Written language impairments in primary progressive aphasia: a reflection of damage to central semantic and phonological processes

Addressing Phonological Deficit in Primary Progressive Aphasia With Behavioral Intervention and Transcranial Direct Current Stimulation

PURPOSE

Despite recognition of the underlying phonological impairment observed in the logopenic and nonfluent variants of primary progressive aphasia (PPA), there is relatively little treatment research directed toward strengthening phonological skills. In this study, we focused on remediating phonological deficits in logopenic and nonfluent PPA. Specifically, we hypothesized that behavioral intervention intended to strengthen phonological manipulation skills and sound-letter correspondences-coupled with transcranial direct current stimulation (tDCS)-would improve language abilities, especially in the written modality.

METHOD

Twelve individuals with logopenic or nonfluent variants of PPA and 24 neurotypical adults completed neuropsychological assessment that documented spoken and written language deficits in those with PPA. Phonological skills were consistently impaired in relation to other language processes. Following a double-blind, crossover design, six individuals with PPA were randomized to receive active tDCS with phonological intervention during the first treatment phase, and after a 2-month break, they received a second phase of behavioral intervention paired with sham tDCS. The other six individuals were randomized to receive sham first and active tDCS second. Language skills were evaluated before and after each treatment phase and 2 months after the intervention.

RESULTS

Both treatment groups (tDCS-first and sham-first) made significant improvement in phonological transcoding skills in response to behavioral intervention, but those who received active tDCS first showed stronger gains in phonological manipulation ability. This group also showed positive changes in written narratives, which contained more grammatical sentences with increased meaningful content and more accurate spelling.

CONCLUSIONS

These data provide compelling evidence supporting an approach that targets phonological deficits in logopenic and nonfluent PPA. Specifically, we found that improved phonological skills resulted in better functional communication ability (text-level writing) relevant to everyday life. Positive outcomes were strongest when tDCS was combined with behavioral treatment from the beginning, suggesting that this combination may potentiate positive changes that extend beyond the initial stimulation period.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.28598195.

The right hemisphere's capacity for language: evidence from primary progressive aphasia

The role of the right hemisphere (RH) in core language processes is still a matter of intense debate. Most of the relevant evidence has come from studies of gray matter, with relatively little research on RH white matter (WM) connectivity. Using Diffusion Tensor Imaging-based tractography, the current work examined the role of the two hemispheres in language processing in 33 individuals with Primary Progressive Aphasia (PPA), aiming to better characterize the contribution of the RH to language processing in the context of left hemisphere (LH) damage. The findings confirm the impact of PPA on the integrity of the WM language tracts in the LH. Additionally, an examination of the relationship between tract integrity and language behaviors provides robust evidence of the involvement of the WM language tracts of both hemispheres in language processing in PPA. Importantly, this study provides novel evidence of a unique contribution of the RH to language processing (i.e. a contribution independent from that of the language-dominant LH). Finally, we provide evidence that the RH contribution is specific to language processing rather than being domain general. These findings allow us to better characterize the role of RH in language processing, particularly in the context of LH damage.

Automated analysis of written language in the three variants of primary progressive aphasia

Despite the important role of written language in everyday life, abnormalities in functional written communication have been sparsely investigated in primary progressive aphasia. Prior studies have analysed written language separately in each of the three variants of primary progressive aphasia-but have rarely compared them to each other or to spoken language. Manual analysis of written language can be a time-consuming process. We therefore developed a program that quantifies content units and total units in written or transcribed language samples. We analysed written and spoken descriptions of the Western Aphasia Battery picnic scene, based on a predefined content unit corpus. We calculated the ratio of content units to units as a measure of content density. Our cohort included 115 participants (20 controls for written, 20 controls for spoken, 28 participants with nonfluent variant primary progressive aphasia, 30 for logopenic variant and 17 for semantic variant). Our program identified content units with a validity of 99.7% (95%CI 99.5-99.8). All patients wrote fewer units than controls (P < 0.001). Patients with the logopenic variant (P = 0.013) and the semantic variant (0.004) wrote fewer content units than controls. The content unit-to-unit ratio was higher in the nonfluent and semantic variants than controls (P = 0.019), but no difference in the logopenic variant (P = 0.962). Participants with the logopenic (P < 0.001) and semantic (P = 0.04) variants produced fewer content units in written compared to spoken descriptions. All variants produced fewer units in written samples compared to spoken (P < 0.001). However, due to a relatively smaller decrease in written content units, we observed a larger content unit-to-unit ratio in writing over speech (P < 0.001). Written and spoken content units (r = 0.5, P = 0.009) and total units (r = 0.64, P < 0.001) were significantly correlated in patients with nonfluent variant, but this was not the case for logopenic or semantic. Considering all patients with primary progressive aphasia, fewer content units were produced in those with greater aphasia severity (Progressive Aphasia Severity Scale Sum of Boxes, r = -0.24, P = 0.04) and dementia severity (Clinical Dementia Rating scale Sum of Boxes, r = -0.34, P = 0.004). In conclusion, we observed reduced written content in patients with primary progressive aphasia compared to controls, with a preference for content over non-content units in patients with the nonfluent and semantic variants. We observed a similar 'telegraphic' style in both language modalities in patients with the nonfluent variant. Lastly, we show how our program provides a time-efficient tool, which could enable feedback and tracking of writing as an important feature of language and cognition.

Picnic, Accident or Cookies? A Systematic Approach to Guide the Selection of the Picture Definition Tasks in Linguistic Assessment

OBJECTIVE

Picture description tasks are used to elicit language samples in individuals with aphasia and other cognitive disorders. However, task selection may affect the type of language variables elicited. In this study, our goal is to compare the strengths and the weaknesses of the two internationally used picture description tasks with a novel picture description task developed specifically for Turkish-speaking individuals.

MATERIALS AND METHODS

In sum, 20 cognitively healthy individuals with a mean age of 52 ± 14/3 were included. Three different picture description tasks composed of single pictures were used: The Picnic Scene from the Western Aphasia Battery-Revised, the Cookie Theft picture from the Boston Diagnostic Aphasia Examination and the Accident Scene from the Turkish Language Assessment Test for Aphasia. All language samples were recorded using a digital voice recorder. Automated and semi-automated approaches were used for the systematic analysis of the language features that were classified into four levels: general language measures, the morphosyntactic level, the lexicosemantic level and the sentence level.

RESULTS

Participants showed greater efficiency and produced the greatest number of subordinate clauses, derivational suffixes, passive voice suffixes and relative past tense construction during the Accident Scene description. On the lexicosemantic level, the Picnic Scene was particularly superior to the Cookie Theft Picture in eliciting nouns. Imperfective aspect use was less frequent in the Accident Scene description.

CONCLUSION

All three tasks had limitations and advantages compared with each other. We recommend the development of novel picture description tasks that would be more effective in eliciting specific language features in Turkish-speaking individuals.

Positive changes to written language following phonological treatment in logopenic variant primary progressive aphasia: Case report

Phonological impairment contributes to deficits in repetition and spoken naming in logopenic variant Primary Progressive Aphasia (lvPPA), but weakened phonology can also affect written language skills. In this experimental case report, we demonstrate phonological text agraphia in a 71-year-old woman in the early stages of lvPPA that undermined her ability to write meaningful, grammatical sentences. We investigated the therapeutic value of a rigorous treatment protocol to strengthen phonological manipulation skills coupled with transcranial direct current stimulation (tDCS). Intervention took place 5 days a week for 2 weeks with active tDCS, followed by a 2-month rest period, and then a second period of phonological treatment with sham tDCS. Over the course of treatment, our participant demonstrated improved phonological transcoding and manipulation skills as well as marked improvement in the proportion of grammatically well-formed, meaningful written narratives. Improvements in spelling and letter selection were also observed. Treatment gains were documented during phonological intervention in both active tDCS and sham treatment phases and were maintained 2 months after the conclusion of intervention. Importantly, improvements were observed in the context of a progressive disorder. These data present compelling evidence regarding the impairment-based approach that targets compromised phonological skills, presenting opportunity for improving functional written communication skills relevant to the everyday lives of individuals with lvPPA.

Common predictors of spoken and written language performance in aphasia, alexia, and agraphia

Language performance requires support from central cognitive/linguistic abilities as well as the more peripheral sensorimotor skills to plan and implement spoken and written communication. Both output modalities are vulnerable to impairment following damage to the language-dominant hemisphere, but much of the research to date has focused exclusively on spoken language. In this study we aimed to examine an integrated model of language processing that includes the common cognitive processes that support spoken and written language, as well as modality-specific skills. To do so, we evaluated spoken and written language performance from 87 individuals with acquired language impairment resulting from damage to left perisylvian cortical regions that collectively constitute the dorsal language pathway. Comprehensive behavioral assessment served to characterize the status of central and peripheral components of language processing in relation to neurotypical controls (n = 38). Performance data entered into principal components analyses (with or without control scores) consistently yielded a strong five-factor solution. In line with a primary systems framework, three central cognitive factors emerged: semantics, phonology, and orthography that were distinguished from peripheral processes supporting speech production and allographic skill for handwriting. The central phonology construct reflected performance on phonological awareness and manipulation tasks and showed the greatest deficit of all the derived factors. Importantly, this phonological construct was orthogonal to the speech production factor that reflected repetition of words/non-words. When entered into regression analyses, semantics and phonological skill were common predictors of language performance across spoken and written modalities. The speech production factor was also a strong, distinct predictor of spoken naming and oral reading, in contrast to allographic skills which only predicted written output. As expected, visual orthographic processing contributed more to written than spoken language tasks and reading/spelling performance was strongly reliant on phonological and semantic abilities. Despite the heterogeneity of this cohort regarding aphasia type and severity, the marked impairment of phonological skill was a unifying feature. These findings prompt greater attention to clinical assessment and potential treatment of underlying phonological skill in individuals with left perisylvian damage.

Sleep as a predictor of tDCS and language therapy outcomes

STUDY OBJECTIVES

To determine whether sleep at baseline (before therapy) predicted improvements in language following either language therapy alone or coupled with transcranial direct current stimulation (tDCS) in individuals with primary progressive aphasia (PPA).

METHODS

Twenty-three participants with PPA (mean age 68.13 ± 6.21) received written naming/spelling therapy coupled with either anodal tDCS over the left inferior frontal gyrus (IFG) or sham condition in a crossover, sham-controlled, double-blind design (ClinicalTrials.gov identifier: NCT02606422). The outcome measure was percent of letters spelled correctly for trained and untrained words retrieved in a naming/spelling task. Given its particular importance as a sleep parameter in older adults, we calculated sleep efficiency (total sleep time/time in bed x100) based on subjective responses on the Pittsburgh Sleep Quality Index (PSQI). We grouped individuals based on a median split: high versus low sleep efficiency.

RESULTS

Participants with high sleep efficiency benefited more from written naming/spelling therapy than participants with low sleep efficiency in learning therapy materials (trained words). There was no effect of sleep efficiency in generalization of therapy materials to untrained words. Among participants with high sleep efficiency, those who received tDCS benefitted more from therapy than those who received sham condition. There was no additional benefit from tDCS in participants with low sleep efficiency.

CONCLUSION

Sleep efficiency modified the effects of language therapy and tDCS on language in participants with PPA. These results suggest sleep is a determinant of neuromodulation effects.Clinical Trial: tDCS Intervention in Primary Progressive Aphasia https://clinicaltrials.gov/ct2/show/NCT02606422.

Utility of the Repeat and Point Test for Subtyping Patients With Primary Progressive Aphasia

BACKGROUND

Primary progressive aphasia (PPA) may present with three distinct clinical sybtypes: semantic variant PPA (svPPA), nonfluent/agrammatic variant PPA (nfvPPA), and logopenic variant PPA (lvPPA).

OBJECTIVE

The aim was to examine the utility of the German version of the Repeat and Point (R&P) Test for subtyping patients with PPA.

METHOD

During the R&P Test, the examiner reads out aloud a noun and the participants are asked to repeat the word and subsequently point to the corresponding picture. Data from 204 patients (68 svPPA, 85 nfvPPA, and 51 lvPPA) and 33 healthy controls were analyzed.

RESULTS

Controls completed both tasks with >90% accuracy. Patients with svPPA had high scores in repetition (mean=9.2±1.32) but low scores in pointing (mean=6±2.52). In contrast, patients with nfvPPA and lvPPA performed comparably in both tasks with lower scores in repetition (mean=7.4±2.7 for nfvPPA and 8.2±2.34 for lvPPA) but higher scores in pointing (mean=8.9±1.41 for nfvPPA and 8.6±1.62 for lvPPA). The R&P Test had high accuracy discriminating svPPA from nfvPPA (83% accuracy) and lvPPA (79% accuracy). However, there was low accuracy discriminating nfvPPA from lvPPA (<60%).

CONCLUSION

The R&P Test helps to differentiate svPPA from 2 nonsemantic variants (nfvPPA and lvPPA). However, additional tests are required for the differentiation of nfvPPA and lvPPA.

Acquired dyslexias following temporal lesions

The acquisition of reading by children is supported by deep changes in the brain systems devoted to vision and language. The left temporal lobe contributes critically to both systems, and lesions affecting it may therefore cause both peripheral vision-related and central language-related reading impairments. The diversity of peripheral dyslexias reflects the anatomical and functional division of the visual cortex into early visual regions, whose lesions have a limited impact on reading; ventral regions, whose lesions are mostly associated to Pure Alexia; and dorsal regions, whose lesions may yield spatial, neglect-related, and attentional dyslexias. Similarly, central alexias reflect the broad distinction, within language processes, between phonological and lexico-semantic components. Phonological and surface dyslexias roughly result from impairment of the former and the latter processes, respectively, while deep dyslexia may be seen as the association of both. In this chapter, we review such types of acquired dyslexias, their clinical features, pathophysiology, and anatomical correlates.

Phonological and surface dyslexia in individuals with brain tumors: Performance pre-, intra-, immediately post-surgery and at follow-up

We address existing controversies regarding neuroanatomical substrates of reading-aloud processes according to the dual-route processing models, in this particular instance in a series of 49 individuals with brain tumors who performed several reading tasks of real-time neuropsychological testing during surgery (low- to high-grade cerebral neoplasms involving the left hemisphere). We explored how reading abilities in individuals with brain tumors evolve during and after surgery for a brain tumor, and we studied the reading performance in a sample of 33 individuals in a 4-month follow-up after surgery. Impaired reading performance was seen pre-surgery in 7 individuals with brain tumors, intra-surgery in 18 individuals, at immediate post-surgery testing in 26 individuals, and at follow-up in 5 individuals. We classified their reading disorders according to operational criteria for either phonological or surface dyslexia. Neuroimaging results are discussed within the theoretical framework of the dual-route model of reading. Lesion-mask subtraction analyses revealed that areas selectively related with phonological dyslexia were located-along with the left hemisphere dorsal stream-in the Rolandic operculum, the inferior frontal gyrus, the precentral gyrus, the supramarginal gyrus, the insula (and/or the underlying external capsule), and parts of the superior longitudinal fasciculus, whereas lesions related to surface dyslexia involved the ventral stream, that is, the left middle and inferior temporal gyrus and parts of the left inferior longitudinal fasciculus.

Does surface dyslexia/dysgraphia relate to semantic deficits in the semantic variant of primary progressive aphasia?

The semantic variant of primary progressive aphasia (sv-PPA) is a degenerative condition which causes surface dyslexia/dysgraphia, resulting in reading/writing errors of irregular words with non-transparent grapheme-to-phoneme correspondences (e.g., 'plaid') as opposed to regular words (e.g., 'cat'). According to connectionist models, most authors have attributed this deficit to semantic impairments, but this assumption is at odds with symbolic models, such as the DRC account, stating that the reading/writing of irregulars relies on the mental lexicon. Our study investigated whether sv-PPA affects the lexicon in addition to the semantic system, and whether semantic or lexical deficits cause surface dyslexia/dysgraphia, while challenging the two major models of written language. We explored a cohort of 12 sv-PPA patients and 25 matched healthy controls using a reading and writing task, a semantic task (category decision: living vs. non-living), and a lexical task (lexical decision: word vs. no-neighbor non-word). Correlation analyses were conducted to assess the relationship between reading/writing scores of irregulars and semantic vs. lexical performance. Furthermore, item-by-item analyses explored the consistency of reading/writing errors with item-specific semantic and lexical errors. Results showed that sv-PPA patients are impaired at reading and writing irregular words, and that they have impaired performance in both the semantic and the lexical task. Reading/writing scores with irregulars correlated significantly with performance in the lexical but not the semantic task. Item-by-item analyses revealed that failure in the lexical task on a given irregular word is a good predictor of reading/writing errors with that item (positive predictive value: 77.5%), which was not the case for the semantic task (positive predictive value: 42.5%). Our findings show that sv-PPA is not restricted to semantic damage but that it also comprises damage to the mental lexicon, which appears to be the major factor for surface dyslexia/dysgraphia. Our data support symbolic models whereas they challenge connectionist accounts.

The use of spelling for variant classification in primary progressive aphasia: Theoretical and practical implications

Currently, variant subtyping in primary progressive aphasia (PPA) requires an expert neurologist and extensive language and cognitive testing. Spelling impairments appear early in the development of the disorder, and the three PPA variants (non-fluent - nfvPPA; semantic - svPPA; logopenic - lvPPA) reportedly show fairly distinct spelling profiles. Given the theoretical and empirical evidence indicating that spelling may serve as a proxy for spoken language, the current study aimed to determine whether spelling performance alone, when evaluated with advanced statistical analyses, allows for accurate PPA variant classification. A spelling to dictation task (with real words and pseudowords) was administered to 33 PPA individuals: 17 lvPPA, 10 nfvPPA, 6 svPPA. Using machine learning classification algorithms, we obtained pairwise variant classification accuracies that ranged between 67 and 100%. In additional analyses that assumed no prior knowledge of each case's variant, classification accuracies ranged between 59 and 70%. To our knowledge, this is the first time that all the PPA variants, including the most challenging logopenic variant, have been classified with such high accuracy when using information from a single language task. These results underscore the rich structure of the spelling process and support the use of a spelling task in PPA variant classification.

Differential intrinsic functional connectivity changes in semantic variant primary progressive aphasia

The semantic variant of primary progressive aphasia (svPPA) is a clinical syndrome characterized by semantic memory deficits with relatively preserved motor speech, syntax, and phonology. There is consistent evidence linking focal neurodegeneration of the anterior temporal lobes (ATL) to the semantic deficits observed in svPPA. Less is known about large-scale functional connectivity changes in this syndrome, particularly regarding the interplay between affected and spared language networks that leads to the unique cognitive dissociations typical of svPPA. Using whole-brain, seed-based connectivity on task-free Magnetic Resonance Imaging (MRI) data, we studied connectivity of networks anchored to three left-hemisphere regions crucially involved in svPPA symptomatology: ATL just posterior to the main atrophic area, opercular inferior frontal gyrus, and posterior inferior temporal lobe. First, in 32 healthy controls, these seeds isolated three networks: a ventral semantic network involving anterior middle temporal and angular gyri, a dorsal articulatory-phonological system involving inferior frontal and supramarginal regions, and a third functional connection between posterior inferior temporal and intraparietal regions likely involved in linking visual and linguistic processes. We then compared connectivity strength of these three networks between 16 svPPA patients and the 32 controls. In svPPA, decreased functional connectivity in the ventral semantic network correlated with weak semantic skills, while connectivity of the network seeded from the posterior inferior temporal lobe, though not significantly different between the two groups, correlated with pseudoword reading skills. Increased connectivity between the inferior frontal gyrus and the superior portion of the angular gyrus suggested possible adaptive changes. Our findings have two main implications. First, they support a functional subdivision of the left IPL based on its connectivity to specific language-related regions. Second, the unique neuroanatomical and linguistic profile observed in svPPA provides a compelling model for the functional interplay of these networks, being either up- or down- regulated in response to disease.

"The effect of tDCS on functional connectivity in primary progressive aphasia" NeuroImage: Clinical, volume 19 (2018), pages 703-715

Transcranial direct current stimulation (tDCS) is an innovative technique recently shown to improve language outcomes even in neurodegenerative conditions such as primary progressive aphasia (PPA), but the underlying brain mechanisms are not known. The present study tested whether the additional language gains with repetitive tDCS (over sham) in PPA are caused by changes in functional connectivity between the stimulated area (the left inferior frontal gyrus (IFG)) and the rest of the language network. We scanned 24 PPA participants (11 female) before and after language intervention (written naming/spelling) with a resting-state fMRI sequence and compared changes before and after three weeks of tDCS or sham coupled with language therapy. We correlated changes in the language network as well as in the default mode network (DMN) with language therapy outcome measures (letter accuracy in written naming). Significant tDCS effects in functional connectivity were observed between the stimulated area and other language network areas and between the language network and the DMN. TDCS over the left IFG lowered the connectivity between the above pairs. Changes in functional connectivity correlated with improvement in language scores (letter accuracy as a proxy for written naming) evaluated before and after therapy. These results suggest that one mechanism for anodal tDCS over the left IFG in PPA is a decrease in functional connectivity (compared to sham) between the stimulated site and other posterior areas of the language network. These results are in line with similar decreases in connectivity observed after tDCS over the left IFG in aging and other neurodegenerative conditions.

The Relationship Between Non-Orthographic Language Abilities and Reading Performance in Chronic Aphasia: An Exploration of the Primary Systems Hypothesis

PURPOSE

This study investigated the relationship between non-orthographic language abilities and reading in order to examine assumptions of the primary systems hypothesis and further our understanding of language processing poststroke.

METHOD

Performance on non-orthographic semantic, phonologic, and syntactic tasks, as well as oral reading and reading comprehension tasks, was assessed in 43 individuals with aphasia. Correlation and regression analyses were conducted to determine the relationship between these measures. In addition, analyses of variance examined differences within and between reading groups (within normal limits, phonological, deep, or global alexia).

RESULTS

Results showed that non-orthographic language abilities were significantly related to reading abilities. Semantics was most predictive of regular and irregular word reading, whereas phonology was most predictive of pseudohomophone and nonword reading. Written word and paragraph comprehension were primarily supported by semantics, whereas written sentence comprehension was related to semantic, phonologic, and syntactic performance. Finally, severity of alexia was found to reflect severity of semantic and phonologic impairment.

CONCLUSIONS

Findings support the primary systems view of language by showing that non-orthographic language abilities and reading abilities are closely linked. This preliminary work requires replication and extension; however, current results highlight the importance of routine, integrated assessment and treatment of spoken and written language in aphasia.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.7403963.

Mapping the intersection of language and reading: the neural bases of the primary systems hypothesis

The primary systems framework has been used to relate behavioural performance across many different language activities to the status of core underpinning domain-general cognitive systems. This study provided the first quantitative investigation of this account at both behavioural and neural levels in a group of patients with chronic post-stroke aphasia. Principal components analysis was used to distil orthogonal measures of phonological and semantic processing, which were then related to reading performance and the underlying lesion distributions using voxel-based correlational methodology. Concrete word reading involved both a ventral semantic pathway, and inferior and anterior aspects of the dorsal phonological pathway. Abstract word reading overlapped with the ventral semantic pathway but also drew more extensively on the superior and posterior aspects of the dorsal phonological pathway. Nonword reading was related to phonological processing along the dorsal pathway and was also supported by a more superior set of regions previously associated with speech motor output. The use of continuous measures of behavioural performance and neural integrity allowed us to elucidate for the first time both the lesion and behavioural correlates for the semantic and phonological components of the primary systems hypothesis and to extend these by identifying the importance of an additional dorsal speech motor output system. These results provide a target for future neuroanatomically constrained computational models of reading.

Assessment of Individuals with Primary Progressive Aphasia

Speech-language pathologists play a crucial role in the assessment and treatment of individuals with primary progressive aphasia (PPA). The speech-language evaluation is a critical aspect of the diagnostic and rehabilitative process, informing differential diagnosis as well as intervention planning and monitoring of cognitive-linguistic status over time. The evaluation should include a thorough case history and interview and a detailed assessment of speech-language and cognitive functions, with tasks designed to detect core and associated deficits outlined in current diagnostic criteria. In this paper, we review assessments that can be utilized to examine communication and cognition in PPA, including general aphasia batteries designed for stroke and/or progressive aphasia as well as tests of specific cognitive-linguistic functions, including naming, object/person knowledge, single-word and sentence comprehension, repetition, spontaneous speech/language production, motor speech, written language, and nonlinguistic cognitive domains. The comprehensive evaluation can inform diagnostic decision making and facilitate planning of interventions that are tailored to the patient's current status and likely progression of deficits. As such, the speech-language evaluation allows the medical team to provide individuals with PPA and their families with appropriate recommendations for the present and the future.

The effect of tDCS on functional connectivity in primary progressive aphasia

Transcranial direct current stimulation (tDCS) is an innovative technique recently shown to improve language outcomes even in neurodegenerative conditions such as primary progressive aphasia (PPA), but the underlying brain mechanisms are not known. The present study tested whether the additional language gains with repetitive tDCS (over sham) in PPA are caused by changes in functional connectivity between the stimulated area (the left inferior frontal gyrus (IFG)) and the rest of the language network. We scanned 24 PPA participants (11 female) before and after language intervention (written naming/spelling) with a resting-state fMRI sequence and compared changes before and after three weeks of tDCS or sham coupled with language therapy. We correlated changes in the language network as well as in the default mode network (DMN) with language therapy outcome measures (letter accuracy in written naming). Significant tDCS effects in functional connectivity were observed between the stimulated area and other language network areas and between the language network and the DMN. TDCS over the left IFG lowered the connectivity between the above pairs. Changes in functional connectivity correlated with improvement in language scores (letter accuracy as a proxy for written naming) evaluated before and after therapy. These results suggest that one mechanism for anodal tDCS over the left IFG in PPA is a decrease in functional connectivity (compared to sham) between the stimulated site and other posterior areas of the language network. These results are in line with similar decreases in connectivity observed after tDCS over the left IFG in aging and other neurodegenerative conditions.

The effect of tDCS on functional connectivity in primary progressive aphasia

Transcranial direct current stimulation (tDCS) is an innovative technique recently shown to improve language outcomes even in neurodegenerative conditions such as primary progressive aphasia (PPA), but the underlying brain mechanisms are not known. The present study tested whether the additional language gains with repetitive tDCS (over sham) in PPA are caused by changes in functional connectivity between the stimulated area (the left inferior frontal gyrus (IFG)) and the rest of the language network. We scanned 24 PPA participants (11 female) before and after language intervention (written naming/spelling) with a resting-state fMRI sequence and compared changes before and after three weeks of tDCS or sham coupled with language therapy. We correlated changes in the language network as well as in the default mode network (DMN) with language therapy outcome measures (letter accuracy in written naming). Significant tDCS effects in functional connectivity were observed between the stimulated area and other language network areas and between the language network and the DMN. TDCS over the left IFG lowered the connectivity between the above pairs. Changes in functional connectivity correlated with improvement in language scores (letter accuracy as a proxy for written naming) evaluated before and after therapy. These results suggest that one mechanism for anodal tDCS over the left IFG in PPA is a decrease in functional connectivity (compared to sham) between the stimulated site and other posterior areas of the language network. These results are in line with similar decreases in connectivity observed after tDCS over the left IFG in aging and other neurodegenerative conditions.

Do You Read How I Read? Systematic Individual Differences in Semantic Reliance amongst Normal Readers

The extent to which meaning is involved in reading aloud has proven an area of longstanding debate, and current computational models differ on this dimension. The connectionist triangle model proposes that normal individuals rely on semantic information for correct reading of words with atypical spelling-sound relationships, but to varying degrees. This proposed individual difference would account for the varying stage of decline at which patients with semantic dementia first show the reading impairment known as surface dyslexia. Recent neuroimaging data has provided validation of this view, showing that individual differences in degree of semantic reliance during exception word reading predict the amount of activation in left anterior temporal regions associated with semantic processing. This study aimed to establish the cognitive correlates of individual differences in semantic reliance during exception word reading. Experiment 1 used a subgrouping approach with 32 participants and found larger imageability and semantic priming effects specifically for exception word reading amongst high relative to low semantic reliance readers. High semantic reliance readers also tended to read nonwords more slowly than low semantic reliance readers. A second experiment used a regression approach with 129 readers and confirmed the relationship of degree of semantic reliance both to imageability effects in exception word reading and speed of nonword reading. Further, while the performance of the higher semantic readers revealed no significant association with semantic processing tasks, there was a negative relationship with rhyme processing tasks. We therefore speculate that differences in phonological abilities may be responsible for varying degrees of semantic reliance in reading aloud. This proposal accords with the results of functional imaging showing that higher semantic reliance during exception word reading corresponds to lower activation in left pre-central gyrus, an area associated with direct spelling sound mapping and phonological processing. Our results therefore establish the nature of systematic individual differences in degree of semantic involvement amongst normal readers, and suggest directions for future neuroimaging and computational modeling research to uncover their origins.

Communication Bridge: A pilot feasibility study of Internet-based speech-language therapy for individuals with progressive aphasia

Introduction

Individuals with aphasia symptoms due to neurodegenerative disease are under-referred for speech–language therapy (SLT) services. We sought to determine the feasibility of utilizing telepractice, via Internet videoconferencing, to connect individuals with progressive aphasia to a speech–language pathologist (SLP) for treatment.

Methods

Participants received an initial evaluation, 8 person-centered Internet-based SLT sessions, and 2 post-therapy evaluations. The feasibility of providing Web-based SLT, strategies used and their compliance, functional gains, and the duration of benefit were assessed.

Results

Thirty-four participants from 21 states and Canada were enrolled. Thirty-one participants completed the 6-month evaluation. SLP-assessed and self-reported functional gains and increased confidence in communication were documented at 2 months and maintained at 6 months postenrollment.

Discussion

Internet-based SLT using person-centered interventions provides a feasible model for delivering care to individuals with dementia and mild and/or moderate aphasia symptoms who have an engaged care-partner and prior familiarity with a computer.

Reading words and other people: A comparison of exception word, familiar face and affect processing in the left and right temporal variants of primary progressive aphasia

Semantic variant primary progressive aphasia (svPPA) typically presents with left-hemisphere predominant rostral temporal lobe (rTL) atrophy and the most significant complaints within the language domain. Less frequently, patients present with right-hemisphere predominant temporal atrophy coupled with marked impairments in processing of famous faces and emotions. Few studies have objectively compared these patient groups in both domains and therefore it is unclear to what extent the syndromes overlap. Clinically diagnosed svPPA patients were characterized as left- (n = 21) or right-predominant (n = 12) using imaging and compared along with 14 healthy controls. Regarding language, our primary focus was upon two hallmark features of svPPA; confrontation naming and surface dyslexia. Both groups exhibited naming deficits and surface dyslexia although the impairments were more severe in the left-predominant group. Familiarity judgments on famous faces and affect processing were more profoundly impaired in the right-predominant group. Our findings suggest that the two syndromes overlap significantly but that early cases at the tail ends of the continuum constitute a challenge for current clinical criteria. Correlational neuroimaging analyses implicated a mid portion of the left lateral temporal lobe in exception word reading impairments in line with proposals that this region is an interface between phonology and semantic knowledge.

Classification of the primary progressive aphasias: principles and review of progress since 2011

Highly influential recommendations published in 2011 for the classification of the primary progressive aphasias (PPA) distinguished three subtypes: the semantic variant, the nonfluent/agrammatic variant, and the logopenic variant. We review empirical evidence published after 2011 that bears relevance to the validity of the recommended classification scheme. The studies that we review principally rely on monocentric, memory clinic-based consecutive series of PPA patients. We review whether a data-driven analysis of neurolinguistic test scores confirms the subtyping that was based on expert consensus, whether the 2011 subtyping covers the diversity of PPA in a comprehensive manner, and whether the proposed subgroups differ along dimensions that are not explicitly part of the defining criteria, such as diffusion tractography. Data-driven mathematical analyses of neurolinguistic data in PPA broadly confirm the presence of separate clusters corresponding to the subtypes but also leave 15–30 % unclassified. A comprehensive description of PPA requires the addition of the mixed variant as a fourth subtype and needs to leave room for cases fulfilling the criteria for a root diagnosis of PPA but not those of any of the three subtypes. Finally, given the limited predictive value of the clinical phenotype for the underlying neuropathology, biomarkers of the underlying pathology are likely of clinical utility in PPA.

Surface errors without semantic impairment in acquired dyslexia: a voxel-based lesion-symptom mapping study

Patients with surface dyslexia have disproportionate difficulty pronouncing irregularly spelled words (e.g. pint), suggesting impaired use of lexical-semantic information to mediate phonological retrieval. Patients with this deficit also make characteristic 'regularization' errors, in which an irregularly spelled word is mispronounced by incorrect application of regular spelling-sound correspondences (e.g. reading plaid as 'played'), indicating over-reliance on sublexical grapheme-phoneme correspondences. We examined the neuroanatomical correlates of this specific error type in 45 patients with left hemisphere chronic stroke. Voxel-based lesion-symptom mapping showed a strong positive relationship between the rate of regularization errors and damage to the posterior half of the left middle temporal gyrus. Semantic deficits on tests of single-word comprehension were generally mild, and these deficits were not correlated with the rate of regularization errors. Furthermore, the deep occipital-temporal white matter locus associated with these mild semantic deficits was distinct from the lesion site associated with regularization errors. Thus, in contrast to patients with surface dyslexia and semantic impairment from anterior temporal lobe degeneration, surface errors in our patients were not related to a semantic deficit. We propose that these patients have an inability to link intact semantic representations with phonological representations. The data provide novel evidence for a post-semantic mechanism mediating the production of surface errors, and suggest that the posterior middle temporal gyrus may compute an intermediate representation linking semantics with phonology.

Phonological Processing in Primary Progressive Aphasia

Individuals with primary progressive aphasia (PPA) show selective breakdown in regions within the proposed dorsal (articulatory-phonological) and ventral (lexical-semantic) pathways involved in language processing. Phonological STM impairment, which has been attributed to selective damage to dorsal pathway structures, is considered to be a distinctive feature of the logopenic variant of PPA. By contrast, phonological abilities are considered to be relatively spared in the semantic variant and are largely unexplored in the nonfluent/agrammatic variant. Comprehensive assessment of phonological ability in the three variants of PPA has not been undertaken. We investigated phonological processing skills in a group of participants with PPA as well as healthy controls, with the goal of identifying whether patterns of performance support the dorsal versus ventral functional-anatomical framework and to discern whether phonological ability differs among PPA subtypes. We also explored the neural bases of phonological performance using voxel-based morphometry. Phonological performance was impaired in patients with damage to dorsal pathway structures (nonfluent/agrammatic and logopenic variants), with logopenic participants demonstrating particular difficulty on tasks involving nonwords. Binary logistic regression revealed that select phonological tasks predicted diagnostic group membership in the less fluent variants of PPA with a high degree of accuracy, particularly in conjunction with a motor speech measure. Brain-behavior correlations indicated a significant association between the integrity of gray matter in frontal and temporoparietal regions of the left hemisphere and phonological skill. Findings confirm the critical role of dorsal stream structures in phonological processing and demonstrate unique patterns of impaired phonological processing in logopenic and nonfluent/agrammatic variants of PPA.

Is descriptive writing useful in the differential diagnosis of logopenic variant of primary progressive aphasia, Alzheimer's disease and mild cognitive impairment?

Current classification of primary progressive aphasia (PPA) encompasses three variants: non-fluent (nfvPPA), semantic (svPPA) and logopenic (lvPPA). Previously lvPPA was regarded as aphasic form of Alzheimer's disease (AD). However, not all patients with lvPPA phenotype present with AD pathology. Despite abundant literature on differentiation of lvPPA from svPPA and nfvPPA, studies comparing lvPPA with AD and mild cognitive impairment (MCI) are scarce. This study aimed at analyzing written descriptive output in lvPPA, AD and MCI. Thirty-five patients participated in the study: 9 with lvPPA, 13 with AD and 13 with MCI. Most aspects of writing performance were comparable in three groups. However, letter insertion errors appeared in 44% patients with lvPPA, while they were absent in AD and MCI. Patients with lvPPA used more verbs than patients with AD. Writing profile may complement other neuropsychological assessment results in the differential diagnosis of lvPPA. Letter insertion errors and frequent verb use may raise a query of lvPPA.

Triangulation of the neurocomputational architecture underpinning reading aloud

The goal of cognitive neuroscience is to integrate cognitive models with knowledge about underlying neural machinery. This significant challenge was explored in relation to word reading, where sophisticated computational-cognitive models exist but have made limited contact with neural data. Using distortion-corrected functional MRI and dynamic causal modeling, we investigated the interactions between brain regions dedicated to orthographic, semantic, and phonological processing while participants read words aloud. We found that the lateral anterior temporal lobe exhibited increased activation when participants read words with irregular spellings. This area is implicated in semantic processing but has not previously been considered part of the reading network. We also found meaningful individual differences in the activation of this region: Activity was predicted by an independent measure of the degree to which participants use semantic knowledge to read. These characteristics are predicted by the connectionist Triangle Model of reading and indicate a key role for semantic knowledge in reading aloud. Premotor regions associated with phonological processing displayed the reverse characteristics. Changes in the functional connectivity of the reading network during irregular word reading also were consistent with semantic recruitment. These data support the view that reading aloud is underpinned by the joint operation of two neural pathways. They reveal that (i) the ATL is an important element of the ventral semantic pathway and (ii) the division of labor between the two routes varies according to both the properties of the words being read and individual differences in the degree to which participants rely on each route.

Treatment of Primary Progressive Aphasia

OPINION STATEMENT

Primary progressive aphasia (PPA) is a neurodegenerative disease that primarily affects language functions and often begins in the fifth or sixth decade of life. The devastating effects on work and home life call for the investigation of treatment alternatives. In this paper, we present a review of the literature on treatment approaches for this neurodegenerative disease. We also present new data from two intervention studies we have conducted, a behavioral one and a neuromodulatory one using transcranial direct current stimulation (tDCS) combined with written production intervention. We show that speech-language intervention improves language outcomes in individuals with PPA, and especially in the short term, tDCS augments generalization and maintenance of positive language outcomes. We also outline current issues and challenges in intervention approaches in PPA.

Capturing multidimensionality in stroke aphasia: mapping principal behavioural components to neural structures

Stroke aphasia is a multidimensional disorder in which patient profiles reflect variation along multiple behavioural continua. We present a novel approach to separating the principal aspects of chronic aphasic performance and isolating their neural bases. Principal components analysis was used to extract core factors underlying performance of 31 participants with chronic stroke aphasia on a large, detailed battery of behavioural assessments. The rotated principle components analysis revealed three key factors, which we labelled as phonology, semantic and executive/cognition on the basis of the common elements in the tests that loaded most strongly on each component. The phonology factor explained the most variance, followed by the semantic factor and then the executive-cognition factor. The use of principle components analysis rendered participants' scores on these three factors orthogonal and therefore ideal for use as simultaneous continuous predictors in a voxel-based correlational methodology analysis of high resolution structural scans. Phonological processing ability was uniquely related to left posterior perisylvian regions including Heschl's gyrus, posterior middle and superior temporal gyri and superior temporal sulcus, as well as the white matter underlying the posterior superior temporal gyrus. The semantic factor was uniquely related to left anterior middle temporal gyrus and the underlying temporal stem. The executive-cognition factor was not correlated selectively with the structural integrity of any particular region, as might be expected in light of the widely-distributed and multi-functional nature of the regions that support executive functions. The identified phonological and semantic areas align well with those highlighted by other methodologies such as functional neuroimaging and neurostimulation. The use of principle components analysis allowed us to characterize the neural bases of participants' behavioural performance more robustly and selectively than the use of raw assessment scores or diagnostic classifications because principle components analysis extracts statistically unique, orthogonal behavioural components of interest. As such, in addition to improving our understanding of lesion-symptom mapping in stroke aphasia, the same approach could be used to clarify brain-behaviour relationships in other neurological disorders.

Theoretical analysis of word production deficits in adult aphasia

The cognitive analysis of adult language disorders continues to draw heavily on linguistic theory, but increasingly it reflects the influence of connectionist, spreading activation models of cognition. In the area of spoken word production, 'localist' connectionist models represent a natural evolution from the psycholingistic theories of earlier decades. By contrast, the parallel distributed processing framework forces more radical rethinking of aphasic impairments. This paper exemplifies these multiple influences in contemporary cognitive aphasiology. Topics include (i) what aphasia reveals about semantic-phonological interaction in lexical access; (ii) controversies surrounding the interpretation of semantic errors and (iii) a computational account of the relationship between naming and word repetition in aphasia. Several of these topics have been addressed using case series methods, including computational simulation of the individual, quantitative error patterns of diverse groups of patients and analysis of brain lesions that correlate with error rates and patterns. Efforts to map the lesion correlates of nonword errors in naming and repetition highlight the involvement of sensorimotor areas in the brain and suggest the need to better integrate models of word production with models of speech and action.

Connectionist neuropsychology: uncovering ultimate causes of acquired dyslexia

Acquired dyslexia offers a unique window on to the nature of the cognitive and neural architecture supporting skilled reading. This paper provides an integrative overview of recent empirical and computational work on acquired dyslexia within the context of the primary systems framework as implemented in connectionist neuropsychological models. This view proposes that damage to general visual, phonological or semantic processing abilities are the root causes of different forms of acquired dyslexia. Recent case-series behavioural evidence concerning pure alexia, phonological dyslexia and surface dyslexia that supports this perspective is presented. Lesion simulations of these findings within connectionist models of reading demonstrate the viability of this approach. The commitment of such models to learnt representations allows them to capture key aspects of performance in each type of acquired dyslexia, particularly the associated non-reading deficits, the role of relearning and the influence of individual differences in the premorbid state of the reading system. Identification of these factors not only advances our understanding of acquired dyslexia and the mechanisms of normal reading but they are also relevant to the complex interactions underpinning developmental reading disorders.

Dysfunctional visual word form processing in progressive alexia

Progressive alexia is an acquired reading deficit caused by degeneration of brain regions that are essential for written word processing. Functional imaging studies have shown that early processing of the visual word form depends on a hierarchical posterior-to-anterior processing stream in occipito-temporal cortex, whereby successive areas code increasingly larger and more complex perceptual attributes of the letter string. A region located in the left lateral occipito-temporal sulcus and adjacent fusiform gyrus shows maximal selectivity for words and has been dubbed the 'visual word form area'. We studied two patients with progressive alexia in order to determine whether their reading deficits were associated with structural and/or functional abnormalities in this visual word form system. Voxel-based morphometry showed left-lateralized occipito-temporal atrophy in both patients, very mild in one, but moderate to severe in the other. The two patients, along with 10 control subjects, were scanned with functional magnetic resonance imaging as they viewed rapidly presented words, false font strings, or a fixation crosshair. This paradigm was optimized to reliably map brain regions involved in orthographic processing in individual subjects. All 10 control subjects showed a posterior-to-anterior gradient of selectivity for words, and all 10 showed a functionally defined visual word form area in the left hemisphere that was activated for words relative to false font strings. In contrast, neither of the two patients with progressive alexia showed any evidence for a selectivity gradient or for word-specific activation of the visual word form area. The patient with mild atrophy showed normal responses to both words and false font strings in the posterior part of the visual word form system, but a failure to develop selectivity for words in the more anterior part of the system. In contrast, the patient with moderate to severe atrophy showed minimal activation of any part of the visual word form system for either words or false font strings. Our results suggest that progressive alexia is associated with a dysfunctional visual word form system, with or without substantial cortical atrophy. Furthermore, these findings demonstrate that functional MRI has the potential to reveal the neural bases of cognitive deficits in neurodegenerative patients at very early stages, in some cases before the development of extensive atrophy.

The dorsal stream contribution to phonological retrieval in object naming

Meaningful speech, as exemplified in object naming, calls on knowledge of the mappings between word meanings and phonological forms. Phonological errors in naming (e.g. GHOST named as 'goath') are commonly seen in persisting post-stroke aphasia and are thought to signal impairment in retrieval of phonological form information. We performed a voxel-based lesion-symptom mapping analysis of 1718 phonological naming errors collected from 106 individuals with diverse profiles of aphasia. Voxels in which lesion status correlated with phonological error rates localized to dorsal stream areas, in keeping with classical and contemporary brain-language models. Within the dorsal stream, the critical voxels were concentrated in premotor cortex, pre- and postcentral gyri and supramarginal gyrus with minimal extension into auditory-related posterior temporal and temporo-parietal cortices. This challenges the popular notion that error-free phonological retrieval requires guidance from sensory traces stored in posterior auditory regions and points instead to sensory-motor processes located further anterior in the dorsal stream. In a separate analysis, we compared the lesion maps for phonological and semantic errors and determined that there was no spatial overlap, demonstrating that the brain segregates phonological and semantic retrieval operations in word production.

The consequences of progressive phonological impairment for reading aloud

The 'primary systems' view of reading disorders proposes that there are no neural regions devoted exclusively to reading, and therefore that acquired dyslexias should reliably co-occur with deficits in more general underlying capacities. This perspective predicted that surface dyslexia, a selective deficit in reading aloud 'exception' words (those with atypical spelling-sound characteristics), should be a consistent feature of semantic dementia, a progressive disorder of conceptual knowledge, and just such a pattern has been observed in previous research. In a similar vein, one might expect the gradual deterioration of phonological processing seen in the nonfluent forms of progressive aphasia to be accompanied by phonological dyslexia, a selective deficit in reading of unfamiliar letter strings, i.e., nonwords. The present study, reporting a case-series consideration of reading-aloud data from 16 progressive nonfluent aphasic patients, revealed a pattern in which both low-frequency exception word and nonword reading were comparably compromised. The severity of the reading disorder was predicted by scores on the expressive language task of picture naming but not the receptive task of spoken word-to-picture matching. Our hypothesis that a phonological deficit underpins diminished performance for both naming and reading was supported by the finding that reading-aloud performance was predicted specifically by the rate of phonological errors in picture naming. Moreover, the strength of this relationship was similar for low-frequency exception words and nonwords, suggesting that reading deficits for these two types of items in this disorder shared a common cause: a progressive impairment of phonological processing.

Anatomic, clinical, and neuropsychological correlates of spelling errors in primary progressive aphasia

This study evaluates spelling errors in the three subtypes of primary progressive aphasia (PPA): agrammatic (PPA-G), logopenic (PPA-L), and semantic (PPA-S). Forty-one PPA patients and 36 age-matched healthy controls were administered a test of spelling. The total number of errors and types of errors in spelling to dictation of regular words, exception words and nonwords, were recorded. Error types were classified based on phonetic plausibility. In the first analysis, scores were evaluated by clinical diagnosis. Errors in spelling exception words and phonetically plausible errors were seen in PPA-S. Conversely, PPA-G was associated with errors in nonword spelling and phonetically implausible errors. In the next analysis, spelling scores were correlated to other neuropsychological language test scores. Significant correlations were found between exception word spelling and measures of naming and single word comprehension. Nonword spelling correlated with tests of grammar and repetition. Global language measures did not correlate significantly with spelling scores, however. Cortical thickness analysis based on MRI showed that atrophy in several language regions of interest were correlated with spelling errors. Atrophy in the left supramarginal gyrus and inferior frontal gyrus (IFG) pars orbitalis correlated with errors in nonword spelling, while thinning in the left temporal pole and fusiform gyrus correlated with errors in exception word spelling. Additionally, phonetically implausible errors in regular word spelling correlated with thinning in the left IFG pars triangularis and pars opercularis. Together, these findings suggest two independent systems for spelling to dictation, one phonetic (phoneme to grapheme conversion), and one lexical (whole word retrieval).