2 Clinical Trials for Various Conditions
While deficits in dopamine D2-type receptor availability have been linked to substance use disorders, higher availability associates with better behavioral treatment outcomes for stimulant dependence and resilience to addiction. Varenicline has been shown to upregulate D2-type receptors in drug-naive rats, and could be a useful therapeutic approach for the treatment of addictive disorders in humans. The purpose of the study is to assess the relationship between varenicline, dopamine signaling (specifically, D2-type receptor availability), functional connectivity within corticostriatal circuitry, genetic markers associated with smoking and methamphetamine abuse, and measures of cognitive performance. The investigators hypothesize that varenicline but not placebo will upregulate (increase) striatal dopamine D2-type receptor availability and improve cognition, and that the change in availability will correlate with the change in cognition. The investigators also hypothesize that varenicline but not placebo treatment will repair dysregulated connectivity between the striatum and prefrontal cortex observed in methamphetamine users, and will correlate with the change in cognition. The study design consists of two positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) scans to measure dopamine D2-type receptor availability and functional connectivity between the prefrontal cortex and striatum, two cognitive testing sessions including a battery of tests assessing working memory, declarative memory, sustained attention, inhibitory control, and reward-based decision making. Following eligibility screening, thirty six methamphetamine users will be enrolled and tested/scanned once prior to initiation of varenicline or placebo treatment and then again after completion of treatment.
This research study aims to determine whether and how caffeine intake affects learning process through reward feedback compared to placebo. The data acquired from this study would improve our understanding on the consequence and mechanism of caffeine intake in the aspect of learning process. Participants will perform a reinforcement learning task (i.e. Probabilistic Selection Task) and a motor inhibition task (i.e. Go/NoGo task) in a brain scan. The scan will be done with the Siemens Biograph mMR positron emission tomography (PET)/ magnetic resonance imaging (MRI) 3 Tesla scanner. The PET allows us to see the changes in the "reward signals" - dopamine - in the brain using a radioactive dye called \[11C\]Raclopride. The MRI, on the other hand, enables us to take detailed pictures of the brain activities during cognitive tasks using a high-powered magnet. Reviewing these pictures will help us understand the influence of caffeine on reward signals and brain activities during the learning process.