Lesion correlates of patholinguistic profiles in chronic aphasia: comparisons of syndrome-, modality- and symptom-level assessment

The Neurofunctional Correlates of Morphosyntactic and Thematic Impairments in Aphasia: A Systematic Review and Meta-analysis

Lesion-symptom studies in persons with aphasia showed that left temporoparietal damage, but surprisingly not prefrontal damage, correlates with impaired ability to process thematic roles in the comprehension of semantically reversible sentences (The child is hugged by the mother). This result has led to challenge the time-honored view that left prefrontal regions are critical for sentence comprehension. However, most studies focused on thematic role assignment and failed to consider morphosyntactic processes that are also critical for sentence processing. We reviewed and meta-analyzed lesion-symptom studies on the neurofunctional correlates of thematic role assignment and morphosyntactic processing in comprehension and production in persons with aphasia. Following the PRISMA checklist, we selected 43 papers for the review and 27 for the meta-analysis, identifying a set of potential bias risks. Both the review and the meta-analysis confirmed the correlation between thematic role processing and temporoparietal regions but also clearly showed the involvement of prefrontal regions in sentence processing. Exploratory meta-analyses suggested that both thematic role and morphosyntactic processing correlate with left prefrontal and temporoparietal regions, that morphosyntactic processing correlates with prefrontal structures more than with temporoparietal regions, and that thematic role assignment displays the opposite trend. We discuss current limitations in the literature and propose a set of recommendations for clarifying unresolved issues.

Investigating Aphasia Recovery: Demographic and Clinical Factors

Post-stroke language recovery remains one of the main unresolved topics in the field of aphasia. In recent years, there have been efforts to identify specific factors that could potentially lead to improved language recovery. However, the exact relationship between the recovery of particular language functions and possible predictors, such as demographic or lesion variables, is yet to be fully understood. In the present study, we attempted to investigate such relationships in 42 patients with aphasia after left hemisphere stroke, focusing on three language domains: auditory comprehension, naming and speech fluency. Structural imaging data were also obtained for the identification of the lesion sites. According to our findings, patients demonstrated an overall improvement in all three language domains, while no demographic factor significantly contributed to aphasia recovery. Interestingly, specific lesion loci seemed to have a differential effect on language performance, depending on the time of testing (i.e., acute/subacute vs. chronic phase). We argue that this variability concerning lesion-deficit associations reflects the dynamic nature of aphasia and further discuss possible explanations in the framework of neuroplastic changes during aphasia recovery.

Anterior connectivity critical for recovery of connected speech after stroke

Connected speech recovers to different degrees across people after left hemisphere stroke, but white matter predictors of differential recovery from the acute stage of stroke are unknown. We assessed changes in lexical-syntactic aspects of connected speech in a longitudinal analysis of 40 individuals (18 females) from the acute stage of left hemisphere stroke (within an average of 4 days post-stroke) to subacute (within 2 months) and chronic stages (early: 6 months, late: 1 year) while measuring the extent of acute lesions on white matter tracts to identify tracts predictive of recovery. We found that acute damage to the frontal aslant tract led to a decreased recovery of the fluency and structural complexity of connected speech during the year following left hemisphere stroke. The results were independent of baseline performance, overall lesion volume and the proportion of damage to tract-adjacent grey matter. This longitudinal analysis from acute to chronic stroke provides the first evidence that recovery of fluent and structurally complex spontaneous connected speech requires intact left frontal connectivity via the frontal aslant tract. That the frontal aslant tract was critical for recovery at early as well as later stages of stroke demonstrates that anterior connectivity plays a lasting and important role for the reorganization of function related to the successful production of connected speech.

Structural disconnections associated with language impairments in chronic post-stroke aphasia using disconnectome maps

Inconsistent findings have been reported about the impact of structural disconnections on language function in post-stroke aphasia. This study investigated patterns of structural disconnections associated with chronic language impairments using disconnectome maps. Seventy-six individuals with post-stroke aphasia underwent a battery of language assessments and a structural MRI scan. Support-vector regression disconnectome-symptom mapping analyses were performed to examine the correlations between disconnectome maps, representing the probability of disconnection at each white matter voxel and different language scores. To further understand whether significant disconnections were primarily representing focal damage or a more extended network of seemingly preserved but disconnected areas beyond the lesion site, results were qualitatively compared to support-vector regression lesion-symptom mapping analyses. Part of the left white matter perisylvian network was similarly disconnected in 90% of the individuals with aphasia. Surrounding this common left perisylvian disconnectome, specific structural disconnections in the left fronto-temporo-parietal network were significantly associated with aphasia severity and with lower performance in auditory comprehension, syntactic comprehension, syntactic production, repetition and naming tasks. Auditory comprehension, repetition and syntactic processing deficits were related to disconnections in areas that overlapped with and extended beyond lesion sites significant in SVR-LSM analyses. In contrast, overall language abilities as measured by aphasia severity and naming seemed to be mostly explained by focal damage at the level of the insular and central opercular cortices, given the high overlap between SVR-DSM and SVR-LSM results for these scores. While focal damage seems to be sufficient to explain broad measures of language performance, the structural disconnections between language areas provide additional information on the neural basis of specific and persistent language impairments at the chronic stage beyond lesion volume. Leveraging routinely available clinical data, disconnectome mapping furthers our understanding of anatomical connectivity constraints that may limit the recovery of some language abilities in chronic post-stroke aphasia.

Vascular syndromes: Revisiting classification of poststroke aphasia

Over 150 years have passed since the first formal description of aphasia associated with localized neurologic damage. In the years since that time, a significant amount of research has been conducted to identify/explain the locations and functions of the brain regions responsible for (or associated with) language as well as to describe the various types of aphasia resulting from injury to these locations. Many of these attempts to associate somewhat predictable patterns of language deficits with damage to specific structures have been confounded by atypical reports and considerable variability in either the behavioral presentation and/or structural damage that directly contradict/oppose some of the proposed theories. However, considering the aphasias as vascular syndromes, or a collection of symptoms associated with damage to various structures supplied by a specific artery, accounts for both the predictability and the variability seen. This chapter presents a brief history of aphasia classification, the vascular territories commonly associated with aphasia, the different aphasic vascular syndromes, and the typical recovery/evolution of aphasia presentation over time.

The Effectiveness of Transcranial Magnetic Stimulation (TMS) Paradigms as Treatment Options for Recovery of Language Deficits in Chronic Poststroke Aphasia

Background

In an effort to boost aphasia recovery, modern rehabilitation, in addition to speech and language therapy (SALT), is increasingly incorporating noninvasive methods of brain stimulation. The present study is aimed at investigating the effectiveness of two paradigms of neuronavigated repetitive transcranial magnetic stimulation (rTMS): (i) 1 Hz rTMS and (ii) continuous theta burst stimulation (cTBS) each as a standalone treatment for chronic aphasia poststroke.

Methods

A single subject experimental design (SSED) trial was carried out in which six people with aphasia (PWA) were recruited, following a single left hemispheric stroke more than six months prior to the study. Three individuals were treated with 1 Hz rTMS, and the remaining three were treated with cTBS. In all cases, TMS was applied over the right pars triangularis (pTr). Language assessment, with standardized and functional measures, and cognitive evaluations were carried out at four time points: twice prior to treatment (baseline), one day immediately posttreatment, and at follow-up two months after treatment was terminated. Quality of life (QoL) was also assessed at baseline and two months posttreatment. In addition, one of the participants with severe global aphasia was followed up again one and two years posttherapy.

Results

For all participants, both rTMS paradigms (1 Hz rTMS and cTBS) generated trends towards improvement in several language skills (i.e., verbal receptive language, expressive language, and naming and reading) one day after treatment and/or two months after therapy. Rated QoL remained stable in three individuals, but for the other three, the communication scores of the QoL were reduced, while two of them also showed a decline in the psychological scores. The participant that was treated with cTBS and followed for up to two years showed that the significant improvement she had initially exhibited in comprehension and reading skills two months after TMS (1^st follow-up) was sustained for at least up to two years.

Conclusion

From the current findings, it is suggested that inhibitory TMS over the right pTr has the potential to drive neuroplastic changes as a standalone treatment that facilitates language recovery in poststroke aphasia.

Independent contributions of structural and functional connectivity: Evidence from a stroke model

Altered functional connectivity is related to severity of language impairment in poststroke aphasia. However, it is not clear whether this finding specifically reflects loss of functional coherence, or more generally, is related to decreased structural connectivity due to cortical necrosis. The aim of the current study was to investigate this issue by factoring out structural connectivity from functional connectivity measures and then relating the residual data to language performance poststroke. Ninety-seven participants with a history of stroke were assessed using language impairment measures (Auditory Verbal Comprehension and Spontaneous Speech scores from the Western Aphasia Battery-Revised) and MRI (structural, diffusion tensor imaging, and resting-state functional connectivity). We analyzed the association between functional connectivity and language and controlled for multiple potential neuroanatomical confounders, namely structural connectivity. We identified functional connections within the left hemisphere ventral stream where decreased functional connectivity, independent of structural connectivity, was associated with speech comprehension impairment. These connections exist in frontotemporal and temporoparietal regions. Our results suggest poor speech comprehension in aphasia is at least partially caused by loss of cortical synchrony in a left hemisphere ventral stream network and is not only reflective of localized necrosis or structural connectivity.

Switching attention deficits in post-stroke individuals with different aphasia types

BACKGROUND

Previous studies have shown that individuals with aphasia have impairments in switching attention compared to healthy controls. However, there is insufficient information about the characteristics of switching attention within one task and whether attention deficits vary depending on aphasia type and lesion location. We aimed to address these knowledge gaps by investigating characteristics of switching attention within one type of task in participants with different types of aphasia and distinct lesion sites.

METHOD

Forty individuals with post-stroke aphasia (20 with non-fluent aphasia and frontal lobe damage, and 20 with fluent aphasia and temporal lobe damage) and 20 neurologically healthy age-matched individuals performed an attention switching task. They listened to sequences of high-pitched and low-pitched tones that were presented to them one by one, tallied them separately, and, at the end of each sequence, had to say how many high- and low-pitched tones they had heard.

RESULTS

Participants with aphasia performed significantly worse on the task compared to healthy controls, and the performance of two aphasia groups also differed. Specifically, individuals with both aphasia types made more errors than healthy individuals, and the participants with non-fluent aphasia responded more slowly than controls, while reaction times of the participants with fluent aphasia did not differ significantly from those of controls. Also, the two groups of participants with aphasia differed significantly in accuracy, with individuals in the non-fluent group making more errors.

CONCLUSIONS

The data demonstrated that people with different types of aphasia have distinct impairments in switching attention. Since cognitive deficits impact language performance, this information is important for differentially addressing their language problems and selecting more specific and optimal rehabilitation programs that target different underlying mechanisms.

Lesion-symptom mapping of language impairments in patients suffering from left perisylvian gliomas

Brain tumors cause local structural impairments of the cerebral network. Moreover, brain tumors can also affect functional brain networks more distant from the lesion. In this study, we analyzed the impact of glioma WHO grade II-IV tumors on grey and white matter in relation to impaired language function. In a retrospective analysis of 60 patients, 14 aphasic and 46 non-aphasic, voxel-based lesion-symptom mapping (VLSM) was used to identify tumor induced lesions in grey (GM) and white matter (WM) related to patients' performance in subtests of the Aachen Aphasia Test (AAT). Significant clusters were analyzed for atlas-based grey and white matter involvements in relation to different linguistic modalities. VLSM analysis indicated significant contribution of a posterior perisylvian cluster covering WM and GM to AAT performance averaged across subtests. When considering individual AAT subtests, a substantial overlap between significant clusters for analysis of the token test, picture naming and language comprehension results could be observed. The WM-cluster intersections reflect the overall importance of the perisylvian area in language function, similarly to GM participations. Especially the constant high percentages of Heschl's gyrus, superior temporal gyrus, inferior longitudinal and middle longitudinal fascicles, but also arcuate and inferior fronto-occipital fascicles highlight the importance of the posterior perisylvian area for language function.

Functional Contributions of the Arcuate Fasciculus to Language Processing

Current evidence strongly suggests that the arcuate fasciculus (AF) is critical for language, from spontaneous speech and word retrieval to repetition and comprehension abilities. However, to further pinpoint its unique and differential role in language, its anatomy needs to be explored in greater detail and its contribution to language processing beyond that of known cortical language areas must be established. We address this in a comprehensive evaluation of the specific functional role of the AF in a well-characterized cohort of individuals with chronic aphasia (n = 33) following left hemisphere stroke. To evaluate macro- and microstructural integrity of the AF, tractography based on the constrained spherical deconvolution model was performed. The AF in the left and right hemispheres were then manually reconstructed using a modified 3-segment model (Catani et al., 2005), and a modified 2-segment model (Glasser and Rilling, 2008). The normalized volume and a measure of microstructural integrity of the long and the posterior segments of the AF were significantly correlated with language indices while controlling for gender and lesion volume. Specific contributions of AF segments to language while accounting for the role of specific cortical language areas – inferior frontal, inferior parietal, and posterior temporal – were tested using multiple regression analyses. Involvement of the following tract segments in the left hemisphere in language processing beyond the contribution of cortical areas was demonstrated: the long segment of the AF contributed to naming abilities; anterior segment – to fluency and naming; the posterior segment – to comprehension. The results highlight the important contributions of the AF fiber pathways to language impairments beyond that of known cortical language areas. At the same time, no clear role of the right hemisphere AF tracts in language processing could be ascertained. In sum, our findings lend support to the broader role of the left AF in language processing, with particular emphasis on comprehension and naming, and point to the posterior segment of this tract as being most crucial for supporting residual language abilities.

A data-driven approach to post-stroke aphasia classification and lesion-based prediction

Aphasia is an acquired impairment in the production or comprehension of language, typically caused by left hemisphere stroke. The subtyping framework used in clinical aphasiology today is based on the Wernicke-Lichtheim model of aphasia formulated in the late 19th century, which emphasizes the distinction between language production and comprehension. The current study used a data-driven approach that combined modern statistical, machine learning, and neuroimaging tools to examine behavioural deficit profiles and their lesion correlates and predictors in a large cohort of individuals with post-stroke aphasia. First, individuals with aphasia were clustered based on their behavioural deficit profiles using community detection analysis (CDA) and these clusters were compared with the traditional aphasia subtypes. Random forest classifiers were built to evaluate how well individual lesion profiles predict cluster membership. The results of the CDA analyses did not align with the traditional model of aphasia in either behavioural or neuroanatomical patterns. Instead, the results suggested that the primary distinction in aphasia (after severity) is between phonological and semantic processing rather than between production and comprehension. Further, lesion-based classification reached 75% accuracy for the CDA-based categories and only 60% for categories based on the traditional fluent/non-fluent aphasia distinction. The results of this study provide a data-driven basis for a new approach to classification of post-stroke aphasia subtypes in both research and clinical settings.

Effect of High Frequency Transcranial Magnetic Stimulation on Recovery of Chronic Post-Stroke Aphasia

BACKGROUND

Both hemispheres have role in post-stroke aphasia recovery but better recovery is expected with the restoration of function by the left hemisphere. Transcranial stimulation has been used to favor recruitment of left-hemispheric language networks and increase activity of the left hemisphere, thus helps aphasia recovery .

OBJECTIVE

The aim of this study is to evaluate the effect of excitatory repetitive transcranial magnetic stimulation (rTMS) on recovery of post stroke aphasic patients .

MATERIALS AND METHODS

Twenty patients with post stroke chronic aphasia were enrolled in the study. Aphasia severity was assessed using Aphasia Severity Rating Scale (ASRS). Linguistic deficits were assessed using Kasr Al-Aini Arabic Aphasia test (KAAT). Real rTMS was applied three for 10 sessions of 10-Hz stimulation, positioned over the left Broca's area of the affected hemisphere. All patients were evaluated before, after the end of treatment sessions and one month later .

RESULTS

There was a significant improvement in the mean total score and mean scores of components of KAAT scale before, immediately after and after one month of rTMS (P< 0.05). Moreover, there was a significant improvement in mean scores of ASRS before, immediately after and after one month of rTMS (P= 0.000). There was a significant difference in mean scores of ASRS and KAAT before, immediately after the last session and after one month between small, medium and large brain infarcts. (P< 0.05).

CONCLUSION

Excitatory rTMS is a beneficial adjuvant therapy that improves language skills in patients with chronic post-stroke non-fluent aphasia in short and long term. The protocol of this observational study was registered in clinical trial registration: www.ClinicalTrials.gov, identifier: NCT04708197.

German Language Adaptation of the NAVS (NAVS-G) and of the NAT (NAT-G): Testing Grammar in Aphasia

Grammar provides the framework for understanding and producing language. In aphasia, an acquired language disorder, grammatical deficits are diversified and widespread. However, the few assessments for testing grammar in the German language do not consider current linguistic, psycholinguistic, and functional imaging data, which have been shown to be crucial for effective treatment. This study developed German language versions of the Northwestern Assessment of Verbs and Sentences (NAVS-G) and the Northwestern Anagram Test (NAT-G) to examine comprehension and production of verbs, controlling for the number and optionality of verb arguments, and sentences with increasing syntactic complexity. The NAVS-G and NAT-G were tested in 27 healthy participants, 15 right hemispheric stroke patients without aphasia, and 15 stroke patients with mild to residual aphasia. Participants without aphasia showed near-perfect performance, with the exception of (object) relative sentences, where accuracy was associated with educational level. In each patient with aphasia, deficits in more than one subtest were observed. The within and between population-groups logistic mixed regression analyses identified significant impairments in processing syntactic complexity at the verb and sentence levels. These findings indicate that the NAVS-G and NAT-G have potential for testing grammatical competence in (German) stroke patients.

Multivariate machine learning-based language mapping in glioma patients based on lesion topography

Diffusive and progressive tumor infiltration within language-related areas of the brain induces functional reorganization. However, the macrostructural basis of subsequent language deficits is less clear. To address this issue, lesion topography data from 137 preoperative patients with left cerebral language-network gliomas (81 low-grade gliomas and 56 high-grade gliomas), were adopted for multivariate machine-learning-based lesion-language mapping analysis. We found that tumor location in the left posterior middle temporal gyrus-a bottleneck where both dorsal and ventral language pathways travel-predicted deficits of spontaneous speech (cluster size = 1356 mm³, false discovery rate corrected P < 0.05) and naming scores (cluster size = 1491 mm³, false discovery rate corrected P < 0.05) in the high-grade glioma group. In contrast, no significant lesion-language mapping results were observed in the low-grade glioma group, suggesting a large functional reorganization. These findings suggest that in patients with gliomas, the macrostructural plasticity mechanisms that modulate brain-behavior relationships depend on glioma grade.

Uncertainty Promotes Neuroreductionism: A Behavioral Online Study on Folk Psychological Causal Inference from Neuroimaging Data

INTRODUCTION

Increased efforts in neuroscience try to understand mental disorders as brain disorders. In the present study, we investigate how common a neuroreductionist inclination is among highly educated people. In particular, we shed light on implicit presuppositions of mental disorders little is known about in the public, exemplified here by the case of body integrity dysphoria (BID) that is considered a mental disorder for the first time in ICD-11.

METHODS

Identically graphed, simulated data of mind-brain correlations were shown in 3 contexts with presumably different presumptions about causality. 738 highly educated lay people rated plausibility of causality attribution from the brain to mind and from mind to the brain for correlations between brain structural properties and mental phenomena. We contrasted participants' plausibility ratings of causality in the contexts of commonly perceived brain lesion-induced behavior (aphasia), behavior-induced training effects (piano playing), and a newly described mental disorder (BID).

RESULTS

The findings reveal the expected context-dependent modulation of causality attributions in the contexts of aphasia and piano playing. Furthermore, we observed a significant tendency to more readily attribute causal inference from the brain to mind than vice versa with respect to BID.

CONCLUSION

In some contexts, exemplified here by aphasia and piano playing, unidirectional causality attributions may be justified. However, with respect to BID, we critically discuss presumably unjustified neuroreductionist inclinations under causal uncertainty. Finally, we emphasize the need for a presupposition-free approach in psychiatry.

Multivariate Lesion-Behavior Mapping of General Cognitive Ability and Its Psychometric Constituents

General cognitive ability, or general intelligence (g), is central to cognitive science, yet the processes that constitute it remain unknown, in good part because most prior work has relied on correlational methods. Large-scale behavioral and neuroanatomical data from neurologic patients with focal brain lesions can be leveraged to advance our understanding of the key mechanisms of g, as this approach allows inference on the independence of cognitive processes along with elucidation of their respective neuroanatomical substrates. We analyzed behavioral and neuroanatomical data from 402 humans (212 males; 190 females) with chronic, focal brain lesions. Structural equation models (SEMs) demonstrated a psychometric isomorphism between g and working memory in our sample (which we refer to as g/Gwm), but not between g and other cognitive abilities. Multivariate lesion-behavior mapping analyses indicated that g and working memory localize most critically to a site of converging white matter tracts deep to the left temporo-parietal junction. Tractography analyses demonstrated that the regions in the lesion-behavior map of g/Gwm were primarily associated with the arcuate fasciculus. The anatomic findings were validated in an independent cohort of acute stroke patients (n = 101) using model-based predictions of cognitive deficits generated from the Iowa cohort lesion-behavior maps. The neuroanatomical localization of g/Gwm provided the strongest prediction of observed g in the new cohort (r = 0.42, p < 0.001), supporting the anatomic specificity of our findings. These results provide converging behavioral and anatomic evidence that working memory is a key mechanism contributing to domain-general cognition.SIGNIFICANCE STATEMENT General cognitive ability (g) is thought to play an important role in individual differences in adaptive behavior, yet its core processes remain unknown, in large part because of difficulties in making causal inferences from correlated data. Using data from patients with focal brain damage, we demonstrate that there is a strong psychometric correspondence between g and working memory - the ability to maintain and control mental information, and that the critical neuroanatomical substrates of g and working memory include the arcuate fasciculus. This work provides converging behavioral and neuroanatomical evidence that working memory is a key mechanism contributing to domain-general cognition.

Clinical and neuroimaging factors associated with aphasia severity in stroke patients: diffusion tensor imaging study

This study investigated factors associated with aphasia severity at both 2 weeks and 3 months after stroke using demographic and clinical variables, brain diffusion tensor imaging (DTI) parameters, and lesion volume measurements. Patients with left hemisphere stroke were assessed at 2 weeks (n = 68) and at 3 months (n = 20) after stroke. Demographic, clinical, and neuroimaging data were collected; language functions were assessed using the Western Aphasia Battery. For neuroimaging, DTI parameters, including the laterality index (LI) of fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity, mean diffusivity and fibre density (FD) of the arcuate fasciculus (AF), and lesion volume, were measured. Lesion volume, cortical involvement, and the National Institutes of Health Stroke Scale score significantly predicted aphasia severity at 2 weeks after stroke, whereas the aphasia quotient and presence of depression during the early subacute stage were significant predictors at 3 months after stroke. According to Pearson correlation, LI-AD and LI-FD were significantly correlated with the aphasia quotient 2 weeks after ischaemic stroke, and the LI-FA was significantly correlated with the aphasia quotient 2 weeks after haemorrhagic stroke, suggesting that the extent and mechanism of AF injuries differ between ischaemic and haemorrhagic strokes. These differences may contribute to aphasia severity.

Structural Characteristic of the Arcuate Fasciculus in Patients with Fluent Aphasia Following Intracranial Hemorrhage: A Diffusion Tensor Tractography Study

This study investigated the relationship between the structural characteristics of the left arcuate fasciculus (AF) reconstructed using diffusion tensor image (DTI) and the type of fluent aphasia according to hemorrhage lesions in patients with fluent aphasia following intracranial hemorrhage (ICH). Five patients with fluent aphasia following ICH (three males, two females; mean age 55.0 years; range 47 to 60 years) and with sixteen age-matched heathy control subjects were involved in this study. The ICHs of patients 1 and 2 were located in the left parietal lobe and the left basal ganglia. ICHs were located in the left anterior temporal of patient 3, the left temporal lobe of patient 4, and the left frontal lobe of patient 5. We assessed patients’ language function using K-WAB (the Korean version of the Western Aphasia Battery) and reconstructed the AF using DTI. We measured DTI parameters including the fractional anisotropy (FA), tract volume (TV), fiber number (FN), and mean diffusivity (MD). All patients showed neural tract injury (the decrement of FA, TV, and FN and increment of MD). The left AFs in patients 1 and 2 were shifted from Broca’s and Wernicke’s territories. The destruction of Wernicke’s territory resulted in conduction or transcortical sensory aphasia in patients 3 and 4. The structural difference of the AF in patients following ICH in the left hemisphere was associated with various types of fluent aphasia.

The Cortical Organization of Syntax

Syntax, the structure of sentences, enables humans to express an infinite range of meanings through finite means. The neurobiology of syntax has been intensely studied but with little consensus. Two main candidate regions have been identified: the posterior inferior frontal gyrus (pIFG) and the posterior middle temporal gyrus (pMTG). Integrating research in linguistics, psycholinguistics, and neuroscience, we propose a neuroanatomical framework for syntax that attributes distinct syntactic computations to these regions in a unified model. The key theoretical advances are adopting a modern lexicalized view of syntax in which the lexicon and syntactic rules are intertwined, and recognizing a computational asymmetry in the role of syntax during comprehension and production. Our model postulates a hierarchical lexical-syntactic function to the pMTG, which interconnects previously identified speech perception and conceptual-semantic systems in the temporal and inferior parietal lobes, crucial for both sentence production and comprehension. These relational hierarchies are transformed via the pIFG into morpho-syntactic sequences, primarily tied to production. We show how this architecture provides a better account of the full range of data and is consistent with recent proposals regarding the organization of phonological processes in the brain.

Mapping eloquent cortex: A voxel-based lesion-symptom mapping study of core speech production capacities in brain tumour patients

This study used voxel-based lesion-symptom mapping to examine the cortical and white matter regions associated with language production impairments in a sample of 63 preoperative tumour patients. We identified four cognitive functions considered crucial for spoken language production: semantic-to-lexical mapping (selecting the appropriate lexical label for the intended concept); phonological encoding (retrieving the word's phonological form); articulatory-motor planning (programming the articulatory motor movements); and goal-driven language selection (exerting top-down control over the words selected for production). Each participant received a score estimating their competence on each function. We then mapped the region(s) where pathology was significantly associated with low scores. For semantic-to-lexical mapping, the critical map encompassed portions of the left posterior middle and inferior temporal gyri, extending into posterior fusiform gyrus, overlapping substantially with the territory of the inferior longitudinal fasciculus. For phonological encoding, the map encompassed the left inferior parietal lobe and posterior middle temporal gyrus, overlapping with the territory of the inferior longitudinal and posterior arcuate fasciculi. For articulatory-motor planning, the map encompassed parts of the left frontal pole, frontal operculum, and inferior frontal gyrus, and overlapped with the territory of the frontal aslant tract. Finally, the map for goal-driven language selection encompassed the left frontal pole and the anterior cingulate cortex. We compare our findings with those from other neuropsychological samples, and conclude that the study of tumour patients offers evidence that complements that available from other populations.

Brain-Derived Neurotrophic Factor Genotype-Specific Differences in Cortical Activation in Chronic Aphasia

Purpose The brain-derived neurotrophic factor (BDNF) gene has been shown to be important for synaptic plasticity in animal models. Human research has suggested that BDNF genotype may influence stroke recovery. Some studies have suggested a genotype-specific motor-related brain activation in stroke recovery. However, recovery from aphasia in relation to BDNF genotype and language-related brain activation has received limited attention. We aimed to explore functional brain activation by BDNF genotype in individuals with chronic aphasia. Consistent with findings in healthy individuals and individuals with poststroke motor impairment, we hypothesized that, among individuals with aphasia, the presence of the Met allele of the BDNF gene is associated with reduced functional brain activation compared to noncarriers of the Met allele. Method Eighty-seven individuals with chronic stroke-induced aphasia performed a naming task during functional magnetic resonance imaging scanning and submitted blood or saliva samples for BDNF genotyping. The mean number of activated voxels was compared between groups, and group-based activation maps were directly compared. Neuropsychological testing was conducted to compare language impairment between BDNF genotype groups. The Western Aphasia Battery Aphasia Quotient (Kertesz, 2007) was included as a covariate in all analyses. Results While lesion size was comparable between groups, the amount of activation, quantified as the number of activated voxels, was significantly greater in noncarriers of the Met allele (whole brain: 98,500 vs. 28,630, p < .001; left hemisphere only: 37,209 vs. 7,000, p < .001; right hemisphere only: 74,830 vs. 30,630, p < .001). This difference was most strongly expressed in the right hemisphere posterior temporal area, pre- and postcentral gyrus, and frontal lobe, extending into the white matter. Correspondingly, the atypical BDNF genotype group was found to have significantly less severe aphasia (Western Aphasia Battery Aphasia Quotient of 64.2 vs. 54.3, p = .033) and performed better on a naming task (Philadelphia Naming Test [Roach, Schwartz, Martin, Grewal, & Brecher, 1996] score of 74.7 vs. 52.8, p = .047). A region of interest analysis of intensity of activation revealed no group differences, and a direct comparison of average activation maps across groups similarly yielded null results. Conclusion BDNF genotype mediates cortical brain activation in individuals with chronic aphasia. Correspondingly, individuals carrying the Met allele present with more severe aphasia compared to noncarriers. These findings warrant further study into the effects of BDNF genotype in aphasia. Supplemental Material https://doi.org/10.23641/asha.10073147 Presentation Video https://doi.org/10.23641/asha.10257581.

Predictive role of subcomponents of the left arcuate fasciculus in prognosis of aphasia after stroke: A retrospective observational study

The relationship between the left arcuate fasciculus (AF) and stroke-related aphasia is unclear. In this retrospective study, we aimed to investigate the role of subcomponents of the left AF in predicting prognosis of aphasia after stroke. Twenty stroke patients with aphasia were recruited and received language assessment as well as diffusion tensor tractography scanning at admission. According to injury of the left AF, the participants were classified into four groups: group A (4 cases), the AF preserved intactly; group B (6 cases), the anterior segment injured; group C (4 cases), the posterior segment injured; and group D (6 cases), completely injured. After a consecutive speech therapy, language assessment was performed again. Changes of language functions among the groups were compared and the relation between these changes with segments injury of the AF was analyzed. After therapy, relatively high increase score percentage changes in terms of all the subcategories of language assessment were observed both in group A and C; by contrast, only naming in group B, and spontaneous speech in group D. Although no statistical difference was demonstrated among the four groups. In addition, there was no significant correlation between improvement of language function with segments injury of the AF. The predictive role of subcomponents of the left AF in prognosis of aphasia is obscure in our study. Nevertheless, it indicates the importance of integrity of the left AF for recovery of aphasia, namely that preservation of the left AF on diffusion tensor tractography could mean recovery potential of aphasia after stroke.

[The prognosis for post-stroke aphasia]

AIM

To determine risk factors and factors of favorable prognosis for regression of post-stroke aphasia in the early recovery period of ischemic stroke (IS).

MATERIAL AND METHODS

A cohort study was undertaken with 40 patients with different clinical forms of aphasia. The duration of study was 3-4 months of the disease. The regression of speech and non-speech cognitive impairment was assessed by the Method of a 10-point evaluation of higher mental functions. The method involves a comprehensive assessment of all mental functions with more than 90 subtests at the beginning and at the end of rehabilitation course and the calculation of the difference in the scoring of each mental function as a measure of treatment efficacy. Using logistic regression and odds ratio estimation, significance of the influence and the prognostic relationship of symptoms related to IS, and a number of biological and social factors (sex, age, and education) were studied.

RESULTS

An independent prognostic value for the aphasia regression on the third month of disease has the severity of neurologic symptomatology (NIHSS score) for the first day of stroke (OR 3,27 95% CI 1,02-9,77) and the third month of the disease (p=0,005, OR 4,6, 95% CI [1,39-15,11]) and the decrease in daily activity assessed by the total score of the Barthel index (p=0,004, OR 3,92, 95% CI [1,01-15,21]). A number of MRI signs (localization of post-stroke changes in the left angular gyrus, frontal-temporal region and focal volume) had a significant effect on the dynamics of non-verbal cognitive impairment. Neuropsychological examination revealed a significant improvement of speech in patients with initially severe forms of aphasias, in particular, sensory and sensorimotor. A direct relationship between age and certain clinical forms of aphasia as well as a significant positive effect of duration (β=1,91, p≤0,01) and level of education (β=1,68, p≤0,007) on aphasia regression were determined.

CONCLUSION

The severity of neurologic symptoms, in particular motor and sensory deficits, both in the acute and in the recovery period of the disease is one of the pathogenetic factors worsening the processes of functional reorganization of neuronal speech networks. The positive dynamics of the recovery of speech function is associated with the initial severity and clinical form of aphasia. The level and duration of education are related to factors positively affecting post-stroke neuroplasticity.

Cortical and structural-connectivity damage correlated with impaired syntactic processing in aphasia

Agrammatism in aphasia is not a homogeneous syndrome, but a characterization of a nonuniform set of language behaviors in which grammatical markers and complex syntactic structures are omitted, simplified, or misinterpreted. In a sample of 71 left-hemisphere stroke survivors, syntactic processing was quantified with the Northwestern Assessment of Verbs and Sentences (NAVS). Classification analyses were used to assess the relation between NAVS performance and morphosyntactically reduced speech in picture descriptions. Voxel-based and connectivity-based lesion-symptom mapping were applied to investigate neural correlates of impaired syntactic processing. Despite a nonrandom correspondence between NAVS performance and morphosyntactic production deficits, there was variation in individual patterns of syntactic processing. Morphosyntactically reduced production was predicted by lesions to left-hemisphere inferior frontal cortex. Impaired verb argument structure production was predicted by damage to left-hemisphere posterior superior temporal and angular gyrus, as well as to a ventral pathway between temporal and frontal cortex. Damage to this pathway was also predictive of impaired sentence comprehension and production, particularly of noncanonical sentences. Although agrammatic speech production is primarily predicted by lesions to inferior frontal cortex, other aspects of syntactic processing rely rather on regional integrity in temporoparietal cortex and the ventral stream.

Language recovery following stroke

Objective: To review the research literature pertaining to post-stroke language recovery, and to discuss neurocognitive assessment in patients in the context of aphasia, time course of language recovery, factors associated with language recovery, and therapeutic techniques designed to facilitate language recovery. Method: Articles were identified through PubMed, MEDLINE, PsychINFO, and Google Scholar searches. Examples of utilized keywords include "post-stroke aphasia," "post-stroke language recovery," "post-stroke neurocognitive assessment," and "neuropsychology and aphasia." Results: Most language recovery occurs in the first few weeks following stroke, but residual recovery may occur for many years. Although initial aphasia severity is the single largest determinant of post-stroke language recovery, a number of other variables also contribute. Several techniques have been developed to aid in the recovery process including speech-language therapy and noninvasive brain stimulation, although the effectiveness of acute and subacute treatment remains unclear. Some degree of valid neurocognitive assessment is possible in patients with aphasia, and the information gained from such an evaluation can aid the rehabilitative process Conclusions: Significant recovery of language function is possible following a stroke, but prediction of level of recovery in an individual patient is difficult. Information about initial aphasia severity and the integrity of cognitive domains other than language can help guide the rehabilitation team, as well as manage expectations for recovery.

Neuronavigated theta burst stimulation for chronic aphasia: two exploratory case studies

The present study reports the findings of a 10-day neuronavigated continuous theta burst stimulation (cTBS) over the right pars triangularis for two individuals with chronic aphasia after a single left hemispheric stroke. Baseline language and quality of life measures were collected prior to the treatment study, post-treatment and at 3-month follow up. Therapy was tolerated well by both participants and no side effects were noticed during and after treatment. Results from one individual showed potential for positive change in performance in comprehension and expressive language both post-treatment and at the follow-up stage. Also, a trend towards improvement post-treatment was noticed in discourse and sentence productivity, and grammatical accuracy. In the follow up stage, grammatical accuracy showed a trend towards improvement; discourse productivity decreased and; sentence productivity skills showed mixed results. Results from the other participant showed potential for positive change in comprehension post-treatment, that was maintained at the follow-up stage. However, a decline in expressive language post-treatment and at follow-up, stronger post-treatment, was noticed. Regarding quality of life measurements, participant one appeared to have improved as his performance increased in the overall, physical and communication domains, but decreased slightly in the psychosocial domain. The second participant improved in the physical and communication domains and declined overall and in the psychosocial domains. Findings from this study indicate that cTBS over the right pars triangularis may have the potential to improve various language skills in patients suffering from chronic aphasia post-stroke. However, the potential benefits of this fast, non-invasive brain stimulation protocol on improvement of language abilities post-stroke need further exploration.

Neurolinguistics Research Advancing Development of a Direct-Speech Brain-Computer Interface

A direct-speech brain-computer interface (DS-BCI) acquires neural signals corresponding to imagined speech, then processes and decodes these signals to produce a linguistic output in the form of phonemes, words, or sentences. Recent research has shown the potential of neurolinguistics to enhance decoding approaches to imagined speech with the inclusion of semantics and phonology in experimental procedures. As neurolinguistics research findings are beginning to be incorporated within the scope of DS-BCI research, it is our view that a thorough understanding of imagined speech, and its relationship with overt speech, must be considered an integral feature of research in this field. With a focus on imagined speech, we provide a review of the most important neurolinguistics research informing the field of DS-BCI and suggest how this research may be utilized to improve current experimental protocols and decoding techniques. Our review of the literature supports a cross-disciplinary approach to DS-BCI research, in which neurolinguistics concepts and methods are utilized to aid development of a naturalistic mode of communication.

Mixed language dominance: insights from a case of unexpected fluent aphasia with semantic jargon resulting from massive left perisylvian lesion

We report a right-handed patient with a massive lesion in left perisylvian language cortex, who unexpectedly presented with fluent aphasia with semantic jargon. Language deficits were assessed with a comprehensive battery of language tests. Comprehension, naming, reading, and writing were severely impaired, and verbal expression was moderately fluent with semantic jargon. Although the patient's lesion included brain areas typically essential for motor speech coordination, he was neither nonfluent nor apraxic. He exhibited strikingly unexpected aphasia with semantic jargon and prominent comprehension deficits, suggesting that this is a case of mixed dominance: the right hemisphere likely controls motor speech and basic syntactic skills, while the severely damaged left hemisphere controls semantic processing, predictably severely impaired.

Neuroimaging of stroke recovery from aphasia - Insights into plasticity of the human language network

The role of left and right hemisphere brain regions in language recovery after stroke-induced aphasia remains controversial. Here, we summarize how neuroimaging studies increase the current understanding of functional interactions, reorganization and plasticity in the language network. We first discuss the temporal dynamics across the time course of language recovery, with a main focus on longitudinal studies from the acute to the chronic phase after stroke. These studies show that the functional contribution of perilesional and spared left hemisphere as well as contralesional right hemisphere regions to language recovery changes over time. The second section introduces critical variables and recent advances on early prediction of subsequent outcome. In the third section, we outline how multi-method approaches that combine neuroimaging techniques with non-invasive brain stimulation elucidate mechanisms of plasticity and reorganization in the language network. These approaches provide novel insights into general mechanisms of plasticity in the language network and might ultimately support recovery processes during speech and language therapy. Finally, the neurobiological correlates of therapy-induced plasticity are discussed. We argue that future studies should integrate individualized approaches that might vary the combination of language therapy with specific non-invasive brain stimulation protocols across the time course of recovery. The way forward will include the combination of such approaches with large data sets obtained from multicentre studies.

Your perspective and my benefit: multiple lesion models of self-other integration strategies during social bargaining

Recursive social decision-making requires the use of flexible, context-sensitive long-term strategies for negotiation. To succeed in social bargaining, participants' own perspectives must be dynamically integrated with those of interactors to maximize self-benefits and adapt to the other's preferences, respectively. This is a prerequisite to develop a successful long-term self-other integration strategy. While such form of strategic interaction is critical to social decision-making, little is known about its neurocognitive correlates. To bridge this gap, we analysed social bargaining behaviour in relation to its structural neural correlates, ongoing brain dynamics (oscillations and related source space), and functional connectivity signatures in healthy subjects and patients offering contrastive lesion models of neurodegeneration and focal stroke: behavioural variant frontotemporal dementia, Alzheimer's disease, and frontal lesions. All groups showed preserved basic bargaining indexes. However, impaired self-other integration strategy was found in patients with behavioural variant frontotemporal dementia and frontal lesions, suggesting that social bargaining critically depends on the integrity of prefrontal regions. Also, associations between behavioural performance and data from voxel-based morphometry and voxel-based lesion-symptom mapping revealed a critical role of prefrontal regions in value integration and strategic decisions for self-other integration strategy. Furthermore, as shown by measures of brain dynamics and related sources during the task, the self-other integration strategy was predicted by brain anticipatory activity (alpha/beta oscillations with sources in frontotemporal regions) associated with expectations about others' decisions. This pattern was reduced in all clinical groups, with greater impairments in behavioural variant frontotemporal dementia and frontal lesions than Alzheimer's disease. Finally, connectivity analysis from functional magnetic resonance imaging evidenced a fronto-temporo-parietal network involved in successful self-other integration strategy, with selective compromise of long-distance connections in frontal disorders. In sum, this work provides unprecedented evidence of convergent behavioural and neurocognitive signatures of strategic social bargaining in different lesion models. Our findings offer new insights into the critical roles of prefrontal hubs and associated temporo-parietal networks for strategic social negotiation.

Comprehensibility and neural substrate of communicative gestures in severe aphasia

Communicative gestures can compensate incomprehensibility of oral speech in severe aphasia, but the brain damage that causes aphasia may also have an impact on the production of gestures. We compared the comprehensibility of gestural communication of persons with severe aphasia and non-aphasic persons and used voxel based lesion symptom mapping (VLSM) to determine lesion sites that are responsible for poor gestural expression in aphasia. On group level, persons with aphasia conveyed more information via gestures than controls indicating a compensatory use of gestures in persons with severe aphasia. However, individual analysis showed a broad range of gestural comprehensibility. VLSM suggested that poor gestural expression was associated with lesions in anterior temporal and inferior frontal regions. We hypothesize that likely functional correlates of these localizations are selection of and flexible changes between communication channels as well as between different types of gestures and between features of actions and objects that are expressed by gestures.

Neural Basis of Acquired Amusia and Its Recovery after Stroke

Although acquired amusia is a relatively common disorder after stroke, its precise neuroanatomical basis is still unknown. To evaluate which brain regions form the neural substrate for acquired amusia and its recovery, we performed a voxel-based lesion-symptom mapping (VLSM) and morphometry (VBM) study with 77 human stroke subjects. Structural MRIs were acquired at acute and 6 month poststroke stages. Amusia and aphasia were behaviorally assessed at acute and 3 month poststroke stages using the Scale and Rhythm subtests of the Montreal Battery of Evaluation of Amusia (MBEA) and language tests. VLSM analyses indicated that amusia was associated with a lesion area comprising the superior temporal gyrus, Heschl's gyrus, insula, and striatum in the right hemisphere, clearly different from the lesion pattern associated with aphasia. Parametric analyses of MBEA Pitch and Rhythm scores showed extensive lesion overlap in the right striatum, as well as in the right Heschl's gyrus and superior temporal gyrus. Lesions associated with Rhythm scores extended more superiorly and posterolaterally. VBM analysis of volume changes from the acute to the 6 month stage showed a clear decrease in gray matter volume in the right superior and middle temporal gyri in nonrecovered amusic patients compared with nonamusic patients. This increased atrophy was more evident in anterior temporal areas in rhythm amusia and in posterior temporal and temporoparietal areas in pitch amusia. Overall, the results implicate right temporal and subcortical regions as the crucial neural substrate for acquired amusia and highlight the importance of different temporal lobe regions for the recovery of amusia after stroke.

SIGNIFICANCE STATEMENT

Lesion studies are essential in uncovering the brain regions causally linked to a given behavior or skill. For music perception ability, previous lesion studies of amusia have been methodologically limited in both spatial accuracy and time domain as well as by small sample sizes, providing coarse and equivocal information about which brain areas underlie amusia. By using longitudinal MRI and behavioral data from a large sample of stroke patients coupled with modern voxel-based analyses methods, we were able provide the first systematic evidence for the causal role of right temporal and striatal areas in music perception. Clinically, these results have important implications for the diagnosis and prognosis of amusia after stroke and for rehabilitation planning.

Multivariate Connectome-Based Symptom Mapping in Post-Stroke Patients: Networks Supporting Language and Speech

Language processing relies on a widespread network of brain regions. Univariate post-stroke lesion-behavior mapping is a particularly potent method to study brain-language relationships. However, it is a concern that this method may overlook structural disconnections to seemingly spared regions and may fail to adjudicate between regions that subserve different processes but share the same vascular perfusion bed. For these reasons, more refined structural brain mapping techniques may improve the accuracy of detecting brain networks supporting language. In this study, we applied a predictive multivariate framework to investigate the relationship between language deficits in human participants with chronic aphasia and the topological distribution of structural brain damage, defined as post-stroke necrosis or cortical disconnection. We analyzed lesion maps as well as structural connectome measures of whole-brain neural network integrity to predict clinically applicable language scores from the Western Aphasia Battery (WAB). Out-of-sample prediction accuracy was comparable for both types of analyses, which revealed spatially distinct, albeit overlapping, networks of cortical regions implicated in specific aspects of speech functioning. Importantly, all WAB scores could be predicted at better-than-chance level from the connections between gray-matter regions spared by the lesion. Connectome-based analysis highlighted the role of connectivity of the temporoparietal junction as a multimodal area crucial for language tasks. Our results support that connectome-based approaches are an important complement to necrotic lesion-based approaches and should be used in combination with lesion mapping to fully elucidate whether structurally damaged or structurally disconnected regions relate to aphasic impairment and its recovery.

SIGNIFICANCE STATEMENT

We present a novel multivariate approach of predicting post-stroke impairment of speech and language from the integrity of the connectome. We compare it with multivariate prediction of speech and language scores from lesion maps, using cross-validation framework and a large (n = 90) database of behavioral and neuroimaging data from individuals with post-stroke aphasia. Connectome-based analysis was similar to lesion-based analysis in terms of predictive accuracy and provided additional details about the importance of specific connections (in particular, between parietal and posterior temporal areas) for preserving speech functions. Our results suggest that multivariate predictive analysis of the connectome is a useful complement to multivariate lesion analysis, being less dependent on the spatial constraints imposed by underlying vasculature.

[Aphasia: a neuronal network disorder]

Language processing requires the coordinated interaction of local and distant neural populations within distributed networks of the temporal, frontal and parietal brain regions. Poststroke aphasia is the consequence of both local as well as remote dysfunction within language-specific and domain-general networks. Language recovery, in turn, rests on reorganization processes within these networks. These comprise the resolution of an acute network failure (i. e. diaschisis), the subacute activation of right hemisphere homologous regions and the gradual reintegration of left hemisphere remote and perilesional areas. The application of unifocal noninvasive brain stimulation over these regions provides a means of modulating neural plasticity in order to enhance the reorganization processes underlying language recovery. The lack of knowledge as to the optimal stimulation site, the appropriate stimulation protocol and the proper timing of interventions might explain the only marginal effects of brain stimulation adjunct to speech and language therapy. In addition, individually different contributions of left and right hemisphere regions to recovery due to heterogeneous lesion sites among patients limit the possibility to identify general principles for brain stimulation. The assumption that aphasia is not only the consequence of the focal effect of a brain lesion but arises from remote dysfunctions within associated functional networks ignites the concept for individualized, potentially multifocal therapeutic network modulation.

The effect of cortical and subcortical lesions on spontaneous expression of memory-encoded and emotionally infused information: Evidence for a role of the ventral stream

The ventral stream of language processing has been implicated in the spontaneous expression of memory-encoded and emotionally infused information. The present study investigated whether left hemispheric lesions in post-stroke right-handed aphasic patients may be selectively associated with specific language functions. Speech rate was assessed with two tasks, one based on autobiographical memory of an emotionally infused event (stroke story narration) and the other based on information that is visually available at the time of speech generation ("cookie theft" picture description). CT and/or MRI scans were obtained for each patient and lesions located in 16 regions of the left hemisphere were identified and coded. The total number of cortical and subcortical areas affected served as a measure of lesion extent. While mean speech rates were similar across conditions, there were different patterns of association between each index and specific lesion sites. Non-parametric quantile regression statistical models constructed to assess dependence of both speech rate indices on each lesion locus indicated that the speech rate in the stroke story had significant inverse associations with total number of lesioned areas, as well as lesions in the inferior frontal gyrus and the external/extreme capsule region. The cookie theft speech rate had significant inverse associations with total number of lesioned areas as well as lesion in the inferior frontal gyrus, but not with the external/extreme capsule region. In sum, integrity of the extreme/external capsule region appears to be important selectively for the Stroke Story task, supporting the hypothesis that the ventral stream plays a central role in spontaneous expression of memory-encoded and emotionally infused information.

Damage to white matter bottlenecks contributes to language impairments after left hemispheric stroke

Damage to the white matter underlying the left posterior temporal lobe leads to deficits in multiple language functions. The posterior temporal white matter may correspond to a bottleneck where both dorsal and ventral language pathways are vulnerable to simultaneous damage. Damage to a second putative white matter bottleneck in the left deep prefrontal white matter involving projections associated with ventral language pathways and thalamo-cortical projections has recently been proposed as a source of semantic deficits after stroke. Here, we first used white matter atlases to identify the previously described white matter bottlenecks in the posterior temporal and deep prefrontal white matter. We then assessed the effects of damage to each region on measures of verbal fluency, picture naming, and auditory semantic decision-making in 43 chronic left hemispheric stroke patients. Damage to the posterior temporal bottleneck predicted deficits on all tasks, while damage to the anterior bottleneck only significantly predicted deficits in verbal fluency. Importantly, the effects of damage to the bottleneck regions were not attributable to lesion volume, lesion loads on the tracts traversing the bottlenecks, or damage to nearby cortical language areas. Multivariate lesion-symptom mapping revealed additional lesion predictors of deficits. Post-hoc fiber tracking of the peak white matter lesion predictors using a publicly available tractography atlas revealed evidence consistent with the results of the bottleneck analyses. Together, our results provide support for the proposal that spatially specific white matter damage affecting bottleneck regions, particularly in the posterior temporal lobe, contributes to chronic language deficits after left hemispheric stroke. This may reflect the simultaneous disruption of signaling in dorsal and ventral language processing streams.

The unbridged gap between clinical diagnosis and contemporary research on aphasia: A short discussion on the validity and clinical utility of taxonomic categories

Even if the traditional aphasia classification is continuously questioned by many scholars, it remains widely accepted among clinicians and included in textbooks as the gold standard. The present study aims to investigate the validity and clinical utility of this taxonomy. For this purpose, 65 left-hemisphere stroke patients were assessed and classified with respect to aphasia type based on performance on a Greek adaptation of the Boston Diagnostic Aphasia Examination. MRI and/or CT scans were obtained for each patient and lesions were identified and coded according to location. Results indicate that 26.5% of the aphasic profiles remained unclassified. More importantly, we failed to confirm the traditional lesion-to-syndrome correspondence for 63.5% of patients. Overall, our findings elucidate crucial vulnerabilities of the neo-associationist classification, and further support a deficit-rather than a syndrome-based approach. The issue of unclassifiable patients is also discussed.

Investigating structure and function in the healthy human brain: validity of acute versus chronic lesion-symptom mapping

Modern voxel-based lesion-symptom mapping (VLSM) analyses techniques provide powerful tools to examine the relationship between structure and function of the healthy human brain. However, there is still uncertainty on the type of and the appropriate time point of imaging and of behavioral testing for such analyses. Here we tested the validity of the three most common combinations of structural imaging data and behavioral scores used in VLSM analyses. Given the established knowledge about the neural substrate of the primary motor system in humans, we asked the mundane question of where the motor system is represented in the normal human brain, analyzing individual arm motor function of 60 unselected stroke patients. Only the combination of acute behavioral scores and acute structural imaging precisely identified the principal brain area for the emergence of hemiparesis after stroke, i.e., the corticospinal tract (CST). In contrast, VLSM analyses based on chronic behavior-in combination with either chronic or acute imaging-required the exclusion of patients who had recovered from an initial paresis to reveal valid anatomical results. Thus, if the primary research aim of a VLSM lesion analysis is to uncover the neural substrates of a certain function in the healthy human brain and if no longitudinal designs with repeated evaluations are planned, the combination of acute imaging and behavior represents the ideal dataset.

Revealing humans' sensorimotor functions with electrical cortical stimulation

Direct electrical stimulation (DES) of the human brain has been used by neurosurgeons for almost a century. Although this procedure serves only clinical purposes, it generates data that have a great scientific interest. Had DES not been employed, our comprehension of the organization of the sensorimotor systems involved in movement execution, language production, the emergence of action intentionality or the subjective feeling of movement awareness would have been greatly undermined. This does not mean, of course, that DES is a gold standard devoid of limitations and that other approaches are not of primary importance, including electrophysiology, modelling, neuroimaging or psychophysics in patients and healthy subjects. Rather, this indicates that the contribution of DES cannot be restricted, in humans, to the ubiquitous concepts of homunculus and somatotopy. DES is a fundamental tool in our attempt to understand the human brain because it represents a unique method for mapping sensorimotor pathways and interfering with the functioning of localized neural populations during the performance of well-defined behavioural tasks.

Taking Sides: An Integrative Review of the Impact of Laterality and Polarity on Efficacy of Therapeutic Transcranial Direct Current Stimulation for Anomia in Chronic Poststroke Aphasia

Anomia is a frequent and persistent symptom of poststroke aphasia, resulting from damage to areas of the brain involved in language production. Cortical neuroplasticity plays a significant role in language recovery following stroke and can be facilitated by behavioral speech and language therapy. Recent research suggests that complementing therapy with neurostimulation techniques may enhance functional gains, even amongst those with chronic aphasia. The current review focuses on the use of transcranial Direct Current Stimulation (tDCS) as an adjunct to naming therapy for individuals with chronic poststroke aphasia. Our survey of the literature indicates that combining therapy with anodal (excitatory) stimulation to the left hemisphere and/or cathodal (inhibitory) stimulation to the right hemisphere can increase both naming accuracy and speed when compared to the effects of therapy alone. However, the benefits of tDCS as a complement to therapy have not been yet systematically investigated with respect to site and polarity of stimulation. Recommendations for future research to help determine optimal protocols for combined therapy and tDCS are outlined.