Cognitive Aging and the Hippocampus in Older Adults

Abstract

The hippocampus is one of the most well studied structures in the human brain. While age-related decline in hippocampal volume is well documented, most of our knowledge about hippocampal structure-function relationships was discovered in the context of neurological and neurodegenerative diseases. The relationship between cognitive aging and hippocampal structure in the absence of disease remains relatively understudied. Furthermore, the few studies that have investigated the role of the hippocampus in cognitive aging have produced contradictory results. To address these issues, we assessed 93 older adults from the general community (mean age = 71.9 ± 9.3 years) on the Montreal Cognitive Assessment (MoCA), a brief cognitive screening measure for dementia, and the NIH Toolbox-Cognitive Battery (NIHTB-CB), a computerized neurocognitive battery. High-resolution structural magnetic resonance imaging (MRI) was used to estimate hippocampal volume. Lower MoCA Total (p = 0.01) and NIHTB-CB Fluid Cognition (p < 0.001) scores were associated with decreased hippocampal volume, even while controlling for sex and years of education. Decreased hippocampal volume was significantly associated with decline in multiple NIHTB-CB subdomains, including episodic memory, working memory, processing speed and executive function. This study provides important insight into the multifaceted role of the hippocampus in cognitive aging.

Keywords: MoCA; NIH toolbox; cognitive aging; hippocampus; structural magnetic resonance imaging.

Figure 1

Hippocampal region of interest (ROI). (A) surface models of the left and right hippocampi ROIs displayed in red. The hippocampi are visualized inside a wireframe mesh provided by Madan (2015). (B) Sagittal view (x = 105), (C) coronal view (z = 110) and (D) axial view (y = 151) of the hippocampi displayed in red. Coordinates are in MNI305 space. A, Anterior; P, Posterior; I, Inferior; S, Superior.

Figure 2

(A) Plots the linear relationship between fluid cognition and hippocampal volume. (B) Plots the linear relationship between crystalized cognition and hippocampal volume. (C) Plots the linear relationship between Montreal Cognitive Assessment (MoCA) total score and hippocampal volume. Confidence bands are 95% confidence intervals of the regression line.

Figure 3

Shows the cognitive domains of the NIH toolbox and their relationship with hippocampal volume. Thick, solid lines represent significant (p < 0.05) effects. Dashed lines represent non-significant effects. The percentage represents the effect size (percent variance explained by the predictor variable).