Neurons in the region at the base of the brain produce dopamine in a two-step process. First, the amino acid tyrosine is converted into another amino acid, called L-dopa. Then L-dopa undergoes another change, as enzymes turn it into dopamine.
Too little dopamine causes the stiff movements that are the hallmark of Parkinson’s disease. Although depression is more often linked to a lack of serotonin, studies find that a dopamine deficiency also contributes to a down mood. In particular, people with depression often suffer from a lack of motivation and concentration.