A, ATNAT showing delayed active muscle tone and total scores in methamphetamine/tobacco-exposed infants compared with the other groups. B, Fiber tracts in bilateral superior corona radiata from a 1-month-old infant are shown in the axial and coronal views. C, Fractional anisotropy (FA) increases with age while diffusivities decrease with age in all groups. However, the developmental trajectory in the FA of methamphetamine/tobacco-exposed boys showed a slightly steeper trajectory than the other 2 groups at an earlier age but normalized at later postmenstrual age (PMA), with no group differences in the age-dependent changes among the female infants. Similarly, diffusivities in both the axial and radial directions, and hence mean diffusivity values, were also higher at baseline in the methamphetamine/tobacco-exposed boys compared with the other 2 groups of boys, but no group differences in diffusivities were observed in either direction in the girls. L indicates left; R, right.