[Microanatomy and functional MRI study of arcuate fasciculus and superior longitudinal fasciculus]

Objectives: To explore the microanatomy and functional MRI(fMRI) of arcuate fasciculus(AF) and superior longitudinal fasciculus(SLF),and to analyze their functions. Methods: Ten normal adult cadaveric head specimens (20 cerebral hemispheres) were fixed with 10% methanal at the Translational Research Institute for Neurological Disorders of the Wannan Medical College from February to December 2022.The Klingler fiber dissection technique was utilized to perform white matter fiber dissection,with a magnification ranging from 6 to 40.The study focused on the microanatomical structures of the AF and SLF,aiming to explore their relationships with deep brain fibers.Furthermore, six healthy adult volunteers who underwent fMRI of the brain were included.The collected diffusion tensor imaging (DTI) data were processed and integrated with the microanatomical findings for a comprehensive analysis. Results: After removing the gray matter of the cerebral cortex,the superficial U fibers were exposed.The long association fibers that beneath the U fibers were the AF and SLF,which were the main long association fibers in the superficial layers of the brain.The AF could be divided into dorsal and ventral parts,while the SLF could be divided into Ⅰ,Ⅱ,and Ⅲ.SLF Ⅰ lied within the upper bank of the cingulate sulcus,travels medial to the callosal sulcus.The SLF Ⅱ,Ⅲ,and the AF were located on the lateral surface of the brain.By removing the gray matter of the insular cortex and the extreme capsule,exposing the external capsule and claustrum.Subsequently,the AF and SLF Ⅱ,Ⅲ were dissected,revealing the corona radiata and sagittal stratum,along with other deep brain fibers.During the dissection,it was observed that there was a close connection between the AF,SLF Ⅱ,and the deep brain fibers.Furthermore,in the regions above the lateral fissure of the cerebral hemisphere,there was no direct connection of long association fibers between the gray matter cortex and the deep U fibers in the coronal plane.These findings were further supported by DTI studies. Conclusions: The AF and SLF are the major long association fibers that located in the superficial layers of the brain,and closely connect to the gray matter cortex and U fibers,even closely relate with deep brain fibers.In the regions above the lateral fissure of the hemisphere,only the AF and SLF Ⅱ and Ⅲ serve as superficial long association fibers in the anterior-posterior direction.These fibers are likely involved in the transmission of brain functional information between the top and bottom gray matter cortex in the coronal plane above the lateral fissure.