High resolution diffusion tensor imaging of the hippocampus across the healthy lifespan

Abstract

The human hippocampus is difficult to image given its small size, location, shape, and complex internal architecture. Structural magnetic resonance imaging (MRI) has shown age-related hippocampal volume changes that vary along the anteriorposterior axis. Diffusion tensor imaging (DTI) provides complementary measures related to microstructure, but there are few hippocampus DTI studies investigating change with age in healthy participants, and all have been limited by low spatial resolution. The current study uses high resolution 1 mm isotropic DTI of 153 healthy volunteers aged 5-74 years to investigate diffusion and volume trajectories of the hippocampus (whole, head, body, and tail) and correlations with memory. Hippocampal volume showed age-related changes that differed between head (peaking at midlife), body (no changes), and tail (decreasing across the age span). Fractional anisotropy (FA) and mean, axial, and radial diffusivities (MD, AD, RD) yielded peaks or minima, respectively, at ~30-35 years in all three subregions of the hippocampus.Greater magnitude changes were observed during development than in aging. Age trajectories for both volume and DTI were similar between males and females. Correlations between tests of memory and FA and/or volume were significant in younger subjects (5-17 years), but not in 18-49 year olds or 50-74 year olds. MD was significantly correlated with memory performance in 18-49 year olds, but not in other age groups. Given the diffusion-weighted image contrast and resolution, head digitations could be examined revealing that the majority of subjects had 3-4 (48%) or 2 (32%) bilaterally with no effect of age. One millimeter isotropic DTI yielded high quality diffusion-weighted maps of the human hippocampus that showed regionally specific age effects and cognitive correlations along the anterior-posterior axis from 5 to 74 years.

Hypothalamic microstructure and function are related to body mass, but not mental or cognitive abilities across the adult lifespan

“…Consistent with prior literature, we observed a decrease in ICVF and MTR, measures of structural integrity and myelin, and an increase of OD [38,39] and ISOVF in older age, which may be related to disorganization of white matter and inflammation, respectively [40,41]. In early adulthood (approximately until the age of 40), age was associated with increased neural integrity, suggested by a quadratic relationship, confirming a recent study by Solar et al [9]. For MTR and ICVF, we also found a tendency for an association between cognitive capabilities and hippocampal microstructure, which is in line with previous research [42].…”

High‐resolution diffusion tensor imaging identifies hippocampal volume loss without diffusion changes in individuals with prenatal alcohol exposure

“…However, large sample size studies of healthy development have suggested that hippocampal volumes increase with age during childhood (Fjell et al, 2019;Solar et al, 2021). In the current study, the lack of age effects for hippocampal volume may be due to the small sample size with substantial intersubject variability (e.g., Figure 4A, whole hippocampus volume for 9 year old controls ranges from ~1.4…”

“…The remaining five studies reported no significant effects of age on hippocampal volume in either group, with samples spanning childhood to early adulthood (Dudek et al, 2014; McLachlan et al, 2020; Nardelli et al, 2011; Treit et al, 2013, 2017). However, large sample size studies of healthy development have suggested that hippocampal volumes increase with age during childhood (Fjell et al, 2019; Solar et al, 2021). In the current study, the lack of age effects for hippocampal volume may be due to the small sample size with substantial intersubject variability (e.g., Figure 4A, whole hippocampus volume for 9 year old controls ranges from ~1.4 to 2.8 cm 3 ), as well as the limited age span.…”

“…The segmentation procedure and intra‐rater reliability (for author KGS) for segmentation of healthy controls are reported in a recent hippocampal DTI lifespan study (Solar et al, 2021). Inter‐rater reliability (authors KGS and ST; bilateral segmentations of 15 healthy controls) was assessed using the Dice similarity index yielding 86% voxel overlap between raters, and an intraclass correlation coefficient of 0.96 for volume.…”

White Matter Diffusion Properties in Chronic Temporomandibular Disorders: An Exploratory Analysis

“…We pooled scans for 33 healthy female control participants (mean age = 32; SD = 10; range = 20 to 61 years) from two studies. Nine of these controls were recruited from a similar study protocol as participants with TMDs (cohort A), while the data for the remaining 24 of the controls were obtained from a healthy aging study ( 47 ) (cohort B). The inclusion criteria from these studies were as follows: Cohort A Controls—All participants spoke English as their native or primary language, had either normal or corrected-to-normal vision, no contraindications to MRI testing, and age-appropriate scores on a non-verbal intelligence testing.…”