Monotonic non-linear transformations as a tool to investigate age-related effects on brain white matter integrity: A Box-Cox investigation.
Non-linear effects of age on white matter integrity are ubiquitous in the brain and indicate that these effects are more pronounced in certain brain regions at specific ages. Box-Cox analysis is a technique to increase the log-likelihood of linear relationships between variables by means of monotonic non-linear transformations. Here we employ Box-Cox transformations to flexibly and parsimoniously determine the degree of non-linearity of age-related effects on white matter integrity by means of model comparisons using a voxel-wise approach. Analysis of white matter integrity in a sample of adults between 20 and 89years of age (n=88) revealed that considerable portions of the white matter in the corpus callosum, cerebellum, pallidum, brainstem, superior occipito-frontal fascicle and optic radiation show non-linear effects of age. Global analyses revealed an increase in the average non-linearity from fractional anisotropy to radial diffusivity, axial diffusivity, and mean diffusivity. These results suggest that Box-Cox transformations are a useful and flexible tool to investigate more complex non-linear effects of age on white matter integrity and extend the functionality of the Box-Cox analysis in neuroimaging.
Department of Psychology, Karl-Franzens-University of Graz, Graz, Austria.
Maria
M
Morozova
Department of Psychology, Karl-Franzens-University of Graz, Graz, Austria; Biotechmed, Graz, Austria.
Karl
K
Koschutnig
Knowledge Media Research Center Tuebingen, Tuebingen, Germany.
Elise
E
Klein
Department of Psychology, Karl-Franzens-University of Graz, Graz, Austria; Biotechmed, Graz, Austria. Electronic address: guilherme.wood@uni-graz.at.
Guilherme
G
Wood
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000473:pathology*; D001921:Brain / Q000473:pathology*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D059906:Neuroimaging / Q000379:methods; D066127:White Matter / Q000473:pathology*; D055815:Young Adult