 GSK618334 strongly binds to dopamine type 3 receptors in the human brain and is being developed as an innovative treatment for substance dependence. This study will evaluate the safety, tolerability, blood concentrations and effect following repeated oral doses of GSK618334 in healthy male and female volunteers. The effect of food on a single oral dose of GSK618334 will also be evaluated. Another portion of this study will investigate dopamine type 3 receptor binding in the human brain by PET scan before and after repeated doses of GSK618334. 