Brain structure changes over time in normal and mildly impaired aged persons.

Charles D Smith,Anders H Andersen,R Ronan Murphy,Frederick A Schmitt,Erin L Abner,Richard J Kryscio,Linda J Van Eldik,Gregory A Jicha,Peter T Nelson

doi:10.3934/neuroscience.2020009

Abstract

Structural brain changes in aging are known to occur even in the absence of dementia, but the magnitudes and regions involved vary between studies. To further characterize these changes, we analyzed paired MRI images acquired with identical protocols and scanner over a median 5.8-year interval. The normal study group comprised 78 elders (25M 53F, baseline age range 70–78 years) who underwent an annual standardized expert assessment of cognition and health and who maintained normal cognition for the duration of the study. We found a longitudinal grey matter (GM) loss rate of 2.56 ± 0.07 ml/year (0.20 ± 0.04%/year) and a cerebrospinal fluid (CSF) expansion rate of 2.97 ± 0.07 ml/year (0.22 ± 0.04%/year). Hippocampal volume loss rate was higher than the GM and CSF global rates, 0.0114 ± 0.0004 ml/year (0.49 ± 0.04%/year). Regions of greatest GM loss were posterior inferior frontal lobe, medial parietal lobe and dorsal cerebellum. Rates of GM loss and CSF expansion were on the low end of the range of other published values, perhaps due to the relatively good health of the elder volunteers in this study. An additional smaller group of 6 subjects diagnosed with MCI at baseline were followed as well, and comparisons were made with the normal group in terms of both global and regional GM loss and CSF expansion rates. An increased rate of GM loss was found in the hippocampus bilaterally for the MCI group.

Highlights

Knowledge of brain structure is an important foundation for understanding and interpreting changes in functional capacity as people age, and for gauging the effects of age-related diseases
The MCI group was older than the normal group, and had evidence of mild global cognitive change and a moderate deficit in delayed verbal memory
Participants underwent imaging with the identical protocol and magnetic resonance imaging (MRI) scanner at both time points, overcoming potential technical difficulties in longitudinal quantitative image analysis due to acquisition and scanner differences [43]

Summary

Introduction

Knowledge of brain structure is an important foundation for understanding and interpreting changes in functional capacity as people age, and for gauging the effects of age-related diseases. Disentangling chronologic structural brain aging effects from those due to common age-associated disease such as Alzheimer’s disease (AD) and microvascular brain injury remains a challenge [1] Despite this challenge, the results of prior structural imaging studies suggest that there is an age related reduction in grey matter (GM) volume and increased ventricular volume even in the absence of significant underlying disease diagnosed at autopsy [2,3,4,5]. We characterized longitudinal rates of global and regional cortical GM volume and cerebrospinal fluid (CSF) volume change in a well-characterized cohort of cognitively normal aged adults undergoing a standardized magnetic resonance imaging (MRI) protocol performed twice over an approximately six year interval. A smaller group of subjects diagnosed with MCI at intake were followed as well for comparison

Results

Discussion

Conclusion