Chronic use of alcohol and marijuana during youth has been associated with poorer neural and cognitive function, which appears to continue into adulthood. A new study looking specifically at white-matter changes provides more support for the idea that adolescent brains may be at particular risk from the damage that substance abuse can bring.
The brain-imaging study compared 41 adolescents (aged 16-20) with extensive marijuana- and alcohol-use histories by mid-adolescence with 51 adolescents with no such history. The study found that substance users showed poorer white matter integrity in seven tracts (right and left superior longitudinal fasciculus, right posterior thalamic radiations, right prefrontal thalamic fibers, right superior temporal gyrus white matter, right inferior longitudinal fasciculus, left posterior corona radiata).
Two brain scans were taken, at baseline and at 18 months. Substance use interviews were given every six months.
More alcohol use during the interval was associated with worse integrity in both the right and left superior longitudinal fasciculi, above and beyond baseline values in these bundles. Marijuana use didn’t predict change over time. Those who had a history of more risk-taking behaviors showed poorer integrity of the right prefrontal thalamic fibers.
The findings add to previous research showing white matter problems in youth with substance-use histories. The study points to alcohol use during adolescence being particularly problematic. It also suggests that youth who engage in risk-taking behaviors may tend to have poorly developed fronto-thalamic tracts.
All of this is particularly worrying because it is thought that maturation of the brain during adolescence is the foundation for self-control, suggesting that substance abuse during this period may have long-lasting effects on the individual’s ability to plan, organize, and self-regulate.
 . Longitudinal Changes in White Matter Integrity Among Adolescent Substance Users. Alcoholism: Clinical and Experimental Research [Internet]. 2012 :n/a - n/a. Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1530-0277.2012.01920.x/abstract