Yvain wrote:

Only now neuroscientists are starting to recognize a difference between "reward" and "pleasure", or call it "wanting" and "liking"... A University of Michigan study analyzed the brains of rats eating a favorite food. They found separate circuits for "wanting" and "liking", and were able to knock out either circuit without affecting the other (it was actually kind of cute - they measured the number of times the rats licked their lips as a proxy for "liking", though of course they had a highly technical rationale behind it). When they knocked out the "liking" system, the rats would eat exactly as much of the food without making any of the satisifed lip-licking expression, and areas of the brain thought to be correlated with pleasure wouldn't show up in the MRI. Knock out "wanting", and the rats seem to enjoy the food as much when they get it but not be especially motivated to seek it out.