions: Why do we need one and what are the key goals? Hippocampus 27:3-11

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