Conduction aphasia, sensory-motor integration, and phonological short-term memory - an aggregate analysis of lesion and fMRI data

Verbal working memory and syntactic comprehension segregate into the dorsal and ventral streams

Syntactic processing and verbal working memory are both essential components to sentence comprehension. Nonetheless, the separability of these systems in the brain remains unclear. To address this issue, we performed causal-inference analyses based on lesion and connectome network mapping using MRI and behavioral testing in 103 individuals with chronic post-stroke aphasia. We employed a rhyme judgment task with heavy working memory load without articulatory confounds, controlling for the overall ability to match auditory words to pictures and to perform a metalinguistic rhyme judgment, isolating the effect of working memory load. We assessed noncanonical sentence comprehension, isolating syntactic processing by incorporating residual rhyme judgment performance as a covariate for working memory load. Voxel-based lesion analyses and structural connectome-based lesion symptom mapping controlling for total lesion volume were performed, with permutation testing to correct for multiple comparisons (4,000 permutations). We observed that effects of working memory load localized to dorsal stream damage: posterior temporal-parietal lesions and frontal-parietal white matter disconnections. These effects were differentiated from syntactic comprehension deficits, which were primarily associated with ventral stream damage: lesions to temporal lobe and temporal-parietal white matter disconnections, particularly when incorporating the residual measure of working memory load as a covariate. Our results support the conclusion that working memory and syntactic processing are associated with distinct brain networks, largely loading onto dorsal and ventral streams, respectively.

Cortical networks responsive to phrase structure and subject island violations

In principle, functional neuroimaging provides uniquely informative data in addressing linguistic questions, because it can indicate distinct processes that are not apparent from behavioral data alone. This could involve adjudicating the source of unacceptability via the different patterns of elicited brain responses to different ungrammatical sentence types. However, it is difficult to interpret brain activations to syntactic violations. Such responses could reflect processes that have nothing intrinsically related to linguistic representations, such as domain-general executive function abilities. In order to facilitate the potential use of functional neuroimaging methods to identify the source of different syntactic violations, we conducted an fMRI experiment to identify the brain activation maps associated with two distinct syntactic violation types: phrase structure (created by inverting the order of two adjacent words within a sentence) and subject islands (created by extracting a wh-phrase out of an embedded subject). The comparison of these violations to control sentences surprisingly showed no indication of a generalized violation response, with almost completely divergent activation patterns. Phrase structure violations seemingly activated regions previously implicated in verbal working memory and structural complexity in sentence processing, whereas the subject islands appeared to activate regions previously implicated in conceptual-semantic processing, broadly defined. We review our findings in the context of previous research on syntactic and semantic violations using event-related potentials. We suggest that functional neuroimaging is a potentially fruitful technique in unpacking the distinct sets of cognitive processes elicited by theoretically-relevant syntactic violations, when interpreted with care and paired with appropriate control conditions.

An inclusive multivariate approach to neural localization of language components

To determine how language is implemented in the brain, it is important to know which brain areas are primarily engaged in language processing and which are not. Existing protocols for localizing language are typically univariate, treating each small unit of brain volume as independent. One prominent example that focuses on the overall language network in functional magnetic resonance imaging (fMRI) uses a contrast between neural responses to sentences and sets of pseudowords (pronounceable nonwords). This contrast reliably activates peri-sylvian language areas but is less sensitive to extra-sylvian areas that are also known to support aspects of language such as word meanings (semantics). In this study, we assess areas where a multivariate, pattern-based approach shows high reproducibility across multiple measurements and participants, identifying these areas as multivariate regions of interest (mROI). We then perform a representational similarity analysis (RSA) of an fMRI dataset where participants made familiarity judgments on written words. We also compare those results to univariate regions of interest (uROI) taken from previous sentences > pseudowords contrasts. RSA with word stimuli defined in terms of their semantic distance showed greater correspondence with neural patterns in mROI than uROI. This was confirmed in two independent datasets, one involving single-word recognition, and the other focused on the meaning of noun-noun phrases by contrasting meaningful phrases > pseudowords. In all cases, areas of spatial overlap between mROI and uROI showed the greatest neural association. This suggests that ROIs defined in terms of multivariate reproducibility can help localize components of language such as semantics. The multivariate approach can also be extended to focus on other aspects of language such as phonology, and can be used along with the univariate approach for inclusively mapping language cortex.

Wernicke's functional neuroanatomy model of language turns 150: what became of its psychological reflex arcs?

Wernicke (Der aphasische Symptomencomplex: Eine psychologische Studie auf anatomischer Basis. Cohn und Weigert, Breslau.  https://wellcomecollection.org/works/dwv5w9rw , 1874) proposed a model of the functional neuroanatomy of spoken word repetition, production, and comprehension. At the heart of this epoch-making model are psychological reflex arcs underpinned by fiber tracts connecting sensory to motor areas. Here, I evaluate the central assumption of psychological reflex arcs in light of what we have learned about language in the brain during the past 150 years. I first describe Wernicke's 1874 model and the evidence he presented for it. Next, I discuss his updates of the model published in 1886 and posthumously in 1906. Although the model had an enormous immediate impact, it lost influence after the First World War. Unresolved issues included the anatomical underpinnings of the psychological reflex arcs, the role of auditory images in word production, and the sufficiency of psychological reflex arcs, which was questioned by Wundt (Grundzüge der physiologischen Psychologie. Engelmann, Leipzig. http://vlp.mpiwg-berlin.mpg.de/references?id=lit46 , 1874; Grundzüge der physiologischen Psychologie (Vol. 1, 5th ed.). Engelmann, Leipzig. http://vlp.mpiwg-berlin.mpg.de/references?id=lit806 , 1902). After a long dormant period, Wernicke's model was revived by Geschwind (Science 170:940-944. https://doi.org/10.1126/science.170.3961.940 , 1970; Selected papers on language and the brain. Reidel, Dordrecht, 1974), who proposed a version of it that differed in several important respects from Wernicke's original. Finally, I describe how new evidence from modern research has led to a novel view on language in the brain, supplementing contemporary equivalents of psychological reflex arcs by other mechanisms such as attentional control and assuming different neuroanatomical underpinnings. In support of this novel view, I report new analyses of patient data and computer simulations using the WEAVER++/ARC model (Roelofs 2014, 2022) that incorporates attentional control and integrates the new evidence.

Situating word deafness within aphasia recovery: A case report

Word deafness is a rare neurological disorder often observed following bilateral damage to superior temporal cortex and canonically defined as an auditory modality-specific deficit in word comprehension. The extent to which word deafness is dissociable from aphasia remains unclear given its heterogeneous presentation, and some have consequently posited that word deafness instead represents a stage in recovery from aphasia, where auditory and linguistic processing are affected to varying degrees and improve at differing rates. Here, we report a case of an individual (Mr. C) with bilateral temporal lobe lesions whose presentation evolved from a severe aphasia to an atypical form of word deafness, where auditory linguistic processing was impaired at the sentence level and beyond. We first reconstructed in detail Mr. C's stroke recovery through medical record review and supplemental interviewing. Then, using behavioral testing and multimodal neuroimaging, we documented a predominant auditory linguistic deficit in sentence and narrative comprehension-with markedly reduced behavioral performance and absent brain activation in the language network in the spoken modality exclusively. In contrast, Mr. C displayed near-unimpaired behavioral performance and robust brain activations in the language network for the linguistic processing of words, irrespective of modality. We argue that these findings not only support the view of word deafness as a stage in aphasia recovery but also further instantiate the important role of left superior temporal cortex in auditory linguistic processing.

Rapid auditory and phonemic processing relies on the left planum temporale

After initial bilateral acoustic processing of the speech signal, much of the subsequent language processing is left-lateralized. The reason for this lateralization remains an open question. Prevailing hypotheses describe a left hemisphere (LH) advantage for rapidly unfolding information-such as the segmental (e.g., phonetic and phonemic) components of speech. Here we investigated whether and where damage to the LH predicted impaired performance on judging the directionality of frequency modulated (FM) sweep stimuli that changed within short (25ms) or longer (250ms) temporal windows. Performance was significantly lower for stroke survivors (n = 50; 18 female) than controls (n = 61; 34 female) on FM Sweeps judgments, particularly on the short sweeps. Support vector regression lesion-symptom mapping (SVR-LSM) revealed that part of the left planum temporale (PT) was related to worse performance on judging the short FM sweeps, controlling for performance on the long sweeps. We then investigated whether damage to this particular area related to diminished performance on two levels of linguistic processing that theoretically depend on rapid auditory processing: stop consonant identification and pseudoword repetition. We separated stroke participants into subgroups based on whether their LH lesion included the part of the left PT that related to diminished short sweeps judgments. Participants with PT lesions (PT lesion+, n = 24) performed significantly worse than those without (PT lesion-, n = 26) on stop consonant identification and pseudoword repetition, controlling for lesion size and hearing ability. Interestingly, PT lesions impacted pseudoword repetition more than real word repetition (PT lesion-by-repetition trial type interaction), which is of interest because pseudowords rely solely on sound perception and sequencing, whereas words can also rely on lexical-semantic knowledge. We conclude that the left PT is a critical region for processing auditory information in short temporal windows, and it may also be an essential transfer point in auditory-to-linguistic processing.

The role of recollection and familiarity in visual working memory: A mixture of threshold and signal detection processes

Whether working memory reflects a thresholded recollection process whereby only a limited number of items are maintained in memory, or a signal detection process in which each studied item is increased in familiarity strength, is a topic of considerable debate. A review of visual working memory studies that have examined receiver operating characteristics (ROCs) across a broad set of materials and test conditions indicates that both signal detection and threshold processes contribute to working memory. In addition, the role that these two processes play varies systematically across conditions, such that a threshold process plays a particularly critical role when binary old/new judgments are required, when changes are relatively discrete, and when the hippocampus does not contribute to performance. In contrast, a signal detection process plays a greater role when confidence judgments are required, when the materials or the changes are global in nature, and when the hippocampus contributes to performance. In addition, the ROC results indicate that in standard single-probe tests of working memory, items that are maintained in an active recollected state support both recall-to-accept and recall-to-reject responses; whereas in complex-probe tests, recollection preferentially supports recall-to-reject; and in item-recognition tests it preferentially supports recall-to-accept. Moreover, there is growing evidence that these threshold and strength-based processes are related to distinct states of conscious awareness whereby they support perceiving- and sensing-based responses, respectively. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

The role of recollection, familiarity, and the hippocampus in episodic and working memory

The hippocampus plays an essential role in long-term episodic memory by supporting the recollection of contextual details, whereas surrounding regions such as the perirhinal cortex support familiarity-based recognition discriminations. Working memory - the ability to maintain information over very brief periods of time - is traditionally thought to rely heavily on frontoparietal attention networks, but recent work has shown that it can also rely on the hippocampus. However, the conditions in which the hippocampus becomes involved in working memory tasks are unclear and whether it contributes to recollection or familiarity-based responses in working memory is only beginning to be explored. In the current paper, we first review and contrast the existing amnesia literature examining recollection and familiarity in episodic and working memory. The results indicate that recollection and familiarity contribute to both episodic and working memory. However, in contrast to episodic memory, in working memory the hippocampus is particularly critical for familiarity-based rather than recollection-based discrimination. Moreover, the results indicate that the role of the hippocampus in working memory can be obscured due to 'criterion-induced process-masking' because it primarily supports intermediate-confidence recognition decisions. We then report results from a new working memory study examining the ability of amnesics to detect global and local changes in novel complex objects (i.e., fribbles), which indicates that the hippocampus plays an especially critical role in working memory when the task requires the detection of global rather than discrete changes. We conclude by considering the results in light of neurocomputational models and proposing a general framework for understanding the relationship between episodic and working memory.

Neural mechanisms of sentence production: a volumetric study of primary progressive aphasia

Studies on the neural bases of sentence production have yielded mixed results, partly due to differences in tasks and participant types. In this study, 101 individuals with primary progressive aphasia (PPA) were evaluated using a test that required spoken production following an auditory prime (Northwestern Assessment of Verbs and Sentences-Sentence Production Priming Test, NAVS-SPPT), and one that required building a sentence by ordering word cards (Northwestern Anagram Test, NAT). Voxel-Based Morphometry revealed that gray matter (GM) volume in left inferior/middle frontal gyri (L IFG/MFG) was associated with sentence production accuracy on both tasks, more so for complex sentences, whereas, GM volume in left posterior temporal regions was exclusively associated with NAVS-SPPT performance and predicted by performance on a Digit Span Forward (DSF) task. Verb retrieval deficits partly mediated the relationship between L IFG/MFG and performance on the NAVS-SPPT. These findings underscore the importance of L IFG/MFG for sentence production and suggest that this relationship is partly accounted for by verb retrieval deficits, but not phonological loop integrity. In contrast, it is possible that the posterior temporal cortex is associated with auditory short-term memory ability, to the extent that DSF performance is a valid measure of this in aphasia.

Enhancing Speech Rehabilitation in a Young Adult with Trisomy 21: Integrating Transcranial Direct Current Stimulation (tDCS) with Rapid Syllable Transition Training for Apraxia of Speech

Apraxia of speech is a persistent speech motor disorder that affects speech intelligibility. Studies on speech motor disorders with transcranial Direct Current Stimulation (tDCS) have been mostly directed toward examining post-stroke aphasia. Only a few tDCS studies have focused on apraxia of speech or childhood apraxia of speech (CAS), and no study has investigated individuals with CAS and Trisomy 21 (T21, Down syndrome). This N-of-1 randomized trial examined the effects of tDCS combined with a motor learning task in developmental apraxia of speech co-existing with T21 (ReBEC RBR-5435x9). The accuracy of speech sound production of nonsense words (NSWs) during Rapid Syllable Transition Training (ReST) over 10 sessions of anodal tDCS (1.5 mA, 25 cm) over Broca's area with the cathode over the contralateral region was compared to 10 sessions of sham-tDCS and four control sessions in a 20-year-old male individual with T21 presenting moderate-severe childhood apraxia of speech (CAS). The accuracy for NSW production progressively improved (gain of 40%) under tDCS (sham-tDCS and control sessions showed < 20% gain). A decrease in speech severity from moderate-severe to mild-moderate indicated transfer effects in speech production. Speech accuracy under tDCS was correlated with Wernicke's area activation (P3 current source density), which in turn was correlated with the activation of the left supramarginal gyrus and the Sylvian parietal-temporal junction. Repetitive bihemispheric tDCS paired with ReST may have facilitated speech sound acquisition in a young adult with T21 and CAS, possibly through activating brain regions required for phonological working memory.

Impairment of the internal forward model and feedback mechanisms for vocal sensorimotor control in post-stroke aphasia: evidence from directional responses to altered auditory feedback

The present study examined opposing and following vocal responses to altered auditory feedback (AAF) to determine how damage to left-hemisphere brain networks impairs the internal forward model and feedback mechanisms in post-stroke aphasia. Forty-nine subjects with aphasia and sixty age-matched controls performed speech vowel production tasks while their auditory feedback was altered using randomized ± 100 cents upward and downward pitch-shift stimuli. Data analysis revealed that when vocal responses were averaged across all trials (i.e., opposing and following), the overall magnitude of vocal compensation was significantly reduced in the aphasia group compared with controls. In addition, when vocal responses were analyzed separately for opposing and following trials, subjects in the aphasia group showed a significantly lower percentage of opposing and higher percentage of following vocal response trials compared with controls, particularly for the upward pitch-shift stimuli. However, there was no significant difference in the magnitude of opposing and following vocal responses between the two groups. These findings further support previous evidence on the impairment of vocal sensorimotor control in aphasia and provide new insights into the distinctive impact of left-hemisphere stroke on the internal forward model and feedback mechanisms. In this context, we propose that the lower percentage of opposing responses in aphasia may be accounted for by deficits in feedback-dependent mechanisms of audio-vocal integration and motor control. In addition, the higher percentage of following responses may reflect aberrantly increased reliance of the speech system on the internal forward model for generating sensory predictions during vocal error detection and motor control.

Language deficits in primary lateral sclerosis: cortical atrophy, white matter degeneration and functional disconnection between cerebral regions

BACKGROUND

Primary lateral sclerosis (PLS) is traditionally regarded as a pure upper motor neuron disorder, but recent cases series have highlighted cognitive deficits in executive and language domains.

METHODS

A single-centre, prospective neuroimaging study was conducted with comprehensive clinical and genetic profiling. The structural and functional integrity of language-associated brain regions and networks were systematically evaluated in 40 patients with PLS in comparison to 111 healthy controls. The structural integrity of the arcuate fascicle, frontal aslant tract, inferior occipito-frontal fascicle, inferior longitudinal fascicle, superior longitudinal fascicle and uncinate fascicle was evaluated. Functional connectivity between the supplementary motor region and the inferior frontal gyrus and connectivity between Wernicke's and Broca's areas was also assessed.

RESULTS

Cortical thickness reductions were observed in both Wernicke's and Broca's areas. Fractional anisotropy reduction was noted in the aslant tract and increased radical diffusivity (RD) identified in the aslant tract, arcuate fascicle and superior longitudinal fascicle in the left hemisphere. Functional connectivity was reduced along the aslant track, i.e. between the supplementary motor region and the inferior frontal gyrus, but unaffected between Wernicke's and Broca's areas. Cortical thickness alterations, structural and functional connectivity changes were also noted in the right hemisphere.

CONCLUSIONS

Disease-burden in PLS is not confined to motor regions, but there is also a marked involvement of language-associated tracts, networks and cortical regions. Given the considerably longer survival in PLS compared to ALS, the impact of language impairment on the management of PLS needs to be carefully considered.

The involvement of language-associated networks, tracts, and cortical regions in frontotemporal dementia and amyotrophic lateral sclerosis: Structural and functional alterations

BACKGROUND

Language deficits are cardinal manifestations of some frontotemporal dementia (FTD) phenotypes and also increasingly recognized in sporadic and familial amyotrophic lateral sclerosis (ALS). They have considerable social and quality-of-life implications, and adaptive strategies are challenging to implement. While the neuropsychological profiles of ALS-FTD phenotypes are well characterized, the neuronal underpinnings of language deficits are less well studied.

METHODS

A multiparametric, quantitative neuroimaging study was conducted to characterize the involvement of language-associated networks, tracts, and cortical regions with a panel of structural, diffusivity, and functional magnetic resonance imaging (MRI) metrics. Seven study groups were evaluated along the ALS-FTD spectrum: healthy controls (HC), individuals with ALS without cognitive impairment (ALSnci), C9orf72-negative ALS-FTD, C9orf72-positive ALS-FTD, behavioral-variant FTD (bvFTD), nonfluent variant primary progressive aphasia (nfvPPA), and semantic variant PPA (svPPA). The integrity of the Broca's area, Wernicke's area, frontal aslant tract (FAT), arcuate fascicle (AF), inferior occipitofrontal fascicle (IFO), inferior longitudinal fascicle (ILF), superior longitudinal fascicle (SLF), and uncinate fascicle (UF) was quantitatively evaluated. The functional connectivity (FC) between Broca's and Wernicke' areas and FC along the FAT was also specifically assessed.

RESULTS

Patients with nfvPPA and svPPA exhibit distinctive patterns of gray and white matter degeneration in language-associated brain regions. Individuals with bvFTD exhibit Broca's area, right FAT, right IFO, and UF degeneration. The ALSnci group exhibits Broca's area atrophy and decreased FC along the FAT. Both ALS-FTD cohorts, irrespective of C9orf72 status, show bilateral FAT, AF, and IFO pathology. Interestingly, only C9orf72-negative ALS-FTD patients exhibit bilateral uncinate and right ILF involvement, while C9orf72-positive ALS-FTD patients do not.

CONCLUSIONS

Language-associated tracts and networks are not only affected in language-variant FTD phenotypes but also in ALS and bvFTD. Language domains should be routinely assessed in ALS irrespective of the genotype.

Beyond Broca: neural architecture and evolution of a dual motor speech coordination system

Classical neural architecture models of speech production propose a single system centred on Broca's area coordinating all the vocal articulators from lips to larynx. Modern evidence has challenged both the idea that Broca's area is involved in motor speech coordination and that there is only one coordination network. Drawing on a wide range of evidence, here we propose a dual speech coordination model in which laryngeal control of pitch-related aspects of prosody and song are coordinated by a hierarchically organized dorsolateral system while supralaryngeal articulation at the phonetic/syllabic level is coordinated by a more ventral system posterior to Broca's area. We argue further that these two speech production subsystems have distinguishable evolutionary histories and discuss the implications for models of language evolution.

Baseline Conceptual-Semantic Impairment Predicts Longitudinal Treatment Effects for Anomia in Primary Progressive Aphasia and Alzheimer's Disease

Background

An individual's diagnostic subtype may fail to predict the efficacy of a given type of treatment for anomia. Classification by conceptual-semantic impairment may be more informative.

Aims

This study examined the effects of conceptual-semantic impairment and diagnostic subtype on anomia treatment effects in primary progressive aphasia (PPA) and Alzheimer's disease (AD).

Methods & Procedures

At baseline, the picture and word versions of the Pyramids and Palm Trees and Kissing and Dancing tests were used to measure conceptual-semantic processing. Based on norming that was conducted with unimpaired older adults, participants were classified as being impaired on both the picture and word versions (i.e., modality-general conceptual-semantic impairment), the picture version (Objects or Actions) only (i.e., visual-conceptual impairment), the word version (Nouns or Verbs) only (i.e., lexical-semantic impairment), or neither the picture nor the word version (i.e., no impairment). Following baseline testing, a lexical treatment and a semantic treatment were administered to all participants. The treatment stimuli consisted of nouns and verbs that were consistently named correctly at baseline (Prophylaxis items) and/or nouns and verbs that were consistently named incorrectly at baseline (Remediation items). Naming accuracy was measured at baseline, and it was measured at three, seven, eleven, fourteen, eighteen, and twenty-one months.

Outcomes & Results

Compared to baseline naming performance, lexical and semantic treatments both improved naming accuracy for treated Remediation nouns and verbs. For Prophylaxis items, lexical treatment was effective for both nouns and verbs, and semantic treatment was effective for verbs, but the pattern of results was different for nouns -- the effect of semantic treatment was initially nonsignificant or marginally significant, but it was significant beginning at 11 Months, suggesting that the effects of prophylactic semantic treatment may become more apparent as the disorder progresses. Furthermore, the interaction between baseline Conceptual-Semantic Impairment and the Treatment Condition (Lexical vs. Semantic) was significant for verb Prophylaxis items at 3 and 18 Months, and it was significant for noun Prophylaxis items at 14 and 18 Months.

Conclusions

The pattern of results suggested that individuals who have modality-general conceptual-semantic impairment at baseline are more likely to benefit from lexical treatment, while individuals who have unimpaired conceptual-semantic processing at baseline are more likely to benefit from semantic treatment as the disorder progresses. In contrast to conceptual-semantic impairment, diagnostic subtype did not typically predict the treatment effects.

Neural evidence suggests phonological acceptability judgments reflect similarity, not constraint evaluation

Acceptability judgments are a primary source of evidence in formal linguistic research. Within the generative linguistic tradition, these judgments are attributed to evaluation of novel forms based on implicit knowledge of rules or constraints governing well-formedness. In the domain of phonological acceptability judgments, other factors including ease of articulation and similarity to known forms have been hypothesized to influence evaluation. We used data-driven neural techniques to identify the relative contributions of these factors. Granger causality analysis of magnetic resonance imaging (MRI)-constrained magnetoencephalography (MEG) and electroencephalography (EEG) data revealed patterns of interaction between brain regions that support explicit judgments of the phonological acceptability of spoken nonwords. Comparisons of data obtained with nonwords that varied in terms of onset consonant cluster attestation and acceptability revealed different cortical regions and effective connectivity patterns associated with phonological acceptability judgments. Attested forms produced stronger influences of brain regions implicated in lexical representation and sensorimotor simulation on acoustic-phonetic regions, whereas unattested forms produced stronger influence of phonological control mechanisms on acoustic-phonetic processing. Unacceptable forms produced widespread patterns of interaction consistent with attempted search or repair. Together, these results suggest that speakers' phonological acceptability judgments reflect lexical and sensorimotor factors.

Correspondence between cognitive and neural representations for phonology, orthography, and semantics in supramarginal compared to angular gyrus

The angular and supramarginal gyri (AG and SMG) together constitute the inferior parietal lobule (IPL) and have been associated with cognitive functions that support reading. How those functions are distributed across the AG and SMG is a matter of debate, the resolution of which is hampered by inconsistencies across stereotactic atlases provided by the major brain image analysis software packages. Schematic results from automated meta-analyses suggest primarily semantic (word meaning) processing in the left AG, with more spatial overlap among phonological (auditory word form), orthographic (visual word form), and semantic processing in the left SMG. To systematically test for correspondence between patterns of neural activation and phonological, orthographic, and semantic representations, we re-analyze a functional magnetic resonance imaging data set of participants reading aloud 465 words. Using representational similarity analysis, we test the hypothesis that within cytoarchitecture-defined subregions of the IPL, phonological representations are primarily associated with the SMG, while semantic representations are primarily associated with the AG. To the extent that orthographic representations can be de-correlated from phonological representations, they will be associated with cortex peripheral to the IPL, such as the intraparietal sulcus. Results largely confirmed these hypotheses, with some nuanced exceptions, which we discuss in terms of neurally inspired computational cognitive models of reading that learn mappings among distributed representations for orthography, phonology, and semantics. De-correlating constituent representations making up complex cognitive processes, such as reading, by careful selection of stimuli, representational formats, and analysis techniques, are promising approaches for bringing additional clarity to brain structure-function relationships.

Continuous theta burst stimulation over left and right supramarginal gyri demonstrates their involvement in auditory feedback control of vocal production

The supramarginal gyrus (SMG) has been implicated in auditory-motor integration for vocal production. However, whether the SMG is bilaterally or unilaterally involved in auditory feedback control of vocal production in a causal manner remains unclear. The present event-related potential (ERP) study investigated the causal roles of the left and right SMG to auditory-vocal integration using neuronavigated continuous theta burst stimulation (c-TBS). Twenty-four young adults produced sustained vowel phonations and heard their voice unexpectedly pitch-shifted by ±200 cents after receiving active or sham c-TBS over the left or right SMG. As compared to sham stimulation, c-TBS over the left or right SMG led to significantly smaller vocal compensations for pitch perturbations that were accompanied by smaller cortical P2 responses. Moreover, no significant differences were found in the vocal and ERP responses when comparing active c-TBS over the left vs. right SMG. These findings provide neurobehavioral evidence for a causal influence of both the left and right SMG on auditory feedback control of vocal production. Decreased vocal compensations paralleled by reduced P2 responses following c-TBS over the bilateral SMG support their roles for auditory-motor transformation in a bottom-up manner: receiving auditory feedback information and mediating vocal compensations for feedback errors.

Brain activity during shadowing of audiovisual cocktail party speech, contributions of auditory-motor integration and selective attention

Selective listening to cocktail-party speech involves a network of auditory and inferior frontal cortical regions. However, cognitive and motor cortical regions are differentially activated depending on whether the task emphasizes semantic or phonological aspects of speech. Here we tested whether processing of cocktail-party speech differs when participants perform a shadowing (immediate speech repetition) task compared to an attentive listening task in the presence of irrelevant speech. Participants viewed audiovisual dialogues with concurrent distracting speech during functional imaging. Participants either attentively listened to the dialogue, overtly repeated (i.e., shadowed) attended speech, or performed visual or speech motor control tasks where they did not attend to speech and responses were not related to the speech input. Dialogues were presented with good or poor auditory and visual quality. As a novel result, we show that attentive processing of speech activated the same network of sensory and frontal regions during listening and shadowing. However, in the superior temporal gyrus (STG), peak activations during shadowing were posterior to those during listening, suggesting that an anterior-posterior distinction is present for motor vs. perceptual processing of speech already at the level of the auditory cortex. We also found that activations along the dorsal auditory processing stream were specifically associated with the shadowing task. These activations are likely to be due to complex interactions between perceptual, attention dependent speech processing and motor speech generation that matches the heard speech. Our results suggest that interactions between perceptual and motor processing of speech relies on a distributed network of temporal and motor regions rather than any specific anatomical landmark as suggested by some previous studies.

The cross-domain functional organization of posterior lateral temporal cortex: insights from ALE meta-analyses of 7 cognitive domains spanning 12,000 participants

The posterior lateral temporal cortex is implicated in many verbal, nonverbal, and social cognitive domains and processes. Yet without directly comparing these disparate domains, the region's organization remains unclear; do distinct processes engage discrete subregions, or could different domains engage shared neural correlates and processes? Here, using activation likelihood estimation meta-analyses, the bilateral posterior lateral temporal cortex subregions engaged in 7 domains were directly compared. These domains comprised semantics, semantic control, phonology, biological motion, face processing, theory of mind, and representation of tools. Although phonology and biological motion were predominantly associated with distinct regions, other domains implicated overlapping areas, perhaps due to shared underlying processes. Theory of mind recruited regions implicated in semantic representation, tools engaged semantic control areas, and faces engaged subregions for biological motion and theory of mind. This cross-domain approach provides insight into how posterior lateral temporal cortex is organized and why.

Semantic network activation facilitates oral word reading in chronic aphasia

People with aphasia often show partial impairments on a given task. This trial-to-trial variability offers a potential window into understanding how damaged language networks function. We test the hypothesis that successful word reading in participants with phonological system damage reflects semantic system recruitment. Residual semantic and phonological networks were defined with fMRI in 21 stroke participants with phonological damage using semantic- and rhyme-matching tasks. Participants performed an oral word reading task, and activation was compared between correct and incorrect trials within the semantic and phonological networks. The results showed a significant interaction between hemisphere, network activation, and reading success. Activation in the left hemisphere semantic network was higher when participants successfully read words. Residual phonological regions showed no difference in activation between correct and incorrect trials on the word reading task. The results provide evidence that semantic processing supports successful phonological retrieval in participants with phonological impairment.

The Neuroanatomy of Speech Processing: A Large-scale Lesion Study

The neural basis of language has been studied for centuries, yet the networks critically involved in simply identifying or understanding a spoken word remain elusive. Several functional-anatomical models of critical neural substrates of receptive speech have been proposed, including (1) auditory-related regions in the left mid-posterior superior temporal lobe, (2) motor-related regions in the left frontal lobe (in normal and/or noisy conditions), (3) the left anterior superior temporal lobe, or (4) bilateral mid-posterior superior temporal areas. One difficulty in comparing these models is that they often focus on different aspects of the sound-to-meaning pathway and are supported by different types of stimuli and tasks. Two auditory tasks that are typically used in separate studies-syllable discrimination and word comprehension-often yield different conclusions. We assessed syllable discrimination (words and nonwords) and word comprehension (clear speech and with a noise masker) in 158 individuals with focal brain damage: left (n = 113) or right (n = 19) hemisphere stroke, left (n = 18) or right (n = 8) anterior temporal lobectomy, and 26 neurologically intact controls. Discrimination and comprehension tasks are doubly dissociable both behaviorally and neurologically. In support of a bilateral model, clear speech comprehension was near ceiling in 95% of left stroke cases and right temporal damage impaired syllable discrimination. Lesion-symptom mapping analyses for the syllable discrimination and noisy word comprehension tasks each implicated most of the left superior temporal gyrus. Comprehension but not discrimination tasks also implicated the left posterior middle temporal gyrus, whereas discrimination but not comprehension tasks also implicated more dorsal sensorimotor regions in posterior perisylvian cortex.

The Wernicke conundrum revisited: evidence from connectome-based lesion-symptom mapping

Wernicke's area has been assumed since the 1800s to be the primary region supporting word and sentence comprehension. However, in 2015 and 2019, Mesulam and colleagues raised what they termed the 'Wernicke conundrum', noting widespread variability in the anatomical definition of this area and presenting data from primary progressive aphasia that challenged this classical assumption. To resolve the conundrum, they posited a 'double disconnection' hypothesis: that word and sentence comprehension deficits in stroke-based aphasia result from disconnection of anterior temporal and inferior frontal regions from other parts of the brain due to white matter damage, rather than dysfunction of Wernicke's area itself. To test this hypothesis, we performed lesion-deficit correlations, including connectome-based lesion-symptom mapping, in four large, partially overlapping groups of English-speaking chronic left hemisphere stroke survivors. After removing variance due to object recognition and associative semantic processing, the same middle and posterior temporal lobe regions were implicated in both word comprehension deficits and complex noncanonical sentence comprehension deficits. Connectome lesion-symptom mapping revealed similar temporal-occipital white matter disconnections for impaired word and noncanonical sentence comprehension, including the temporal pole. We found an additional significant temporal-parietal disconnection for noncanonical sentence comprehension deficits, which may indicate a role for phonological working memory in processing complex syntax, but no significant frontal disconnections. Moreover, damage to these middle-posterior temporal lobe regions was associated with both word and noncanonical sentence comprehension deficits even when accounting for variance due to the strongest anterior temporal and inferior frontal white matter disconnections, respectively. Our results largely agree with the classical notion that Wernicke's area, defined here as middle superior temporal gyrus and middle-posterior superior temporal sulcus, supports both word and sentence comprehension, suggest a supporting role for temporal pole in both word and sentence comprehension, and speak against the hypothesis that comprehension deficits in Wernicke's aphasia result from double disconnection.

Neural correlates of impaired vocal feedback control in post-stroke aphasia

We used left-hemisphere stroke as a model to examine how damage to sensorimotor brain networks impairs vocal auditory feedback processing and control. Individuals with post-stroke aphasia and matched neurotypical control subjects vocalized speech vowel sounds and listened to the playback of their self-produced vocalizations under normal (NAF) and pitch-shifted altered auditory feedback (AAF) while their brain activity was recorded using electroencephalography (EEG) signals. Event-related potentials (ERPs) were utilized as a neural index to probe the effect of vocal production on auditory feedback processing with high temporal resolution, while lesion data in the stroke group was used to determine how brain abnormality accounted for the impairment of such mechanisms. Results revealed that ERP activity was aberrantly modulated during vocalization vs. listening in aphasia, and this effect was accompanied by the reduced magnitude of compensatory vocal responses to pitch-shift alterations in the auditory feedback compared with control subjects. Lesion-mapping revealed that the aberrant pattern of ERP modulation in response to NAF was accounted for by damage to sensorimotor networks within the left-hemisphere inferior frontal, precentral, inferior parietal, and superior temporal cortices. For responses to AAF, neural deficits were predicted by damage to a distinguishable network within the inferior frontal and parietal cortices. These findings define the left-hemisphere sensorimotor networks implicated in auditory feedback processing, error detection, and vocal motor control. Our results provide translational synergy to inform the theoretical models of sensorimotor integration while having clinical applications for diagnosis and treatment of communication disabilities in individuals with stroke and other neurological conditions.

Learning From Mistakes: Cognitive and Metabolic Correlates of Errors on Picture Naming in the Alzheimer’s Disease Spectrum

Background: Analysis of subtypes of picture naming errors produced by patients with Alzheimer’s disease (AD) have seldom been investigated yet may clarify the cognitive and neural underpinnings of naming in the AD spectrum. Objective: To elucidate the neurocognitive bases of picture naming in AD through a qualitative analysis of errors. Methods: Over 1000 naming errors produced by 70 patients with amnestic, visuospatial, linguistic, or frontal AD were correlated with general cognitive tests and with distribution of hypometabolism on FDG-PET. Results: Principal component analysis identified 1) a Visual processing factor clustering visuospatial tests and unrecognized stimuli, pure visual errors and visual-semantic errors, associated with right parieto-occipital hypometabolism; 2) a Concept-Lemma factor grouping language tests and anomias, circumlocutions, superordinates, and coordinates, correlated with left basal temporal hypometabolism; 3) a Lemma-Phonology factor including the digit span and phonological errors, linked with left temporo-parietal hypometabolism. Regression of brain metabolism on individual errors showed that errors due to impairment of basic and higher-order processing of object visual attributes or of their interaction with semantics, were related with bilateral occipital and left occipito-temporal dysfunction. Omissions and superordinates were linked to degradation of broad and basic concepts in the left basal temporal cortex. Semantic-lexical errors derived from faulty semantically- and phonologically-driven lexical retrieval in the left superior and middle temporal gyri. Generation of nonwords was underpinned by of phonological impairment within the left inferior parietal cortex. Conclusion: Analysis of individual naming errors allowed to outline a comprehensive anatomo-functional model of picture naming in classical and atypical AD.

Individual Differences in Singing Behavior during Childhood Predicts Language Performance during Adulthood

Research on singing and language abilities has gained considerable interest in the past decade. While several studies about singing ability and language capacity have been published, investigations on individual differences in singing behavior during childhood and its relationship to language capacity in adulthood have largely been neglected. We wanted to focus our study on whether individuals who had sung more often during childhood than their peers were also better in language and music capacity during adulthood. We used questionnaires to assess singing behavior of adults during childhood and tested them for their singing ability, their music perception skills, and their ability to perceive and pronounce unfamiliar languages. The results have revealed that the more often individuals had sung during childhood, the better their singing ability and language pronunciation skills were, while the amount of childhood singing was less predictive on music and language perception skills. We suggest that the amount of singing during childhood seems to influence the ability to sing and the ability to acquire foreign language pronunciation later in adulthood.

The third branch of the superior longitudinal system

One of the major associative fiber pathways in the brain is the superior longitudinal system. This review discusses the current knowledge gained from studies on the third branch of the superior longitudinal system (SLS) regarding its anatomy, functional role in healthy individuals, results from lesion-symptom mapping studies and intraoperative electrostimulation studies. The results of these studies clearly indicate that the third branch of the SLS is a distinct pathway, as seen both from a functional and anatomical perspective. The third branch of the SLS should be distinguished from the long segment of the arcuate fasciculus, that courses along its trajectory but seems implicated in different functions. Moreover, these studies also provide substantial evidence that the right and left third branch of the SLS have different functional roles. Finally, a hypothesis for an integrated anatomo-functional model is proposed, that describes three subcomponents of the third branch of the superior longitudinal system.

The dual stream model of speech and language processing

The Wernicke-Lichtheim-Geschwind model of the neurology of language has served the field well despite its limited scope. More recent work has updated the basic architecture of the classical model and expanded its scope. This chapter briefly reviews the Wernicke-Lichtheim-Geschwind model and points out its shortcomings, then describes and motivates the dual stream model and how it solves several empirical shortcomings of the classical model. The chapter also (i) underscores how the dual stream model relates to the organization of nonlinguistic cortical networks, integrating language systems with the broader functional-anatomical landscape, (ii) describes recent work that further specifies the computational architecture and neural correlates of the dorsal speech production system, and (iii) summarizes recent extensions of the architectural framework to include syntax.

Musical Performance in Adolescents with ADHD, ADD and Dyslexia—Behavioral and Neurophysiological Aspects

Research has shown that dyslexia and attention deficit (hyperactivity) disorder (AD(H)D) are characterized by specific neuroanatomical and neurofunctional differences in the auditory cortex. These neurofunctional characteristics in children with ADHD, ADD and dyslexia are linked to distinct differences in music perception. Group-specific differences in the musical performance of patients with ADHD, ADD and dyslexia have not been investigated in detail so far. We investigated the musical performance and neurophysiological correlates of 21 adolescents with dyslexia, 19 with ADHD, 28 with ADD and 28 age-matched, unaffected controls using a music performance assessment scale and magnetoencephalography (MEG). Musical experts independently assessed pitch and rhythmic accuracy, intonation, improvisation skills and musical expression. Compared to dyslexic adolescents, controls as well as adolescents with ADHD and ADD performed better in rhythmic reproduction, rhythmic improvisation and musical expression. Controls were significantly better in rhythmic reproduction than adolescents with ADD and scored higher in rhythmic and pitch improvisation than adolescents with ADHD. Adolescents with ADD and controls scored better in pitch reproduction than dyslexic adolescents. In pitch improvisation, the ADD group performed better than the ADHD group, and controls scored better than dyslexic adolescents. Discriminant analysis revealed that rhythmic improvisation and musical expression discriminate the dyslexic group from controls and adolescents with ADHD and ADD. A second discriminant analysis based on MEG variables showed that absolute P1 latency asynchrony |R-L| distinguishes the control group from the disorder groups best, while P1 and N1 latencies averaged across hemispheres separate the control, ADD and ADHD groups from the dyslexic group. Furthermore, rhythmic improvisation was negatively correlated with auditory-evoked P1 and N1 latencies, pointing in the following direction: the earlier the P1 and N1 latencies (mean), the better the rhythmic improvisation. These findings provide novel insight into the differences between music processing and performance in adolescents with and without neurodevelopmental disorders. A better understanding of these differences may help to develop tailored preventions or therapeutic interventions.

Structural disconnection of the posterior medial frontal cortex reduces speech error monitoring

Optimal performance in any task relies on the ability to detect and correct errors. The anterior cingulate cortex and the broader posterior medial frontal cortex (pMFC) are active during error processing. However, it is unclear whether damage to the pMFC impairs error monitoring. We hypothesized that successful error monitoring critically relies on connections between the pMFC and broader cortical networks involved in executive functions and the task being monitored. We tested this hypothesis in the context of speech error monitoring in people with post-stroke aphasia. Diffusion weighted images were collected in 51 adults with chronic left-hemisphere stroke and 37 age-matched control participants. Whole-brain connectomes were derived using constrained spherical deconvolution and anatomically-constrained probabilistic tractography. Support vector regressions identified white matter connections in which lost integrity in stroke survivors related to reduced error detection during confrontation naming. Lesioned connections to the bilateral pMFC were related to reduce error monitoring, including many connections to regions associated with speech production and executive function. We conclude that connections to the pMFC support error monitoring. Error monitoring in speech production is supported by the structural connectivity between the pMFC and regions involved in speech production, comprehension, and executive function. Interactions between pMFC and other task-relevant processors may similarly be critical for error monitoring in other task contexts.

Multivariate FMRI Signatures of Learning in a Hebb Repetition Paradigm With Tone Sequences

Important information from the environment often arrives to the brain in temporally extended sequences. Language, music, actions, and complex events generally unfold over time. When such informational sequences exceed the limited capacity of working memory, the human brain relies on its ability to accumulate information in long-term memory over several encounters with a complex stimulus. A longstanding question in psychology and neuroscience is whether the neural structures associated with working memory storage—often viewed as capacity limited and temporary—have any builtin ability to store information across longer temporal delays. According to the classic Hebbian dual memory theory, temporally local “activity traces” underlie immediate perception and working memory, whereas “structural traces” undergird long-term learning. Here we examine whether brain structures known to be involved in working maintenance of auditory sequences, such as area Spt, also show evidence of memory persistence across trials. We used representational similarity analysis (RSA) and the Hebb repetition paradigm with supracapacity tonal sequences to test whether repeated sequences have distinguishable multivoxel activity patterns in the auditory-motor networks of the brain. We found that, indeed, area Spt and other nodes of the auditory dorsal stream show multivoxel patterns for tone sequences that become gradually more distinct with repetition during working memory for supracapacity tone-sequences. The findings suggest that the structures are important for working memory are not “blank slates,” wiped clean from moment to moment, but rather encode information in a way can lead to cross-trial persistence.

Isolating the white matter circuitry of the dorsal language stream: Connectome-Symptom Mapping in stroke induced aphasia

The application of ℓ1-regularized machine learning models to high-dimensional connectomes offers a promising methodology to assess clinical-anatomical correlations in humans. Here, we integrate the connectome-based lesion-symptom mapping framework with sparse partial least squares regression (sPLS-R) to isolate elements of the connectome associated with speech repetition deficits. By mapping over 2,500 connections of the structural connectome in a cohort of 71 stroke-induced cases of aphasia presenting with varying left-hemisphere lesions and repetition impairment, sPLS-R was trained on 50 subjects to algorithmically identify connectomic features on the basis of their predictive value. The highest ranking features were subsequently used to generate a parsimonious predictive model for speech repetition whose predictions were evaluated on a held-out set of 21 subjects. A set of 10 short- and long-range parieto-temporal connections were identified, collectively delineating the broader circuitry of the dorsal white matter network of the language system. The strongest contributing feature was a short-range connection in the supramarginal gyrus, approximating the cortical localization of area Spt, with parallel long-range pathways interconnecting posterior nodes in supramarginal and superior temporal cortex with anterior nodes in both ventral and-notably-in dorsal premotor cortex, respectively. The collective disruption of these pathways indexed repetition performance in the held-out set of participants, suggesting that these impairments might be characterized as a parietotemporal disconnection syndrome impacting cortical area Spt and its associated white matter circuits of the frontal lobe as opposed to being purely a disconnection of the arcuate fasciculus.

Topological signal processing and inference of event-related potential response

BACKGROUND

Topological signal processing is a novel approach for decoding multiscale features of signals recorded through electroencephalography (EEG) based on topological data analysis (TDA). New method: We establish stability properties of the TDA descriptor persistence landscape (PL) in event-related potential (ERP) across multi-trial EEG signals, state algorithms for computing PL, and propose an exact inference framework on persistence and PLs.

RESULTS

We apply the topological signal processing and inference framework to compare ERPs between individuals with post-stroke aphasia and healthy controls under a speech altered auditory feedback (AAF) paradigm. Results show significant PL difference in the ERP response of aphasic individuals and healthy controls over the parietal-occipital and occipital regions with respect to speech onset, and no significant PL difference in any regions with respect to the two pitch-shift stimuli. Comparison with existing methods: In comparison, spatial patterns of difference between aphasic individuals and healthy controls by persistence, local variance, and spectral powers are much more diffuse than the PL patterns. In simulation results, the exact test on persistence and PLs has more robust performance than the baseline tests on local variance and spectral powers.

CONCLUSIONS

Persistence features provide a more robust EEG marker than local variance, and spectral powers. It could be a potentially powerful tool for comparing electrophysiological correlates in neurological disorders.

Multiple dimensions underlying the functional organization of the language network

Understanding the different neural networks that support human language is an ongoing challenge for cognitive neuroscience. Which divisions are capable of distinguishing the functional significance of regions across the language network? A key separation between semantic cognition and phonological processing was highlighted in early meta-analyses, yet these seminal works did not formally test this proposition. Moreover, organization by domain is not the only possibility. Regions may be organized by the type of process performed, as in the separation between representation and control processes proposed within the Controlled Semantic Cognition framework. The importance of these factors was assessed in a series of activation likelihood estimation meta-analyses that investigated which regions of the language network are consistently recruited for semantic and phonological domains, and for representation and control processes. Whilst semantic and phonological processing consistently recruit many overlapping regions, they can be dissociated (by differential involvement of bilateral anterior temporal lobes, precentral gyrus and superior temporal gyri) only when using both formal analysis methods and sufficient data. Both semantic and phonological regions are further dissociable into control and representation regions, highlighting this as an additional, distinct dimension on which the language network is functionally organized. Furthermore, some of these control regions overlap with multiple-demand network regions critical for control beyond the language domain, suggesting the relative level of domain-specificity is also informative. Multiple, distinct dimensions are critical to understand the role of language regions. Here we present a proposal as to the core principles underpinning the functional organization of the language network.

Two types of phonological reading impairment in stroke aphasia

Alexia is common in the context of aphasia. It is widely agreed that damage to phonological and semantic systems not specific to reading causes co-morbid alexia and aphasia. Studies of alexia to date have only examined phonology and semantics as singular processes or axes of impairment, typically in the context of stereotyped alexia syndromes. However, phonology, in particular, is known to rely on subprocesses, including sensory-phonological processing, motor-phonological processing, and sensory-motor integration. Moreover, many people with stroke aphasia demonstrate mild or mixed patterns of reading impairment that do not fit neatly with one syndrome. This cross-sectional study tested whether the hallmark symptom of phonological reading impairment, the lexicality effect, emerges from damage to a specific subprocess of phonology in stroke patients not selected for alexia syndromes. Participants were 30 subjects with left-hemispheric stroke and 37 age- and education-matched controls. A logistic mixed-effects model tested whether post-stroke impairments in sensory phonology, motor phonology, or sensory-motor integration modulated the effect of item lexicality on patient accuracy in reading aloud. Support vector regression voxel-based lesion-symptom mapping localized brain regions necessary for reading and non-orthographic phonological processing. Additionally, a novel support vector regression structural connectome-symptom mapping method identified the contribution of both lesioned and spared but disconnected, brain regions to reading accuracy and non-orthographic phonological processing. Specifically, we derived whole-brain structural connectomes using constrained spherical deconvolution-based probabilistic tractography and identified lesioned connections based on comparisons between patients and controls. Logistic mixed-effects regression revealed that only greater motor-phonological impairment related to lower accuracy reading aloud pseudowords versus words. Impaired sensory-motor integration was related to lower overall accuracy in reading aloud. No relationship was identified between sensory-phonological impairment and reading accuracy. Voxel-based and structural connectome lesion-symptom mapping revealed that lesioned and disconnected left ventral precentral gyrus related to both greater motor-phonological impairment and lower sublexical reading accuracy. In contrast, lesioned and disconnected left temporoparietal cortex is related to both impaired sensory-motor integration and reduced overall reading accuracy. These results clarify that at least two dissociable phonological processes contribute to the pattern of reading impairment in aphasia. First, impaired sensory-motor integration, caused by lesions disrupting the left temporoparietal cortex and its structural connections, non-selectively reduces accuracy in reading aloud. Second, impaired motor-phonological processing, caused at least partially by lesions disrupting left ventral premotor cortex and structural connections, selectively reduces sublexical reading accuracy. These results motivate a revised cognitive model of reading aloud that incorporates a sensory-motor phonological circuit.

[Conduction aphasia in patients with glioma in the left hemisphere]

Background. According to Wernicke-Geschwind model, conduction aphasia following arcuate tract lesion was canonized as primary disorder of repetition in relatively intact speech.

OBJECTIVE

Syndromic analysis of speech and writing disorders in patients with arcuate tract lesion using the method by A.R. Luria and their comparison with well-known types of aphasia.

MATERIAL AND METHODS

Clinical and neuropsychological survey was performed in 14 patients with gliomas who underwent surgical treatment at the Burdenko Neurosurgical Center (10 gliomas of the frontal lobe and 4 tumors of the temporal lobe). All patients underwent MRI, HARDI MRI tractography and A.R. Luria's neuropsychological examination prior to surgery and after 5-6 postoperative days. Thirteen patients underwent awake craniotomy, 3 of them were examined one year after surgery.

RESULTS

In all patients, the tumor was localized near arcuate tract and its infiltration was noted. No intraoperative damage to the tract was ever noted according to speech monitoring data. However, postoperative edema followed by infiltration and dislocation of the tract (in all patients), as well as local ischemia in 4 patients were observed. After resection of prefrontal and premotor gliomas, aphasia included frontal (perseveration) and temporal components (disorders of naming, auditory-speech memory). Unusual verbal paraphrases were noted. We also observed severe violation of writing (temporal type) even if spontaneous speech and repetition were preserved. In case of resection of deep posterior temporal gliomas, speech disorders included signs of frontal lobe lesion (perseveration) and writing disorders. Similar motor abnormalities were identified in writing.

CONCLUSION

Arcuate tract lesion can result speech and writing disorders as signs of damage to certain cortical speech zones (frontal and temporal lobe). Violations of repetition were not predominant in any case. At the same time, interruption of connection between motor and auditory image of the word could be revealed in writing.

The bilingual structural connectome: Dual-language experiential factors modulate distinct cerebral networks

Bilingualism is a natural laboratory for studying whether the brain's structural connectome is influenced by different aspects of language experience. However, evidence on how distinct components of bilingual experience may contribute to structural brain adaptations is mixed. The lack of consistency, however, may depend, at least in part, on methodological choices in data acquisition and processing. Herein, we adopted the Network Neuroscience framework to investigate how individual differences in second language (L2) exposure, proficiency, and age of acquisition (AoA) - measured as continuous between-subject variables - relate to whole-brain structural organization. We observed that L2 exposure modulated the connectivity of two networks of regions subserving language comprehension and production. L2 proficiency was associated with enhanced connectivity within a rostro-caudal network, which supports language selection and word learning. Moreover, L2 AoA and exposure affected inter-hemispheric communication between control-related regions. These findings expand mechanistic knowledge about particular environmental factors associated with specific variation in brain structure.

Speech-Driven Spectrotemporal Receptive Fields Beyond the Auditory Cortex

We recently developed a method to estimate speech-driven spectrotemporal receptive fields (STRFs) using fMRI. The method uses spectrotemporal modulation filtering, a form of acoustic distortion that renders speech sometimes intelligible and sometimes unintelligible. Using this method, we found significant STRF responses only in classic auditory regions throughout the superior temporal lobes. However, our analysis was not optimized to detect small clusters of STRFs as might be expected in non-auditory regions. Here, we re-analyze our data using a more sensitive multivariate statistical test for cross-subject alignment of STRFs, and we identify STRF responses in non-auditory regions including the left dorsal premotor cortex (dPM), left inferior frontal gyrus (IFG), and bilateral calcarine sulcus (calcS). All three regions responded more to intelligible than unintelligible speech, but left dPM and calcS responded significantly to vocal pitch and demonstrated strong functional connectivity with early auditory regions. Left dPM's STRF generated the best predictions of activation on trials rated as unintelligible by listeners, a hallmark auditory profile. IFG, on the other hand, responded almost exclusively to intelligible speech and was functionally connected with classic speech-language regions in the superior temporal sulcus and middle temporal gyrus. IFG's STRF was also (weakly) able to predict activation on unintelligible trials, suggesting the presence of a partial 'acoustic trace' in the region. We conclude that left dPM is part of the human dorsal laryngeal motor cortex, a region previously shown to be capable of operating in an 'auditory mode' to encode vocal pitch. Further, given previous observations that IFG is involved in syntactic working memory and/or processing of linear order, we conclude that IFG is part of a higher-order speech circuit that exerts a top-down influence on processing of speech acoustics. Finally, because calcS is modulated by emotion, we speculate that changes in the quality of vocal pitch may have contributed to its response.

Functional Topography of Auditory Areas Derived From the Combination of Electrophysiological Recordings and Cortical Electrical Stimulation

The posterior part of the superior temporal gyrus (STG) has long been known to be a crucial hub for auditory and language processing, at the crossroad of the functionally defined ventral and dorsal pathways. Anatomical studies have shown that this "auditory cortex" is composed of several cytoarchitectonic areas whose limits do not consistently match macro-anatomic landmarks like gyral and sulcal borders. The only method to record and accurately distinguish neuronal activity from the different auditory sub-fields of primary auditory cortex, located in the tip of Heschl and deeply buried in the Sylvian fissure, is to use stereotaxically implanted depth electrodes (Stereo-EEG) for pre-surgical evaluation of patients with epilepsy. In this prospective, we focused on how anatomo-functional delineation in Heschl's gyrus (HG), Planum Temporale (PT), the posterior part of the STG anterior to HG, the posterior superior temporal sulcus (STS), and the region at the parietal-temporal boundary commonly labeled "SPT" can be achieved using data from electrical cortical stimulation combined with electrophysiological recordings during listening to pure tones and syllables. We show the differences in functional roles between the primary and non-primary auditory areas, in the left and the right hemispheres. We discuss how these findings help understanding the auditory semiology of certain epileptic seizures and, more generally, the neural substrate of hemispheric specialization for language.

Evidence and implications of abnormal predictive coding in dementia

The diversity of cognitive deficits and neuropathological processes associated with dementias has encouraged divergence in pathophysiological explanations of disease. Here, we review an alternative framework that emphasizes convergent critical features of cognitive pathophysiology. Rather than the loss of ‘memory centres’ or ‘language centres’, or singular neurotransmitter systems, cognitive deficits are interpreted in terms of aberrant predictive coding in hierarchical neural networks. This builds on advances in normative accounts of brain function, specifically the Bayesian integration of beliefs and sensory evidence in which hierarchical predictions and prediction errors underlie memory, perception, speech and behaviour. We describe how analogous impairments in predictive coding in parallel neurocognitive systems can generate diverse clinical phenomena, including the characteristics of dementias. The review presents evidence from behavioural and neurophysiological studies of perception, language, memory and decision-making. The reformulation of cognitive deficits in terms of predictive coding has several advantages. It brings diverse clinical phenomena into a common framework; it aligns cognitive and movement disorders; and it makes specific predictions on cognitive physiology that support translational and experimental medicine studies. The insights into complex human cognitive disorders from the predictive coding framework may therefore also inform future therapeutic strategies.

Neural substrates of verbal repetition deficits in primary progressive aphasia

In this cross-sectional study, we examined the relationship between cortical thickness and performance on several verbal repetition tasks in a cohort of patients with primary progressive aphasia in order to test predictions generated by theoretical accounts of phonological working memory that predict phonological content buffers in left posterior inferior frontal sulcus and supramarginal gyrus. Cortical surfaces were reconstructed from magnetic resonance imaging scans from 42 participants diagnosed with primary progressive aphasia. Cortical thickness was measured in a set of anatomical regions spanning the entire cerebral cortex. Correlation analyses were performed between cortical thickness and average score across three phonological working memory-related tasks: the Repetition sub-test from the Western Aphasia Battery, a forward digit span task, and a backward digit span task. Significant correlations were found between average working memory score across tasks and cortical thickness in left supramarginal gyrus and left posterior inferior frontal sulcus, in support of prior theoretical accounts of phonological working memory. Exploratory whole-brain correlation analyses performed for each of the three behavioural tasks individually revealed a distinct set of positively correlated regions for each task. Comparison of cortical thickness measures from different primary progressive aphasia sub-types to cortical thickness in age-matched controls further revealed unique patterns of atrophy in the different subtypes.

Maintaining verbal short-term memory representations in non-perceptual parietal regions

Buffer accounts of verbal short-term memory (STM) assume dedicated buffers for maintaining different types of information (e.g., phonological, visual) whereas embedded processes accounts argue against the existence of buffers and claim that STM consists of the activated portion of long-term memory (LTM). We addressed this debate by determining whether STM recruits the same neural substrate as LTM, or whether additional regions are involved in short-term storage. Using fMRI with representational similarity analysis (RSA), we examined the representational correspondence of multi-voxel neural activation patterns with the theoretical predictions for the maintenance of both phonological and semantic codes in STM. We found that during the delay period of a phonological STM task, phonological representations could be decoded in the left supramarginal gyrus (SMG) but not the superior temporal gyrus (STG), a speech processing region, for word stimuli. Whereas the pattern in the SMG was specific to phonology, a different region in the left angular gyrus showed RSA decoding evidence for the retention of either phonological or semantic codes, depending on the task context. Taken together, the results provide clear support for a dedicated buffer account of phonological STM, although evidence for a semantic buffer is equivocal.

A Review of Cortical and Subcortical Stimulation Mapping for Language

Since the early descriptions of language function based on observations of patients with language deficits by Broca and Wernicke, neurosurgeons have been focused on characterizing the anatomic regions necessary for language perception and production, and preserving these structures during surgery to minimize patient deficits post operatively. In this supplementary issue on awake intraoperative mapping, we review language processing across multiple domains, highlighting key advances in direct electrical stimulation of different cortical and subcortical regions involved in naming, repetition, reading, writing, and syntax. We then discuss different intraoperative tasks for assessing the function of a given area and avoiding injury to critical, eloquent regions.

Neuro-Clinical Signatures of Language Impairments: A Theoretical Framework for Function-to-structure Mapping in Clinics

In the past decades, neuroscientists and clinicians have collected a considerable amount of data and drastically increased our knowledge about the mapping of language in the brain. The emerging picture from the accumulated knowledge is that there are complex and combinatorial relationships between language functions and anatomical brain regions. Understanding the underlying principles of this complex mapping is of paramount importance for the identification of the brain signature of language and Neuro-Clinical signatures that explain language impairments and predict language recovery after stroke. We review recent attempts to addresses this question of language-brain mapping. We introduce the different concepts of mapping (from diffeomorphic one-to-one mapping to many-to-many mapping). We build those different forms of mapping to derive a theoretical framework where the current principles of brain architectures including redundancy, degeneracy, pluri-potentiality and bow-tie network are described.

Effect of Bilateral Opercular Syndrome on Speech Perception

Speech perception ability and structural neuroimaging were investigated in two cases of bilateral opercular syndrome. Due to bilateral ablation of the motor control center for the lower face and surrounds, these rare cases provide an opportunity to evaluate the necessity of cortical motor representations for speech perception, a cornerstone of some neurocomputational theories of language processing. Speech perception, including audiovisual integration (i.e., the McGurk effect), was mostly unaffected in these cases, although verbal short-term memory impairment hindered performance on several tasks that are traditionally used to evaluate speech perception. The results suggest that the role of the cortical motor system in speech perception is context-dependent and supplementary, not inherent or necessary.

Slowed Compensation Responses to Altered Auditory Feedback in Post-Stroke Aphasia: Implications for Speech Sensorimotor Integration

Developing a clearer understanding of impairments that underlie the behavioral characteristics of aphasia is essential for the development of targeted treatments and will help inform theories of speech motor control. Impairments in sensorimotor integration of speech in individuals with conduction aphasia have previously been implicated in their repetition deficits. However, much less is known about the extent to which these integrative deficits occur outside of conduction aphasia and how this manifests behaviorally in areas other than speech repetition. In this study, we aimed to address these issues by examining the behavioral correlates of speech sensorimotor impairment under altered auditory feedback (AAF) and their relationship with the impaired ability to independently correct for online errors during picture naming in people with aphasia. We found that people with aphasia generate slower vocal compensation response to pitch-shift AAF stimuli compared with controls. However, when the timing of responses was controlled for, no significant difference in the magnitude of vocal pitch compensation was observed between aphasia and control groups. Moreover, no relationship was found between self-correction of naming errors and the timing and magnitude of vocal compensation responses to AAF. These findings suggest that slowed compensation is a potential behavioral marker of impaired sensorimotor integration in aphasia.

Analysis of an Unusual Case of Nonfluent Aphasia With Predominantly Posterior Perisylvian Lesion: An Apparent Paradox

Lesion site-aphasia type discordance has garnered increasing interest in cognitive neuroscience over the last century. Diaschisis, the network concept of cognitive functions, and interindividual variability are among the plausible explanations cited in the literature for such unusual clinical cases. We describe here the case of a nonfluent type of aphasia following an ischemic stroke predominantly affecting the left posterior perisylvian cortex in a right-handed Bengali-speaking woman. The patient's comprehension was well preserved; however, she presented with a severe motor speech defect. MRI revealed an ischemic lesion in the left parietotemporal area, with slight involvement of the postero-inferior frontal cortex. We suggest two plausible explanations for this lesion-aphasia discordance: Our patient had bilateral representation of language receptive functions in her brain, and additional areas neighboring the classical Broca area may support some critical mechanisms of speech production. Taken together, these explanations may clarify why our patient was able to maintain the ability to decode language even though her language production was significantly affected.

Neural Components of Reading Revealed by Distributed and Symbolic Computational Models

Determining how the cognitive components of reading - orthographic, phonological, and semantic representations - are instantiated in the brain has been a longstanding goal of psychology and human cognitive neuroscience. The two most prominent computational models of reading instantiate different cognitive processes, implying different neural processes. Artificial neural network (ANN) models of reading posit non-symbolic, distributed representations. The dual-route cascaded (DRC) model instead suggests two routes of processing, one representing symbolic rules of spelling-sound correspondence, the other representing orthographic and phonological lexicons. These models are not adjudicated by behavioral data and have never before been directly compared in terms of neural plausibility. We used representational similarity analysis to compare the predictions of these models to neural data from participants reading aloud. Both the ANN and DRC model representations corresponded with neural activity. However, ANN model representations correlated to more reading-relevant areas of cortex. When contributions from the DRC model were statistically controlled, partial correlations revealed that the ANN model accounted for significant variance in the neural data. The opposite analysis, examining the variance explained by the DRC model with contributions from the ANN model factored out, revealed no correspondence to neural activity. Our results suggest that ANNs trained using distributed representations provide a better correspondence between cognitive and neural coding. Additionally, this framework provides a principled approach for comparing computational models of cognitive function to gain insight into neural representations.

Intrinsic functional architecture of the human speech processing network

Speech engages distributed temporo-fronto-parietal brain regions, however a comprehensive understanding of its intrinsic functional network architecture is lacking. Here we investigate the human speech processing network using the largest sample to date, high temporal resolution resting-state fMRI data, network stability analysis, and theoretically informed models. Network consensus analysis revealed three stable functional modules encompassing: (1) superior temporal plane (STP) and Area Spt, (2) superior temporal sulcus (STS) + ventral frontoparietal cortex, and (3) dorsal frontoparietal cortex. The STS + ventral frontoparietal cortex module showed the highest participation coefficient, and a hub-like organization linking STP with frontoparietal cortical nodes. Node-wise analysis revealed key connectivity features underlying this modular architecture, including a leftward asymmetric connectivity profile, and differential connectivity of STS and STP, with frontoparietal cortex. Our findings, replicated across cohorts, reveal a tripartite functional network architecture supporting speech processing and provide a novel template for future studies.