Table 2.

Fitting parameters and p values for age-related changes of FA and MD for all 10 white matter fibers

Fractional anisotropyMean diffusivity (mm2/s)
InterceptAge (×10−2)Age2 (×10−3)SexaIntercept (×10−3)Age (×10−5)Age2 (×10−6)Sex (×10−5)a
Commissural tracts
    Genu of corpus callosum0.52 <0.0010.51 <0.001−0.13 <0.001n.s.0.88 <0.001−0.87 <0.0010.18 <0.001
0.16 0.004
n.s.
    Body of corpus callosum0.48 <0.0010.60 <0.001−0.14 <0.001n.s.0.97 <0.001−0.97 <0.001n.s.
    Splenium of corpus callosum0.53 <0.0010.52 0.001−0.11 0.0130.013 0.0010.93 <0.001−1.36 <0.0010.31 <0.001n.s.
Projection tracts
    Corticospinal tractsb0.86 <0.001−0.20 <0.001n.s.1.2 0.007
    Left CSTb0.43 <0.0011.03 <0.001−0.24 <0.001−0.009 0.004
    Right CSTb0.46 <0.0010.60 <0.001−0.13 <0.001−0.011 0.001
Association tracts
    Cingulum0.43 <0.0010.54 <0.001−0.07 0.038−0.014 <0.0010.88 <0.001−0.94 <0.0010.17 <0.0010.89 0.021
    Inferior longitudinal fasciculus0.41 <0.0010.47 <0.001−0.01 0.001n.s.0.93 <0.001−0.79 <0.0010.16 <0.001n.s.
    Inferior fronto-occipital fasciculus0.45 <0.0010.68 <0.001−0.13 <0.001n.s.0.88 <0.001−0.68 <0.0010.15 <0.001n.s.
    Superior longitudinal fasciculus0.42 <0.0010.67 <0.001−0.14 <0.001−0.005 0.0270.85 <0.001−0.89 <0.0010.17 <0.001n.s.
    Superior fronto-occipital fasciculus0.41 <0.0010.53 <0.001−0.13 <0.001n.s.0.82 <0.001−0.62 <0.0010.11 0.0020.81 0.017
    Uncinate fasciculus0.37 <0.0010.44 <0.001−0.08 0.011−0.009 0.0020.90 <0.001−0.58 <0.0010.10 <0.001n.s.
  • CST, Corticospinal tract; n.s., not significant.

  • aPositive values for sex term indicate higher FA or MD values in females.

  • bThe CST was assessed separately for each hemisphere for FA measures, where there were significant differences in the age and age2 parameters; for MD, there were no significant differences, so hemispheres were combined.