School of Medicine, University of Nottingham, Nottingham, UK.
Laboratory for Neuro- and Psychophysiology, KU Leuven, Leuven, Belgium.
Adv Exp Med Biol. 2023;1423:11-20. doi: 10.1007/978-3-031-31978-5_2.
The fornix, the limbic system's white matter tract connecting the extended hippocampal system to subcortical structures of the medial diencephalon, is strongly associated with learning and memory in humans and nonhuman primates (NHPs). Here, we sought to investigate alterations in structural connectivity across key cortical and subcortical regions after fornix transection in NHPs. We collected diffusion-weighted MRI (dMRI) data from three macaque monkeys that underwent bilateral fornix transection during neurosurgery and from four age- and cohort-matched control macaques that underwent surgery to implant a head-post but remained neurologically intact. dMRI data were collected from both groups at two time points, before and after the surgeries, and scans took place at around the same time for the two groups. We used probabilistic tractography and employed the number of tracking streamlines to quantify connectivity across our regions of interest (ROIs), in all dMRI sessions. In the neurologically intact monkeys, we observed high connectivity across certain ROIs, including the CA3 hippocampal subfield with the retrosplenial cortex (RSC), the anterior thalamus with the RSC, and the RSC with the anterior cingulate cortex (ACC). However, we found that, compared to the control group, the fornix-transected monkeys showed marked, significant, connectivity changes including increases between the anterior thalamus and the ACC and between the CA3 and the ACC, as well as decreases between the CA3 and the RSC. Our results highlight cortical and subcortical network changes after fornix transection and identify candidate indirect connectivity routes that may support memory functions after damage and/or neurodegeneration.
穹窿，连接扩展的海马体系统和内侧间脑的皮质下结构的边缘系统的白质束，与人及非人类灵长类动物（NHPs）的学习和记忆密切相关。在这里，我们试图研究穹窿切断后关键皮质和皮质下区域的结构连接变化。我们从三只在神经外科手术中接受双侧穹窿切断的猕猴和四只接受植入头钉但保持神经完整的年龄和队列匹配的对照猕猴中收集弥散张量 MRI（dMRI）数据。两组猕猴在手术前后的两个时间点采集 dMRI 数据，且两组的扫描时间大致相同。我们使用概率追踪技术，并使用跟踪流线的数量来量化所有 dMRI 会话中我们的感兴趣区域（ROI）之间的连接。在神经功能完整的猕猴中，我们观察到某些 ROI 之间具有高连接性，包括 CA3 海马亚区与后扣带回皮层（RSC）、前丘脑与 RSC 以及 RSC 与前扣带回皮层（ACC）之间的连接。然而，我们发现与对照组相比，穹窿切断的猕猴表现出明显的、显著的连接性变化，包括前丘脑与 ACC 之间以及 CA3 与 ACC 之间的连接增加，以及 CA3 与 RSC 之间的连接减少。我们的研究结果强调了穹窿切断后的皮质和皮质下网络变化，并确定了可能支持损伤和/或神经退行性病变后记忆功能的候选间接连接途径。
