Researchers have sought to understand how language is processed in the brain, how brain damage affects language abilities, and what can be expected during the recovery period since the early 19th ...century. In this review, we first discuss mechanisms of damage and plasticity in the post-stroke brain, both in the acute and the chronic phase of recovery. We then review factors that are associated with recovery. First, we review organism intrinsic variables such as age, lesion volume and location and structural integrity that influence language recovery. Next, we review organism extrinsic factors such as treatment that influence language recovery. Here, we discuss recent advances in our understanding of language recovery and highlight recent work that emphasizes a network perspective of language recovery. Finally, we propose our interpretation of the principles of neuroplasticity, originally proposed by Kleim and Jones (1) in the context of extant literature in aphasia recovery and rehabilitation. Ultimately, we encourage researchers to propose sophisticated intervention studies that bring us closer to the goal of providing precision treatment for patients with aphasia and a better understanding of the neural mechanisms that underlie successful neuroplasticity.
Reorganization of language networks in aphasia takes advantage of the facts that (a) the brain is an organ of plasticity, with neuronal changes occurring throughout the life span, including following ...brain damage; (b) plasticity is highly experience dependent; and (c) as with any learning system, language reorganization involves a synergistic interplay between organism-intrinsic (i.e., cognitive and brain) and organism-extrinsic (i.e., environmental) variables. A major goal for clinical treatment of aphasia is to be able to prescribe treatment and predict its outcome based on the neurocognitive deficit profiles of individual patients. This review article summarizes the results of research examining the neurocognitive effects of psycholinguistically based treatment (i.e., Treatment of Underlying Forms; Thompson & Shapiro, 2005) for sentence processing impairments in individuals with chronic agrammatic aphasia resulting from stroke and primary progressive aphasia and addresses both behavioral and brain variables related to successful treatment outcomes. The influences of lesion volume and location, perfusion (blood flow), and resting-state neural activity on language recovery are also discussed as related to recovery of agrammatism and other language impairments. Based on these and other data, principles for promoting neuroplasticity of language networks are presented.
Comprehending and producing sentences is a complex endeavor requiring the coordinated activity of multiple brain regions. We examined three issues related to the brain networks underlying sentence ...comprehension and production in healthy individuals: First, which regions are recruited for sentence comprehension and sentence production? Second, are there differences for auditory sentence comprehension vs. visual sentence comprehension? Third, which regions are specifically recruited for the comprehension of syntactically complex sentences? Results from activation likelihood estimation (ALE) analyses (from 45 studies) implicated a sentence comprehension network occupying bilateral frontal and temporal lobe regions. Regions implicated in production (from 15 studies) overlapped with the set of regions associated with sentence comprehension in the left hemisphere, but did not include inferior frontal cortex, and did not extend to the right hemisphere. Modality differences between auditory and visual sentence comprehension were found principally in the temporal lobes. Results from the analysis of complex syntax (from 37 studies) showed engagement of left inferior frontal and posterior temporal regions, as well as the right insula. The involvement of the right hemisphere in the comprehension of these structures has potentially important implications for language treatment and recovery in individuals with agrammatic aphasia following left hemisphere brain damage.
Wernicke's aphasia is characterized by severe word and sentence comprehension impairments. The location of the underlying lesion site, known as Wernicke's area, remains controversial. Questions ...related to this controversy were addressed in 72 patients with primary progressive aphasia who collectively displayed a wide spectrum of cortical atrophy sites and language impairment patterns. Clinico-anatomical correlations were explored at the individual and group levels. These analyses showed that neuronal loss in temporoparietal areas, traditionally included within Wernicke's area, leave single word comprehension intact and cause inconsistent impairments of sentence comprehension. The most severe sentence comprehension impairments were associated with a heterogeneous set of cortical atrophy sites variably encompassing temporoparietal components of Wernicke's area, Broca's area, and dorsal premotor cortex. Severe comprehension impairments for single words, on the other hand, were invariably associated with peak atrophy sites in the left temporal pole and adjacent anterior temporal cortex, a pattern of atrophy that left sentence comprehension intact. These results show that the neural substrates of word and sentence comprehension are dissociable and that a circumscribed cortical area equally critical for word and sentence comprehension is unlikely to exist anywhere in the cerebral cortex. Reports of combined word and sentence comprehension impairments in Wernicke's aphasia come almost exclusively from patients with cerebrovascular accidents where brain damage extends into subcortical white matter. The syndrome of Wernicke's aphasia is thus likely to reflect damage not only to the cerebral cortex but also to underlying axonal pathways, leading to strategic cortico-cortical disconnections within the language network. The results of this investigation further reinforce the conclusion that the left anterior temporal lobe, a region ignored by classic aphasiology, needs to be inserted into the language network with a critical role in the multisynaptic hierarchy underlying word comprehension and object naming.
The frontal aslant tract is a direct pathway connecting Broca's region with the anterior cingulate and pre-supplementary motor area. This tract is left lateralized in right-handed subjects, ...suggesting a possible role in language. However, there are no previous studies that have reported an involvement of this tract in language disorders. In this study we used diffusion tractography to define the anatomy of the frontal aslant tract in relation to verbal fluency and grammar impairment in primary progressive aphasia. Thirty-five patients with primary progressive aphasia and 29 control subjects were recruited. Tractography was used to obtain indirect indices of microstructural organization of the frontal aslant tract. In addition, tractography analysis of the uncinate fasciculus, a tract associated with semantic processing deficits, was performed. Damage to the frontal aslant tract correlated with performance in verbal fluency as assessed by the Cinderella story test. Conversely, damage to the uncinate fasciculus correlated with deficits in semantic processing as assessed by the Peabody Picture Vocabulary Test. Neither tract correlated with grammatical or repetition deficits. Significant group differences were found in the frontal aslant tract of patients with the non-fluent/agrammatic variant and in the uncinate fasciculus of patients with the semantic variant. These findings indicate that degeneration of the frontal aslant tract underlies verbal fluency deficits in primary progressive aphasia and further confirm the role of the uncinate fasciculus in semantic processing. The lack of correlation between damage to the frontal aslant tract and grammar deficits suggests that verbal fluency and grammar processing rely on distinct anatomical networks.
Purpose: Analysis of spontaneous speech samples is important for determining patterns of language production in people with aphasia. To accomplish this, researchers and clinicians can use either hand ...coding or computer-automated methods. In a comparison of the two methods using the hand-coding NNLA (Northwestern Narrative Language Analysis) and automatic transcript analysis by CLAN (Computerized Language Analysis), Hsu and Thompson (2018) found good agreement for 32 of 51 linguistic variables. The comparison showed little difference between the two methods for coding most general (i.e., utterance length, rate of speech production), lexical, and morphological measures. However, the NNLA system coded grammatical measures (i.e., sentence and verb argument structure) that CLAN did not. Because of the importance of quantifying these aspects of language, the current study sought to implement a new, single, composite CLAN command for the full set of 51 NNLA codes and to evaluate its reliability for coding aphasic language samples. Method: Eighteen manually coded NNLA transcripts from eight people with aphasia and 10 controls were converted into CHAT (Codes for the Human Analysis of Talk) files for compatibility with CLAN commands. Rules from the NNLA manual were translated into programmed rules for CLAN computation of lexical, morphological, utterance-level, sentence-level, and verb argument structure measures. Results: The new C-NNLA (CLAN command to compute the full set of NNLA measures) program automatically computes 50 of the 51 NNLA measures and generates the results in a summary spreadsheet. The only measure it does not compute is the number of verb particles. Statistical tests revealed no significant difference between C-NNLA results and those generated by manual coding for 44 of the 50 measures. C-NNLA results were not comparable to manual coding for the six verb argument measures. Conclusion: Clinicians and researchers can use the automatic C-NNLA to analyze important variables required for quantification of grammatical deficits in aphasia in a way that is fast, replicable, and accessible without extensive linguistic knowledge and training.
Background: Verbs and sentences are often impaired in individuals with aphasia, and differential impairment patterns are associated with different types of aphasia. With currently available test ...batteries, however, it is challenging to provide a comprehensive profile of aphasic language impairments because they do not examine syntactically important properties of verbs and sentences.
Aims: This study presents data derived from the Northwestern Assessment of Verbs and Sentences (NAVS; Thompson,
2011
), a new test battery designed to examine syntactic deficits in aphasia. The NAVS includes tests for verb naming and comprehension, and production of verb argument structure in simple active sentences, with each examining the effects of the number and optionality of arguments. The NAVS also tests production and comprehension of canonical and non-canonical sentences.
Methods & Procedures: A total of 59 aphasic participants (35 agrammatic and 24 anomic) were tested using a set of action pictures. Participants produced verbs or sentences for the production subtests and identified pictures corresponding to auditorily provided verbs or sentences for the comprehension subtests.
Outcomes & Results: The agrammatic group, compared to the anomic group, performed significantly more poorly on all subtests except verb comprehension, and for both groups comprehension was less impaired than production. On verb naming and argument structure production tests both groups exhibited difficulty with three-argument verbs, affected by the number and optionality of arguments. However, production of sentences using three-argument verbs was more impaired in the agrammatic, compared to the anomic, group. On sentence production and comprehension tests, the agrammatic group showed impairments in all types of non-canonical sentences, whereas the anomic group exhibited difficulty primarily with the most difficult, object relative, structures.
Conclusions: Results show that verb and sentence deficits seen in individuals with agrammatic aphasia are largely influenced by syntactic complexity; however, individuals with anomic aphasia appear to exhibit these impairments only for the most complex forms of verbs and sentences. The present data indicate that the NAVS is useful for characterising verb and sentence deficits in people with aphasia.
Primary progressive aphasia (PPA) is caused by selective neurodegeneration of the language-dominant cerebral hemisphere; a language deficit initially arises as the only consequential impairment and ...remains predominant throughout most of the course of the disease. Agrammatic, logopenic and semantic subtypes, each reflecting a characteristic pattern of language impairment and corresponding anatomical distribution of cortical atrophy, represent the most frequent presentations of PPA. Such associations between clinical features and the sites of atrophy have provided new insights into the neurology of fluency, grammar, word retrieval, and word comprehension, and have necessitated modification of concepts related to the functions of the anterior temporal lobe and Wernicke's area. The underlying neuropathology of PPA is, most commonly, frontotemporal lobar degeneration in the agrammatic and semantic forms, and Alzheimer disease (AD) pathology in the logopenic form; the AD pathology often displays atypical and asymmetrical anatomical features consistent with the aphasic phenotype. The PPA syndrome reflects complex interactions between disease-specific neuropathological features and patient-specific vulnerability. A better understanding of these interactions might help us to elucidate the biology of the language network and the principles of selective vulnerability in neurodegenerative diseases. We review these aspects of PPA, focusing on advances in our understanding of the clinical features and neuropathology of PPA and what they have taught us about the neural substrates of the language network.
We conducted a retrospective review of fMRI studies of complex syntax, in order to study the stability of the neural bases of mechanisms engaged in syntactic processing. Our review set out rigorous ...selection criteria of studies which we discuss, including transparency and minimality of the contrasts between stimuli, and the presence of whole brain analyses corrected for multiple comparisons. Seventeen studies with 316 participants survived our sieve. We mapped the 65 resulting maxima onto JuBrain, a state-of-the-art cytoarchitectonic brain atlas (Amunts et al., 2020), and a sharp picture emerged: syntactic displacement operations (a k a MOVE) produce highly consistent results, activating left Broca's region across-the-board and unambiguously; to a somewhat lesser extent, maxima clustered in left posterior brain regions, including the STS/STG. The few studies of syntactic tree-building operations (a k a MERGE) produce a murkier picture regarding the involvement of the left IFG. We conclude that the extant data decisively point to the JuBrain-defined Broca's region as the main locus of complex receptive syntax in healthy people; the STS/STG also are involved, but to a lesser extent.
This paper examined the effects of treatment on both offline and online sentence processing and associated neuroplasticity within sentence processing and dorsal attention networks in chronic ...stroke-induced agrammatic aphasia. Twenty-three neurotypical adults and 19 individuals with aphasia served as participants. Aphasic individuals were randomly assigned to receive a 12-week course of linguistically-based treatment of passive sentence production and comprehension (N = 14, treatment group) or to serve as control participants (N = 5, natural history group). Both aphasic groups performed two offline tasks at baseline and three months following (at post-testing) to assess production and comprehension of trained passive structures and untrained syntactically related and unrelated structures. The aphasic participants and a healthy age-matched group also performed an online eyetracking comprehension task and a picture-verification fMRI task, which were repeated at post-testing for the aphasic groups. Results showed that individuals in the treatment, but not in the natural history, group improved on production and comprehension of both trained structures and untrained syntactically related structures. Treatment also resulted in a shift toward more normal-like eye movements and a significant increase in neural activation from baseline to post-testing. Upregulation encompassed right hemisphere regions homologs of left hemisphere regions involved in both sentence processing and domain-general functions and was positively correlated with treatment gains, as measured by offline comprehension accuracy, and with changes in processing strategies during sentence comprehension, as measured by eyetracking. These findings provide compelling evidence in favor of the contribution of both networks within the right hemisphere to the restoration of normal-like sentence processing patterns in chronic aphasia.
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