A connectivity model of the anatomic substrates underlying Gerstmann syndrome

Abstract

The Gerstmann syndrome is a constellation of neurological deficits that include agraphia, acalculia, left-right discrimination and finger agnosia. Despite a growing interest in this clinical phenomenon, there remains controversy regarding the specific neuroanatomic substrates involved. Advancements in data-driven, computational modeling provides an opportunity to create a unified cortical model with greater anatomic precision based on underlying structural and functional connectivity across complex cognitive domains. A literature search was conducted for healthy task-based functional MRI and PET studies for the four cognitive domains underlying Gerstmann’s tetrad using the electronic databases PubMed, Medline, and BrainMap Sleuth (2.4). Coordinate based, meta-analytic software was utilized to gather relevant regions of interest from included studies to create an activation likelihood estimation (ALE) map for each cognitive domain. Machine-learning was used to match activated regions of the activation likelihood estimation to the corresponding parcellation from the cortical parcellation scheme previously published under the Human Connectome Project (HCP). Diffusion spectrum imaging-based tractography was performed to determine the structural connectivity between relevant parcellations in each domain on 51 healthy subjects from the Human Connectome Project database. Ultimately 102 functional MRI studies met our inclusion criteria. A frontoparietal network was found to be involved in the four cognitive domains: calculation, writing, finger gnosis, and left–right orientation. There were three parcellations in the left hemisphere where the activation likelihood estimation of at least three cognitive domains were found to be overlapping, specifically the anterior intraparietal area (AIP), area 7 postcentral (7PC) and the medial intraparietal sulcus. These parcellations surround the anteromedial portion of the intraparietal sulcus. Area 7 postcentral was found to be involved in all four domains. These regions were extensively connected in the intraparietal sulcus as well as with a number of surrounding large-scale brain networks involved in higher-order functions. We present a tractographic model of the four neural networks involved in the functions which are impaired in Gerstmann syndrome. We identified a “Gerstmann Core” of extensively connected functional regions where at least 3 of the four networks overlap. These results provide clinically actionable and precise anatomic information which may help guide clinical translation in this region, such as during resective brain surgery in or near the intraparietal sulcus, and provides an empiric basis for future study.

Preserving the ability to discriminate between left and right; A case study

“…Our case report shows that left‐right orientation can also be linked to right parietal processing without a mental rotation component. This is consistent with a recent meta‐analysis of the four components of Gerstmann syndrome that showed that for left‐right orientation, in addition to left parietal foci, the right posterior parietal cortex (in particular the anterior and middle intraparietal sulcus and the parieto‐occipital sulcus) was involved (Shahab et al, 2022). In addition, a study by van Stralen et al (2018) reported that problems with left‐right orientation are also associated with cortical lesions in the right hemisphere, especially the insula.…”

Deconvoluting human Brodmann area 8 based on its unique structural and functional connectivity

“…Namely, area 8C demonstrates less functional connectivity with subdivisions of area 9 and more connectivity with inferior frontal lobe regions (IFSp, IFJp, a47r, p47r, and 44). However, a number of similar structural connections are also found between the two regions as area 8C is connected via the arcuate/SLF as well, but instead terminates in parietal visual areas PH and PHT unlike how the connections of 8AV via the arcuate/SLF terminate in different parietal areas (6a, 7PC, MIP, PFm, 2), which are largely implicated in praxis ( Shahab et al, 2022 ).…”

A parcellation‐based connectomic model of hemispatial neglect

“…Lesions in the subcortical white matter near the temporal, frontal, and parietal lobes and corresponding cortical regions have been studied extensively in literature and seem to be, in part, responsible for neglect 10,18–21 . Thus, further examination of the literature on the white matter connectivity underlying these regions and related neglect functions may help unify our understanding of the substrates involved in neglect as has been demonstrated in other neurological conditions 22 …”

“…10,[18][19][20][21] Thus, further examination of the literature on the white matter connectivity underlying these regions and related neglect functions may help unify our understanding of the substrates involved in neglect as has been demonstrated in other neurological conditions. 22 To address this gap, we attempted to create an anatomically specific connectivity model of the neuroanatomic substrates likely involved in hemispatial neglect. These areas have been collectively referred to as the neglect system in this manuscript.…”