Contributions of Hippocampal Volume to Cognition in Healthy Older Adults.

Cheshire Hardcastle,Georg A Hishaw,Steven Dekosky,Pradyumna K Bharadwaj,Alejandro Albizu,Emily J Van Etten,Nicole D Evangelista,Hanna K Hausman,Andrew O’Shea,Ronald Cohen,Eric C Porges,Adam J Woods,Michael Marsiske,Samuel S Wu,Samantha G Smith,Gene E Alexander,Jessica N Kraft,Hyun Song,Emanuel M Boutzoukas

doi:10.3389/fnagi.2020.593833

Abstract

Objective: The association between hippocampal volume and memory is continuing to be characterized in healthy older adults. Prior research suggests smaller hippocampal volume in healthy older adults is associated with poorer episodic memory and processing speed, as well as working memory, verbal learning, and executive functioning as measured by the NIH Toolbox Fluid (Fluid Cognition Composite, FCC) and Crystalized Cognition Composites (CCC). This study aimed to replicate these findings and to evaluate the association between: (1) hippocampal asymmetry index and cognition; and (2) independent contributions of the left and right hippocampal volume and cognition in a large sample of healthy older adults.Participants and Methods: One-hundred and eighty-three healthy older adults (M age = 71.72, SD = 5.3) received a T1-weighted sequence on a 3T scanner. Hippocampal subfields were extracted using FreeSurfer 6.0 and combined to provide left, right, and total hippocampal volumes. FCC subtests include Dimensional Change Card Sort, Flanker Inhibitory Control and Attention, List Sorting, Picture Sequence Memory, and Pattern Comparison. CCC subtests include Picture Vocabulary and Oral Reading Recognition. Multiple linear regressions were performed predicting cognition composites from the total, left and right, and asymmetry of hippocampal volume, controlling for sex, education, scanner, and total intracranial volume. Multiple comparisons in primary analyses were corrected using a false discovery rate (FDR) of p < 0.05.Results: FCC scores were positively associated with total (β = 0.226, FDR q = 0.044) and left (β = 0.257, FDR q = 0.024) hippocampal volume. Within FCC, Picture Sequence Memory scores positively associated with total (β = 0.284, p = 0.001) and left (β = 0.98, p = 0.001) hippocampal volume. List Sorting scores were also positively associated with left hippocampal volume (β = 0.189, p = 0.029).Conclusions: These results confirm previous research suggesting that bilateral hippocampal volume is associated with FCC, namely episodic memory. The present study also suggests the left hippocampal volume may be more broadly associated with both episodic and working memory. Studies should continue to investigate lateralized hippocampal contributions to aging processes to better identify predictors of cognitive decline.

Highlights

The hippocampus is a bilateral medial temporal lobe structure known for its important role in episodic learning and memory function, or the ability to remember ongoing experiences (Vargha-Khadem et al, 1997; Tulving and Markowitsch, 1998)
Participants were excluded for left-handedness, if they were outside the age range of 65–89, had a history of brain or head injury that resulted in a loss of consciousness for greater than 20 min, identified a pre-existing neurological condition, psychiatric disorder, MRI contraindications, diagnosis of neurodegenerative brain disease (i.e., AD, Parkinson’s disease, amyotrophic lateral sclerosis), or self-reported difficulties in thinking and/or memory
At the in-person screening visit, participants were further screened for MCI through the use of the Unified Data Set (UDS) of the National Alzheimer’s Coordinating Center (NACC; Weintraub et al, 2009) and administration of the Montreal Cognitive Assessment (MoCA)

Summary

Introduction

The hippocampus is a bilateral medial temporal lobe structure known for its important role in episodic learning and memory function, or the ability to remember ongoing experiences (Vargha-Khadem et al, 1997; Tulving and Markowitsch, 1998). Hippocampal volume has been associated with domains of cognition such as processing speed, working memory, spatial navigation, and abstract reasoning (Reuben et al, 2011; Lövdén et al, 2012; O’Shea et al, 2016; Gorbach et al, 2017). These cognitive domains are vulnerable to a decline in non-pathological aging (Salthouse, 2009), and have been further studied in the context of hippocampal volume reduction in cognitive aging. Findings from this study were consistent with prior research supporting a clear role of the hippocampus in episodic memory and suggest hippocampal volume may play a broader role in cognitive aging other than memory, such as processing speed

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Discussion

Conclusion