Neuroplasticity in Post-Stroke Aphasia: A Systematic Review and Meta-Analysis of Functional Imaging Studies of Reorganization of Language Processing

Abstract

Recovery from aphasia is thought to depend on neural plasticity, that is, functional reorganization of surviving brain regions such that they take on new or expanded roles in language processing. We carried out a systematic review and meta-analysis of all articles published between 1995 and early 2020 that have described functional imaging studies of six or more individuals with post-stroke aphasia, and have reported analyses bearing on neuroplasticity of language processing. Each study was characterized and appraised in detail, with particular attention to three critically important methodological issues: task performance confounds, contrast validity, and correction for multiple comparisons. We identified 86 studies describing a total of 561 relevant analyses. We found that methodological limitations related to task performance confounds, contrast validity, and correction for multiple comparisons have been pervasive. Only a few claims about language processing in individuals with aphasia are strongly supported by the extant literature: first, left hemisphere language regions are less activated in individuals with aphasia than neurologically normal controls, and second, in cohorts with aphasia, activity in left hemisphere language regions, and possibly a temporal lobe region in the right hemisphere, is positively correlated with language function. There is modest, equivocal evidence for the claim that individuals with aphasia differentially recruit right hemisphere homotopic regions, but no compelling evidence for differential recruitment of additional left hemisphere regions or domain-general networks. There is modest evidence that left hemisphere language regions return to function over time, but no compelling longitudinal evidence for dynamic reorganization of the language network.

Testing the perilesional neuroplastic recruitment hypothesis in aphasia

“…These cross-sectional chronic results also complement studies of spontaneous aphasia recovery that found a recovery trajectory in which good outcomes in the chronic phase were correlated with taskrelated activity returning to normal levels (Saur, 2006;Stockert et al, 2020). More broadly, these findings are consistent with a recent review of aphasia recovery, which found that lesions caused overall reduced activation in people with aphasia, with activity in left-hemisphere language regions relating to better language function (Wilson & Schneck, 2021).…”

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

“…The bulk of neuroimaging studies investigating patterns of reorganization associated with language recovery in aphasia have used task-based functional magnetic resonance imaging (fMRI; Wilson and Schneck, 2020). fMRI has clearly been valuable for studying neuroplasticity in this population.…”

“…In the language tasks, several different activation patterns were expected. Extrapolated from fMRI studies, individuals with aphasia were hypothesized to recruit spared left hemisphere language regions (i.e., LIFGtri, LIFGoper, LPCG, LMTG, LAG, Sebastian and Kiran, 2011;Sims et al, 2016;Wilson and Schneck, 2020), right hemisphere homologous language regions (i.e., RMTG; Sebastian and Kiran, 2011) and/or domain-general areas (i.e., LMFG, LIFGoper, BLPCG, LSMG, LAG; Meier et al, 2016Meier et al, , 2018Meier et al, , 2019 while naming or judging semantic features of real pictures. In the arithmetic task, they were anticipated to activate regions in the spared domaingeneral network when solving hard versus easy addition problems with potential for diminished extent or magnitude of activation relative to healthy controls (Blank et al, 2015).…”

Vagus Nerve Stimulation as a Potential Adjuvant to Rehabilitation for Post-stroke Motor Speech Disorders

“…Neuroplasticity allows the brain to reorganize speech circuits disrupted by stroke and is a driving force behind recovery from motor speech disorders ( Hartwigsen and Saur, 2019 ; Wilson and Schneck, 2021 ). Though speech production is heavily lateralized to the left hemisphere, increases in neuroplasticity during speech therapy can shift speech processing toward the right hemisphere ( Anglade et al, 2014 ; Wan et al, 2014 ).…”