Aging, gender, and the elderly adult brain: An examination of analytical strategies

Abstract

We sought to examine the relations between age, gender and brain volumes in an elderly population; we also sought to examine ways of measuring these relations. Three sets of analyses were used: correlational analyses, in which correlations between independent variables and brain volumes were calculated without correction for intracranial volume (ICV); covariational analyses, in which ICV was used as a covariate in regression equations; and ratio analyses, in which the dependent variable was the ratio of brain volume to ICV. These analyses yielded similar results, except that (as expected) adjusting for ICV altered estimates of gender differences. Analyses of age showed decreases in left caudate, putamen, and right hippocampus and an increase in CSF, a result generally in accord with previous findings. However, we also found a significant decrease of white-matter volumes and no significant decrease in total gray-matter volumes. Correlational analyses showed that men did not always have larger volumes despite their larger head size; women generally had larger volumes after adjusting for ICV. We found no age-gender interactions.

Gradual Lesion Expansion and Brain Shrinkage Years After Stroke

“…10 The whole brain binary mask of each patient was applied to the biasfree T1w scan to generate a skull-stripped brain scan and its total size was used as an approximation of the total intracranial volume, 11 which is needed to adjust for individual differences in cranial/brain size in statistical analyses. 12,13 Across our 56 patients, total intracranial volume was 1493cm 3 on average (SD=148cm 3 ) at the first visit and 1477cm 3 on average (SD=128cm 3 ) at the last visit, which is comparable to previous literature. 14 These estimates at first and last visit were almost perfectly correlated (Pearson correlation r=0.98, see Supplementary Figure II-B), showing the robustness of the segmentation procedure when dealing with T1w scans with large lesions.…”

“…A Spearman partial rank correlation analysis was used to test for significant associations while controlling for many factors at the first visit including age, lesion volume, time post-stroke and total intracranial volume. We repeated the same partial correlation analysis after normalizing longitudinal changes in brain damage [in %] to the total intracranial volume 27 while controlling for age, lesion volume and time post-stroke (see discussion in 12,13 ). We derived accurate estimates of the median rate of lesion growth with time between repeated visits [cm 3 per year] using the longitudinal data available in the 13 patients who were scanned three or four times.…”

Preserved hippocampus activation in normal aging as revealed by fMRI

“…A majority of previous studies did not find any interaction between aging and gender in HC volume (Allen et al, 2005;Greenberg et al, 2008) neither when considering pathology (Bai et al, 2009). Nonetheless, little is known regarding an interaction between aging Coronal sections of an anatomical template brain on which are superimposed loci where activation in the young (A) and old groups (B) was significantly greater during VISUAL/VIS-UAL encoding (top-left) and retrieval (bottom-left) trials than control trials (FDR corrected threshold at P < 0.05).…”

When does brain aging accelerate? Dangers of quadratic fits in cross-sectional studies

“…Thus, estimation of age-decline after 60 years will ultimately depend on how early in the life-span sampling begins. Some aging studies sample from childhood (Courchesne et al, 2000;Sowell et al, 2007), some from young adulthood (Allen et al, 2005;Fjell et al, 2009;Raz et al, 2004;Walhovd et al, 2005), and some from middle-age or higher (Du et al, 2006;Greenberg et al, 2008;Van Petten, 2004). This variation may exert substantial effects on the observed age-trajectories, but has not been tested with real neuroanatomical data.…”