Mapping articulatory and grammatical subcomponents of fluency deficits in post-stroke aphasia

Abstract

Fluent speech production is a critical aspect of language processing and is central to aphasia diagnosis and treatment. Multiple cognitive processes and neural subsystems must be coordinated to produce fluent narrative speech. To refine the understanding of these systems, measures that minimize the influence of other cognitive processes were defined for articulatory deficits and grammatical deficits. Articulatory deficits were measured by the proportion of phonetic errors (articulatory and prosodic) in a word repetition task in 115 participants with aphasia following left hemisphere stroke. Grammatical deficits were assessed in 46 participants based on two measures-proportion of closed class words and proportion of words in sentences-generated during semistructured narrative speech production (telling the Cinderella story). These measures were used to identify brain regions critical for articulatory and grammatical aspects of speech production using a multivariate lesion-symptom mapping approach based on support vector regression. Phonetic error proportion was associated with damage to the postcentral gyrus and the inferior parietal lobule (particularly the supramarginal gyrus). Proportion of closed class words in narrative speech did not have consistent lesion correlates. Proportion of words in sentences was strongly associated with frontal lobe damage, particularly the inferior and middle frontal gyri. Grammatical sentence structuring relies on frontal regions, particularly the inferior and middle frontal gyri, whereas phonetic-articulatory planning and execution relies on parietal regions, particularly the postcentral and supramarginal gyri. These results clarify and extend current understanding of the functional components of the frontoparietal speech production system.

Dissociation between Frontal and Temporal-Parietal Contributions to Connected Speech in Acute Stroke

“…Ferreira, 1993). Although our analysis of connected speech did not quantify deficits at a phonological level of specificity, the postcentral and SMG foci we identified are similar to damaged regions associated with phonological and phonetic errors during picture naming by speakers with chronic stroke (Mirman et al, 2019). Damage to the left IFG and insula was associated with deficits producing words with grammatical functions and nearby regions were also associated with reduced syntactic accuracy.…”

“…This study demonstrated neuroanatomical and functional divisions within grammatical encoding during connected speech which dovetail with existing neurobiological sentence production evidence. In chronic stroke speakers, LBM analysis demonstrated that reduced numbers of words produced in sentences during story-telling was associated largely with damage to the left IFG with smaller foci in the postcentral gyrus and IPL (Mirman et al, 2019). When speakers undergoing awake craniotomies described pictures depicting actions, direct cortical stimulation of the pars opercularis and triangularis of the LIFG resulted in 50 % of patients producing grammatical errors during sentence production (Chang et al, 2018).…”

“…Studies of speakers with chronic stroke often preselect subjects based on aphasia diagnosis (e.g. Schnur et al, 2009;Yourganov et al, 2016;Halai et al, 2017;Mirman et al, 2019) which limits behavioral and lesion location variability. Speakers with chronic aphasia typically have large lesions spanning crucial language areas (e.g.…”

“…Relatively little is known about how individual differences in focal brain damage affect the ability to accurately produce syntactic structure independent from content. In the only LBM study of content and structure deficits during spontaneous connected speech of which we are aware, Mirman et al (2019) examined story-telling narratives from 46 speakers with diagnosed aphasia after chronic left hemisphere stroke. After controlling for the contribution of lesion size, the proportion of words produced in sentences (utterances with both a subject noun and verb) was associated with damage to left MFG, IFG, postcentral gyrus, and inferior parietal lobe (IPL).…”

Combination of structural and functional connectivity explains unique variation in specific domains of cognitive function

“…Consequently, they risk masking relevant variation in performance across the relevant domains. In contrast, approaches that explore individual cognitive domains have great potential to improve our understanding and prediction of cognitive health and pathology (Barch & Ceaser, 2012;Covey et al, 2011;Rivera-Fernández et al, 2021), and have been effectively applied to predict performance in various populations, including dementia (Hackett et al, 2018;Rivera-Fernández et al, 2021) stroke aphasia (Butler et al, 2014;Mirman et al, 2019) and healthy aging (Reddy et al, 2015). We therefore considered a wide range of behavioural measures from the HCP dataset, and PCA analysis revealed four components underpinning performance on these cognitive tasks: retention and retrieval, processing speed, self-regulation, and encoding processes.…”