- Six testing visits will involve fMRI and EEG measurements of brain activity. Each visit will contain two 2-hour scanning sessions, and each session will involve thinking tests. During these visits, participants will receive varenicline and placebo tablets, and wear nicotine patches and placebo patches that do not contain nicotine. Participants will not be told which tablet or patch they are given. This is a crossover study so all participants eventually get nicotine and placebo, as well as varenicline and placebo.