Probing overtly spoken language at sentential level: a comprehensive high-field BOLD-fMRI protocol reflecting everyday language demands

Improving language mapping in clinical fMRI through assessment of grammar

Introduction

Brain surgery in the language dominant hemisphere remains challenging due to unintended post-surgical language deficits, despite using pre-surgical functional magnetic resonance (fMRI) and intraoperative cortical stimulation. Moreover, patients are often recommended not to undergo surgery if the accompanying risk to language appears to be too high. While standard fMRI language mapping protocols may have relatively good predictive value at the group level, they remain sub-optimal on an individual level. The standard tests used typically assess lexico-semantic aspects of language, and they do not accurately reflect the complexity of language either in comprehension or production at the sentence level. Among patients who had left hemisphere language dominance we assessed which tests are best at activating language areas in the brain.

Method

We compared grammar tests (items testing word order in actives and passives, wh-subject and object questions, relativized subject and object clauses and past tense marking) with standard tests (object naming, auditory and visual responsive naming), using pre-operative fMRI. Twenty-five surgical candidates (13 females) participated in this study. Sixteen patients presented with a brain tumor, and nine with epilepsy. All participants underwent two pre-operative fMRI protocols: one including CYCLE-N grammar tests (items testing word order in actives and passives, wh-subject and object questions, relativized subject and object clauses and past tense marking); and a second one with standard fMRI tests (object naming, auditory and visual responsive naming). fMRI activations during performance in both protocols were compared at the group level, as well as in individual candidates.

Results

The grammar tests generated more volume of activation in the left hemisphere (left/right angular gyrus, right anterior/posterior superior temporal gyrus) and identified additional language regions not shown by the standard tests (e.g., left anterior/posterior supramarginal gyrus). The standard tests produced more activation in left BA 47. Ten participants had more robust activations in the left hemisphere in the grammar tests and two in the standard tests. The grammar tests also elicited substantial activations in the right hemisphere and thus turned out to be superior at identifying both right and left hemisphere contribution to language processing.

Conclusion

The grammar tests may be an important addition to the standard pre-operative fMRI testing.

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We added comprehensive grammar tests to standard presurgical fMRI of language.

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The grammar tests generated more volume of activation bilaterally.

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The tests identified additional language regions not shown by the standard tests.

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The grammar tests may be an important addition to standard pre-operative fMRI.

A rostro-caudal axis for language in the frontal lobe: the role of executive control in speech production

The present article promotes a formal executive model of frontal functions underlying speech production, bringing together hierarchical theories of adaptive behavior in the (pre-)frontal cortex (pFC) and psycho- and neurolinguistic approaches to spoken language within an information-theoretic framework. Its biological plausibility is revealed through two Activation Likelihood Estimation meta-analyses carried out on a total of 41 hemodynamic studies of overt word and continuous speech production respectively. Their principal findings, considered in light of neuropsychological evidence and earlier models of speech-related frontal functions, support the engagement of a caudal-to-rostral gradient of pFC activity operationalized by the nature and quantity of speech-related information conveyed by task-related external cues (i.e., cue codability) on the one hand, and the total informational content of generated utterances on the other. In particular, overt reading or repetition and picture naming recruit primarily caudal motor-premotor regions involved in the sensorimotor and phonological aspects of speech; word and sentence generation engage mid- ventro- and dorsolateral areas supporting its basic predicative and syntactic functions; finally, rostral- and fronto-polar cortices subsume domain-general strategic processes of discourse generation for creative speech. These different levels interact in a top-down fashion, ranging representationally and temporally from the most general and extended to the most specific and immediate. The end-result is an integrative theory of pFC as the main executive component of the language cortical network, which supports the existence of areas specialized for speech communication and articulation and regions subsuming internal reasoning and planning. Prospective avenues of research pertaining to this model's principal predictions are discussed.

Differential functional benefits of ultra highfield MR systems within the language network

Several investigations have shown limitations of fMRI reliability with the current standard field strengths. Improvement is expected from ultra highfield systems but studies on possible benefits for cognitive networks are lacking. Here we provide an initial investigation on a prominent and clinically highly-relevant cognitive function: language processing in individual brains. 26 patients evaluated for presurgical language localization were investigated with a standardized overt language fMRI paradigm on both 3T and 7T MR scanners. During data acquisition and analysis we made particular efforts to minimize effects not related to static magnetic field strength differences. Six measures relevant for functional activation showed a large dissociation between essential language network nodes: although in Wernicke's area 5/6 measures indicated a benefit of ultra highfield, in Broca's area no comparison was significant. The most important reason for this discrepancy was identified as being an increase in susceptibility-related artifacts in inferior frontal brain areas at ultra high field. We conclude that functional UHF benefits are evident, however these depend crucially on the brain region investigated and the ability to control local artifacts.

The neural correlates of agrammatism: Evidence from aphasic and healthy speakers performing an overt picture description task

Functional brain imaging studies have improved our knowledge of the neural localization of language functions and the functional reorganization after a lesion. However, the neural correlates of agrammatic symptoms in aphasia remain largely unknown. The present fMRI study examined the neural correlates of morpho-syntactic encoding and agrammatic errors in continuous language production by combining three approaches. First, the neural mechanisms underlying natural morpho-syntactic processing in a picture description task were analyzed in 15 healthy speakers. Second, agrammatic-like speech behavior was induced in the same group of healthy speakers to study the underlying functional processes by limiting the utterance length. In a third approach, five agrammatic participants performed the picture description task to gain insights in the neural correlates of agrammatism and the functional reorganization of language processing after stroke. In all approaches, utterances were analyzed for syntactic completeness, complexity, and morphology. Event-related data analysis was conducted by defining every clause-like unit (CLU) as an event with its onset-time and duration. Agrammatic and correct CLUs were contrasted. Due to the small sample size as well as heterogeneous lesion sizes and sites with lesion foci in the insula lobe, inferior frontal, superior temporal and inferior parietal areas the activation patterns in the agrammatic speakers were analyzed on a single subject level. In the group of healthy speakers, posterior temporal and inferior parietal areas were associated with greater morpho-syntactic demands in complete and complex CLUs. The intentional manipulation of morpho-syntactic structures and the omission of function words were associated with additional inferior frontal activation. Overall, the results revealed that the investigation of the neural correlates of agrammatic language production can be reasonably conducted with an overt language production paradigm.

Attention shifts the language network reflecting paradigm presentation

OBJECTIVES

Functional magnetic resonance imaging (fMRI) is a reliable and non-invasive method with which to localize language function in pre-surgical planning. In clinical practice, visual stimulus presentation is often difficult or impossible, due to the patient's restricted language or attention abilities. Therefore, our aim was to investigate modality-specific differences in visual and auditory stimulus presentation.

METHODS

Ten healthy subjects participated in an fMRI study comprising two experiments with visual and auditory stimulus presentation. In both experiments, two language paradigms (one for language comprehension and one for language production) used in clinical practice were investigated. In addition to standard data analysis by the means of the general linear model (GLM), independent component analysis (ICA) was performed to achieve more detailed information on language processing networks.

RESULTS

GLM analysis revealed modality-specific brain activation for both language paradigms for the contrast visual > auditory in the area of the intraparietal sulcus and the hippocampus, two areas related to attention and working memory. Using group ICA, a language network was detected for both paradigms independent of stimulus presentation modality. The investigation of language lateralization revealed no significant variations. Visually presented stimuli further activated an attention-shift network, which could not be identified for the auditory presented language.

CONCLUSION

The results of this study indicate that the visually presented language stimuli additionally activate an attention-shift network. These findings will provide important information for pre-surgical planning in order to preserve reading abilities after brain surgery, significantly improving surgical outcomes. Our findings suggest that the presentation modality for language paradigms should be adapted on behalf of individual indication.

The benefits of skull stripping in the normalization of clinical fMRI data

Establishing a reliable correspondence between lesioned brains and a template is challenging using current normalization techniques. The optimum procedure has not been conclusively established, and a critical dichotomy is whether to use input data sets which contain skull signal, or whether skull signal should be removed. Here we provide a first investigation into whether clinical fMRI benefits from skull stripping, based on data from a presurgical language localization task. Brain activation changes related to deskulled/not-deskulled input data are determined in the context of very recently developed (New Segment, Unified Segmentation) and standard normalization approaches. Analysis of structural and functional data demonstrates that skull stripping improves language localization in MNI space — particularly when used in combination with the New Segment normalization technique.

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First investigation of the possible effects of skull-stripping with clinical fMRI data.

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Comparison of standard and most recent normalization approaches.

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Skull stripping improves language localization in MNI space.

Applying independent component analysis to clinical FMRI at 7 t

Increased BOLD sensitivity at 7 T offers the possibility to increase the reliability of fMRI, but ultra-high field is also associated with an increase in artifacts related to head motion, Nyquist ghosting, and parallel imaging reconstruction errors. In this study, the ability of independent component analysis (ICA) to separate activation from these artifacts was assessed in a 7 T study of neurological patients performing chin and hand motor tasks. ICA was able to isolate primary motor activation with negligible contamination by motion effects. The results of General Linear Model (GLM) analysis of these data were, in contrast, heavily contaminated by motion. Secondary motor areas, basal ganglia, and thalamus involvement were apparent in ICA results, but there was low capability to isolate activation in the same brain regions in the GLM analysis, indicating that ICA was more sensitive as well as more specific. A method was developed to simplify the assessment of the large number of independent components. Task-related activation components could be automatically identified via these intuitive and effective features. These findings demonstrate that ICA is a practical and sensitive analysis approach in high field fMRI studies, particularly where motion is evoked. Promising applications of ICA in clinical fMRI include presurgical planning and the study of pathologies affecting subcortical brain areas.

The neuronal infrastructure of speaking

Models of speaking distinguish producing meaning, words and syntax as three different linguistic components of speaking. Nevertheless, little is known about the brain's integrated neuronal infrastructure for speech production. We investigated semantic, lexical and syntactic aspects of speaking using fMRI. In a picture description task, we manipulated repetition of sentence meaning, words, and syntax separately. By investigating brain areas showing response adaptation to repetition of each of these sentence properties, we disentangle the neuronal infrastructure for these processes. We demonstrate that semantic, lexical and syntactic processes are carried out in partly overlapping and partly distinct brain networks and show that the classic left-hemispheric dominance for language is present for syntax but not semantics.

The neural correlates of inner speech defined by voxel-based lesion-symptom mapping

The neural correlates of inner speech have been investigated previously using functional imaging. However, methodological and other limitations have so far precluded a clear description of the neural anatomy of inner speech and its relation to overt speech. Specifically, studies that examine only inner speech often fail to control for subjects' behaviour in the scanner and therefore cannot determine the relation between inner and overt speech. Functional imaging studies comparing inner and overt speech have not produced replicable results and some have similar methodological caveats as studies looking only at inner speech. Lesion analysis can avoid the methodological pitfalls associated with using inner and overt speech in functional imaging studies, while at the same time providing important data about the neural correlates essential for the specific function. Despite its advantages, a study of the neural correlates of inner speech using lesion analysis has not been carried out before. In this study, 17 patients with chronic post-stroke aphasia performed inner speech tasks (rhyme and homophone judgements), and overt speech tasks (reading aloud). The relationship between brain structure and language ability was studied using voxel-based lesion-symptom mapping. This showed that inner speech abilities were affected by lesions to the left pars opercularis in the inferior frontal gyrus and to the white matter adjacent to the left supramarginal gyrus, over and above overt speech production and working memory. These results suggest that inner speech cannot be assumed to be simply overt speech without a motor component. It also suggests that the use of overt speech to understand inner speech and vice versa might result in misleading conclusions, both in imaging studies and clinical practice.

The sentence verification task: a reliable fMRI protocol for mapping receptive language in individual subjects

OBJECTIVE

To test the capacity of a sentence verification (SV) task to reliably activate receptive language areas. Presurgical evaluation of language is useful in predicting postsurgical deficits in patients who are candidates for neurosurgery. Productive language tasks have been successfully elaborated, but more conflicting results have been found in receptive language mapping.

MATERIALS AND METHODS

Twenty-two right-handed healthy controls made true-false semantic judgements of brief sentences presented auditorily.

RESULTS

Group maps showed reliable functional activations in the frontal and temporoparietal language areas. At the individual level, the SV task showed activation located in receptive language areas in 100% of the participants with strong left-sided distributions (mean lateralisation index of 69.27).

CONCLUSION

The SV task can be considered a useful tool in evaluating receptive language function in individual subjects. This study is a first step towards designing the fMRI task which may serve to presurgically map receptive language functions.

[Methodological problems with clinical functional MRI investigations]

During presurgical diagnostics clinical functional magnetic resonance imaging is increasingly being performed to improve the management of epilepsy and tumor patients. Rapid technical developments in fMRI technology continuously further new diagnostic applications. Safe clinical application requires a profound and critical handling of the various methodological problems inherent with this complex technique. This article reviews relevant problems and solutions for patient investigations up to the preparation of an individual clinical fMRI report.

Improvement of clinical language localization with an overt semantic and syntactic language functional MR imaging paradigm

BACKGROUND AND PURPOSE

Functional MR imaging (fMRI) is a promising but, in some aspects, still debated noninvasive tool for functional language mapping. We developed a clinical fMRI overt language design at the sentential level to optimize sensitivity for language-related areas of the brain. To evaluate applicability and sensitivity, we investigated a consecutive series of presurgical patients with epilepsy with minimal morphologic brain abnormalities.

MATERIALS AND METHODS

Thirty right-handed patients with temporal lobe epilepsy (TLE) and a control group of 23 right-handed healthy subjects participated in the study. The language design included semantic and syntactic error-detection tasks and was constructed to represent the most relevant aspects of everyday language demands. It was applied during block-designed fMRI runs. We performed image preprocessing and statistical analysis with SPM5 at a group level, applying widely used statistical criteria. The study was approved by the local ethics committee, and all participants gave written informed consent.

RESULTS

Given the strict statistical criteria, the sensitivity for inferior frontal and posterior temporal activations (comprising Broca and Wernicke regions) was improved relative to previous findings in the literature. For both language areas, we found 100% sensitivity in healthy subjects (Brodmann areas, BA22 and BA44) and 97% sensitivity in patients (when including BA47). Lateralization results demonstrated the capability to detect atypical language lateralizations in patients, which were more frequent in than those in healthy subjects.

CONCLUSIONS

We developed a clinical language fMRI design that integrates various relevant aspects of everyday language demands and provides robust localization of core language areas.