Glass Half Full: Preserved Anatomical Bypasses Predict Variance in Language Functions After Stroke

The severity of post-stroke aphasia is related to damage to white matter connections. However, neural signaling can route not only through direct connections, but also along multi-step network paths. When brain networks are damaged by stroke, paths can bypass around the damage to restore communication. The shortest network paths between regions could be the most efficient routes for mediating bypasses. We examined how shortest-path bypasses after left hemisphere strokes were related to language performance. Regions within and outside of the canonical language network could be important in aphasia recovery. Therefore, we innovated methods to measure the influence of bypasses in the whole brain. Distinguishing bypasses from all residual shortest paths is difficult without pre-stroke imaging. We identified bypasses by finding shortest paths in subjects with stroke that were longer than those observed in the average network of the most reliably observed connections in age-matched controls. We tested whether features of those bypasses predicted scores in four orthogonal dimensions of language performance derived from a factor analysis of a battery of language tasks. The features were the length of each bypass in steps, and how many bypasses overlapped on each individual direct connection. We related these bypass features to language factors using grid-search cross-validated Support Vector Regression, a technique that extracts robust relationships in high-dimensional data analysis. We discovered that the length of bypasses reliably predicted variance in lexical production (R2 = .576) and auditory comprehension scores (R2 = .164). Bypass overlaps reliably predicted variance in Lexical Production scores (R2 = .247). The predictive elongation features revealed that bypass efficiency along the dorsal stream and ventral stream were most related to Lexical Production and Auditory Comprehension, respectively. Among the predictive bypass overlaps, increased bypass routing through the right hemisphere putamen was negatively related to lexical production ability.

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Right Hemisphere Grey Matter Volume and Language Functions in Stroke Aphasia

Neural Plasticity ◽

10.1155/2017/5601509 ◽

2017 ◽

Vol 2017 ◽

pp. 1-14 ◽

Cited By ~ 8

Author(s):

Sladjana Lukic ◽

Elena Barbieri ◽

Xue Wang ◽

David Caplan ◽

Swathi Kiran ◽

...

Keyword(s):

Grey Matter ◽

Right Hemisphere ◽

Language Ability ◽

Grey Matter Volume ◽

Lesion Site ◽

Language Performance ◽

Support Functions ◽

Language Functions ◽

Lesion Symptom Mapping ◽

The Right

The role of the right hemisphere (RH) in recovery from aphasia is incompletely understood. The present study quantified RH grey matter (GM) volume in individuals with chronic stroke-induced aphasia and cognitively healthy people using voxel-based morphometry. We compared group differences in GM volume in the entire RH and in RH regions-of-interest. Given that lesion site is a critical source of heterogeneity associated with poststroke language ability, we used voxel-based lesion symptom mapping (VLSM) to examine the relation between lesion site and language performance in the aphasic participants. Finally, using results derived from the VLSM as a covariate, we evaluated the relation between GM volume in the RH and language ability across domains, including comprehension and production processes both at the word and sentence levels and across spoken and written modalities. Between-subject comparisons showed that GM volume in the RH SMA was reduced in the aphasic group compared to the healthy controls. We also found that, for the aphasic group, increased RH volume in the MTG and the SMA was associated with better language comprehension and production scores, respectively. These data suggest that the RH may support functions previously performed by LH regions and have important implications for understanding poststroke reorganization.

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The Role of the Right Hemisphere White Matter Tracts in Chronic Aphasic Patients After Damage of the Language Tracts in the Left Hemisphere

Frontiers in Human Neuroscience ◽

10.3389/fnhum.2021.635750 ◽

2021 ◽

Vol 15 ◽

Author(s):

Evie Kourtidou ◽

Dimitrios Kasselimis ◽

Georgia Angelopoulou ◽

Efstratios Karavasilis ◽

Georgios Velonakis ◽

...

Keyword(s):

White Matter ◽

Left Hemisphere ◽

Right Hemisphere ◽

Diffusion Tensor ◽

Inferior Frontal Gyrus ◽

Language Performance ◽

White Matter Tracts ◽

Post Stroke ◽

Language Functions ◽

The Right

The involvement of the right hemisphere (RH) in language, and especially after aphasia resulting from left hemisphere (LH) lesions, has been recently highlighted. The present study investigates white matter structure in the right hemisphere of 25 chronic post-stroke aphasic patients after LH lesions in comparison with 24 healthy controls, focusing on the four cortico-cortical tracts that link posterior parietal and temporal language-related areas with Broca’s region in the inferior frontal gyrus of the LH: the Superior Longitudinal Fasciculi II and III (SLF II and SLF III), the Arcuate Fasciculus (AF), and the Temporo-Frontal extreme capsule Fasciculus (TFexcF). Additionally, the relationship of these RH white matter tracts to language performance was examined. The patients with post-stroke aphasia in the chronic phase and the healthy control participants underwent diffusion tensor imaging (DTI) examination. The aphasic patients were assessed with standard aphasia tests. The results demonstrated increased axial diffusivity in the RH tracts of the aphasic patients. Patients were then divided according to the extent of the left hemisphere white matter loss. Correlations of language performance with radial diffusivity (RD) in the right hemisphere homologs of the tracts examined were demonstrated for the TFexcF, SLF III, and AF in the subgroup with limited damage to the LH language networks and only with the TFexcF in the subgroup with extensive damage. The results argue in favor of compensatory roles of the right hemisphere tracts in language functions when the LH networks are disrupted.

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Engagement of Language and Domain General Networks during Word Monitoring in a Native and Unknown Language

Brain Sciences ◽

10.3390/brainsci11081063 ◽

2021 ◽

Vol 11 (8) ◽

pp. 1063

Author(s):

Kelly Cotosck ◽

Jed Meltzer ◽

Mariana Nucci ◽

Katerina Lukasova ◽

Letícia Mansur ◽

...

Keyword(s):

Phonological Processing ◽

Right Hemisphere ◽

Functional Neuroimaging ◽

Native Language ◽

Dorsal Stream ◽

Ventral Stream ◽

Language Performance ◽

Monitoring Task ◽

Auditory Word ◽

The Right

Functional neuroimaging studies have highlighted the roles of three networks in processing language, all of which are typically left-lateralized: a ventral stream involved in semantics, a dorsal stream involved in phonology and speech production, and a more dorsal “multiple demand” network involved in many effortful tasks. As lateralization in all networks may be affected by life factors such as age, literacy, education, and brain pathology, we sought to develop a task paradigm with which to investigate the engagement of these networks, including manipulations to selectively emphasize semantic and phonological processing within a single task performable by almost anyone regardless of literacy status. In young healthy participants, we administered an auditory word monitoring task, in which participants had to note the occurrence of a target word within a continuous story presented in either their native language, Portuguese, or the unknown language, Japanese. Native language task performance activated ventral stream language networks, left lateralized but bilateral in the anterior temporal lobe. Unfamiliar language performance, being more difficult, activated left hemisphere dorsal stream structures and the multiple demand network bilaterally, but predominantly in the right hemisphere. These findings suggest that increased demands on phonological processing to accomplish word monitoring in the absence of semantic support may result in the bilateral recruitment of networks involved in speech perception under more challenging conditions.

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Shifting of global aphasia to Wernicke’s aphasia in a patient with intact motor function: a case report

BMC Neurology ◽

10.1186/s12883-021-02131-w ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Ya-Chi Chuang ◽

Chuan-Ching Liu ◽

I-Ching Yu ◽

Yu-Lin Tsai ◽

Shin-Tsu Chang

Keyword(s):

Computed Tomography ◽

Right Hemisphere ◽

Single Photon ◽

Ct Perfusion ◽

Single Case ◽

Photon Emission ◽

Emission Computed Tomography ◽

Speech Fluency ◽

Language Functions ◽

The Right

Abstract Background Global aphasia without hemiparesis (GAWH) is a rare stroke syndrome characterized by the dissociation of motor and language functions. Here, we present a case of GAWH with the patient later regaining speech fluency. Case presentation A 73-year-old man was admitted to our emergency department immediately after an episode of syncope. On arrival, we noted his global aphasia but without any focal neurologic signs. Computed tomography (CT) perfusion scans showed a large hypodense region over his left perisylvian area. Under the impression of acute ischaemic stroke, he received recombinant tissue plasminogen activator (rtPA) injection and was treated as an inpatient. The patient was later discharged with GAWH status and received regular speech rehabilitation. After 14 months of rehabilitation, the patient gradually recovered his language expression ability. The degree of aphasia was evaluated with the Concise Chinese Aphasia Test (CCAT), and we obtained brain single photon emission computed tomography (SPECT) scans to assess cerebral blood flow. Conclusion A patient with severe impairments of Broca’s and Wernicke’s areas was able to talk fluently despite being unintelligible. SPECT revealed relative high level of radioactivity uptake in the right frontal lobe, suggesting the deficits in speech fluency could have been compensated by the right hemisphere. Although this is a single case demonstration, the results may strengthen the role of the right hemisphere in GAWH patients and suggests additional study that examines the possible benefits of stimulating activity at right homologous regions for recovering language function after global aphasia.

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Bihemispheric Language: How the Two Hemispheres Collaborate in the Processing of Language

The Speciation of Modern Homo Sapiens ◽

10.5871/bacad/9780197263112.003.0010 ◽

2004 ◽

Author(s):

Norman D. Cook

Keyword(s):

Language Processing ◽

Right Hemisphere ◽

Central Question ◽

Linguistic Processing ◽

Figures Of Speech ◽

Language Functions ◽

Left And Right ◽

Level Of Understanding ◽

The Right

Speech production in most people is strongly lateralized to the left hemisphere (LH), but language understanding is generally a bilateral activity. At every level of linguistic processing that has been investigated experimentally, the right hemisphere (RH) has been found to make characteristic contributions, from the processing of the affective aspects of intonation, through the appreciation of word connotations, the decoding of the meaning of metaphors and figures of speech, to the understanding of the overall coherency of verbal humour, paragraphs and short stories. If both hemispheres are indeed engaged in linguistic decoding and both processes are required to achieve a normal level of understanding, a central question concerns how the separate language functions on the left and right are integrated. This chapter reviews relevant studies on the hemispheric contributions to language processing and the role of interhemispheric communications in cognition.

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Discrepant findings for Wada test and functional magnetic resonance imaging with regard to language function: use of electrocortical stimulation mapping to confirm results

Journal of Neurosurgery ◽

10.3171/jns.2005.102.1.0169 ◽

2005 ◽

Vol 102 (1) ◽

pp. 169-173 ◽

Cited By ~ 25

Author(s):

Kuan H. Kho ◽

Frans S. S. Leijten ◽

Geert-Jan Rutten ◽

Jan Vermeulen ◽

Peter van Rijen ◽

...

Keyword(s):

Magnetic Resonance ◽

Right Hemisphere ◽

Test Results ◽

Functional Magnetic Resonance ◽

Resonance Imaging ◽

Wada Test ◽

Content Type ◽

Language Functions ◽

Imaging Results ◽

The Right

✓ The Wada test is still considered the gold standard for determining the language-dominant hemisphere prior to brain surgery. The authors report on a 34-year-old right-handed woman whose Wada test results indicated that the right hemisphere was dominant for language. In contrast, functional magnetic resonance (fMR) imaging was indicative of bilaterally represented language functions. Activation in the left hemisphere demonstrated on fMR imaging was most pronounced in the Broca area. Importantly, fMR imaging results in this area were confirmed on electrocortical stimulation mapping. These contradictory findings indicated that a right hemispherre dominance for language according to the Wada test should be questioned and verified using electrocortical stimulation. Nonetheless, the question remains whether involvement of these areas in the left frontal hemisphere is critical for language, as these were spared during surgery.

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Lateralization of Language

The Oxford Handbook of Neurolinguistics ◽

10.1093/oxfordhb/9780190672027.013.34 ◽

2019 ◽

pp. 876-906

Author(s):

Lise Van der Haegen ◽

Qing Cai

Keyword(s):

Human Brain ◽

Speech Processing ◽

Right Hemisphere ◽

Hemispheric Specialization ◽

Unique Contribution ◽

Language Impaired ◽

Language Functions ◽

Hemisphere Dominance ◽

The Right

It is intriguing that the two brain halves of the human brain look so similar, but are in fact quite different at the anatomical level, and even more so at the functional level. In particular, the highly frequent co-occurrence of right-handedness and left hemisphere dominance of language has led to an abundance of laterality research. This chapter discusses the most important recent finding on laterality (i.e., left or right hemisphere) and degree of hemispheric specialization for speech production, auditory speech processing, and reading. Following a descriptive overview of these three core sub-processes of language, the chapter summarizes possible influences on the lateralization of each, including anatomical, evolutionary, genetic, developmental, and experiential factors, as well as handedness and impairment. It will become clear that language is a heterogeneous cognitive function driven by a variety of underpinning origins. Next, the often-underestimated role of the right hemisphere for language is discussed with respect to prosody and metaphor comprehension, as well as individual differences in the lateralization of healthy and language-impaired brains. Finally, recent insights into the relationship between lateralized language and non-language functions are discussed, highlighting the unique contribution of lateralization research to the growing knowledge of general human brain mechanisms.

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PRAXIS AND LANGUAGE ORGANIZATION IN LEFT-HANDERS

Acta Neuropsychologica ◽

10.5604/01.3001.0013.9738 ◽

2020 ◽

Vol 18 (1) ◽

pp. 15-28

Author(s):

Grzegorz Króliczak ◽

Brian J. Piper ◽

Weronika Potok ◽

Mikołaj Buchwald ◽

Paweł Kleka ◽

...

Keyword(s):

Bimanual Coordination ◽

Right Hemisphere ◽

Functional Neuroimaging ◽

Spatial Processing ◽

Language Functions ◽

Attentional Resources ◽

Neural Processes ◽

The Mean ◽

The Right

The performance of learned manual gestures (praxis) and the production of speech are thought to depend on related neural processes. If this relationship is not invoked by an unknown, third variable then shifts in their laterality, including dissociations of these two functions, would be unlikely unless the sharing of some neural resources with other functions is advantageous. This could be the case in lefthanders, in whom actions requiring manual precision are controlled by their right hemispheres, and whose representations could attract the control of skilled gesture. Functional neuroimaging (fMRI) was used to study praxis and language functions. Their lateralization indices were measured in 56 consecutively tested lefthanders (28 females), with the mean age of 23.3±4.9 years (range 18.4 – 47 years), and an Edinburgh Handedness Inventory quotient between –100 and –55.6 (with the mean of –83.8±14.2). We show that atypical, bilateral organization or right-lateralization of praxis is more common than atypical organization/lateralization of language, observed, respectively, in 23 (41%) vs. 15 (26.8%) of cases. Specifically, we found: (a) seven cases (12.5%) of clear, and an additional three cases (5.4%) of less pronounced dissociations of atypically represented praxis from typically represented language; (b) 13 cases (23.2%) with atypically organized praxis also associated with atypically organized language, and (c) only two cases (3.6%) of rather strongly atypical lateralization of language, yet with quite typical lateralization of praxis. These outcomes are consistent with an idea that, in some lefthanders, the guidance of skilled manual actions can profit from tighter links with the right hemisphere, whose motor specialization is linked in this particular population to manual precision, but in general to attentional resources, visuo-spatial processing and even bimanual coordination. Because of the presumed links of praxis with productive language, such transfers are often, and unsurprisingly accompanied by the reorganization of the latter. Yet, the very rare cases of reversed language functions, without any pronounced shifts in representations of praxis, indicate that such a pattern of segregation – or inverse dissociation – of these two functions could be maladaptive.

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The Brain Basis of Language Processing: From Structure to Function

Physiological Reviews ◽

10.1152/physrev.00006.2011 ◽

2011 ◽

Vol 91 (4) ◽

pp. 1357-1392 ◽

Cited By ~ 734

Author(s):

Angela D. Friederici

Keyword(s):

Language Processing ◽

Right Hemisphere ◽

Structural Connectivity ◽

Temporal Cortex ◽

Brain Regions ◽

Posterior Portion ◽

Language Functions ◽

Marker Studies ◽

The Right ◽

The Brain

Language processing is a trait of human species. The knowledge about its neurobiological basis has been increased considerably over the past decades. Different brain regions in the left and right hemisphere have been identified to support particular language functions. Networks involving the temporal cortex and the inferior frontal cortex with a clear left lateralization were shown to support syntactic processes, whereas less lateralized temporo-frontal networks subserve semantic processes. These networks have been substantiated both by functional as well as by structural connectivity data. Electrophysiological measures indicate that within these networks syntactic processes of local structure building precede the assignment of grammatical and semantic relations in a sentence. Suprasegmental prosodic information overtly available in the acoustic language input is processed predominantly in a temporo-frontal network in the right hemisphere associated with a clear electrophysiological marker. Studies with patients suffering from lesions in the corpus callosum reveal that the posterior portion of this structure plays a crucial role in the interaction of syntactic and prosodic information during language processing.

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