Linking left hemispheric tissue preservation to fMRI language task activation in chronic stroke patients

Abstract

The preservation of near-typical function in distributed brain networks is associated with less severe deficits in chronic stroke patients. However, it remains unclear how task-evoked responses in networks that support complex cognitive functions such as semantic processing relate to the post-stroke brain anatomy. Here, we used recently developed methods for the analysis of multimodal MRI data to investigate the relationship between regional tissue concentration and functional MRI activation evoked during auditory semantic decisions in a sample of 43 chronic left hemispheric stroke patients and 43 age, handedness, and sex-matched controls. Our analyses revealed that closer-to-normal levels of tissue concentration in left temporo-parietal cortex and the underlying white matter correlated with the level of task-evoked activation in distributed regions associated with the semantic network. This association was not attributable to the effects of left hemispheric lesion or brain volumes, and similar results were obtained when using explicit lesion data. Left temporo-parietal tissue concentration and the associated task-evoked activations predicted patient performance on the in-scanner task, and also predicted patient performance on out-of-scanner naming and verbal fluency tasks. Exploratory analyses using the average HCP-842 tractography dataset revealed the presence of fronto-temporal, fronto-parietal, and temporo-parietal semantic network connections in the locations where tissue concentration was found to correlate with task-evoked activation in the semantic network. In summary, our results link the preservation of left posterior temporo-parietal structures with the preservation of task-evoked semantic network function in chronic left hemispheric stroke patients. Speculatively, this relationship may reflect the status of posterior temporo-parietal areas as cortical and white matter convergence zones that support coordinated processing in the distributed semantic network. Damage to these regions may contribute to atypical task-evoked responses during semantic processing in chronic stroke patients.

Perilesional and homotopic area activation during proverb comprehension after stroke

“…In our own previous study in a normal population of proverb comprehension, we reported that the right precuneus and right supramarginal gyrus are involved in abstract language processing (Yi et al, 2017). In our current study, we observed that transcallosal inhibition (Elkana, Frost, Kramer, Ben-Bashat, & Schweiger, 2013;Griffis et al, 2017;Hartwigsen, 2016;Hartwigsen et al, 2010;Hylin et al, 2017;Lim & Kang, 2015) through the right hemisphere might be reduced because right hemisphere stroke patients show a persistent lesion for about 30 days even when the recovery mechanism has begun. The contralateral homologous cortex may be activated when these patients attempt to comprehend an opaque proverb that requires semantic processing.…”

Structural disconnections explain brain network dysfunction after stroke

“…SDC measures were defined for each patient based on the intersection of their lesion with a structural connectome atlas constructed with data from healthy individuals (see Methods). Similar atlas-based approaches have been used by other recent lesion studies (Carter et al, 2017;Foulon et al, 2018a;Griffis et al, 2017bGriffis et al, , 2017aHope et al, 2018;Kuceyeski et al, 2013Kuceyeski et al, , 2014Kuceyeski et al, , 2015Kuceyeski et al, , 2016bPustina et al, 2017a;Ramsey et al, 2017), and analogous strategies are often employed to study SC-FC relationships in animal models (Adachi et al, 2011;Grandjean et al, 2017;Grayson et al, 2016;Shen et al, 2015b). While these approaches assume similar approximations of individual structural connectomes by the atlas and cannot account for interindividual variability in the properties of un-damaged fiber pathways (Forkel and Catani, 2018;Forkel et al, 2014), they also offer some protection against potential biases arising from interindividual differences in diffusion MRI data quality, lesion effects on data processing/reconstruction, etc.…”

“…Our results argue against a popular account of FC disruptions in patients with focal brain lesions, namely that most focal lesions selectively disrupt function within damaged functional systems (Nomura et al, 2010;Warren et al, 2014) while lesions affecting FC connector nodes broadly disrupt system organization (Gratton et al, 2012). This account has been highly influential, but it has been challenged by recent evidence indicating that lesions can disrupt FC between undamaged systems while sparing FC within damaged systems (Eldaief et al, 2016), that damage to "connector" regions may not be particularly important for predicting FC disruptions in multivariate GM damage models (Yuan et al, 2017), and that disruptions of task-evoked systems are linked to lesions that minimally overlap with constituent regions but that broadly disrupt withinsystem SC (Griffis et al, 2017a). While we directly replicated the effect of FC connector damage on modularity, adding total parcel SDC information increased the variance explained by a factor of 2.5, and the effect of connector damage did not persist when SDC information was simultaneously modeled (Fig.…”

Facilitation of Auditory Comprehension After Theta Burst Stimulation of Wernicke's Area in Stroke Patients: A Pilot Study

“…A growing body of evidence highlights the crucial role of the left hemispheric spared areas in aphasia recovery also at chronic stages (53)(54)(55)(56)(57)(58). Functional neuroimaging studies also confirmed that improved speech and language functioning following aphasia treatment relies, at least partly, on the activation of spared regions of the left hemisphere (59)(60)(61)(62).…”