Some parts of the brain may be able to recover when adults stop drinking, but what happens to teenagers who begin drinking? White-matter circuits may be particularly vulnerable in them, because these fibers continue to develop during adolescence. Susan Tapert, a psychologist at the University of California in San Diego, is studying white-matter development in teenagers who use alcohol and marijuana. “Because white matter is so clearly affected in adult alcoholics, we wonder when in the course of heavy drinking these problems develop,” says Tapert. “And because there is so much white-matter growth during adolescence, we want to know what happens if you damage those fibers early on.”
Previous studies using structural MRI show hints of white matter abnormalities in alcoholic teenagers. Now Tapert will use DTI to better characterize these changes, and to see how the defects are linked to cognitive problems in teenagers who drink. Preliminary results suggest that wiring defects relate to poorer performance on many kinds of tests, such as verbal skills, planning, and organization. “The differences are relatively subtle – it would probably translate to the difference between an A and B in school performance,” says Tapert. “But that is still enough to impact the outcome.”
Alcohol can also affect white matter very early in development: when a baby is still in the womb. For example, in rare cases, children with fetal alcohol syndrome are missing a corpus callosum. Other children exposed to prenatal alcohol have more subtle problems with their white matter. Claire Coles, a psychiatrist at Emory University in Atlanta, GA, has followed a population of children with fetal alcohol exposure since birth. Coles and colleagues found that these people, now in their early twenties, have significant differences in their corpus callosa compared with controls. The white-matter defects correlate with a slower speed of processing, as well as overall IQ, she says.
Edward Riley, at psychologist at UC San Diego who’s starting up similar studies, says the research could help doctors to distinguish children who have learning disabilities linked to prenatal alcohol exposure from those who have learning disabilities from other causes.
“In mental health disorders such as alcoholism, we are not very sophisticated in terms of figuring out what is wrong with a particular person and how to help them,” says David Oslin, a psychiatrist at the University of Pennsylvania in Philadelphia. “Tools that help us understand subpopulations of patients and their neurophysiology are potentially very helpful. DTI may be a good way of determining that.”
Images on home page are DTI images of a brain with fetal alcohol syndrome. Colors in righthand image indicate the direction of fiber tracts in the brain. (Images courtesy of Xiaoping Hu, Department of Biomedical Engineering, Emory School of Medicine, Atlanta GA.)