A Behavioral and Functional Neuroimaging Study of Inhibitory Motor Control

The inability to exert appropriate inhibitory control over one's behavior is an important symptom of many psychiatric illnesses. The stop signal paradigm, which involves withholding a prepotent motor response to a signal, has proved useful in assessing this deficit in children with a range of disorders, particularly attention deficit hyperactivity disorder (ADHD). In order to adapt the paradigm for use in fMRI studies, it is important to address two methodological issues: 1) the substitution of a visual stop signal for the more commonly-employed auditory stop signal, and 2) the fact that, on the traditional stop task (in which the subject withholds a motor response to the stop signal), correct trials do not involve a motor response whereas incorrect trials do. The latter problem can be addressed using the stop-change task (in which the subject executes alternative motor responses to the stop and go signals). The first aim of this protocol is to compare behavioral data from the stop and stop-change tasks in control adults, control children, and children with ADHD. These data will be used to test the hypotheses that, on each of these paradigms, children with ADHD will show an inhibitory deficit compared to control children, and control children will show an inhibitory deficit compared to control adults. The second aim of the protocol is to conduct a pilot fMRI study of the stop and stop-change tasks in control adults. The study has an event-related design and will test the hypotheses that ventral prefrontal activation will be greater during successful than unsuccessful stop (or stop-change) trials, and that stop and stop-change trials will be associated with more anterior cingulate and right inferior frontal activation than will go trials.