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Topic Name: New link of demonstration which relates between cognition and execution

Category: Electrical

Research persons: Thomas Boraud
University Victor Ségalen, Bord
T 05 57 57 47 95
Mail ; tboraud@ u-bordeaux2.fr

Location: CNRS/University Victor Ségalen, Bordeaux, France

Details

There are two phases in the genesis of a movement directed towards a target when several choices are possible: firstly decision-making (cognitive information) and then the direction of this movement towards to the target (motor information). The brain is endowed with one or several structures which can integrate both cognitive information (enabling a reasoned choice which is not based on chance) and motor information. It is supposed that the basal ganglia play an essential role in these processes. However, the underlying mechanisms are still generally unknown.
A certain number of studies have suggested that the striatum(1) the cerebral structure considered as the portal of entry for the basal ganglia, may intervene in decision-making processes; as soon as a choice is offered to an individual, it evaluates the degree of incentive provided by each of the options possible. This phenomenon is probably controlled by dopamine(2), one of the neuromodulators present in large quantities in the basal ganglia. Furthermore, it has been shown that the electrical activity of neurons in the internal globus pallidus(3), the brain structure qualified as the exit point for the basal ganglia, codes the kinetic properties of the movement (direction, amplitude, speed, etc.). However, until now, no studies had demonstrated the existence of a link between the decision-making phase and the executive phase.
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(4), 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.

Notes :
1) Made up of several types of neurons, the striatum is a specific region in the brain involved in controlling movement at the decision-making level.
2) Dopamine is a neurotransmitter or neuromodulator, i.e. a molecule which modulates the activity of neurons in the brain.
3) Considered as the structure providing the exit point for the basal ganglia, the internal globus pallidus is made up of neurons which influence the activity of neurons in the motor cortex.
4) This associated international laboratory provides financial support for collaborations between teams of CNRS neuroscientists and researchers in the Interdisciplinary Center of Neuro-Computation, which is part of the Hebrew University of Jerusalem.
References :
Shaping of motor responses by incentive values through the basal ganglia. B. Pasquereau, A. Nadjar, D. Arkadir, E. Bezard, M. Goillandeau, B. Bioulac, C.-E. Gross, T. Boraud (2007). The Journal of Neuroscience. 27:1176-1183.