Longitudinal changes in cortical thickness associated with normal aging

Abstract

Imaging studies of anatomic changes in regional gray matter volumes and cortical thickness have documented age effects in many brain regions, but the majority of such studies have been cross-sectional investigations of individuals studied at a single point in time. In this study, using serial imaging assessments of participants in the Baltimore Longitudinal Study of Aging (BLSA), we investigate longitudinal changes in cortical thickness during aging in a cohort of 66 older adults (mean age 68.78; sd. 6.6; range 60-84 at baseline) without dementia. We used the Cortical Reconstruction Using Implicit Surface Evolution CRUISE suite of algorithms to automatically generate a reconstruction of the cortical surface and identified twenty gyral based regions of interest per hemisphere. Using mixed effects regression, we investigated longitudinal changes in these regions over a mean follow-up interval of 8 years. The main finding in this study is that age-related decline in cortical thickness is widespread, but shows an anterior-posterior gradient with frontal and parietal regions, in general, exhibiting greater rates of decline than temporal and occipital. There were fewer regions in the right hemisphere showing statistically significant age-associated longitudinal decreases in mean cortical thickness. Males showed greater rates of decline in the middle frontal, inferior parietal, parahippocampal, postcentral, and superior temporal gyri in the left hemisphere, right precuneus and bilaterally in the superior parietal and cingulate regions. Significant nonlinear changes over time were observed in the postcentral, precentral, and orbitofrontal gyri on the left and inferior parietal, cingulate, and orbitofrontal gyri on the right.

Figure 1

(a) Cut-away of MR image of a whole head showing the inner (white outline) and outer (pink outline) cortical surface reconstructions. (b) Inner cortical surface. (c) Outer cortical surface. (d) Gyral regions over which thickness data is pooled.

Figure 2

Two views showing automatically generated gyral regions of interest. Some regions are labeled for reference.

Figure 3

Reliability map displayed on various views of an outer surface.

Figure 4

A dot plot showing median thickness changes by cortical region. The black dots are the estimated sex-adjusted rates of change and the black lines represent the 95% confidence intervals. If the 95% confidence interval crosses the zero line, then the slopes are not statistically significant. For regions that also show a sex difference, red and blue points are also printed, where red and blue are the estimated slopes for females and males, respectively. Units are mm/decade. Asterisks indicate regions showing significant nonlinear changes.

Figure 5

A typical outer cortical surface with the mean thickness trends for the entire population used to color the entire corresponding gyral region. The color scale is in mm/decade.