Projections of Brodmann Area 6 to the Pyramidal Tract in Humans: Quantifications Using High Angular Resolution Data.

Zhen-Ming Wang,Ya-Yan Yin,Jie Lu,Qiong-Ge Li,Miao Zhang,Yi Shan,Peng-Hu Wei

doi:10.3389/fncir.2019.00062

Abstract

Primate studies indicate that the pyramidal tract (PyT) could originate from Brodmann area (BA) 6. However, in humans, the accurate origin of PyT from BA 6 is still uncertain owing to difficulties in visualizing anatomical features such as the fanning shape at the corona radiata and multiple crossings at the semioval centrum. High angular-resolution diffusion imaging (HARDI) could reliably replicate these anatomical features. We explored the origin of the human PyT from BA 6 using HARDI. With HARDI data of 30 adults from the Massachusetts General Hospital-Human Connectome Project (MGH-HCP) database and the HCP 1021 template (average of 1021 HCP diffusion data), we visualized the PyT at the 30-averaged group level and the 1021 large-sample level and validated the observations in each of the individuals. Endpoints of the fibers within each subregion were quantified. PyT fibers originating from the BA 6 were consistently visualized in all images. Specifically, the bilateral supplementary motor area (SMA) and dorsal premotor area (dPMA) were consistently found to contribute to the PyT. PyT fibers from BA 6 and those from BA 4 exhibited a twisting topology. The PyT contains fibers originating from the SMA and dPMA in BA 6. Infarction of these regions or aging would result in incomplete provision of information to the PyT and concomitant decreases in motor planning and coordination abilities.

Highlights

The pyramidal tract (PyT) is a longitudinal pathway that delivers information regarding voluntary motor behavior
The superior-inferior oriented fibers of the pyramidal tract were visualized as follows: to track the potential PyT fibers issuing from Brodmann area (BA) 4 (PyT4) and 6 (PyT6), we introduced the Brainnetome Atlas4, which is a structural connectome based template (Fan L. et al, 2016) in which BA 6 was parceled into the caudal dorsolateral region (A6cdl), caudal ventrolateral region
Triple crossings were visualized at the semioval centrum, which consisted of fibers of the corpus callosum in a left-right direction; arcuate fasciculus in the anterior-posterior direction; and PyT in the superior-inferior direction (Figure 2)

Summary

Introduction

The pyramidal tract (PyT) is a longitudinal pathway that delivers information regarding voluntary motor behavior. It is constituted of the corticospinal tract and the corticobulbar tract (Rea, 2015). According to experiments using non-human primates, beside the primary motor area, the PyT could still originate from Brodmann area (BA) 6. In the BA 6, the PyT predominately derives from the supplementary motor area (SMA), dorsal premotor area (dPMA), and cingulate cortex (Dum and Strick, 1991; Galea and Darian-Smith, 1994). Diffusion tensor imaging (DTI) has been introduced to visualize the PyT (Kumar et al, 2009; Zolal et al, 2012; George et al, 2014). As the DTI technique cannot discriminate fanning or crossing fibers, or flipped angles

Methods

Results

Conclusion