Dissecting the default mode network: direct structural evidence on the morphology and axonal connectivity of the fifth component of the cingulum bundle

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>Although a growing body of data support the functional connectivity between the precuneus and the medial temporal lobe during states of resting consciousness as well as during a diverse array of higher-order functions, direct structural evidence on this subcortical circuitry is scarce. Here, the authors investigate the very existence, anatomical consistency, morphology, and spatial relationships of the cingulum bundle V (CB-V), a fiber tract that has been reported to reside close to the inferior arm of the cingulum (CingI).</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>Fifteen normal, formalin-fixed cerebral hemispheres from adults were treated with Klingler’s method and subsequently investigated through the fiber microdissection technique in a medial to lateral direction.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>A distinct group of fibers is invariably identified in the subcortical territory of the posteromedial cortex, connecting the precuneus and the medial temporal lobe. This tract follows the trajectory of the parietooccipital sulcus in a close spatial relationship with the CingI and the sledge runner fasciculus. It extends inferiorly to the parahippocampal place area and retrosplenial complex area, followed by a lateral curve to terminate toward the fusiform face area (Brodmann area [BA] 37) and lateral piriform area (BA35). Taking into account the aforementioned subcortical architecture, the CB-V allegedly participates as a major subcortical stream within the default mode network, possibly subserving the transfer of multimodal cues relevant to visuospatial, facial, and mnemonic information to the precuneal hub. Although robust clinical evidence on the functional role of this stream is lacking, the modern neurosurgeon should be aware of this tract when manipulating cerebral areas en route to lesions residing in or around the ventricular trigone.</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>Through the fiber microdissection technique, the authors were able to provide original, direct structural evidence on the existence, morphology, axonal connectivity, and correlative anatomy of what proved to be a discrete white matter pathway, previously described as the CB-V, connecting the precuneus and medial temporal lobe.</jats:p></jats:sec>

Ventral temporal and posteromedial sulcal morphology in autism spectrum disorder

“…Shortly thereafter, Wu et al (2016) dissected the cingulum bundle into five segments, one of which they referred to as Cingulum Bundle V (CB-V), which also connected the PMC to VTC. Similar observations were also made by Skandalakis et al (2020), who noted that the functional role, as well as clinical implications of this bundle, were presently lacking. Thus, future studies can test the following hypotheses, if: i) CB-V connects the IFRMS to the MFS and ii) features of CB-V are different in ASD and NT participants.…”

“…Similar observations were also made by Skandalakis et al (2020), who noted that the functional role, as well as clinical implications of this bundle, were presently lacking. Thus, future studies can test the following hypotheses, if: i) CB-V connects the IFRMS to the MFS and ii) features of CB-V are different in ASD and NT participants.…”

Altered Functional Activity and Functional Connectivity of Seed Regions Based on ALFF Following Acupuncture Treatment in Patients with Stroke Sequelae with Unilateral Limb Numbness

“… 16 Additionally, MTG is a key node in the default mode network (DMN), while MFG participates in the executive control network (ECN), and the PUT is comprised in the basal ganglia network (BGN), indicating that patients with abnormal functional activity regions following stroke were mainly involved in the SMN but also included other critical brain networks. 17 Numerous studies demonstrate that the SMN is the most vulnerable network to stroke. On the other hand, advanced cognitive control networks related to sensorimotor function, such as the frontoparietal executive control network, will also experience functional impairments or compensation, a process referred to as functional reorganization.…”

Role of the parietooccipital fissure and its implications in the pathophysiology of posterior medial temporal gliomas

“…18,38 CB-V is also called the parahippocampal cingulum. 18 Fibers from the parahippocampal gyrus to the superior frontal gyrus along the cingulate gyrus are CB-II, 18 and fibers interconnecting the parietal lobe, occipital lobe, posterior cingulate cortex, and medial temporal lobe are CB-V. 4,18,39 The fourth set of fibers from the posterior medial temporal lobe to the contralateral hemisphere are transcallosal fibers connecting the splenium (region V) and the inferior temporal lobe. [40][41][42] Therefore, fibers running through the posterior medial temporal lobe have been well investigated and matched the invasion pattern of the posterior medial temporal gliomas in the present study.…”

“…3,5,16 Furthermore, as the Klingler white matter fiber dissection technique and diffusion tensor imaging (DTI) have revealed, the parahippocampal gyrus has fiber connections with surrounding structures of the parietal and occipital lobes, retrosplenial cortex, and posterior cingulate cortex. 4,18,19 In this study, we extracted anatomical and radiological features of posterior medial temporal gliomas to address the hypothesis that the parietooccipital fissure strongly affects the invasion pattern of gliomas. Increased understanding of glioma invasion patterns can be applied when choosing surgical strategies.…”