Stimulants used in the treatment of ADHD, according to the article, work more through activation of the vigilance and reward systems than direct improvement in the ability to concentrate. Brain scans have shown that these drugs increase activity in brain regions associated with vigilance and reward, which helps children maintain interest in tasks they would otherwise avoid. The drugs also reversed brain patterns that are associated with sleep deprivation. The article's authors caution that if ADHD symptoms are in fact the result of insufficient sleep, it can make diagnosing the disorder more difficult. The article does not give specific percentage statistics or effect sizes; it describes the main findings based on brain scans and the researchers' interpretation. Thus, the main finding of the study reported in the article is that stimulants may primarily "wake up" the brain and increase motivation for tasks instead of directly improving attention.