Fractional anisotropy of water diffusion in cerebral white matter across the lifespan

Abstract

Determining the time of peak of cerebral maturation is vital for our understanding of when cerebral maturation ceases and the cerebral degeneration in healthy aging begins. We carefully mapped changes in fractional anisotropy (FA) of water diffusion for eleven major cerebral white matter tracts in a large group (831) of healthy human subjects aged 11-90. FA is a neuroimaging index of micro-structural white matter integrity, sensitive to age-related changes in cerebral myelin levels, measured using diffusion tensor imaging. The average FA values of cerebral white matter (WM) reached peak at the age 32±6 years. FA measurements for all but one major cortical white matter tract (cortico-spinal) reached peaks between 23 and 39 years of age. The maturation rates, prior to age-of-peak were significantly correlated (r=0.74; p=.01) with the rates of decline, past age-of-peak. Regional analysis of corpus callosum (CC) showed that thinly-myelinated, densely packed fibers in the genu, that connect pre-frontal areas, maturated later and showed higher decline in aging than the more thickly myelinated motor and sensory areas in the body and splenium of CC. Our findings can be summarized as: associative, cerebral WM tracts that reach their peak FA values later in life also show progressively higher age-related decline than earlier maturing motor and sensory tracts. These findings carry multiple and diverse implications for both theoretical studies of the neurobiology of maturation and aging and for the clinical studies of neuropsychiatric disorders.

Genetic basis of neurocognitive decline and reduced white-matter integrity in normal human brain aging

“…We observed a substantial decrease in neurocognitive and DTI measures from young adulthood to old age, replicating several prior reports (6,37). Also, consistent with the literature, we found evidence for modest phenotypic correlations between neurocognitive and white-matter integrity, particularly for tests of speed of processing (27,38,39), working and declarative memory (12,13), and IQ (14,25).…”

Brain oscillatory complexity across the life span

“…The FA is a diffusion tensor imaging (DTI)-derived measure that is particularly useful as an estimate of the microstructure and specific organisation of myelinated axonal fibres, and may be considered an estimate of WM integrity (Basser & Pierpaoli, 1996). Using this measure, several authors (Hasan et al, 2007, Hasan et al, 2009Kochunov et al, 2012;McLaughlin et al, 2007) reported quadratic effects of age on FA values, with ages of peak between the third and fifth decades of life and a very slow decrease of FA values from these peaks to late senescence. Consequently, we can affirm that the quadratic relationship between age and oscillatory complexity shown by our results parallels the quadratic relationship between age and cortical WM.…”

Tryptophan Metabolism and White Matter Integrity in Schizophrenia

“…The sequence parameters were: TE/ TR = 87/8000 ms, FOV = 200 mm, axial slice orientation with 50 slices and no gaps, five b = 0 images, and 64 isotropically distributed diffusion-weighted directions with b = 700 s/ mm2. These parameters maximized the contrast to noise ratio for FA measurements (Kochunov et al, 2012). A tractbased spatial statistics (TBSS) method was used for tractbased analysis of diffusion anisotropy (Smith et al, 2006).…”