Description
Fetal alcohol spectrum disorder (FASD) affects 2-5% of the population and is associated with cognitive deficits in overall intellectual functioning and on indices of learning, memory, and attention. Individuals with prenatal alcohol exposure may demonstrate behavioral problems including hyperactivity and impulsivity and show neural abnormalities including reductions in overall and regional brain volumes, reduced white matter density, and increased gray matter density. White matter abnormalities throughout the brain have been recognized in children with prenatal exposure to alcohol. These structural abnormalities have been hypothesized to underlie many of the cognitive and behavioral deficits observed in this population. The purpose of the current study was to use diffusion tensor imaging (DTI) to examine white matter integrity in children with and without prenatal alcohol exposure. Participants included 47 children between the ages 10-16 years: children with heavy prenatal exposure to alcohol (AE = 25) and non-exposed children (CON = 22). Consistent with previous studies, prenatal alcohol exposure was associated with low fractional anisotropy (FA), high mean diffusivity (MD), and high radial diffusivity (RD), compared to non-exposed controls, in clusters in the frontal and parietal lobes, as well as the brainstem, fornix, external capsule, and cerebellum. More surprisingly, prenatal alcohol exposure was associated with clusters of high FA and low MD/RD in white matter tracts in all four lobes of the brain. To better understand these novel results, correlations between measures of white matter integrity and behavioral performance on measures of executive functioning (EF) using the Delis-Kaplan Executive Function System (D-KEFS) were assessed. In clusters in the frontal and parietal lobe, decreased FA and increased MD/RD in the AE group were associated with impaired performance on several EF measures. Within areas where the AE group showed more homogenous white matter than controls, clusters in the temporal and occipital indicated that high FA and/or low MD/RD in the AE group were negatively associated with verbal and non-verbal fluency, while clusters showing reduced MD/RD (but not high FA) in the AE group in frontal-striatal tracts were positively associated with EF performance across several domains. These results suggest that white matter abnormalities in individuals with prenatal alcohol exposure may be more complex than initially believed, and are characterized by areas of both increased and decreased anisotropy relative to unaffected controls. Consistent with previous reports, we identified several clusters in which the AE group showed less homogenous white matter that were associated with impaired neuropsychological performance. However, this study also found that the AE group demonstrated higher FA and lower MD/RD than the CON group in clusters throughout the brain. This novel finding may be explained by either decreased neural branching (associated with impaired executive functioning) or compensatory mechanisms for other damaged structures (associated with improved cognition) differentially throughout the brain in individuals with prenatal alcohol exposure.
