@article {Cox051771, author = {Simon R. Cox and Stuart J. Ritchie and Elliot M. Tucker-Drob and David C. Liewald and Saskia P. Hagenaars and Gail Davies and Joanna M. Wardlaw and Catharine R Gale and Mark E. Bastin and Ian J. Deary}, title = {Age differences in brain white matter microstructure in UK Biobank (N = 3,513)}, elocation-id = {051771}, year = {2016}, doi = {10.1101/051771}, publisher = {Cold Spring Harbor Laboratory}, abstract = {Quantifying the microstructural properties of the human brain{\textquoteright}s connections is necessary for understanding normal ageing and disease states. We examined brain white matter MRI data in 3,513 generally healthy people aged 45-75 years from the UK Biobank sample. Using conventional water diffusion measures and newer, as-yet rarely-studied indices from neurite orientation dispersion and density imaging (NODDI), we document large age differences in white matter microstructure. Mean diffusivity was the most age-sensitive diffusion measure, with negative age associations strongest in the thalamic radiation and association fibres. Inter-individual differences in white matter microstructure across brain tracts become increasingly correlated in older age. This connectivity {\textquoteleft}de-differentiation{\textquoteright} may reflect an age-related aggregation of systemic detrimental effects on the brain. We report several other novel results, including comparative age associations with volumetric indices and associations with hemisphere and sex. Results from this unusually large, single-scanner sample provide one of the most definitive characterisations to date of age differences in major white matter tracts in the human brain.TractsARacoustic radiationATRanterior thalamic radiationCingGcingulum bundle; gyrusCingPHcingulum gyrus; parahippocampalCSTcorticospinal tractFMajforceps majorFMinforceps minorIFOFinferior fronto-occipital fasciculusILFinferior longitudinal fasciculusMCPmiddle cerebellar peduncleMLmedial lemniscusPTRposterior thalamic radiationSLFsuperior longitudinal fasciculusSTRsuperior thalamic radiationUncuncinate fasciculusMeasures of white matter microstructureFAfractional anisotropyICVFintracellular volume fractionISOVFisotropic volume fractionMDmean diffusivityNODDIneurite orientation dispersion and density imagingODorientation dispersion}, URL = {https://www.biorxiv.org/content/early/2016/05/04/051771}, eprint = {https://www.biorxiv.org/content/early/2016/05/04/051771.full.pdf}, journal = {bioRxiv} }