Fine-Grained Topography and Modularity of the Macaque Frontal Pole Cortex Revealed by Anatomical Connectivity Profiles

Bin He,Xiaoluan Xia,Long Cao,Baogui Zhang,Dan Zhang,Lingzhong Fan,Bo You,Tianzi Jiang

doi:10.1007/s12264-020-00589-1

Abstract

The frontal pole cortex (FPC) plays key roles in various higher-order functions and is highly developed in non-human primates. An essential missing piece of information is the detailed anatomical connections for finer parcellation of the macaque FPC than provided by the previous tracer results. This is important for understanding the functional architecture of the cerebral cortex. Here, combining cross-validation and principal component analysis, we formed a tractography-based parcellation scheme that applied a machine learning algorithm to divide the macaque FPC (2 males and 6 females) into eight subareas using high-resolution diffusion magnetic resonance imaging with the 9.4T Bruker system, and then revealed their subregional connections. Furthermore, we applied improved hierarchical clustering to the obtained parcels to probe the modular structure of the subregions, and found that the dorsolateral FPC, which contains an extension to the medial FPC, was mainly connected to regions of the default-mode network. The ventral FPC was mainly involved in the social-interaction network and the dorsal FPC in the metacognitive network. These results enhance our understanding of the anatomy and circuitry of the macaque brain, and contribute to FPC-related clinical research.

Highlights

The macaque frontal pole cortex (FPC) has a homotypical cytoarchitecture and a location relative to other prefrontal regions that is similar to that of humans [1], which means that it has the potential to be an excellent model for understanding the mechanisms of the human brain [2, 3]
Studies based on the diffusion tensor imaging (DTI) connectivity could further improve our understanding of the relationship between the macaque FPC and different functional networks, including the default-mode network (DMN), social-interaction network (SIN), and metacognitive networks, but relevant studies are lacking
These results were transformed and combined into F99 brain space [64] with Caret software [65] to create population-based parcellations of the FPC, and we further presented the probabilistic map for each subarea that could help to understand the consistency between subjects in the topography of the clusters

Summary

Introduction

The macaque frontal pole cortex (FPC) has a homotypical cytoarchitecture and a location relative to other prefrontal regions that is similar to that of humans [1], which means that it has the potential to be an excellent model for understanding the mechanisms of the human brain [2, 3]. A variety of findings suggest that the macaque FPC can be divided into multiple functional subareas with different connectivity [10, 11], this area still lacks specialized research on its anatomical connections and a detailed parcellation map. Three primary studies have revealed markedly different cytoarchitectonic parcellation results [18,19,20], and many trace-injection experiments involving the FPC were based on previous rough maps of this area. Studies based on the diffusion tensor imaging (DTI) connectivity could further improve our understanding of the relationship between the macaque FPC and different functional networks, including the DMN, SIN, and metacognitive networks, but relevant studies are lacking. Many trace-injection studies related to the FPC have been based on previous rough parcellation maps and relevant studies based on DTI are still a rarity

Methods

Results

Discussion

Conclusion