http://www.sciam.com/article.cfm?id=dopami...tivation-reward

'Researchers have for the first time found that the neurotransmitter dopamine is central to the human brain network governing motivation and a sense of reward and pleasure—and that it changes with age. The finding could provide clues to healthy, happy aging and pave the way to new treatments for neurological disorders, including Parkinson's disease and schizophrenia as well as addictive behaviors from alcoholism and drug abuse to compulsive gambling.

The U.S. National Institute of Mental Health (NIMH) team used two imaging methods, positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), to examine the normal human brain reward circuit, a complex neurochemical network that centers around a path from the ventral tegmental area in the midbrain (where dopamine is synthesized) to the nucleus accumbens in the forebrain (where it is released). Comparing brain activity in volunteers playing video slot machines, the researchers identified processes involved both in anticipating a reward and actually getting one—and discerned age-dependent changes in those processes.' [...]