Investigating Language and Domain-General Processing in Neurotypicals and Individuals With Aphasia - A Functional Near-Infrared Spectroscopy Pilot Study.

Xinge Li,David A Boas,Natalie Gilmore,Meryem Ayse Yücel,Swathi Kiran

doi:10.3389/fnhum.2021.728151

Abstract

Brain reorganization patterns associated with language recovery after stroke have long been debated. Studying mechanisms of spontaneous and treatment-induced language recovery in post-stroke aphasia requires a network-based approach given the potential for recruitment of perilesional left hemisphere language regions, homologous right hemisphere language regions, and/or spared bilateral domain-general regions. Recent hardware, software, and methodological advances in functional near-infrared spectroscopy (fNIRS) make it well-suited to examine this question. fNIRS is cost-effective with minimal contraindications, making it a robust option to monitor treatment-related brain activation changes over time. Establishing clear activation patterns in neurotypical adults during language and domain-general cognitive processes via fNIRS is an important first step. Some fNIRS studies have investigated key language processes in healthy adults, yet findings are challenging to interpret in the context of methodological limitations. This pilot study used fNIRS to capture brain activation during language and domain-general processing in neurotypicals and individuals with aphasia. These findings will serve as a reference when interpreting treatment-related changes in brain activation patterns in post-stroke aphasia in the future. Twenty-four young healthy controls, seventeen older healthy controls, and six individuals with left hemisphere stroke-induced aphasia completed two language tasks (i.e., semantic feature, picture naming) and one domain-general cognitive task (i.e., arithmetic) twice during fNIRS. The probe covered bilateral frontal, parietal, and temporal lobes and included short-separation detectors for scalp signal nuisance regression. Younger and older healthy controls activated core language regions during semantic feature processing (e.g., left inferior frontal gyrus pars opercularis) and lexical retrieval (e.g., left inferior frontal gyrus pars triangularis) and domain-general regions (e.g., bilateral middle frontal gyri) during hard versus easy arithmetic as expected. Consistent with theories of post-stroke language recovery, individuals with aphasia activated areas outside the traditional networks: left superior frontal gyrus and left supramarginal gyrus during semantic feature judgment; left superior frontal gyrus and right precentral gyrus during picture naming; and left inferior frontal gyrus pars opercularis during arithmetic processing. The preliminary findings in the stroke group highlight the utility of using fNIRS to study language and domain-general processing in aphasia.

Highlights

Cognitive processes, including language, are supported by largescale brain networks (Mesulam, 1990; Greicius et al, 2003; Fox et al, 2005; Yeo et al, 2011)
Individuals with stroke demonstrated no significant differences in HbO concentration change between arithmetic task conditions in any of the right hemisphere regions of interest (ROIs)
When activation patterns were qualitatively compared between the healthy control groups, older healthy controls demonstrated more extensive right hemisphere engagement during the semantic feature task (i.e., RSFG, RMFG, RIFGtri, RPCG) than younger healthy controls (i.e., RSFG, RMTG) as hypothesized based on previous neuroimaging studies investigating age-related changes in language function

Summary

Introduction

Cognitive processes, including language, are supported by largescale brain networks (Mesulam, 1990; Greicius et al, 2003; Fox et al, 2005; Yeo et al, 2011). While the language network can be challenging to clearly define (Yeo et al, 2011), a subset of regions seems to consistently engage during language production and expression activities (i.e., left inferior frontal; IFG and middle temporal gyri; MTG; Fedorenko and ThompsonSchill, 2014; Ji et al, 2019). Relevant to the present study, lexical retrieval and semantic processing in healthy individuals includes LIFG and MTG, and, middle frontal (MFG), precentral (PCG), supramarginal (SMG), and angular gyri (AG; see Johnson et al, 2019, 2020). Language activities may be supported by the domain-general cognitive control network (MFG, inferior frontal gyrus opercularis [IFGoper], PCG, supplementary motor area [SMA], insula, superior parietal lobule, SMG, AG, anterior cingulate cortex [ACC]; Fedorenko et al, 2013) as this bilaterally represented network is engaged when tasks are challenging irrespective of modality. Language activities may be supported by the domain-general cognitive control network (MFG, inferior frontal gyrus opercularis [IFGoper], PCG, supplementary motor area [SMA], insula, superior parietal lobule, SMG, AG, anterior cingulate cortex [ACC]; Fedorenko et al, 2013) as this bilaterally represented network is engaged when tasks are challenging irrespective of modality. Fedorenko et al (2011, 2013) have demonstrated this phenomenon extensively across a range of cognitive domains (e.g., spatial working memory, verbal working memory, Stroop), including arithmetic as investigated in the present study

Methods

Results

Conclusion