Word-producing brain: Contribution of the left anterior middle temporal gyrus to word production patterns in spoken language

Vocabulary is based on semantic knowledge. The anterior temporal lobe (ATL) has been considered an essential region for processing semantic knowledge; nonetheless, the association between word production patterns and the structural and functional characteristics of the ATL remains unclear. To examine this, we analyzed over one million words from group conversations among community-dwelling older adults and their multimodal magnetic resonance imaging data. A quantitative index for the word production patterns, namely the exponent β of Heaps' law, positively correlated with the left anterior middle temporal gyrus volume. Moreover, β negatively correlated with its resting-state functional connectivity with the precuneus. There was no significant correlation with the diffusion tensor imaging metrics in any fiber. These findings suggest that the vocabulary richness in spoken language depends on the brain status characterized by the semantic knowledge-related brain structure and its activation dissimilarity with the precuneus, a core region of the default mode network.

Cortical maps as a fundamental neural substrate for visual representation

Visual perception is the product of serial hierarchical processing, parallel processing, and remapping on a dynamic network involving several topographically organized cortical visual areas. Here, we will focus on the topographical organization of cortical areas and the different kinds of visual maps found in the primate brain. We will interpret our findings in light of a broader representational framework for perception. Based on neurophysiological data, our results do not support the notion that vision can be explained by a strict representational model, where the objective visual world is faithfully represented in our brain. On the contrary, we find strong evidence that vision is an active and constructive process from the very initial stages taking place in the eye and from the very initial stages of our development. A constructive interplay between perceptual and motor systems (e.g., during saccadic eye movements) is actively learnt from early infancy and ultimately provides our fluid stable visual perception of the world.

The Role of the Right Hemisphere White Matter Tracts in Chronic Aphasic Patients After Damage of the Language Tracts in the Left Hemisphere

The involvement of the right hemisphere (RH) in language, and especially after aphasia resulting from left hemisphere (LH) lesions, has been recently highlighted. The present study investigates white matter structure in the right hemisphere of 25 chronic post-stroke aphasic patients after LH lesions in comparison with 24 healthy controls, focusing on the four cortico-cortical tracts that link posterior parietal and temporal language-related areas with Broca’s region in the inferior frontal gyrus of the LH: the Superior Longitudinal Fasciculi II and III (SLF II and SLF III), the Arcuate Fasciculus (AF), and the Temporo-Frontal extreme capsule Fasciculus (TFexcF). Additionally, the relationship of these RH white matter tracts to language performance was examined. The patients with post-stroke aphasia in the chronic phase and the healthy control participants underwent diffusion tensor imaging (DTI) examination. The aphasic patients were assessed with standard aphasia tests. The results demonstrated increased axial diffusivity in the RH tracts of the aphasic patients. Patients were then divided according to the extent of the left hemisphere white matter loss. Correlations of language performance with radial diffusivity (RD) in the right hemisphere homologs of the tracts examined were demonstrated for the TFexcF, SLF III, and AF in the subgroup with limited damage to the LH language networks and only with the TFexcF in the subgroup with extensive damage. The results argue in favor of compensatory roles of the right hemisphere tracts in language functions when the LH networks are disrupted.

Manual dexterity predicts phonological decoding speed in typical reading adults

Manual dexterity and phonological decoding involve the posterior parietal cortex, which controls location coding for visually guided actions, as well as a large fronto-cerebellar network. We studied the relationship between manual dexterity and reading ability in adult typical readers. Two measurements of manual dexterity were collected to index the procedural learning effect. A linear regression model demonstrated that phonological short-term memory, manual dexterity at time 1 and procedural learning of manual dexterity predicted phonological decoding speed. Similar results were found when left-hand dexterity at time 1 and procedural learning dexterity were entered last. The better one's phonological decoding skill was, the less fluent their manual dexterity was, suggesting a recycle from object-location to letter-location coding. However, the greater the procedural learning, the faster phonological decoding was, suggesting that larger plasticity of object-location coding was linked to better letter-location coding. An independent role of the interhemispheric connections or of the right posterior parietal cortex is also suggested.

Relational vs. attributive interpretation of nominal compounds differentially engages angular gyrus and anterior temporal lobe

The angular gyrus (AG) and anterior temporal lobe (ATL) have been found to respond to a number of tasks involving combinatorial processing. In this study, we investigate the conceptual combination of nominal compounds, and ask whether ATL/AG activity is modulated by the type of combinatorial operation applied to a nominal compound. We compare relational and attributive interpretations of nominal compounds and find that ATL and AG both discriminate these two types, but in distinct ways. While right AG demonstrated greater positive task-responsive activity for relational compounds, there was a greater negative deflection in the BOLD response in left AG for relational compounds. In left ATL, we found an earlier peak in subjects' BOLD response curves for attributive interpretations. In other words, we observed dissociations in both AG and ATL between relational and attributive nominal compounds, with regard to magnitude in the former and to timing in the latter. These findings expand on prior studies that posit roles for both AG and ATL in conceptual processing generally, and in conceptual combination specifically, by indicating possible functional specializations of these two regions within a larger conceptual knowledge network.

Mapping Language in Epilepsy with Functional Imaging

Surgery is an important therapeutic alternative for patients with uncontrolled epilepsy. Preoperative identification of brain regions important for language is important to reduce the risk of functional impairment after surgery. The Wada test suffers from several technical and clinical disadvantages and provides hemispheric data at best. More invasive methods such as intraoperative or chronic subdural cortical mapping have more limited application. New approaches using neuroimaging methods offer the opportunity to localize, as well as lateralize, language. In addition, normal volunteers can be studied with the same techniques, providing comparative and control data. Although most normal studies have been reported as group data, it is important for individual scans to be available for comparison with patient studies to understand the normal range of interindividual variability. Two techniques, PET with 15O-water-PET and fMRI, have been used. Both detect signal changes associated with increased regional blood flow during neuronal activity. Usually, scans performed during a language task are compared with those obtained during control conditions. It is important to choose activation tasks carefully, to make sure one is imaging activation associated with the particular process of interest. PET has advantages, including a fully diffusible tracer, standardized analytic methods, a more comfortable environment, and less sensitivity to movement artifact. On the other hand, it involves a cyclotron-produced tracer, radiation exposure, and is more difficult to repeat. FMRI over represents the effects of large vascular structures and is very sensitive to movement but uses widely available equipment and has no limitation on the number of studies. For both studies, it is important to understand the potential effects of such factors as attention, fatigue, and familiarity with the material. Several studies comparing 15O-water-PET and fMRI to the Wada test found that the former are at least as accurate for language lateralization. In addition, we compared 15O-water-PET to direct subdural electrode cortical stimulation and found that regions showing increased cerebral blood flow during naming tasks co-registered with subdural electrodes that disrupted language during electrical stimulation. In this and other studies, PET detected more regions than electrical stimulation techniques. The whole brain cannot be covered with electrodes, but some areas participating in a task may not be crucial for it. FMRI is particularly useful for children. We compared cortical activation patterns in normal children, adolescents, and adults. The activation patterns, and laterality of language dominance, in children 8 years and above, were similar to adults, although some differences could reflect maturation and evolving focality of cognitive processes. In children with epilepsy, fMRI successfully identified language laterality and provided data on intrahemispheric localization. Studies also showed the effects of the epileptic focus on normal activation patterns for several tasks. Neuroimaging functional mapping is an important tool, still in the process of development and evolution. Although potentially of great clinical and scientific value, it should be used and interpreted cautiously.

Eye Gaze Behavior at Turn Transition: How Aphasic Patients Process Speakers' Turns during Video Observation

The human turn-taking system regulates the smooth and precise exchange of speaking turns during face-to-face interaction. Recent studies investigated the processing of ongoing turns during conversation by measuring the eye movements of noninvolved observers. The findings suggest that humans shift their gaze in anticipation to the next speaker before the start of the next turn. Moreover, there is evidence that the ability to timely detect turn transitions mainly relies on the lexico-syntactic content provided by the conversation. Consequently, patients with aphasia, who often experience deficits in both semantic and syntactic processing, might encounter difficulties to detect and timely shift their gaze at turn transitions. To test this assumption, we presented video vignettes of natural conversations to aphasic patients and healthy controls, while their eye movements were measured. The frequency and latency of event-related gaze shifts, with respect to the end of the current turn in the videos, were compared between the two groups. Our results suggest that, compared with healthy controls, aphasic patients have a reduced probability to shift their gaze at turn transitions but do not show significantly increased gaze shift latencies. In healthy controls, but not in aphasic patients, the probability to shift the gaze at turn transition was increased when the video content of the current turn had a higher lexico-syntactic complexity. Furthermore, the results from voxel-based lesion symptom mapping indicate that the association between lexico-syntactic complexity and gaze shift latency in aphasic patients is predicted by brain lesions located in the posterior branch of the left arcuate fasciculus. Higher lexico-syntactic processing demands seem to lead to a reduced gaze shift probability in aphasic patients. This finding may represent missed opportunities for patients to place their contributions during everyday conversation.

Asymmetric intra- and interhemispheric interactions during covert and overt sentence reading

Covert and overt sentence reading evoke lateralized activations in overall bihemispheric networks. We assumed that the study of functional connectivity may reveal underlying principles of functional lateralization. Left-lateralized activations could relate to stronger reading-related modulation of intrahemispheric functional connectivity in the left than the right hemisphere. Alternatively, left-lateralization could result from suppression of contralateral processing and thus reflect asymmetric interhemispheric interactions. To address this issue, this functional MRI study investigated the regional lateralization of covert and overt German sentence reading in 39 healthy participants. Further, it revealed the modulation of the lateralized brain regions' functional connectivity and their contralateral homotopes by covert and overt reading (psychophysiological interactions). Left-lateralization during covert reading was associated with stronger intrahemispheric coupling particularly in the left dorsal stream rather than with suppression of contralateral processing. Lateralization during overt sentence reading instead went along with additional recruitment of right perisylvian cortices involved in articulation by asymmetric positive heterotopic interhemispheric interactions. Given the paucity of interhemispheric anti-correlations with homotopic regions, functional lateralization is likely a consequence of a task-dependent interplay between asymmetric positive intra- and interhemispheric coupling.

Compositionality and the angular gyrus: A multi-voxel similarity analysis of the semantic composition of nouns and verbs

The cognitive and neural systems that enable conceptual processing must support the ability to combine (and recombine) concepts to form an infinite number of ideas. Two candidate neural systems for conceptual combination-the left anterior temporal lobe (ATL) and the left angular gyrus (AG)-have been characterized as "semantic hubs" due to both functional and anatomical properties; however, these two regions likely support different aspects of composition. Here we consider two hypotheses for the role of AG in conceptual combination, both of which differ from a putative role for the ATL in "feature-based" combinatorics (i.e., meaning derived by combining concepts' features). Firstly, we examine whether AG is more sensitive to function-argument relations of the sort that arise when a predicate is combined with its arguments. Secondly, we examine the non-mutually exclusive possibility that AG represents information carried on a verb in particular, whether this be information about event composition or about thematic relations denoted uniquely by verbs. We identified voxels that respond differentially to two-word versus one-word stimuli, and we measured the similarity of the patterns in these voxels evoked by (1) pairs of two-word phrases that shared a noun that was an argument, thus sharing function-argument composition (e.g. eats meat and with meat), in comparison with two-word phrases that shared only a noun, not an argument (e.g., eats meat and tasty meat); and (2) stimulus pairs that shared only an event (operationalized here as sharing a verb; e.g. eats meat and eats quickly), in comparison to both of the above. We found that activity patterns in left AG tracked information relating to the presence of an event-denoting verb in a pair of two-word phrases. We also found that the neural similarity in AG voxel patterns between two phrases sharing a verb correlated with subjects' ratings of how similar the meanings of those two verb phrases were. These findings indicate that AG represents information specific to verbs, perhaps event structure or thematic relations mediated by verbs, as opposed to argument structure in general.

The LATL as locus of composition: MEG evidence from English and Arabic

Neurolinguistic investigations into the processing of structured sentences as well as simple adjective-noun phrases point to the left anterior temporal lobe (LATL) as a leading candidate for basic linguistic composition. Here, we characterized the combinatory profile of the LATL over a variety of syntactic and semantic environments, and across two languages, English and Arabic. The contribution of the LATL was investigated across two types of composition: the optional modification of a predicate (modification) and the satisfaction of a predicate's argument position (argument saturation). Target words were presented during MEG recordings, either in combinatory contexts (e.g. "eats meat") or in non-combinatory contexts (preceded by an unpronounceable consonant string, e.g. "xqkr meat"). Across both languages, the LATL showed increased responses to words in combinatory contexts, an effect that was robust to composition type and word order. Together with related findings, these results solidify the role of the LATL in basic semantic composition.

Coupled neural systems underlie the production and comprehension of naturalistic narrative speech

Neuroimaging studies of language have typically focused on either production or comprehension of single speech utterances such as syllables, words, or sentences. In this study we used a new approach to functional MRI acquisition and analysis to characterize the neural responses during production and comprehension of complex real-life speech. First, using a time-warp based intrasubject correlation method, we identified all areas that are reliably activated in the brains of speakers telling a 15-min-long narrative. Next, we identified areas that are reliably activated in the brains of listeners as they comprehended that same narrative. This allowed us to identify networks of brain regions specific to production and comprehension, as well as those that are shared between the two processes. The results indicate that production of a real-life narrative is not localized to the left hemisphere but recruits an extensive bilateral network, which overlaps extensively with the comprehension system. Moreover, by directly comparing the neural activity time courses during production and comprehension of the same narrative we were able to identify not only the spatial overlap of activity but also areas in which the neural activity is coupled across the speaker's and listener's brains during production and comprehension of the same narrative. We demonstrate widespread bilateral coupling between production- and comprehension-related processing within both linguistic and nonlinguistic areas, exposing the surprising extent of shared processes across the two systems.

Cortical dynamics of semantic processing during sentence comprehension: evidence from event-related optical signals

Using the event-related optical signal (EROS) technique, this study investigated the dynamics of semantic brain activation during sentence comprehension. Participants read sentences constituent-by-constituent and made a semantic judgment at the end of each sentence. The EROSs were recorded simultaneously with ERPs and time-locked to expected or unexpected sentence-final target words. The unexpected words evoked a larger N400 and a late positivity than the expected ones. Critically, the EROS results revealed activations first in the left posterior middle temporal gyrus (LpMTG) between 128 and 192 ms, then in the left anterior inferior frontal gyrus (LaIFG), the left middle frontal gyrus (LMFG), and the LpMTG in the N400 time window, and finally in the left posterior inferior frontal gyrus (LpIFG) between 832 and 864 ms. Also, expected words elicited greater activation than unexpected words in the left anterior temporal lobe (LATL) between 192 and 256 ms. These results suggest that the early lexical-semantic retrieval reflected by the LpMTG activation is followed by two different semantic integration processes: a relatively rapid and transient integration in the LATL and a relatively slow but enduring integration in the LaIFG/LMFG and the LpMTG. The late activation in the LpIFG, however, may reflect cognitive control.

Multilingualism and fMRI: Longitudinal Study of Second Language Acquisition

BOLD fMRI is often used for the study of human language. However, there are still very few attempts to conduct longitudinal fMRI studies in the study of language acquisition by measuring auditory comprehension and reading. The following paper is the first in a series concerning a unique longitudinal study devoted to the analysis of bi- and multilingual subjects who are: (1) already proficient in at least two languages; or (2) are acquiring Russian as a second/third language. The focus of the current analysis is to present data from the auditory sections of a set of three scans acquired from April, 2011 through April, 2012 on a five-person subject pool who are learning Russian during the study. All subjects were scanned using the same protocol for auditory comprehension on the same General Electric LX 3T Signa scanner in Duke University Hospital. Using a multivariate analysis of covariance (MANCOVA) for statistical analysis, proficiency measurements are shown to correlate significantly with scan results in the Russian conditions over time. The importance of both the left and right hemispheres in language processing is discussed. Special attention is devoted to the importance of contextualizing imaging data with corresponding behavioral and empirical testing data using a multivariate analysis of variance. This is the only study to date that includes: (1) longitudinal fMRI data with subject-based proficiency and behavioral data acquired in the same time frame; and (2) statistical modeling that demonstrates the importance of covariate language proficiency data for understanding imaging results of language acquisition.

Neurobiological bases of reading comprehension: Insights from neuroimaging studies of word level and text level processing in skilled and impaired readers

For accurate reading comprehension, readers must first learn to map letters to their corresponding speech sounds and meaning and then they must string the meanings of many words together to form a representation of the text. Furthermore, readers must master the complexities involved in parsing the relevant syntactic and pragmatic information necessary for accurate interpretation. Failure in this process can occur at multiple levels and cognitive neuroscience has been helpful in identifying the underlying causes of success and failure in reading single words and in reading comprehension. In general, neurobiological studies of skilled reading comprehension indicate a highly overlapping language circuit for single word reading, reading comprehension and listening comprehension with largely quantitative differences in a number of reading and language related areas. This paper reviews relevant research from studies employing neuroimaging techniques to study reading with a focus on the relationship between reading skill, single word reading, and text comprehension.

Can skilled readers perform a second task in parallel? A functional connectivity MRI study

When asked to search for a target letter while reading, the patterns with which people miss the target letter reveal information about the process of reading itself. Questions remain as to whether this paradigm reflects normal reading processes however. We used a novel continuous-performance neuroimaging paradigm to address this question. In separate scanning runs, subjects either read alone, read while searching for a target letter, or searched non-words continuously. Functional connectivity analysis recovered the full extent of brain areas identified for reading in a localizer scan, with no differences between reading alone and the dual task condition. Differences were found, however, between both reading conditions and the nonword search condition. These results demonstrate that in skilled readers brain activation associated with reading is unaffected by a concurrent letter-search task. They further demonstrate the utility of a naturalistic, continuous-performance paradigm for studying the neural basis of language processing.

Cognitive neuroscience from a behavioral perspective: A critique of chasing ghosts with geiger counters

Cognitive neuroscience is a growing new discipline concerned with relating complex behavior to neuroanatomy. Relatively new advances in the imaging of brain function, such as positron emission tomography (PET), have generated hundreds of studies that have demonstrated a number of interesting but also potentially problematic brain-behavior relations. For example, cognitive neuroscientists largely favor interpretations of their data that rely on unobserved hypothetical mechanisms. Their reports often contain phraseology such as central executive, willed action, and mental imagery. As B. F. Skinner argued for decades, cognitive constructs of neurological data may yield nothing more than a conceptual nervous system.

Using Complement Coercion to Understand the Neural Basis of Semantic Composition: Evidence from an fMRI Study

Previous research regarding the neural basis of semantic composition has relied heavily on violation paradigms, which often compare implausible sentences that violate world knowledge to plausible sentences that do not violate world knowledge. This comparison is problematic as it may involve extralinguistic operations such as contextual repair and processes that ultimately lead to the rejection of an anomalous sentence, and these processes may not be part of the core language system. Also, it is unclear if violations of world knowledge actually affect the linguistic operations for semantic composition. Here, we compared two types of sentences that were grammatical, plausible, and acceptable and differed only in the number of semantic operations required for comprehension without the confound of implausible sentences. Specifically, we compared complement coercion sentences (the novelist began the book), which require an extra compositional operation to arrive at their meaning, to control sentences (the novelist wrote the book), which do not have this extra compositional operation, and found that the neural response to complement coercion sentences activated Brodmann's area 45 in the left inferior frontal gyrus more than control sentences. Furthermore, the processing of complement coercion recruited different brain regions than more traditional semantic and syntactic violations (the novelist astonished/write the book, respectively), suggesting that coercion processes are a part of the core of the language faculty but do not recruit the wider network of brain regions underlying semantic and syntactic violations.

Simple composition: a magnetoencephalography investigation into the comprehension of minimal linguistic phrases

The expressive power of language lies in its ability to construct an infinite array of ideas out of a finite set of pieces. Surprisingly, few neurolinguistic investigations probe the basic processes that constitute the foundation of this ability, choosing instead to focus on relatively complex combinatorial operations. Contrastingly, in the present work, we investigate the neural circuits underlying simple linguistic composition, such as required by the minimal phrase "red boat." Using magnetoencephalography, we examined activity in humans generated at the visual presentation of target nouns, such as "boat," and varied the combinatorial operations induced by its surrounding context. Nouns in minimal compositional contexts ("red boat") were compared with those appearing in matched non-compositional contexts, such as after an unpronounceable consonant string ("xkq boat") or within a list ("cup, boat"). Source analysis did not implicate traditional language areas (inferior frontal gyrus, posterior temporal regions) in such basic composition. Instead, we found increased combinatorial-related activity in the left anterior temporal lobe (LATL) and ventromedial prefrontal cortex (vmPFC). These regions have been linked previously to syntactic (LATL) and semantic (vmPFC) combinatorial processing in more complex linguistic contexts. Thus, we suggest that these regions play a role in basic syntactic and semantic composition, respectively. Importantly, the temporal ordering of the effects, in which LATL activity (∼225 ms) precedes vmPFC activity (∼400 ms), is consistent with many processing models that posit syntactic composition before semantic composition during the construction of linguistic representations.

Brain systems mediating semantic and syntactic processing in deaf native signers: biological invariance and modality specificity

Studies of written and spoken language suggest that nonidentical brain networks support semantic and syntactic processing. Event-related brain potential (ERP) studies of spoken and written languages show that semantic anomalies elicit a posterior bilateral N400, whereas syntactic anomalies elicit a left anterior negativity, followed by a broadly distributed late positivity. The present study assessed whether these ERP indicators index the activity of language systems specific for the processing of aural-oral language or if they index neural systems underlying any natural language, including sign language. The syntax of a signed language is mediated through space. Thus the question arises of whether the comprehension of a signed language requires neural systems specific for this kind of code. Deaf native users of American Sign Language (ASL) were presented signed sentences that were either correct or that contained either a semantic or a syntactic error (1 of 2 types of verb agreement errors). ASL sentences were presented at the natural rate of signing, while the electroencephalogram was recorded. As predicted on the basis of earlier studies, an N400 was elicited by semantic violations. In addition, signed syntactic violations elicited an early frontal negativity and a later posterior positivity. Crucially, the distribution of the anterior negativity varied as a function of the type of syntactic violation, suggesting a unique involvement of spatial processing in signed syntax. Together, these findings suggest that biological constraints and experience shape the development of neural systems important for language.

A cortical network for semantics: (de)constructing the N400

Measuring event-related potentials (ERPs) has been fundamental to our understanding of how language is encoded in the brain. One particular ERP response, the N400 response, has been especially influential as an index of lexical and semantic processing. However, there remains a lack of consensus on the interpretation of this component. Resolving this issue has important consequences for neural models of language comprehension. Here we show that evidence bearing on where the N400 response is generated provides key insights into what it reflects. A neuroanatomical model of semantic processing is used as a guide to interpret the pattern of activated regions in functional MRI, magnetoencephalography and intracranial recordings that are associated with contextual semantic manipulations that lead to N400 effects.

Retrieval and unification of syntactic structure in sentence comprehension: an FMRI study using word-category ambiguity

Sentence comprehension requires the retrieval of single word information from long-term memory, and the integration of this information into multiword representations. The current functional magnetic resonance imaging study explored the hypothesis that the left posterior temporal gyrus supports the retrieval of lexical-syntactic information, whereas left inferior frontal gyrus (LIFG) contributes to syntactic unification. Twenty-eight subjects read sentences and word sequences containing word-category (noun-verb) ambiguous words at critical positions. Regions contributing to the syntactic unification process should show enhanced activation for sentences compared to words, and only within sentences display a larger signal for ambiguous than unambiguous conditions. The posterior LIFG showed exactly this predicted pattern, confirming our hypothesis that LIFG contributes to syntactic unification. The left posterior middle temporal gyrus was activated more for ambiguous than unambiguous conditions (main effect over both sentences and word sequences), as predicted for regions subserving the retrieval of lexical-syntactic information from memory. We conclude that understanding language involves the dynamic interplay between left inferior frontal and left posterior temporal regions.

The extended language network: a meta-analysis of neuroimaging studies on text comprehension

Language processing in context requires more than merely comprehending words and sentences. Important subprocesses are inferences for bridging successive utterances, the use of background knowledge and discourse context, and pragmatic interpretations. The functional neuroanatomy of these text comprehension processes has only recently been investigated. Although there is evidence for right-hemisphere contributions, reviews have implicated the left lateral prefrontal cortex, left temporal regions beyond Wernicke's area, and the left dorso-medial prefrontal cortex (dmPFC) for text comprehension. To objectively confirm this extended language network and to evaluate the respective contribution of right hemisphere regions, meta-analyses of 23 neuroimaging studies are reported here. The analyses used replicator dynamics based on activation likelihood estimates. Independent of the baseline, the anterior temporal lobes (aTL) were active bilaterally. In addition, processing of coherent compared with incoherent text engaged the dmPFC and the posterior cingulate cortex. Right hemisphere activations were seen most notably in the analysis of contrasts testing specific subprocesses, such as metaphor comprehension. These results suggest task dependent contributions for the lateral PFC and the right hemisphere. Most importantly, they confirm the role of the aTL and the fronto-medial cortex for language processing in context.

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

Regarding the application of functional magnetic resonance imaging (fMRI) to preoperative mapping of language, the majority of previous studies applied silent vocalization at word level. Since mapping of language targets the protection of overt communication, the selection of the stimulation paradigm is a crucial issue. Typically, everyday language demands overt speech with construction of syntactically and semantically complete sentences. Here, 23 healthy right-handed subjects performed overt vocalization of complete german sentences. Subjects produced these sentences based on visually presented semantic choices. Special efforts were undertaken to minimize motion artifacts and maximize signal gain on a 3-T MR unit. Compared to previous studies, results showed a larger amount of highly reliable fMRI activations over the whole brain. Particularly, high sensitivity was found for Broca's and Wernicke's regions, as well as anterior and inferior temporal areas. Regarding the left hemisphere, simultaneous "Broca" and "Wernicke" activities were found in 95% of all subjects. When including atypical lateralizations, "Broca" and "Wernicke" activations were found in every subject. Overt vocalization at sentential level represents a new comprehensive language task with the potential to generate reliable activation maps that reflect brain activity associated with everyday language demands.

Localization of Syntactic and Semantic Brain Responses using Magnetoencephalography

Electrophysiological methods have been used to study the temporal sequence of syntactic and semantic processing during sentence comprehension. Two responses associated with syntactic violations are the left anterior negativity (LAN) and the P600. A response to semantic violation is the N400. Although the sources of the N400 response have been identified in the left (and right) temporal lobe, the neural signatures of the LAN and P600 have not been revealed. The present study used magnetoencephalography to localize sources of syntactic and semantic activation in Finnish sentence reading. Participants were presented with sentences that ended in normally inf lected nouns, nouns in an unacceptable case, verbs instead of nouns, or nouns that were correctly inflected but made no sense in the context. Around 400 msec, semantically anomalous last words evoked strong activation in the left superior temporal lobe with significant activation also for word class errors (N400). Weaker activation was seen for the semantic errors in the right hemisphere. Later, 600-800 msec after word onset, the strongest activation was seen to word class and morphosyntactic errors (P600). Activation was significantly weaker to semantically anomalous and correct words. The P600 syntactic activation was localized to bilateral sources in the temporal lobe, posterior to the N400 sources. The results suggest that the same general region of the superior temporal cortex gives rise to both LAN and N400 with bilateral reactivity to semantic manipulation and a left hemisphere effect to syntactic manipulation. The bilateral P600 response was sensitive to syntactic but not semantic factors.

Cognitive adaptations arising from nonnative experience of sign language in hearing adults

Three experiments examined spatial transformation abilities in hearing people who acquired sign language in early adulthood. The performance of the nonnative hearing signers was compared with that of hearing people with no knowledge of sign language. The two groups were matched for age and gender. Using an adapted Corsi blocks paradigm, the experimental task simulated spatial relations in sign discourse but offered no opportunity for linguistic coding. Experiment 1 showed that the hearing signers performed significantly better than the nonsigners on a task that entailed 180 degree rotation, which is the canonical spatial relationship in sign language discourse. Experiment 2 found that the signers did not show the typical costs associated with processing rotated stimuli, and Experiment 3 ruled out the possibility that their advantage relied on seen hand movements. We conclude that sign language experience, even when acquired in adulthood by hearing people, can give rise to adaptations in cognitive processes associated with the manipulation of visuospatial information.

Cortical Representation of Verb Processing in Sentence Comprehension: Number of Complements, Subcategorization, and Thematic Frames

The processing of various attributes of verbs is crucial for sentence comprehension. Verb attributes include the number of complements the verb selects, the number of different syntactic phrase types (subcategorization options), and the number of different thematic roles (thematic options). Two functional magnetic resonance imaging experiments investigated the cerebral location and pattern of activation of these attributes. Experiment 1 tested the effect of number of complements. Experiment 2 tested the number of options of subcategorization and of thematic frames. A group of mismatch verbs with different number of options for subcategorization and thematic frames was included to distinguish between the effects of these attributes. Fourteen Hebrew speakers performed a semantic decision task on auditorily presented sentences. Parametric analysis revealed graded activations in the left superior temporal gyrus and the left inferior frontal gyrus in correlation with the number of options. By contrast, the areas that correlated with the number of complements, the right precuneus and the right cingulate, were not conventionally linguistic. This suggests that processing the number of options is more specifically linguistic than processing the number of complements. The mismatch verbs showed a pattern of activation similar to that of the subcategorization group but unlike that of the thematic frames group. By implication, and contrary to claims by some linguists, subcategorization seems indispensable in verb processing.

Orienting attention to semantic categories

We investigated the ability to orient attention to a complex, non-perceptual attribute of stimuli-semantic category. Behavioral consequences and neural correlates of semantic orienting were revealed and compared with those of spatial orienting, using event-related functional magnetic-resonance imaging. Semantic orienting significantly shortened response times to identify word stimuli, showing that it is possible to focus attention on non-perceptual attributes of stimuli to enhance behavioral performance. Semantic-orienting cues engaged parietal and frontal areas that were also involved in spatial orienting, but in addition engaged brain areas associated with semantic analysis of words, such as the left anterior inferior frontal cortex. These findings show that attentional orienting selectively engages brain areas with functional specialization for the predicted attributes. They also support the existence of a core frontoparietal network, which controls attentional orienting in speeded response tasks independently of the type of expectations, interacting with task-relevant functionally specialized areas to optimize perception and action.

Syntactic and semantic modulation of neural activity during auditory sentence comprehension

In previous functional neuroimaging studies, left anterior temporal and temporal-parietal areas responded more strongly to sentences than to randomly ordered lists of words. The smaller response for word lists could be explained by either (1) less activation of syntactic processes due to the absence of syntactic structure in the random word lists or (2) less activation of semantic processes resulting from failure to combine the content words into a global meaning. To test these two explanations, we conducted a functional magnetic resonance imaging study in which word order and combinatorial word meaning were independently manipulated during auditory comprehension. Subjects heard six different stimuli: normal sentences, semantically incongruent sentences in which content words were randomly replaced with other content words, pseudoword sentences, and versions of these three sentence types in which word order was randomized to remove syntactic structure. Effects of syntactic structure (greater activation to sentences than to word lists) were observed in the left anterior superior temporal sulcus and left angular gyrus. Semantic effects (greater activation to semantically congruent stimuli than either incongruent or pseudoword stimuli) were seen in widespread, bilateral temporal lobe areas and the angular gyrus. Of the two regions that responded to syntactic structure, the angular gyrus showed a greater response to semantic structure, suggesting that reduced activation for word lists in this area is related to a disruption in semantic processing. The anterior temporal lobe, on the other hand, was relatively insensitive to manipulations of semantic structure, suggesting that syntactic information plays a greater role in driving activation in this area.

Normative data on 372 stimuli for descriptive naming

Naming problems are common in patients with dominant temporal lobe epilepsy (TLE) and anterior temporal lobectomy (ATL). Descriptive naming may be an especially useful procedure for the presurgical workup of candidates for ATL, given its sensitivity for detecting subtle naming problems in TLE and its localization to anterior temporal regions that are commonly targeted for resection in ATL. This study provides normative data pertaining to difficulty level (accuracy and reaction time) on 372 descriptive naming items in four conceptual categories: common non-living, common living, unique non-living, and unique living things. These data will be useful to investigators who wish to develop protocols for clinical assessment or stimuli for functional imaging paradigms aimed at assessing the function of the anterior temporal lobes.

Differential components of sentence comprehension: beyond single word reading and memory

A number of studies have used functional neuroimaging to examine the neural mechanisms of sentence comprehension; however, few fMRI studies have examined activation patterns associated with sentence comprehension after accounting for activation attributable to single-word-level tasks important for sentence comprehension. To investigate the patterns of activation associated with sentence comprehension after controlling for single word reading and maintaining single words in memory, 20 unimpaired adult readers completed a block design paradigm which included sentence comprehension, single word reading, and short-term memory (for words) tasks. Results indicated that, regardless of the aspect of sentence comprehension being controlled for, activation was observed in bilateral temporal lobes (left > right) as well as bilateral occipital lobes and middle frontal gyri. Additional findings showed that bilateral superior parietal lobe activation was greatest for short-term memory for words, while left anterior inferior frontal gyri activation (centered around Brodmann's area 47) was greatest for single word reading. Results suggest that temporal cortex (left > right) is a core region important for sentence comprehension beyond the short-term memory and semantic requirements inherent in processing sentences.

Event-related potentials suggest early interaction between syntax and semantics during on-line sentence comprehension

Event-related potentials (ERPs) were used to investigate interaction between syntactic parsing and semantic integration processes during a visual sentence comprehension task. The linguistic stimuli were Finnish five-word sentences containing morphosyntactic and/or semantic violations. Single morphosyntactic violations evoked left anterior negativity (LAN) and P600 components. Single semantic violations elicited a robust N400 effect over the left hemisphere. A later and weaker N400-like response was also observed in the right hemisphere, left-right hemispheric latency difference being 40 ms. Combined morphosyntactic and semantic violations elicited a P600 component and a negative ERP component within the latency range of the LAN and N400 components. Further analysis of these ERP effects provided evidence for early processual interaction between syntax and semantics during on-line sentence comprehension. The hemispheric distribution of the LAN and N400 components was taken to suggest lateralization of initial morphosyntactic parsing and semantic integration processes to the left hemisphere. In contrast, the later syntax-related P600 component was observed as being more pronounced over the posterior areas of the right hemisphere.

Emotional and Temporal Aspects of Situation Model Processing during Text Comprehension: An Event-Related fMRI Study

Language comprehension in everyday life requires the continuous integration of prior discourse context and general world knowledge with the current utterance or sentence. In the neurolinguistic literature, these so-called situation model building processes have been ascribed to the prefrontal cortex or to the right hemisphere. In this study, we use whole-head event-related fMRI to directly map the neural correlates of narrative comprehension in context. While being scanned using a spin-echo sequence, 20 participants listened to 32 short stories, half of which contained globally inconsistent information. The inconsistencies concerned either temporal or chronological information or the emotional status of the protagonist. Hearing an inconsistent word elicited activation in the right anterior temporal lobe. The comparison of different information aspects revealed activation in the left precuneus and a bilateral frontoparietal network for chronological information. Emotional information elicited activation in the ventromedial prefrontal cortex and the extended amygdaloid complex. In addition, the integration of inconsistent emotional information engaged the dorsal frontomedial cortex (Brodmann's area 8/9), whereas the integration of inconsistent temporal information required the lateral prefrontal cortex bilaterally. These results indicate that listening to stories can elicit activation reflecting content-specific processes. Furthermore, updating of the situation model is not a unitary process but it also depends on the particular requirements of the text. The right hemisphere contributes to language processing in context, but equally important are the left medial and bilateral prefrontal cortices.

Distinct and shared cortical regions of the human brain activated by pictorial depictions versus verbal descriptions: an fMRI study

Using fMRI, we observed that there were functionally disjunctive regions in the human brain that were specifically activated during the silent reading of sentences (i.e., the symbolical representation at the propositional level) but not during the perception of arranged objects (i.e., analogical representation), or vice versa: Parts of the left and right lingual gyri, the left fusiform gyrus, the left and right inferior occipital gyri, the right cuneus, and the left middle occipital gyrus were activated exclusively during the silent reading of sentences, whereas perception of the arranged objects activated distinct regions in the lingual gyrus, the declive, the fusiform gyrus, and the cuneus in the right hemisphere. A large proportion (86% in cortical volume) of the occipito-temporal regions was functionally conjunctive: these neural structures were activated during both silent reading of sentences and perception of arranged objects. We observed a similar trend of functional disjunction and conjunction between single words (the symbolical mode at the lexical level) and single objects (analogical mode): the degree of functional conjunction in the latter case was about 96%. These results suggest that the degree of functional disjunction between the pictorial depictions and the verbal descriptions tended to increase as the complexity of mental representation increased from the single word (lexical) level (4%) to the sentence (propositional) level (14%).

Grammatical gender in the brain: Evidence from an fMRI study on Italian

The grammatical gender of a word is a lexical-syntactic property determining agreement among different sentence parts. Recent fMRI investigations identified the areas involved in the retrieval of grammatical gender near the left Broca's area providing further evidence to confirm the preeminent syntactic role of this area. However, these studies employed categorical designs based on the controversial methodology of the cognitive subtraction of neural activations related to different tasks. In the present study we identified the neural substrates of grammatical gender assignment using an fMRI parametric study. Participants decided the grammatical gender of visually presented Italian words whose gender-to-ending regularity varied. The results showed activation in left and right fronto-temporal areas suggesting an interplay of both hemispheres in the processing of grammatical gender.

Linking semantic priming effect in functional MRI and event-related potentials

The aim of this study is to examine the neural substrates involved in semantic priming using a combined event-related functional magnetic resonance imaging (fMRI) and event-related potentials (ERP) study. Twelve subjects were instructed to judge whether the presented target word was a real word or a nonword. Under the related condition, target words were preceded by a semantically related prime word. On the other hand, under the unrelated condition, prime words did not have semantic relatedness with the target word. The reaction time for reaching a judgment was longer under the unrelated condition than under the related condition, indicating that the recognition of target words is promoted by semantic priming under the related condition. In the fMRI results, we found reduced activity in the dorsal and ventral left inferior frontal gyrus, the anterior cingulate, and left superior temporal cortex for related versus unrelated conditions (i.e., the repetition suppression effect). ERP analysis revealed that the amplitude of the N400 component was reduced under the related condition compared with the unrelated condition (i.e., the N400 priming effect). Correlation analysis between the BOLD repetition suppression effect and the N400 priming effect decomposed by independent component analysis (ICA) across subjects showed significant correlation in the left superior temporal gyrus. This finding is consistent with the recent MEG data suggesting that the source of N400 is judged to be the bilateral superior temporal lobe. We discussed this finding herein in relation to the modulation of access to the phonological representation caused by semantic priming.

Renewal of the neurophysiology of language: functional neuroimaging

Functional neuroimaging methods have reached maturity. It is now possible to start to build the foundations of a physiology of language. The remarkable number of neuroimaging studies performed so far illustrates the potential of this approach, which complements the classical knowledge accumulated on aphasia. Here we attempt to characterize the impact of the functional neuroimaging revolution on our understanding of language. Although today considered as neuroimaging techniques, we refer less to electroencephalography and magnetoencephalography studies than to positron emission tomography and functional magnetic resonance imaging studies, which deal more directly with the question of localization and functional neuroanatomy. This review is structured in three parts. 1) Because of their rapid evolution, we address technical and methodological issues to provide an overview of current procedures and sketch out future perspectives. 2) We review a set of significant results acquired in normal adults (the core of functional imaging studies) to provide an overview of language mechanisms in the "standard" brain. Single-word processing is considered in relation to input modalities (visual and auditory input), output modalities (speech and written output), and the involvement of "central" semantic processes before sentence processing and nonstandard language (illiteracy, multilingualism, and sensory deficits) are addressed. 3) We address the influence of plasticity on physiological functions in relation to its main contexts of appearance, i.e., development and brain lesions, to show how functional imaging can allow fine-grained approaches to adaptation, the fundamental property of the brain. In closing, we consider future developments for language research using functional imaging.

An fMRI Study to Investigate Auditory Attention: A Model of the Cocktail Party Phenomenon

In human life, discrimination of a target voice from other voices or sounds is indispensable, and inability for such discrimination results in sensory aphasia. To investigate the neuronal basis of the attentional system for human voices, we evaluated brain activity during listening comprehension tasks using functional magnetic resonance imaging (fMRI) at 3T. Diotic listening comprehension tasks, in which a narration was superimposed by another given by the same speaker (SV experiment) or by a different speaker (DV experiment), were presented to normal volunteers. The story indicated in the baseline task blocks, in which only one narration was presented, was intensively followed during the superimposed task blocks. In each experiment, 6 task blocks, 3 blocks for each condition, and 7 rest blocks were alternatively repeated, and the contrast of the superimposed condition to the baseline condition in each session was obtained. In the DV experiment, compared with the control condition, activation in Wernicke's area (BA22) was increased. In the SV experiment, activation in the frontal association cortex (BA6, BA9/ 46, BA32, BA13/47) was additionally increased. These results suggested that difficulty in phonological processing to discriminate human voices calls for further semantic, syntactic, and prosodic processing, as well as augmented selective attention.

Linguistic processing in visual and modality-nonspecific brain areas: PET recordings during selective attention

Positron emission tomography (PET) was used to investigate the neural basis of selective processing of linguistic material during concurrent presentation of multiple stimulus streams ("cocktail-party effect"). Fifteen healthy right-handed adult males were to attend to one of three simultaneously presented messages: one presented visually, one to the left ear, and one to the right ear. During the control condition, subjects attended to visually presented consonant letter strings and ignored auditory messages. This paper reports the modality-nonspecific language processing and visual word-form processing, whereas the auditory attention effects have been reported elsewhere [Cogn. Brain Res. 17 (2003) 201]. The left-hemisphere areas activated by both the selective processing of text and speech were as follows: the inferior prefrontal (Brodmann's area, BA 45, 47), anterior temporal (BA 38), posterior insular (BA 13), inferior (BA 20) and middle temporal (BA 21), occipital (BA 18/30) cortices, the caudate nucleus, and the amygdala. In addition, bilateral activations were observed in the medial occipito-temporal cortex and the cerebellum. Decreases of activation during both text and speech processing were found in the parietal (BA 7, 40), frontal (BA 6, 8, 44) and occipito-temporal (BA 37) regions of the right hemisphere. Furthermore, the present data suggest that the left occipito-temporal cortex (BA 18, 20, 37, 21) can be subdivided into three functionally distinct regions in the posterior-anterior direction on the basis of their activation during attentive processing of sublexical orthography, visual word form, and supramodal higher-level aspects of language.

Reading with the ears

We studied the cortical networks of Morse code reading with functional magnetic resonance imaging (fMRI). Four expert radio telegraphists performed two closely matched reading experiments, one in binaurally presented high speed Morse code and one in print. Performance was equal for both conditions. Reading single nouns in Morse code resulted in predominantly left-sided activation of the frontal and temporal perisylvian language areas, prefrontal cortex, and premotor cortex. In a within-subject comparison between reading Morse code and reading print, the activation pattern in the left temporoparietal association cortex was similar for both forms of reading, suggesting that reading Morse code shares part of its cortical networks with reading print.

The cortical organization of audio-visual sentence comprehension: an fMRI study at 4 Tesla

Neuroimaging studies of written and spoken sentence processing report greater left hemisphere than right hemisphere activation. However, a large majority of our experience with language is face-to-face interaction, which is much richer in information. The current study examines the neural organization of audio-visual (AV) sentence processing using functional magnetic resonance imaging (fMRI) at 4 Tesla. Participants viewed the face and upper body of a speaker via a video screen while listening to her produce, in alternating blocks, English sentences and sentences composed of pronounceable non-words. Audio-visual sentence processing was associated with activation in the left hemisphere in Broca's area, dorsolateral prefrontal cortex, the superior precentral sulcus, anterior and middle portions of the lateral sulcus, middle superior portions of the temporal sulcus, supramarginal gyrus and angular gyrus. Further, AV sentence processing elicited activation in the right anterior and middle lateral sulcus. Between-hemisphere analyses revealed a left hemisphere dominant pattern of activation. The findings support the hypothesis that the left hemisphere may be biased to process language independently of the modality through which it is perceived. These results are discussed in the context of previous neuroimaging results using American Sign Language (ASL).

Retrieval of abstract semantics

Behavioural and neuropsychological evidence suggests that abstract and concrete concepts might be represented, retrieved and processed differently in the human brain. Using fMRI, we demonstrate that retrieval of abstract relative to sensory-based semantics during synonym judgements increased activation in a left frontotemporal system that has been associated with semantic processing particularly at the sentence level. Since activation increases were observed irrespective of the degree of difficulty, we suggest that these differential activations might reflect a particular retrieval mechanism or strategy for abstract concepts. In contrast to sensory-based semantics, the meaning of abstract concepts is largely specified by their usage in language rather than by their relations to the physical world. Subjects might therefore generate an appropriate semantic sentential context to fully explore and specify the meaning of abstract concepts. Our results also explain why abstract semantics is vulnerable to left frontotemporal lesions.

An fMRI Study of Syntactic Adaptation

It is easier to produce and comprehend a series of sentences when they have similar syntactic structures. This “syntactic priming” effect was investigated during silent sentence reading using (i) blood oxygenation level-dependent (BOLD) response as a physiological measure in an f MRI study and (ii) reading time as a behavioral measure in a complementary selfpaced reading paradigm. We found that reading time and left anterior temporal activation were decreased when subjects read sentences with similar relative to dissimilar syntactic forms. Thus, syntactic adaptation during sentence comprehension is demonstrated in a neural area that has previously been linked to both lexical semantic and sentence processing.

The visual word form area and the frequency with which words are encountered: evidence from a parametric fMRI study

Cohen and Dehaene et al. proposed that the Visual Word Form Area (VWFA) in the left midfusiform gyrus, contrary to its name, is limited to the extraction of an abstract letter string and not involved in proper visual word recognition. We examined this prelexical function of the VWFA by a parametric block design with five levels of written word frequency. The lowest level was represented by pseudowords and the highest level by words of very high frequency. Contrary to the assumed prelexical function of the VWFA, increasing frequency was associated with decreasing brain activation in a large posterior cluster of the left hemisphere including middle and posterior fusiform regions. The same negative relation between frequency and activation was found in several left frontal clusters. The relation of increasing frequency and decreasing activation in occipitotemporal regions corresponds to a similar relation in the same brain regions found by studies which experimentally manipulated object or face familiarity. This convergence suggests that fusiform regions are specialized for extracting and storing abstract patterns when processing visual objects and these patterns serve as recognition units in subsequent encounters with the same objects.

Neural Correlates of Letter-String Length and Lexicality during Reading in a Regular Orthography

Behavioral studies have shown that short letter strings are read faster than long letter-strings and words are read faster than nonwords. Here, we describe the dynamics of letter-string length and lexicality effects at the cortical level, using magnetoencephalography, during a reading task in Finnish with long (eight-letter) and short (four-letter) word/nonword stimuli. Length effects were observed in two spatially and temporally distinct cortical activations: (1) in the occipital cortex at about 100 msec by the strength of activation, regardless of the lexical status of the stimuli, and (2) in the left superior temporal cortex between 200 and 600 msec by the duration of activation, with words showing a smaller effect than nonwords. A significant lexicality effect was also evident in this later activation, with stronger activation and longer duration for nonwords than words. There seem to be no distinct cortical areas for reading words and nonwords. The early length effect is likely to be due to the low-level visual analysis common to all stimulus letter-strings. The later lexicality and length effects apparently reflect converging lexico-semantic and phonological influences, and are discussed in terms of dual-route and single-route connectionist models of reading.