To establish this interaction, researchers in the Movement, Adaptation, Cognition Laboratory, a joint CNRS and University of Bordeaux 2 unit affiliated to the Franco-Israeli Neurophysiology and Neurophysics of Systems Laboratory , simultaneously recorded in primates the electrical activity of neurons in the two structures concerned, the striatum and internal globus pallidus. The animals were required to choose between two targets which were rewarded differently, and then perform a movement towards the target chosen. It had previously been determined that each animal had learnt to associate each target with a different probability of obtaining a reward. They therefore had to have memorised these combinations and chosen the target associated with the greatest probability of an optimum reward.
This experiment showed that cognitive information modulates the coding of motor information via neurons which belong to the two key structures in the basal ganglia: at entry and exit. This is the first time that a cellular interaction has been demonstrated between purely cognitive and purely motor information. Above all, the mechanisms by which the basal ganglia integrate these two types of information have been elucidated. This discovery will have a considerable impact on our knowledge of Parkinson's disease, as this condition is caused by a degeneration of dopamine-producing neurons. As a result, it will be necessary to adopt a new approach to this disease. Although Parkinson's disease expresses itself through severely incapacitating motor disorders, such as an increasing difficulty in initiating and executing movements, marked muscle rigidity and tremor, it should no longer be considered as a purely motor pathology: it will now be necessary to take account of its cognitive dimension as well.