Implication of Prefrontal Cortex and Basal Ganglia in decision making and learning processes : behavioural and pharmacological study in non-human primates

décembre 2014

Directeur(s) de thèse : Thomas BORAUD

Résumé de thèse

Many studies are interested in decision making and learning processes and in brain areas which are engaged in. Among them, the implication Prefrontal Cortex (PFC) and a sub cortical structures’ network, the Basal Ganglia (BG) has been shown. Nevertheless, the precise role of each structure has not yet been defined. There are two main hypotheses. The first one holds that GB and PFC function independently. BG would support habitual behaviors and PFC planned behaviors. The second hypothesis proposes that both structures are collaborating: the basal ganglia drive a low kinetic learning process in the prefrontal cortex and become less and less engaged as the task is learned. It means reversing the roles: BG would be necessary for decision making processes as soon as PFC finishes its learning. This latter would then function as an automatic mode. The main problem which avoids us to disentangle the role of each structure is the experimental paradigms used which mix up learning and decision making. Our first aim was to design an experimental task in which there was learning phase and decision making phase per se. Then, we blocked basal ganglia influence on PFC by inhibiting their exit structure, the Globus Pallidus internal, with intracerebral muscimol injections in non-human primates performing a “two-armed bandit task”. Our results show that monkeys are able to do decision making after GPi inhibition but they are unable to learn new values. These results confirm that, in non-human primates, BG and PFC are well involved as co-workers in one process: integrity of all the circuit is necessary for learning whereas only cortex is sufficient once the choice is in habitual context.