The Effects of Expectation on Natural and Drug -Induced Rewards

Objective: Environmental cues frequently induce expectancies in the course of normal daily life. When an individual smells and sees the coffee before tasting it, an expectancy of the coming experience is formed that influences the actual experience of consuming the coffee. Similarly, when an addicted individual experiences cues associated with imminent drug taking, an expectancy of the coming experience is also formed. This protocol will examine neural responses to cues predictive of a stimulus (neutral or rewarding) and to the subsequent receipt of the predicted stimulus. Study Population: Study participants will include 18-50 year old, male and non-pregnant female otherwise healthy cocaine dependent individuals and control individuals who have a history of some stimulant use but no history of abuse or dependence on any other drug other than nicotine. Design: The study will employ fMRI to elucidate the neural underpinnings of reward processing. The rewarding stimuli to be studied will be taste stimuli (small squirt of juice or chocolate) and a drug stimulus (intravenous methylphenidate (IV MPH)). For taste stimuli, cues will vary in sensory modality (visual vs. olfactory) and in novelty (well-known vs. novel). Novel and well-known cue stimuli will be included on each experimental day so the development of expectancy can be studied as the cue-taste pairing is learned and compared to the well-known cue-taste pairing. The MPH/saline injections will receive a written cue. Outcome Measures: BOLD fMRI signal to reward stimuli will be compared in the various cuing conditions.