Neuroanatomical Norms in the UK Biobank: The Impact of Allometric Scaling, Sex, and Age.

Few neuroimaging studies are sufficiently large to adequately describe population-wide variations. This studys primary aim was to generate neuroanatomical norms and individual markers that consider age, sex, and brain size, from 629 cerebral measures in the UK Biobank (N = 40 028). The secondary aim was to examine the effects and interactions of sex, age, and brain allometry - the non-linear scaling relationship between a region and brain size (e.g., Total Brain Volume) across cerebral measures. Allometry was a common property of brain volumes, thicknesses, and surface areas (83%) and was largely stable across age and sex. Sex differences occurred in 67% of cerebral measures (median |{beta}|= 0.13): 37% of regions were larger in males and 30% in females. Brain measures (49%) generally decreased with age, although aging effects varied across regions and sexes. While models with an allometric or linear covariate adjustment for brain size yielded similar significant effects, omitting brain allometry influenced reported sex differences in variance. This large scale-study advances our understanding of age, sex, and brain allometrys impact on brain structure and provides data for future UK Biobank studies to identify the cerebral regions that covary with specific phenotypes, independently of sex, age, and brain size. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=77 SRC="FIGDIR/small/422684v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@405c3borg.highwire.dtl.DTLVardef@1673e3corg.highwire.dtl.DTLVardef@126fee4org.highwire.dtl.DTLVardef@128545b_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIWe created neuroanatomical norms and individual markers for the UK Biobank (N=40 028) C_LIO_LIAllometry was common across 83% of brain volumes, thicknesses, and surface areas C_LIO_LI67% of regions differed between sexes: 37% were larger in males and 30% in females C_LIO_LIOmitting brain allometry influenced reported sex differences in variance C_LIO_LI49% of regions declined with age, with variations across regions and sexes C_LI