Although attention deficit hyperactivity disorder (ADHD) and substance abuse have both been linked to more impulsive behavior, different brain networks are involved in ADHD and substance abuse in adolescents, reports a study in Nature Neuroscience.
Robert Whelan and his colleagues used fMRI to track brain activity in nearly 2,000 adolescents as they attempted to stop a movement in response to an unpredictable 'stop' signal. In general more impulsive people find this task harder, and drug users, as well as ADHD patients, take longer to respond to the 'stop' signal. The researchers found that the adolescents with ADHD symptoms and those who had used drugs or alcohol did the task equally well, but only the teenagers who used drugs or alcohol in early adolescence were more likely to have reduced activity centred around a brain area known as the orbitofrontal cortex. In contrast, activity in another brain area, the right inferior frontal cortex was modulated specifically by the use of illegal drugs, rather than tobacco and alcohol. The change in activity here correlated with how often illicit drugs were used, suggesting that this change may be caused by the repeated use of such drugs, rather than a pre-existing difference.
These results demonstrate how similar-seeming behaviour may actually reflect activity in quite different brain networks.