Dopamine (C6H3(OH)2-CH2-CH2-NH2) is a catecholamine neurotransmitter in the brain.
Dopamine in the basal ganglia plays a critical role in the way our brain controls our movements. Thus, shortage of dopamine, particularly the death of dopamine neurons in the nigrostriatal pathway, is a cause of Parkinson's disease, in which a person loses the ability to execute smooth, controlled movements.
In the frontal lobes, dopamine plays a role in controlling the flow of information from other areas of the brain. Dopamine disorders in the frontal lobes can cause a decline in neurocognitive function, particularly those linked to the frontal lobes, such as memory, attention and problem solving.
Disruption to the dopamine system has also been strongly linked to psychosis and schizophrenia. Dopamine neurons in the mesolimbic pathway are particularly associated these conditions. This is partly due to the discovery of a class of drugs called the phenothiazines (which block dopamine D2 receptors) which can reduce psychotic symptoms and partly due to the finding that drugs such as amphetamines and cocaine (which are known to greatly increase dopamine levels) can cause psychosis when used in excess. Because of this all modern antipsychotic medication is designed to blocks dopamine function to varying degrees.
In addition, dopamine is involved in the chemistry of pleasure. Release of dopamine into that part of the limbic system known as the "pleasure center" (an area just below the thalamus) causes pleasure. Although meant to reward vital activities such as eating and sex, this same mechanism is responsible for the craving connected with addiction to drugs, cocaine for example.