Allometric scaling of brain regions to intra-cranial volume: An epidemiological MRI study

Abstract

There is growing evidence that sub-structures of the brain scale allometrically to total brain size, that is, in a non-proportional and non-linear way. Here, scaling of different volumes of interest (VOI) to intra-cranial volume (ICV) was examined. It was assessed whether scaling was allometric or isometric and whether scaling coefficients significantly differed from each other. We also tested to what extent allometric scaling of VOI was introduced by the automated segmentation technique. Furthermore, reproducibility of allometric scaling was studied different age groups and study populations. Study samples included samples of cognitively healthy adults from the community-based Age Gene/Environment Susceptibility-Reykjavik Study (AGES-Reykjavik Study) (N = 3,883), the Coronary Artery Risk Development in Young Adults Study (CARDIA) (N =709), and the Alzheimer's Disease Neuroimaging Initiative (ADNI) (N = 180). Data encompassed participants with different age, ethnicity, risk factor profile, and ICV and VOI obtained with different automated MRI segmentation techniques. Our analysis showed that (1) allometric scaling is a trait of all parts of the brain, (2) scaling of neo-cortical white matter, neo-cortical gray matter, and deep gray matter structures including the cerebellum are significantly different from each other, and (3) allometric scaling of brain structures cannot solely be explained by age-associated atrophy, sex, ethnicity, or a systematic bias from study-specific segmentation algorithm, but appears to be a true feature of brain geometry. Hum Brain Mapp 38:151-164, 2017. © 2016 Wiley Periodicals, Inc.

Keywords: ADNI; AGES-Reykjavik; CARDIA; MRI; allometry; brain; cortex; intra-cranial volume; striatum; thalamus; white matter.

Figure 1

Allometric coefficients of VOI with ICV. Gray line, isometry line; Red line, line of allometric log–log model between ICV and VOI.

Figure 2

Accuracy of automated segmentation pipeline; scaling of artificially linearly scaled data.

Figure 3

Comparison of allometric log‐log model to linear model of VOI to ICV. Red line, line of the allometric log–log model between the ICV and the VOI; Blue line, line of the linear model between the ICV and the VOI.