relative to the other two exposure groups and included the genu of CC, left frontal WM, right superior longitudinal fasciculus, and the anterior limb of the right IC. Direct comparison of adolescent smokers with no PEMCS to prenatally exposed non-smokers revealed significantly higher FA in anterior limb of right IC in the former group. Significant increase in regional white matter FA, primarily in anterior cortical and subcortical areas, was observed following exposure to smoking during the prenatal period alone, the adolescent period alone, and during both developmental epochs. However, increases in FA were more pronounced in adolescent smokers irrespective of PEMCS. This pattern suggests that WM maturation, while potentially affected by PEMCS, is particularly vulnerable to the disruptive effects of nicotine during adolescent development. The IC contains corticospinal, corticopontine, corticothalamic and the corticofugal fibers. FA of the posterior limb of the left IC correlated well with reaction time during an auditory attention task performance in smokers. However, FA did not correlate with tests of motor efficacy, hinting at the specificity of nicotine effects on the development of thalamocortical and corticofugal fibers, modulating ascending auditory signals, thereby reducing the efficiency of this circuitry. The corticospinal and corticopontine fibers, on the other
