Benefit of Action Naming Over Object Naming for Visualization of Subcortical Language Pathways in Navigated Transcranial Magnetic Stimulation-Based Diffusion Tensor Imaging-Fiber Tracking.

Ann-Katrin Ohlerth,Severin Schramm,Roelien Bastiaanse,Sandro M Krieg,Nico Sollmann,Chiara Negwer,Axel Schröder

doi:10.3389/fnhum.2021.748274

Abstract

Visualization of functionally significant subcortical white matter fibers is needed in neurosurgical procedures in order to avoid damage to the language network during resection. In an effort to achieve this, positive cortical points revealed during preoperative language mapping with navigated transcranial magnetic stimulation (nTMS) can be employed as regions of interest (ROIs) for diffusion tensor imaging (DTI) fiber tracking. However, the effect that the use of different language tasks has on nTMS mapping and subsequent DTI-fiber tracking remains unexplored. The visualization of ventral stream tracts with an assumed lexico-semantic role may especially benefit from ROIs delivered by the lexico-semantically demanding verb task, Action Naming. In a first step, bihemispheric nTMS language mapping was administered in 18 healthy participants using the standard task Object Naming and the novel task Action Naming to trigger verbs in a small sentence context. Cortical areas in which nTMS induced language errors were identified as language-positive cortical sites. In a second step, nTMS-based DTI-fiber tracking was conducted using solely these language-positive points as ROIs. The ability of the two tasks’ ROIs to visualize the dorsal tracts Arcuate Fascicle and Superior Longitudinal Fascicle, the ventral tracts Inferior Longitudinal Fascicle, Uncinate Fascicle, and Inferior Fronto-Occipital Fascicle, the speech-articulatory Cortico-Nuclear Tract, and interhemispheric commissural fibers was compared in both hemispheres. In the left hemisphere, ROIs of Action Naming led to a significantly higher fraction of overall visualized tracts, specifically in the ventral stream’s Inferior Fronto-Occipital and Inferior Longitudinal Fascicle. No difference was found between tracking with Action Naming vs. Object Naming seeds for dorsal stream tracts, neither for the speech-articulatory tract nor the inter-hemispheric connections. While the two tasks appeared equally demanding for phonological-articulatory processes, ROI seeding through the task Action Naming seemed to better visualize lexico-semantic tracts in the ventral stream. This distinction was not evident in the right hemisphere. However, the distribution of tracts exposed was, overall, mirrored relative to those in the left hemisphere network. In presurgical practice, mapping and tracking of language pathways may profit from these findings and should consider inclusion of the Action Naming task, particularly for lesions in ventral subcortical regions.

Highlights

In the past decades, there has been a shift in allocation of language representation in the brain, from a focus on mostly cortical structures to an emphasis on the importance of the subcortical networks (Duffau, 2008; Dick et al, 2014), labeled as a “hodotopical approach” (Duffau et al, 2014)
Cortical areas in which errors are elicited during picture naming under navigated transcranial magnetic stimulation (nTMS) disturbance, are considered positive language areas, and defined as regions of interest (ROIs) to visualize tracts during subsequent tractography (Sollmann et al, 2015a, 2016, 2018a,b; Raffa et al, 2016; Negwer et al, 2017a, 2018; Ille et al, 2018)
The current study aimed to evaluate nTMS-based Diffusion tensor imaging (DTI)-fiber tracking results made on the basis of ROIs through Object Naming or Action Naming in healthy volunteers

Summary

Introduction

There has been a shift in allocation of language representation in the brain, from a focus on mostly cortical structures to an emphasis on the importance of the subcortical networks (Duffau, 2008; Dick et al, 2014), labeled as a “hodotopical approach” (Duffau et al, 2014). Diffusion tensor imaging (DTI) is used as a means of structural depiction of subcortical white matter, where, in combination with fiber tracking, single tracts can be identified that are relevant for language functions. For this tracking, information in the form of regions of interest (ROIs) is needed for seeding, that is, start and/or end points at the cortical level that are connected by the subcortical tracts to be visualized. Cortical areas in which errors are elicited during picture naming under nTMS disturbance, are considered positive language areas, and defined as ROIs to visualize tracts during subsequent tractography (Sollmann et al, 2015a, 2016, 2018a,b; Raffa et al, 2016; Negwer et al, 2017a, 2018; Ille et al, 2018)

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Conclusion