- Nicotine addiction often makes it difficult to stop smoking. Researchers want to understand the areas of the brain that are important in nicotine addiction. They will use a type of brain stimulation called repetitive transcranial magnetic stimulation (rTMS) to look at part of the brain that may be involved in nicotine addiction. They will see how these areas affect brain function, thinking, and decision making. For this study, rTMS will first be tested on nonsmokers, then smokers will be recruited at a later time.