The purpose of the study is to determine whether the presentation of various foods produces an increase or decrease in responses on a motivational computer task. In addition, the study determines if energy intake or motivation to obtain food is related to the dopamine receptor genotype.

One of the most important research areas in obesity is developing a better understanding of individual differences in factors that influence excess energy intake and positive energy balance. One key to understanding these individual differences is determining what factors underlie the motivation to eat. We have demonstrated in a series of studies that obese adults and children are more motivated to work for palatable, favorite foods than leaner peers and that those high in food reinforcement consume more food in an ad libitum eating task than those who do not find food as reinforcing. Dopamine (DA) is one of the major neurotransmitters involved in establishing the reinforcing value of food, and low levels of dopamine activity and a reduction in the number of DA receptors is associated with obesity. The general aim of the proposed research is to build upon this research to examine relationships between food reinforcement, obesity, and polymorphisms of genes within the dopaminergic system.

Inclusion Criteria:

• Non-smokers
• 18-50 years of age
• No known eating disorder
• Moderate liking for study foods
• No current diagnosis of psychiatric disorder (e.g., anxiety or depression)
• Not on medications that would interfere with appetite (e.g., methylphenidate) or dopaminergic activity
• Non-diabetics

Exclusion Criteria:

• Smoker
• Pregnant women
• Current diagnosis of a psychiatric or eating disorder
• Dietary restrictions that would interfere with participation
• On medications that could interfere with appetite or olfactory responsiveness or use of antidepressants or any medication or dietary supplement that could affect appetite or dopaminergic activity
• Excessive use of alcohol (>21 drinks/week), alcoholism,current addiction to opiates, cocaine or stimulants

Subjects will be recruited from newspaper ads, posters on campus and in community settings, web based recruitment (ads on Craig's list and on the department's website) and direct mail targeted to community residents between 18-50 years of age.