Control of Cognition (Naltrexone, Methylphenidate, and ADHD Study (NMAS))

The goal of this research is to understand the functioning of 'regulatory circuits' in the brain. We are also interested in how the medications methylphenidate and naltrexone affect these regulatory circuits. This research study will use a scanning technique known as functional magnetic resonance imaging (fMRI) which takes a special kind of picture of the brain that enables us to "see the brain at work". Adult participants will be given a one-time dose of either methylphenidate, naltrexone,or placebo before each fMRI scan session.

The main purpose for this research is to better understand the functioning of regulatory circuits in healthy individuals and individuals with psychiatric disorders. This research may one day help us develop better treatments for these disorders.

The goal of this research is to understand the functioning of 'regulatory circuits' in the brain. These are brain circuits which allow a person to regulate their attention, regulate their behavioral responses, and regulate their decision-making. We are also interested in how the medications methylphenidate and naltrexone affect these regulatory circuits. Methylphenidate is a widely-used, FDA approved medication used to treat Attention Deficit Hyperactivity Disorder (ADHD) and is also known as Ritalin. Naltrexone is an FDA approved medication used to help treat alcohol and substance abuse.

This research study will use a scanning technique known as functional magnetic resonance imaging (fMRI)which takes a special kind of picture of the brain that enables us to "see the brain at work". Adult participants will be given a one-time dose of either methylphenidate, naltrexone,or placebo before each fMRI scan session. There are three total fMRI scan sessions. Therefore, each participant will receive each possible medication/placebo only once.

Using the fMRI technique, the main purpose of this research is to better understand the functioning of regulatory circuits in healthy individuals and individuals with psychiatric disorders. This research may one day help us develop better treatments for these disorders.

Eligibility Criteria:
Inclusion Criteria for all study participants:

* Right-Handedness

Exclusion Criteria for all study participants:

* Any clinically significant history of cardiac problems
* Any current Axis I psychiatric diagnosis as verified by the Structured Clinical Interview for DSM-IV (other than participants with ADHD or history of alcohol dependence)
* A previous adequate trial with methylphenidate (Ritalin) or naltrexone (ReVia)
* Currently taking any psychoactive medications
* Any clinically significant medical condition
* Any clinically significant neurological problem (seizures, tics, serious head injury)
* Contraindications to MRI (metal objects in body or claustrophobia)
* Currently pregnant or lactating
* Alcohol or substance abuse (current or in the past 2 years)
* Left-handedness or ambidextrous
* Liver or kidney disease

Inclusion Criteria for the participants with ADHD:

* Currently un-medicated adults with ADHD
* Has met full DSM-IV-R criteria (at least six of nine symptoms)for inattentive or hyperactive/impulsive subtypes (or both) by age 7 as well within the past month
* Has described a chronic course of ADHD symptomatology from childhood to adulthood
* Has endorsed a moderate or severe level of impairment attributed to the ADHD symptoms