Individuals with attention-deficit/hyperactivity disorder (ADHD) are often treated with stimulants, which directly manipulate the levels of dopamine in the brain. Behaviorally, this treatment dynamically improves inhibitory control over time, reducing impulsive behavior, which is one of the hallmarks of ADHD. However, the extent of these dynamic modulations and their neural source is still unknown. We propose to perform a synergistic cross-species study in humans and in monkeys to study the temporal dynamics of ADHD treatment and its neural sources. In humans, we will apply novel behavioral techniques developed in the Nahum lab to characterize the dynamics of the behavioral effects of Methylphenidate (Ritalin) on inhibitory control in young adults with ADHD. Concurrently, we will use recently developed dopamine recording techniques in monkeys, uniquely used in the Joshua lab, to test whether and how the dynamics of dopamine after Methylphenidate administration follow the dynamics of the behavioral effects. By bridging the gap between animal and human, this study is expected to advance our understanding of the behavioral and neural dynamics of treatment effects for ADHD. If successful, our research, utilizing novel technologies, will provide important markers for optimizing future treatments of ADHD.