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PROBLEM: If I were to list everything that causes brains to release dopamine -- the neurotransmitter that tells us we like doing something and should do it again -- we'd be here all day. So, here are all the things that cause brains to release dopamine: ... kidding! But alcohol, sex, love, exercise, sunshine, and methamphetamines are among them. How, when, and how much dopamine our brains release are integral to both happiness and addiction.

METHODOLOGY: Researchers led by Dr. David Kareken an Indiana University scanned the brains of 49 men, taking pictures with positron emission tomography while the subjects drank just a sip (15 milliliters) of Gatorade, and one scan while drinking the same amount of beer. Some of the men were social drinkers; some were heavy drinkers. None were non-drinkers. Some had a family history of alcoholism; some did not.

Importantly, the scans took place before the alcohol would have time to get into their bloodstreams.

RESULTS: The brains of the men who tasted the beer released more dopamine from the ventral striatum than the men who drank the Gatorade. The men with a family history of alcoholism released more dopamine than the men without. The amount of dopamine released correlated directly with the man's genetic risk for alcoholism.