The role of dopamine in normal and abnormal behavior has been the subject of a massive amount of research since dopamine was first shown to be linked to Parkinson's disease, schizophrenia, and motivation and reward mechanisms in the 1960s and 1970s. Based on the number of publications that have dealt with it, dopamine is arguably the most important or at least most intriguing neurotransmitter in the brain. It has been implicated in a very large number of behaviors, with a theoretical ubiquitousness that has led it to be facetiously referred to as “everyman's transmitter because it does everything” (Koob, cited in Blum, 1997).

There is one general conclusion regarding dopamine and behavior that a clear majority of neuroscientists would agree on: dopamine enables and stimulates motor behavior. Increased dopamine transmission, at least up to a certain point, leads to behavioral activation (e.g. increased locomotion, vocalizations, and movements of the face and upper-extremities) and speeds up motor responses; conversely, diminished dopamine transmission leads to akinetic syndromes, including in the extreme mutism (Beninger, 1983; Salamone et al., 2005; Tucker and Williamson, 1984). One of the distinguishing features of excessive dopamine in the brain is motor behavior known in lower animals as “stereotypy” – constant, repetitive movements that would resemble compulsive behavior in humans (Ridley and Baker, 1982). A dramatic example of dopamine's role in motor behavior is the “stargazer” rat, which has very high dopamine levels and activity levels four to five times those of normals (Brock and Ashby, 1996; Truett et al., 1994).