Carlsson received a medical degree from the University of Lund in 1951 and subsequently held teaching positions there until 1959, when he became professor of pharmacology at the University of Gothenburg. When Carlsson began his pioneering studies in the 1950s, scientists thought that dopamine worked only indirectly, by causing brain cells to make another neurotransmitter, noradrenaline. Using a sensitive test that he had devised, Carlsson detected particularly high levels of the compound in areas of the brain that controlled walking and other voluntary movements. In animal experiments he showed that depletion of dopamine impairs the ability to move. When Carlsson treated dopamine-depleted animals with the amino acid l-dopa, the symptoms disappeared, and the animals moved normally again. This led to the use of l-dopa as a treatment for Parkinson disease, and it eventually became the single most important medication for the disease. Carlsson's work also contributed to an understanding of the relationship between neurotransmitters and mental states and led to the introduction of new antidepressant drugs.