The involvement of the primate frontal cortex-basal ganglia system in arbitrary visuomotor association learning

Abstract

It is the goal of this thesis to examine the frontal cortex-basal ganglia system during arbitrary visuomotor association learning, the forming of arbitrary links between visual stimuli and motor responses (e.g. red means stop), a fundamental learning process that underlies much of our complex behavior such as written language. The experiments contained in this thesis investigate the involvement of four components of this system in the acquisition of these associations: dorsolateral prefrontal cortex (dlPFC), caudate nucleus (Cd), frontal eye field (FEF), and the internal segment of the globus pallidus (GPi). Extracellular electrophysiological recordings were performed in awake-behaving primates performing three different learning tasks. In the different behavioral paradigms used in these studies, learning with and without reversals is investigated and compared both directly within the same experiment and indirectly across experiments. The results of these studies suggest that a complex interplay between brain areas in the frontal cortex-basal ganglia system exists. The study of FEF during reversal learning revealed that FEF contains task-related information from the start of learning, suggesting that it may be passing information onto PFC and Cd to aid the learning process. In addition, GPi is shown to contain more specific information about the learned association during the reversal task, providing evidence for an increase in the complexity of information processing through the basal ganglia.

(cont.) The in-depth study of dlPFC and Cd suggests that the frontal cortex-basal ganglia system functions only when competition between learning contexts exist. When all competition is eliminated by removing reversal learning from the behavioral task, Cd does not show involvement in the learning process. But when competition exists, both Cd and PFC show learning-related changes in task-relevant information. As determined by coherence analysis of local field potentials, communication between dlPFC and Cd is greater during reversal learning, when competition is heightened. This communication also decreases as learning progresses suggesting a role in the transfer of information between areas in facilitating the learning process. Overall, these studies further the understanding of the role of the frontal cortex-basal ganglia system in arbitrary visuomotor learning and posit that the function of the system is dependent on the existence of competition between learned information.