Role of Theta Frequency Oscillations in Proactive and Reactive Control Processes in Youth With Attention Deficit Hyperactivity Disorder (ADHD) and Obsessive Compulsive Disorder (OCD)

Background: Attention deficit hyperactivity disorder (ADHD) is common in children. It can cause problems with attention and the ability to control actions and impulses. Obsessive compulsive disorder (OCD) is less common in children but not rare. It involves ongoing thoughts, urges, impulses, and repeated behaviors. Researchers want to study differences in brain activity between healthy children, those with ADHD, and those with OCD. Objective: To learn more about how the brain controls thinking and behavior. Eligibility: People aged 10 to 17 years with ADHD, OCD, or neither. Design: Participants will have 3 to 10 clinic visits in up to 1 year. Each visit will last 2 to 3 hours. Three visits are required: Behavioral. Participants will complete a computer task. Their mood, memory, attention, and thinking skills will be tested. EEG. Participants will undergo electroencephalography (EEG) to measure signals in their brain. Small electrodes will be placed on the scalp. A cap will be stretched over the head. Signals will be recorded while participants rest or do tasks on a computer. MRI. Participants will have a magnetic resonance imaging scan (MRI). They will lie on a table that rolls into a tube. The MRI will take pictures of their brain while they do tasks on a computer. Seven more visits are optional. These include 2 more EEG visits and 2 more MRI visits. Three will be magnetoencephalography (MEG) visits: MEG measures small magnetic field changes in the brain. A helmet with sensors will be placed on the head. Brain changes will be recorded while participants rest or do tasks on a computer.

* INCLUSION CRITERIA: 1. Ability to provide informed assent and parent consent 2. Age: 10-17 years 3. ADHD Group: Diagnosis of ADHD based on DSM-5 criteria OCD Group: Diagnosis of OCD based on DSM-5 criteria HV Group: No Neurological or Psychiatric diagnosis based on DSM-5 criteria 4. Wechsler Abbreviated Scale of Intelligence, Second Edition (WASI-II). WASI-II will be used as a measure of intellectual function. Children will be included when FSIQ \> 70. 5. Normal or corrected to normal vision EXCLUSION CRITERIA: Participants will be screened to exclude participants in whom MRI or EEG might result in increased risk of side effects or complications or whose data would not be scientifically valid. 1. Non-English Speakers 2. Pregnancy 3. Any implant, prosthesis or alteration of the body that, in the opinion of the investigator, would be unsafe with MRI or EEG or that would produce an artifact that would compromise the integrity of data; 4. Active or History of psychosis, bipolar I disorder, Level 2 or 3 autism spectrum disorder, active severe substance use disorders (within the last month), have active suicidal intent or plan as detected on screening instruments; 5. Individuals currently taking stimulant medications who cannot tolerate being off their medication for up to 48 hours prior to the study visit and experience an exacerbation of symptoms that necessitates the resumption of medication prior to completion of the study visit. 6. Past or present medical or neurological condition, disease, disorder, genetic finding, or injury that, in the opinion of the Investigator, may significantly increase the potential risks of study participation, reduce or compromise a subject s ability to fully comply with all study requirements for the duration of the study or may compromise the integrity of the data. 7. For the HV group, any impairing current psychiatric diagnosis.