Motivation implies activation of the organism by external or internal stimuli resulting in goal-directed behaviors. Loss of motivation constitutes the core symptom of apathy, a syndrome frequently found among patients with acute or chronic neurological conditions such as stroke, traumatic brain injury, and dementia. The mechanism of motivated behavior is based on neural structures that attach salience and valence to a given stimulus, and activate and direct an appropriate behavior in response to that stimulus. Dopamine (DA) is considered to play a central role in the mechanism of motivation and regulation of effort-related processes. The classical studies linking DA to motivation were based on stereotaxic injections of neurotoxin into the afferent projections of the mesolimbic and mesocortical pathways, which produced severe aphagia and adipsia. The nucleus accumbens seems to mediate the primary motivational characteristics of feeding and reproductive behavior as well as reward-motivated behaviors.