The external globus pallidus: progress and perspectives

<jats:title>Abstract</jats:title><jats:p>The external globus pallidus (<jats:styled-content style="fixed-case">GP</jats:styled-content>e) of the basal ganglia is in a unique and powerful position to influence processing of motor information by virtue of its widespread projections to all basal ganglia nuclei. Despite the clinical importance of the <jats:styled-content style="fixed-case">GP</jats:styled-content>e in common motor disorders such as Parkinson's disease, there is only limited information about its cellular composition and organizational principles. In this review, recent advances in the understanding of the diversity in the molecular profile, anatomy, physiology and corresponding behaviour during movement of <jats:styled-content style="fixed-case">GP</jats:styled-content>e neurons are described. Importantly, this study attempts to build consensus and highlight commonalities of the cellular classification based on existing but contentious literature. Additionally, an analysis of the literature concerning the intricate reciprocal loops formed between the <jats:styled-content style="fixed-case">GP</jats:styled-content>e and major synaptic partners, including both the striatum and the subthalamic nucleus, is provided. In conclusion, the <jats:styled-content style="fixed-case">GP</jats:styled-content>e has emerged as a crucial node in the basal ganglia macrocircuit. While subtleties in the cellular makeup and synaptic connection of the <jats:styled-content style="fixed-case">GP</jats:styled-content>e create new challenges, modern research tools have shown promise in untangling such complexity, and will provide better understanding of the roles of the <jats:styled-content style="fixed-case">GP</jats:styled-content>e in encoding movements and their associated pathologies.</jats:p>