A biologically constrained model of the whole basal ganglia addressing the paradoxes of connections and selection

TL;DR

This study presents a comprehensive mean-field model of the basal ganglia that reconciles conflicting anatomical and electrophysiological data, providing new insights into intra-pallidal connections and their role in action selection.

Contribution

It introduces a biologically constrained model that unifies conflicting views on intra-pallidal projections and predicts the unbalanced afferent projections and diffuse connection patterns.

Findings

Intra-pallidal projections are weakly inhibitory, supporting similar activity in external and internal globus pallidus.

External segment receives stronger excitation from STN and weaker inhibition from striatum.

Diffuse intra-pallidal connection pattern enhances action selection efficiency.

Abstract

The basal ganglia nuclei form a complex network of nuclei often assumed to perform selection, yet their individual roles and how they influence each other is still largely unclear. In particular, the ties between the external and internal parts of the globus pallidus are paradoxical, as anatomical data suggest a potent inhibitory projection between them while electrophys-iological recordings indicate that they have similar activities. Here we introduce a theoretical study that reconciles both views on the intra-pallidal projection, by providing a plausible characterization of the relationship between the external and internal globus pallidus. Specifically, we developed a mean-field model of the whole basal ganglia, whose parameterization is optimized to respect best a collection of numerous anatomical and electrophysiological data. We first obtained models respecting all our constraints, hence anatomical and electrophysiological data on the intrapallidal projection are globally consistent. This model furthermore predicts that both aforementioned views about the intra-pallidal projection may be reconciled when this projection is weakly inhibitory, thus making it possible to support similar neural activity in both nuclei and for the entire basal ganglia to select between actions. Second, we predicts that afferent projections are substantially unbalanced towards the external segment, as it receives the strongest excitation from STN and the weakest inhibition from the striatum. Finally, our study strongly suggest that the intrapallidal connection pattern is not focused but diffuse, as this latter pattern is more efficient for the overall selection performed in the basal ganglia.