Rewards wanted: Molecular mechanisms of motivation

Extract: Brain dopamine was first recognized as a neurotransmitter when it was found to be concentrated in a small group of cells that degenerate in Parkinson's disease. Since Parkinson's disease results in tremor, rigidity, and an inability to initiate voluntary movement, and since the cells are localized in the basal ganglia, a region with the primary motor mechanism of the sub-mammalian brain, dopamine was initially identified with motor function. Recent studies indicate, however, that the basal ganglia is much more than simple motor structures. Brain dopamine is now known to play a major role in the ability of rewards to establish learned response habits and preferences. While its importance in reward has caused it to be identified primarily with motivational function, close inspection reveals that one of its primary roles in motivated behavior is a role in the stamping-in of learning and memory.