ABSTRACT
Dopaminergic neurotransmission in the central nervous system has long been implicated in motor function, sensory-motor integration, and behavioral reinforcement (1-4). With regard to reinforcement, experiments performed in 1954 by Olds and Milner (1) revealed that the brain has specialized regions that reinforce behavioral output when stimulated electrically. High rates of self-controlled electrical stimulation were maintained when electrodes were placed in dopamine-rich brain regions, and these selfstimulation points were found to overlap with the distribution of dopaminergic neurons in the ventral tegmental area (VTA) and substantia nigra (SN) and closely follow anterior dopaminergic projections to the forebrain (5, 6). These findings led to the characterization of dopamine (DA) as a “motivational” neurotransmitter and fueled an enormous amount of research on the neurobiology of motivation and reward. More recently, evidence has been provided that DA also participates in higher order processes such as associative learning, temporal processing, and cognition (for review, see 7-9). In this chapter we will review evidence that the dopaminergic system is activated by external stimuli, both rewarding and aversive, and that this activation contributes to the processes of incentive-motivational learning (associate learning) and cognition.
