In the proposed study, the investigators will assess the brain response to medication probes the investigators have previously studied with SPECT. The brain response to ondansetron and lidocaine infusions will be measured Arterial Spin Labeling and functional connectivity MRI (fcMRI).

An extensive effort has been mounted to understand the neurobiologic mechanisms involved in the development and persistence of cocaine addiction and tendency to relapse. Although the last two decades have resulted in an explosion in our understanding of the biological mechanisms of reward, establishing the relevance of this knowledge to the addictive process has been problematic. Most importantly, this information has been of limited utility in offering new pharmacologic treatment approaches to addicted patients - particularly those with cocaine addiction. Over the past 15 years our laboratory has published multiple studies using pharmacologic probes to explore the biologic underpinnings of cocaine addiction using single photon emissions computerized tomography (SPECT) technology. More recently, however, functional magnetic resonance imaging (fMRI) has offered several advantages over SPECT and is now a favored approach, e.g. fMRI allows the continuous measurement of neural responses rather than a very limited time period with SPECT (1-3 minutes every 48 hours). Using fMRI [including both ASL (Arterial Spin Labeling) and fcMRI (functional connectivity], the neural response can be measured throughout the 60 min that follows infusion, allowing identification and capture of the maximal brain response period that may occur at any time during this 60 min. In the proposed study, we will assess the brain response to two of the probes (scopolamine and lidocaine) we have previously studied with SPECT.

Inclusion Criteria:

• Cocaine dependence (cocaine patients)
• identify cocaine as their present primary drug of use
• Patients must have used cocaine within the previous 4 weeks (by patient history) and be abstinent for at least 1 week.
• No drug dependence (healthy control population).

Exclusion Criteria:

• Other medical or psychiatric disorders that may effect neural functioning.
• Medications that may effect brain functioning

Subjects with cocaine addiction will be recruited from patients requesting treatment for addiction at the Dallas VA Medical Center and Homeward Bound,Inc. Recently using cocaine patients and healthy controls will be recruited from flyers and internet ads.