Aphasic Deficits in Syntactic Processing

Common Neuroanatomical Substrate of Cholinergic Pathways and Language-Related Brain Regions as an Explanatory Framework for Evaluating the Efficacy of Cholinergic Pharmacotherapy in Post-Stroke Aphasia: A Review

Despite the relative scarcity of studies focusing on pharmacotherapy in aphasia, there is evidence in the literature indicating that remediation of language disorders via pharmaceutical agents could be a promising aphasia treatment option. Among the various agents used to treat chronic aphasic deficits, cholinergic drugs have provided meaningful results. In the current review, we focused on published reports investigating the impact of acetylcholine on language and other cognitive disturbances. It has been suggested that acetylcholine plays an important role in neuroplasticity and is related to several aspects of cognition, such as memory and attention. Moreover, cholinergic input is diffused to a wide network of cortical areas, which have been associated with language sub-processes. This could be a possible explanation for the positive reported outcomes of cholinergic drugs in aphasia recovery, and specifically in distinct language processes, such as naming and comprehension, as well as overall communication competence. However, evidence with regard to functional alterations in specific brain areas after pharmacotherapy is rather limited. Finally, despite the positive results derived from the relevant studies, cholinergic pharmacotherapy treatment in post-stroke aphasia has not been widely implemented. The present review aims to provide an overview of the existing literature in the common neuroanatomical substrate of cholinergic pathways and language related brain areas as a framework for interpreting the efficacy of cholinergic pharmacotherapy interventions in post-stroke aphasia, following an integrated approach by converging evidence from neuroanatomy, neurophysiology, and neuropsychology.

The Unfolding of Cognitive Effort During Sentence Processing: Pupillometric Evidence From People With and Without Aphasia

PURPOSE

Arousal and cognitive effort are relevant yet often overlooked components of attention during language processing. Pupillometry can be used to provide a psychophysiological index of arousal and cognitive effort. Given that much is unknown regarding the relationship between cognition and language deficits seen in people with aphasia (PWA), pupillometry may be uniquely suited to explore those relationships. The purpose of this study was to examine arousal and the time course of the allocation of cognitive effort related to sentence processing in people with and without aphasia.

METHOD

Nineteen PWA and age- and education-matched control participants listened to relatively easy (subject-relative) and relatively difficult (object-relative) sentences and were required to answer occasional comprehension questions. Tonic and phasic pupillary responses were used to index arousal and the unfolding of cognitive effort, respectively, while sentences were processed. Group differences in tonic and phasic responses were examined.

RESULTS

Group differences were observed for both tonic and phasic responses. PWA exhibited greater overall arousal throughout the task compared with controls, as evidenced by larger tonic pupil responses. Controls exhibited more effort (greater phasic responses) for difficult compared with easy sentences; PWA did not. Group differences in phasic responses were apparent during end-of-sentence and postsentence time windows.

CONCLUSIONS

Results indicate that the attentional state of PWA in this study was not consistently supportive of adequate task engagement. PWA in our sample may have relatively limited attentional capacity or may have challenges with allocating existing capacity in ways that support adequate task engagement and performance. This work adds to the body of evidence supporting the validity of pupillometric tasks for the study of aphasia and contributes to a better understanding of the nature of language deficits in aphasia. Supplemental Material https://doi.org/10.23641/asha.16959376.

Implicit-statistical learning in aphasia and its relation to lesion location

BACKGROUND

Implicit-statistical learning (ISL) research investigates whether domain-general mechanisms are recruited in the linguistic processes that require manipulation of patterned regularities (e.g. syntax). Aphasia is a language disorder caused by focal brain damage in the left fronto-temporal-parietal network. Research shows that people with aphasia (PWA) with frontal lobe lesions manifest convergent deficits in syntax and ISL mechanisms. So far, ISL mechanisms in PWA with temporal or parietal lobe lesions have not been systematically investigated.

AIMS

We investigated two complementary hypotheses: 1) the anatomical hypothesis, that PWA with frontal lesions display more severely impaired ISL abilities than PWA with posterior lesions and 2) the behavioural hypothesis, that the magnitude of impairment in ISL mechanisms correlates to syntactic deficits in aphasia.

METHODS

We tested 13 PWA, 5 with frontal lesions and 8 with posterior lesions, and 11 non-brain-damaged controls on a visual statistical learning (VSL) task. In addition, all PWA completed several linguistic tasks. Reaction times, obtained in the VSL task, were analyzed using linear mixed-effects model. Correlational statistics were used to assess the relationship between VSL task performance and linguistic measures.

RESULTS AND DISCUSSION

We did not find support for the anatomical hypothesis as patients with spared frontal regions also manifested impaired ISL mechanisms. This is attributed to a) ISL mechanisms being vulnerable to other cognitive dysfunctions and/or b) ISL mechanisms anatomically extending to the posterior brain regions. Notably, ISL mechanisms were impaired, but not absent in aphasia. With regards to the behavioural hypothesis, we provide empirical evidence of correlation between ISL mechanisms and syntactic, but not lexical impairment in aphasia. We discuss both the theoretical contributions to the debate of domain-independence of ISL mechanisms and clinical implications for implicit language therapy.

Bilingual aphasia: Assessing cross-linguistic asymmetries and bilingual advantage in sentence comprehension deficits

People with aphasia frequently have difficulties understanding semantically reversible sentences presented in derived word order. This impairment may be related to the inconsistent processing of morphological information, as well as to difficulties inhibiting the inverse interpretation of the sentence. Studies on bilingual aphasia may contribute to our understanding of these issues by shedding light on i) differences in processing of morphology across languages; ii) enhanced control mechanisms. We studied early Basque-Spanish bilingual speakers with aphasia and monolingual Spanish speakers with aphasia, as well as unimpaired individuals. Using comparable sets of materials across languages, we combined behavioural and eye-tracking methods. Results indicate that i) at the group level, bilingual speakers perform better in Spanish than in Basque, particularly in sentences with Theme-Agent argument order. Individual case analysis shows a pattern of weak dissociation across languages in several participants; ii) bilingual people with aphasia do not outperform monolingual people with aphasia in comprehension accuracy, although gaze data suggests that bilingual speakers exhibit higher inhibition and monitoring abilities.

Why is measuring communication difficult? A critical review of current speech pathology concepts and measures

Human society is organised through communicative interactions between co-present people. Speech pathology (SP) assessment and intervention strategies aim to access these sites of communication in order to facilitate participation in life situations for people with communication disorders. Surprisingly, however, there is no explicit theory of communication underpinning SP practice and research. As a result, the conceptual and practical basis for rigorous, empirical measurement of communication remains limited, which is a significant challenge for professional practice and research. This critical review discusses the prevailing ways that co-present communication has been conceptualised and measured in SP. In particular, we examine how models of health have informed current ideas and measurement practices. We argue that although patently valuable for SP, they are largely incommensurate with the realities of co-present communication. Drawing on current empirical research in Sociology and Linguistics, we specify the properties of real-time co-present communication and discuss their relationship to current SP concepts and measurement practices. We conclude by suggesting directions for conceptual development and empirical research that will draw SP assessment and intervention strategies closer to real-time co-present communication.

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.

Verbal comprehension ability in aphasia: demographic and lexical knowledge effects

Background. Assessment of sentence-level auditory comprehension can be performed with a variety of tests varying in response requirements. A brief and easy to administer measure, not requiring an overt verbal or a complex motor response, is essential in any test battery for aphasia. Objective. The present study examines the clinical utility of receptive language indices for individuals with aphasia based on the Comprehension of Instructions in Greek (CIG), a variant of the Token Test, and the Greek version of PPVT-R. Methods. Normative data from a large community sample of Greek adults aged 46–80 years was available on both measures. A word-level-independent measure of auditory comprehension was computed as the standard score difference between the two tests and used to compare patients with and without comprehension deficits as indicated by their Boston Diagnostic Aphasia Examination profile. Results and Conclusions. Indices of internal consistency and test-retest reliability were very good. Education and age effects on performance were significant, with the former being stronger. The potential clinical utility of differential ability indices (contrasting sentence- and word-level auditory comprehension tests) is discussed.

A neuropsychological perspective on the link between language and praxis in modern humans

Hypotheses about the emergence of human cognitive abilities postulate strong evolutionary links between language and praxis, including the possibility that language was originally gestural. The present review considers functional and neuroanatomical links between language and praxis in brain-damaged patients with aphasia and/or apraxia. The neural systems supporting these functions are predominantly located in the left hemisphere. There are many parallels between action and language for recognition, imitation and gestural communication suggesting that they rely partially on large, common networks, differentially recruited depending on the nature of the task. However, this relationship is not unequivocal and the production and understanding of gestural communication are dependent on the context in apraxic patients and remains to be clarified in aphasic patients. The phonological, semantic and syntactic levels of language seem to share some common cognitive resources with the praxic system. In conclusion, neuropsychological observations do not allow support or rejection of the hypothesis that gestural communication may have constituted an evolutionary link between tool use and language. Rather they suggest that the complexity of human behaviour is based on large interconnected networks and on the evolution of specific properties within strategic areas of the left cerebral hemisphere.

Verbal fluency in Alzheimer's disease and Aphasia

This study examined the impact of two neurological diseases on access to semantic knowledge and the status of semantic representations. Patients with Alzheimer's disease (AD) and Aphasia (APH) were compared with control groups using the supermarket fluency task. We measured several aspects: number of category names produced, number of categories sampled to produce the words, the number of words per category sampled, number of exemplars and kinds of errors recorded. Both AD and APH groups produced significantly fewer words on the fluency task than control groups. As compared with the APH and control groups, in the AD group verbal fluency was characterized by a tendency to generate more category names with fewer exemplars within a category. The findings are consistent with the view that a bottom-up disruption in semantic knowledge occurs in AD and a general semantic disruption occurs in Aphasia.

Brain embodiment of syntax and grammar: discrete combinatorial mechanisms spelt out in neuronal circuits

Neuroscience has greatly improved our understanding of the brain basis of abstract lexical and semantic processes. The neuronal devices underlying words and concepts are distributed neuronal assemblies reaching into sensory and motor systems of the cortex and, at the cognitive level, information binding in such widely dispersed circuits is mirrored by the sensorimotor grounding of form and meaning of symbols. Recent years have seen the emergence of evidence for similar brain embodiment of syntax. Neurophysiological studies have accumulated support for the linguistic notion of abstract combinatorial rules manifest as functionally discrete neuronal assemblies. Concepts immanent to the theory of abstract automata could be grounded in observations from modern neuroscience, so that it became possible to model abstract pushdown storage - which is critical for building linguistic tree structure representations - as ordered dynamics of memory circuits in the brain. At the same time, neurocomputational research showed how sequence detectors already known from animal brains can be neuronally linked so that they merge into larger functionally discrete units, thereby underpinning abstract rule representations that syntactically bind lexicosemantic classes of morphemes and words into larger meaningful constituents. Specific predictions of brain-based grammar models could be confirmed by neurophysiological and brain imaging experiments using MEG, EEG and fMRI. Neuroscience and neurocomputational research offering perspectives on understanding abstract linguistic mechanisms in terms of neuronal circuits and their interactions therefore point programmatic new ways to future theory-guided experimental investigation of the brain basis of grammar.

Neural aspects of sentence comprehension: syntactic complexity, reversibility, and reanalysis

Broca's area is preferentially activated by reversible sentences with complex syntax, but various linguistic factors may be responsible for this finding, including syntactic movement, working-memory demands, and post hoc reanalysis. To distinguish between these, we tested the interaction of syntactic complexity and semantic reversibility in a functional magnetic resonance imaging study of sentence–picture matching. During auditory comprehension, semantic reversibility induced selective activation throughout the left perisylvian language network. In contrast, syntactic complexity (object-embedded vs. subject-embedded relative clauses) within reversible sentences engaged only the left inferior frontal gyrus (LIFG) and left precentral gyrus. Within irreversible sentences, only the LIFG was sensitive to syntactic complexity, confirming a unique role for this region in syntactic processing. Nonetheless, larger effects of reversibility itself occurred in the same regions, suggesting that full syntactic parsing may be a nonautomatic process applied as needed. Complex reversible sentences also induced enhanced signals in LIFG and left precentral regions on subsequent picture selection, but with additional recruitment of the right hemisphere homolog area (right inferior frontal gyrus) as well, suggesting that post hoc reanalysis of sentence structure, compared with initial comprehension, engages an overlapping but larger network of brain regions. These dissociable effects may offer a basis for studying the reorganization of receptive language function after brain damage.