In an article (1) published in The Journal of Neuroscience, researchers at the University of Liège's Cyclotron Research Center, in collaboration with scientists from the United States, demonstrated that the role dopamine plays in motor learning depends on its release at the cortical level. More specifically, dopamine produced in two cerebral areas, i.e. the supplementary motor area and the globus pallidus, might influence the speed at which certain movements are learned.

Parkinson's disease is commonly defined as the result of a dopamine deficiency in the extrapyramidal system, which is made up of basal grey nuclei (or ganglia)(also known as midbrain grey nuclei) and the connections binding them together. The disease is characterized more precisely by the premature death of dopaminergic neurons of the locus niger (or black matter), one of the basal ganglia.

The black matter plays an essential role in motor control. Its dopaminergic neurons project to various brain structures, particularly to striatum, another grey nucleus also deeply involved in motor control. However, even though Parkinson's disease is at first associated with a loss of dopaminergic neurons, the first signs of degeneration, according to certain theories, might be found in the brain stem, with the black matter only being affected at a later stage. Non-motor symptoms, such as loss of the sense of smell, would thus precede motor symptons and forewarn their manifestation.

In any case, slowing movement is observed in Parkinsonian patients, once the diagnosis is confirmed. This led researchers at the University of Liège's Cyclotron Research Center (CRC), in collaboration with a team from the National Institutes of Health (NIH) in the United States, to study the role of dopamine in motor control and the acquisition of new motor skills. Earlier studies had shown that this neurotransmitter aided movement acquisition in animals, but no data existed for man.

A second question perplexing the Belgian-American team was that of the relationship between the dopamine produced in very high concentrations in the basal grey nuclei and that present in much lower concentrations in the cortex. The question was of even greater relevance then as the role played by dopamine in motor control in both normal and Parkinsonian patients was still unknown.

(1) Task-Related Interaction Between Basal Ganglia and Cortical Dopamine Release, by Gaëtan Garraux, Philippe Peigneux, Richard E. Carson et Mark Hallett, in The Journal of Neuroscience, December 26^th 2007.