 The study population will consist of adult 18-50 y.o. non-treatment seeking smokers and age and gender matched non-smoking control subjects. The control subjects will provide normative data on cognitive task performance and corresponding neural activation, as well as providing control for any time effects e.g. practice effect on repeated cognitive task performance. Smokers will smoke at least 10 cigarettes per day for a period of 1 year. Both smokers and controls will be suitable for fMRI scanning. Subjects may not be dependent on any other drug except nicotine or caffeine. 