Abstract
Background and objectives: The internal (GPi) and external segments (GPe) of the globus pallidus represent key nodes in the basal ganglia system. Connections to and from pallidal segments are topographically organized, delineating limbic, associative and sensorimotor territories. The topography of pallidal afferent and efferent connections with brainstem structures has been poorly investigated. In this study we sought to characterize in-vivo connections between the globus pallidus and the pedunculopontine nucleus (PPN) via diffusion tractography. Materials and Methods: We employed structural and diffusion data of 100 subjects from the Human Connectome Project repository in order to reconstruct the connections between the PPN and the globus pallidus, employing higher order tractography techniques. We assessed streamline count of the reconstructed bundles and investigated spatial relations between pallidal voxels connected to the PPN and pallidal limbic, associative and sensorimotor functional territories. Results: We successfully reconstructed pallidotegmental tracts for the GPi and GPe in all subjects. The number of streamlines connecting the PPN with the GPi was greater than the number of those joining it with the GPe. PPN maps within pallidal segments exhibited a distinctive spatial organization, being localized in the ventromedial portion of the GPi and in the ventral-anterior portion in the GPe. Regarding their spatial relations with tractography-derived maps of pallidal functional territories, the highest value of percentage overlap was noticed between PPN maps and the associative territory. Conclusions: We successfully reconstructed the anatomical course of the pallidotegmental pathways and comprehensively characterized their topographical arrangement within both pallidal segments. PPM maps were localized in the ventromedial aspect of the GPi, while they occupied the anterior pole and the most ventral portion of the GPe. A better understanding of the spatial and topographical arrangement of the pallidotegmental pathways may have pathophysiological and therapeutic implications in movement disorders.
Highlights
The globus pallidus (GP) is subdivided into internal (GPi) and external segments (GPe) by the lamina medullaris interna, a thin strip of white matter [1]
Tracts joining the pedunculopontine nucleus (PPN) and both pallidal segments were successfully reconstructed in all subjects (n = 100) and showed an overall similar anatomical course, which was well-summarized by the maximum probability maps (MPMs) (Figure 2)
The present study was aimed at reconstructing in vivo and non-invasively the structural connections between pallidal segments and the PPN, in order to provide an anatomical characterization of ipsilateral and contralateral pallidotegmental tracts
Summary
The globus pallidus (GP) is subdivided into internal (GPi) and external segments (GPe) by the lamina medullaris interna, a thin strip of white matter [1]. Primates studies revealed that the main connectional systems of both pallidal segments are topographically organized, delineating limbic, associative and sensorimotor territories [3,4,5]. This peculiarity is shared across basal ganglia nuclei and it has been confirmed in human imaging studies carried out via diffusion magnetic resonance imaging (dMRI) and tractography-related techniques [6,7,8,9].
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