The functional anatomy of word comprehension and production

The different time courses of reading different levels of Chinese characters: an ERP study

The dual route processing was generally accepted in the reading of alphabetic languages, which suggests alphabetic words can be read by either addressed pathway or assembled pathway. However, it was still unclear whether there was a particular 'dual route mechanism' during reading Chinese characters. In our previous fMRI study, the result showed that there might be a particular 'dual route mechanism', and its addressed pathway was similar between Chinese and English, whereas for the need of spatial analysis, the assembled pathway of Chinese was different from that of English which involved grapheme-to-phoneme correspondences. The present study, using event-related potential, which provide more temporal information, aimed to further support our previous view, and peered inside the different time courses of reading different types of Chinese characters. It was found that reading high frequency Chinese characters increased the N170 component which was believed to enhance attention to the addressed pathway in the left occipital-temporal area. Pseudo Chinese characters could be read by a particular assembled pathway, which caused the largest amplitude of P320 component in the right occipital-temporal area, which considered as a key brain area for radical analysis.

Brain activations associated with sign production using word and picture inputs in deaf signers

Effective literacy education in deaf students calls for psycholinguistic research revealing the cognitive and neural mechanisms underlying their written language processing. When learning a written language, deaf students are often instructed to sign out printed text. The present fMRI study was intended to reveal the neural substrates associated with word signing by comparing it with picture signing. Native deaf signers were asked to overtly sign in Chinese Sign Language (CSL) common objects indicated with written words or presented as pictures. Except in left inferior frontal gyrus and inferior parietal lobule where word signing elicited greater activation than picture signing, the two tasks engaged a highly overlapping set of brain regions previously implicated in sign production. The results suggest that word signing in the deaf signers relies on meaning activation from printed visual forms, followed by similar production processes from meaning to signs as in picture signing. The present study also documents the basic brain activation pattern for sign production in CSL and supports the notion of a universal core neural network for sign production across different sign languages.

Role of distinct parietal areas in arithmetic: an fMRI-guided TMS study

Although several parietal areas are known to be involved in number processing, their possible role in arithmetic operations remains debated. It has been hypothesized that the horizontal segment of the intraparietal sulcus (hIPS) and the posterior superior parietal lobule (PSPL) contribute to operations solved by calculation procedures, such as subtraction, but whether these areas are also involved in operations solved by memory retrieval, such as multiplication, is controversial. In the present study, we first identified the parietal areas involved in subtraction and multiplication by means of functional magnetic resonance imaging (fMRI) and we found an increased activation, bilaterally, in the hIPS and PSPL during both arithmetic operations. In order to test whether these areas are causally involved in subtraction and multiplication, we used transcranial magnetic stimulation (TMS) to create, in each participant, a virtual lesion of either the hIPS or PSPL, over the sites corresponding to the peaks of activation gathered in fMRI. When compared to a control site, we found an increase in response latencies in both operations after a virtual lesion of either the left or right hIPS, but not of the PSPL. Moreover, TMS over the hIPS increased the error rate in the multiplication task. The present results indicate that even operations solved by memory retrieval, such as multiplication, rely on the hIPS. In contrast, the PSPL seems to underlie processes that are nonessential to solve basic subtraction and multiplication problems.

TMS over the left angular gyrus impairs the ability to discriminate left from right

The underlying cognitive and neural mechanisms of the ability to discriminate left from right are hardly explored. Clinical studies from patients with impairments of left-right discrimination (LRD) and neuroimaging data suggest that the left angular gyrus is particularly involved in LRD. Moreover, it is argued that the often reported sex difference in LRD, with women being more susceptible to left-right errors than men, is the result of a stronger lateralization in men than women. Offline repetitive transcranial magnetic stimulation (rTMS) was used to test whether the left angular gyrus is involved in LRD and whether men have a stronger lateralization in LRD than women. Twenty-four participants (12 men, 12 women) completed a behavioral LRD task in three different conditions: after rTMS of the left and right angular gyrus and after 'sham' rTMS (control). The results revealed that after rTMS of the left angular gyrus, LRD accuracy rates were significantly reduced compared to the control condition. After rTMS of the right angular gyrus no difference to the control condition was observed. In addition, there was no overall sex difference in the LRD task and men and women were similarly affected by stimulation over the left and right angular gyrus, suggesting that the functional cerebral organization of LRD does not differ in men and women with similar LRD skills. Taken together, the findings suggest that the left angular gyrus is critically involved in LRD. It is argued that the left angular gyrus integrates spatial information with the meaning of the words 'left' and 'right', thereby assigning the labels 'left' and 'right' to a certain state or direction, etc.

Speaking words in two languages with one brain: neural overlap and dissociation

The present study investigated the neural overlap and dissociation underlying overt word production in the first language (L1) and second language (L2). Twenty-four Chinese-English bilinguals named pictures in either L1 or L2 while being scanned with functional magnetic resonance imaging (fMRI). When comparing picture naming in L2 to naming in L1, increased activity in the left inferior frontal gyrus, bilateral supplementary motor areas (SMA), left precentral gyrus, left lingual gyrus, left cuneus, bilateral putamen, bilateral globus pallidus, bilateral caudate and bilateral cerebellum were observed. This suggested that word production in L2 is less automatic and needs to recruit more neural resources for lexical retrieval, articulatory processing and cognitive control than in L1. In contrast, picture naming in L1 relative to picture naming in L2 revealed increased activity in the right putamen and right globus pallidus probably due to different phonological features between Chinese and English. In addition, the conjunction analysis, for the first time, revealed the common neural correlates underlying picture naming in L1 and L2.

Is semantic memory impaired in schizophrenia? A systematic review and meta-analysis of 91 studies

INTRODUCTION

Semantic memory impairments in schizophrenia have been reported across a wide range of neuropsychological tests. Set against a backdrop of fairly widespread cognitive impairments, it is difficult to know whether there is a primary, or secondary, impairment of semantic memory in schizophrenia. Also, whether there is a profile of differential impairment across the range of neuropsychological tests.

METHODS

Employing a systematic search strategy, 91 papers were identified which have assessed participants with schizophrenia on a measure of semantic memory. A series of meta-analyses were then conducted which provided combined weighted means for performance on tasks of naming, word-picture matching, verbal fluency, priming, and categorisation.

RESULTS

An uneven profile of impairment is reported with large effect sizes for tests of naming and verbal fluency, medium effect sizes for word-picture matching and association and small effect sizes for categorisation and priming tests.

CONCLUSIONS

This uneven profile supports the claim that a degradation of semantic knowledge may not be adequate in explaining the semantic memory impairment in schizophrenia. This conclusion is supported by the data which report a relationship between an executive dysfunction and poor priming and fluency performance particularly. The data support a link between Formal Thought Disorder and semantic memory impairments on tests of naming and verbal fluency but on other tests evidence is equivocal.

CHRONOMETRY OF VISUAL WORD RECOGNITION DURING PASSIVE AND LEXICAL DECISION TASKS: AN ERP INVESTIGATION

In order to investigate the neuroanatomical chronometry of word processing, two experiments using: Event-Related Potentials (ERPs) have been performed. The first one was designed to test the effects of orthographic, phonologic, and lexical properties of linguistic items on the pre-semantic components of ERPs during a passive reading task and massive repetition used to reduce familiarity effect between words and nonwords. In a second study, the level of familiarity was investigated by varying stimulus repetition and frequency in a lexical decision task. Overall results suggest a functional discrimination between orthographic and nonorthographic stimuli begun as early as 170 ms (N170 component) whereas the next components (N230 and N320) were sensitive to the orthographic nature of the stimuli, but also to their lexical/phonologic proprieties. The N320 associated to phonological processing (Bentin et al., 1999) was modulated by word frequency and massive repetition caused its disappearance. This suggests that this component may reflect a nonobligatory phonologic stage of grapheme-phoneme conversion postulated by the DRC model (Coltheart et al., 2001) or semantic phonologically mediated pathway (Harm & Seidenberg, in press).

Changes in fMRI activation following rehabilitation of reading and visual processing deficits in subjects with traumatic brain injury

In this case series fMRI was used to examine activation patterns during presentation of a reading comprehension (RC) task in three adult subjects with a history of severe traumatic brain injury (TBI). These subjects received cognitive rehabilitation therapy (CRT) for visual processing and acquired reading deficits. fMRI and neuropsychological testing occurred pre- and post-rehabilitation. The study's objective was to evaluate the neurobiological changes using fMRI occurring with CRT and to compare these results to repeat fMRI in matched controlsubjects. While improvements in neuropsychologicaltesting occurred post-CRT, diffuse and variable activation patterns in the subjects with TBI were still demonstrated when compared to the control subjects repeat imaging. Multiple networks exist to accomplish the complex task of sentence reading and rehabilitation of the cognitive components of reading, such as visual processing; in subjects with TBI, can alter the activation pattern demonstrated during reading comprehension in subjects many years post-injury. This is the first demonstration of changes in network activation patterns post-CRT in patients with severe, chronic TBI on an fMRI task shown to have imaging stability in a normal control sample.

Topographical functional connectivity pattern in the perisylvian language networks

We performed a resting-state functional connectivity study to investigate directly the functional correlations within the perisylvian language networks by seeding from 3 subregions of Broca's complex (pars opercularis, pars triangularis, and pars orbitalis) and their right hemisphere homologues. A clear topographical functional connectivity pattern in the left middle frontal, parietal, and temporal areas was revealed for the 3 left seeds. This is the first demonstration that a functional connectivity topology can be observed in the perisylvian language networks. The results support the assumption of the functional division for phonology, syntax, and semantics of Broca's complex as proposed by the memory, unification, and control (MUC) model and indicated a topographical functional organization in the perisylvian language networks, which suggests a possible division of labor for phonological, syntactic, and semantic function in the left frontal, parietal, and temporal areas.

A comparison of brain activity evoked by single content and function words: an fMRI investigation of implicit word processing

Content and function words have different roles in language and differ greatly in their semantic content. Although previous research has suggested that these different roles may be mediated by different neural substrates, the neuroimaging literature on this topic is particularly scant. Moreover, fMRI studies that have investigated differences between content and function words have utilized tasks that focus the subjects' attention on the differences between these word types. It is possible, then, that task-related differences in attention, working memory, and decision-making contribute to the differential patterns of activation observed. Here, subjects were engaged in a continuous working memory cover task while single, task-irrelevant content and function words were infrequently and irregularly presented. Nonword letter strings were displayed in black font at a fast rate (2/s). Subjects were required to either remember or retrieve occasional nonwords that were presented in colored fonts. Incidental and irrelevant to the memory task, content and function words were interspersed among nonwords at intervals of 12 to 15 s. Both word types strongly activated temporal-parietal cortex, middle and anterior temporal cortex, inferior frontal gyrus, parahippocampal gyrus, and orbital frontal cortex. Activations were more extensive in the left hemisphere. Content words elicited greater activation than function words in middle and anterior temporal cortex, a sub-region of orbital frontal cortex, and the parahippocampal region. Words also evoked extensive deactivation, most notably in brain regions previously associated with working memory and attention.

Cultural neurolinguistics

As the only species that evolved to possess a language faculty, humans have been surprisingly generative in creating a diverse array of language systems. These systems vary in phonology, morphology, syntax, and written forms. Before the advent of modern brain-imaging techniques, little was known about how differences across languages are reflected in the brain. This chapter aims to provide an overview of an emerging area of research - cultural neurolinguistics - that examines systematic cross-cultural/crosslinguistic variations in the neural networks of languages. We first briefly describe general brain networks for written and spoken languages. We then discuss language-specific brain regions by highlighting differences in neural bases of different scripts (logographic vs. alphabetic scripts), orthographies (transparent vs. nontransparent orthographies), and tonality (tonal vs. atonal languages). We also discuss neural basis of second language and the role of native language experience in second-language acquisition. In the last section, we outline a general model that integrates culture and neural bases of language and discuss future directions of research in this area.

Articulatory mediation of speech perception: a causal analysis of multi-modal imaging data

The inherent confound between the organization of articulation and the acoustic-phonetic structure of the speech signal makes it exceptionally difficult to evaluate the competing claims of motor and acoustic-phonetic accounts of how listeners recognize coarticulated speech. Here we use Granger causation analyzes of high spatiotemporal resolution neural activation data derived from the integration of magnetic resonance imaging, magnetoencephalography and electroencephalography, to examine the role of lexical and articulatory mediation in listeners' ability to use phonetic context to compensate for place assimilation. Listeners heard two-word phrases such as pen pad and then saw two pictures, from which they had to select the one that depicted the phrase. Assimilation, lexical competitor environment and the phonological validity of assimilation context were all manipulated. Behavioral data showed an effect of context on the interpretation of assimilated segments. Analysis of 40 Hz gamma phase locking patterns identified a large distributed neural network including 16 distinct regions of interest (ROIs) spanning portions of both hemispheres in the first 200 ms of post-assimilation context. Granger analyzes of individual conditions showed differing patterns of causal interaction between ROIs during this interval, with hypothesized lexical and articulatory structures and pathways driving phonetic activation in the posterior superior temporal gyrus in assimilation conditions, but not in phonetically unambiguous conditions. These results lend strong support for the motor theory of speech perception, and clarify the role of lexical mediation in the phonetic processing of assimilated speech.

Delta EEG activity as a marker of dysfunctional linguistic processing in developmental dyslexia

The present study used delta EEG band to test the hypothesis of a cerebral maturational delay and a functional altered cerebral asymmetry for phonological processing in dyslexic children. A group of 14 children with dyslexia and 28 matched controls participated in a linguistic paradigm in which the same words were processed in three tasks: phonological, semantic, and orthographic. Delta amplitude was computed as an index of cortical inhibition in four different phases of word processing. In anterior sites, controls showed left activation (reduced delta) during the phonological task and bilateral activation in the other two tasks. Conversely, children with dyslexia showed greater overall delta amplitude, indexing a cerebral maturation delay and an altered language laterality pattern. In the phonological task they had larger left anterior delta (inhibition of left frontal linguistic locations) and smaller left posterior delta amplitude (activation of left posterior sites silent in controls). Results support the phonological deficit hypothesis of developmental dyslexia and the validity of EEG delta band as functional and clinical measure of language laterality.

Top-down attentional control in spatially coincident stimuli enhances activity in both task-relevant and task-irrelevant regions of cortex

Models of selective attention predict that focused attention to spatially contiguous stimuli may result in enhanced activity in areas of cortex specialized for processing task-relevant and task-irrelevant information. We examined this hypothesis by localizing color-sensitive areas (CSA) and word and letter sensitive areas of cortex and then examining modulation of these regions during performance of a modified version of the Stroop task in which target and distractors are spatially coincident. We report that only the incongruent condition with the highest cognitive demand showed increased activity in CSA relative to other conditions, indicating an attentional enhancement in target processing areas. We also found an enhancement of activity in one region sensitive to word/letter processing during the most cognitively demanding incongruent condition indicating greater processing of the distractor dimension. Correlations with performance revealed that top-down modulation during the task was critical for effective filtering of irrelevant information in conflict conditions. These results support predictions made by models of selective attention and suggest an important mechanism of top-down attentional control in spatially contiguous stimuli.

Lexical influences on speech perception: a Granger causality analysis of MEG and EEG source estimates

Behavioral and functional imaging studies have demonstrated that lexical knowledge influences the categorization of perceptually ambiguous speech sounds. However, methodological and inferential constraints have so far been unable to resolve the question of whether this interaction takes the form of direct top-down influences on perceptual processing, or feedforward convergence during a decision process. We examined top-down lexical influences on the categorization of segments in a /s/-/integral/ continuum presented in different lexical contexts to produce a robust Ganong effect. Using integrated MEG/EEG and MRI data we found that, within a network identified by 40 Hz gamma phase locking, activation in the supramarginal gyrus associated with wordform representation influences phonetic processing in the posterior superior temporal gyrus during a period of time associated with lexical processing. This result provides direct evidence that lexical processes influence lower level phonetic perception, and demonstrates the potential value of combining Granger causality analyses and high spatiotemporal resolution multimodal imaging data to explore the functional architecture of cognition.

Group independent component analysis of language fMRI from word generation tasks

Language fMRI has been used to study brain regions involved in language processing and has been applied to pre-surgical language mapping. However, in order to provide clinicians with optimal information, the sensitivity and specificity of language fMRI needs to be improved. Type II error of failing to reach statistical significance when the language activations are genuinely present may be particularly relevant to pre-surgical planning, by falsely indicating low surgical risk in areas where no activations are shown. Furthermore, since the execution of language paradigms involves cognitive processes other than language function per se, the conventional general linear model (GLM) method may identify non-language-specific activations. In this study, we assessed an exploratory approach, independent component analysis (ICA), as a potential complementary method to the inferential GLM method in language mapping applications. We specifically investigated whether this approach might reduce type II error as well as generate more language-specific maps. Fourteen right-handed healthy subjects were studied with fMRI during two word generation tasks. A similarity analysis across tasks was proposed to select components of interest. Union analysis was performed on the language-specific components to increase sensitivity, and conjunction analysis was performed to identify language areas more likely to be essential. Compared with GLM, ICA identified more activated voxels in the putative language areas, and signals from other sources were isolated into different components. Encouraging results from one brain tumor patient are also presented. ICA may be used as a complementary tool to GLM in improving pre-surgical language mapping.

Pictures of a thousand words: investigating the neural mechanisms of reading with extremely rapid event-related fMRI

Reading is one of the most important skills human beings can acquire, but has proven difficult to study naturalistically using functional magnetic resonance imaging (fMRI). We introduce a novel Event-Related Reading (ERR) fMRI approach that enables reliable estimation of the neural correlates of single-word processing during reading of rapidly presented narrative text (200-300 ms/word). Application to an fMRI experiment in which subjects read coherent narratives and made no overt responses revealed widespread effects of orthographic, phonological, contextual, and semantic variables on brain activation. Word-level variables predicted activity in classical language areas as well as the inferotemporal visual word form area, specifically supporting a role for the latter in mapping visual forms onto articulatory or acoustic representations. Additional analyses demonstrated that ERR results replicate across experiments and predict reading comprehension. The ERR approach represents a powerful and extremely flexible new approach for studying reading and language behavior with fMRI.

Voxelwise Bayesian lesion-deficit analysis

Relating cognitive deficits to the presence of lesions has been an important means of delineating structure-function associations in the human brain. We propose a voxel-based Bayesian method for lesion-deficit analysis, which identifies complex linear or nonlinear associations among brain-lesion locations, and neurological status. We validated this method using a simulated data set, and we applied this algorithm to data obtained from an acute-stroke study to identify associations among voxels with infarct or hypoperfusion, and impaired word reading. We found that a distributed region involving Brodmann areas (BA) 22, 37, 39, and 40 was implicated in word reading.

Role of left superior temporal gyrus during name recall process: an event-related fMRI study

When we cannot recall the name of a well-known person despite preserved access to his/her semantic knowledge, a phonological hint such as his/her initials sometimes helps us to recall the name. This type of recall failure appeared to occur by the transmission deficit from the lexical-semantic stage to the lexical-phonological stage in name recall processes, and the phonological cue appeared to activate this transmission, which leads to successful recall. We hypothesized that the brain regions responsible for the transmission would respond to the phonological cue that facilitates name recall, and would also respond to successful recall. A famous face image was presented with a phonological cue, and the subjects were required to recall and overtly pronounce the name during fMRI scanning. The behavioral results showed that the first syllable cue induced greater number of successful recall trials than both the non-verbal sound of the chime and the non-first syllable cue, suggesting that the first syllable facilitated name recall. The fMRI results demonstrated that two regions in the left superior temporal gyrus responded more strongly to the first syllable than both to the non-verbal sound of the chime and to the non-first syllable. In addition, these two regions were activated when the name recall was successful. These results suggest that two regions in the left superior temporal gyrus may play a crucial role in the transmission from the lexical-semantic to the lexical-phonological stage in the name recall processes.

A developmental fMRI study of reading and repetition reveals changes in phonological and visual mechanisms over age

In this study of reading development, children (ages 7-10) and adults (ages 18-32) performed overt single-word reading and aural repetition tasks on high-frequency word stimuli during functional magnetic resonance imaging. Most regions showed similar activity across age groups. These widespread regions of similarity indicate that children and adults use largely overlapping mechanisms when processing high-frequency words. Significant task-related differences included greater activity in occipital cortex for the read task, and greater activity in temporal cortex for the repeat task; activity levels in these regions were similar for adults and children. However, age group differences were found in several posterior regions, including a set of regions implicated in adult reading: the left supramarginal gyrus, the left angular gyrus, and bilateral anterior extrastriate cortex. The angular and supramarginal gyrus regions, hypothesized to play a role in phonology, showed decreased activity in adults relative to children for high-frequency words. The extrastriate regions had significant activity for both the visual read task and auditory repeat task in children, but just for the read task in adults, showing significant task and age interactions. These results are consistent with decreasing reliance on phonological processing, and increasing tuning of visual mechanisms, with age.

Neural regions essential for reading and spelling of words and pseudowords

OBJECTIVE

To identify dysfunctional brain regions critical for impaired reading/spelling of words/pseudowords by evaluating acute stroke patients on lexical tests and magnetic resonance imaging, before recovery or reorganization of structure-function relationships.

METHODS

A series of 106 consenting patients were administered oral reading and spelling tests within 24 hours of left supratentorial stroke onset. Patients underwent diffusion- and perfusion-weighted magnetic resonance examination the same day to identify regions of hypoperfusion/infarct of 16 Brodmann areas.

RESULTS

Simultaneous logistic regression analysis demonstrated that dysfunction of left Brodmann areas 40 (supramarginal gyrus) and 37 (posterior-inferior temporal/fusiform gyrus) best predicted impairment in reading words (odds ratio [OR], 6.20 [95% confidence interval (CI), 1.54-24.96] and 2.71 [95% CI, 0.87-8.45], respectively), reading pseudowords (OR, 39.65 [95% CI 3.9-400.78] and 4.41 [95% CI, 1.1-17.51], respectively), spelling words (OR, 14.11 [95% CI 1.37-144.93] and 7.41 [95% CI, 1.48-37.24], respectively), and spelling pseudowords (OR, 4.84 [95% CI, 0.73-32.13] and 7.74 [95% CI, 1.56-38.51], respectively). Whole-brain voxel-wise analyses demonstrated voxel clusters within these regions that were most strongly associated with task deficits.

INTERPRETATION

Results indicate that a shared network of regions including parts of left Brodmann areas 37 and 40 is necessary for reading and spelling of words and pseudowords. Further studies may define the precise roles of these brain regions in language. Identification of any neural regions specific to one of these tasks or one type of stimuli will require study of more patients with selective deficits.

Unconscious Word Processing Engages a Distributed Network of Brain Regions

A briefly exposed visual stimulus may not be consciously perceived if it is preceded and followed by a dissimilar visual pattern or mask. Despite the subject's lack of awareness, prior behavioral studies have shown that such masked stimuli, nevertheless, engage domain-specific processes [Dehaene, S., Naccache, L., Cohen, L., Le Bihan, D., Mangin, J.-F., Poline, J.-B., et al. Cerebral mechanisms of word masking and unconscious repetition priming. Nature Neuroscience, 4, 752–758, 2001; Bar, M., & Biederman, I. Subliminal visual priming. Psychological Science, 9, 464–469, 1998; Dehaene, S., Naccache, L., Le Clec'H, G., Koechlin, E., Mueller, M., Dehaene-Lambertz, G., et al. Imaging unconscious semantic priming. Nature, 395, 597–600, 1998; Whalen, P. J., Rauch, S. L., Etcoff, N. L., McInerney, S. C., Lee, M. B., & Jenike, M. A. Masked presentations of emotional facial expressions modulate amygdala activity without explicit knowledge. Journal of Neuroscience, 18, 411–418, 1998; Marcel, A. J. Conscious and unconscious perception: Experiments on visual masking and word recognition. Cognitive Psychology, 15, 197–237, 1983]. Masking thus provides a method for identifying language processes that are preattentive and automatic. Functional magnetic resonance imaging used in concert with masking may identify brain regions engaged by these unconscious language processes. In an adaptation design, subjects viewed a continuous stream of masked words and masked nonwords while performing an unrelated detection task, in which they were asked to make a response to a visible colored nonword stimulus (i.e., ampersands in red or blue font). Most trials were masked nonwords and masked words were presented once every 12–15 sec. The task ensured participant engagement, while the masked nonword baseline controlled for perceptual and orthographic processing. Participants were naïve to the purpose of the experiment and testing indicated that they did not consciously perceive either the words or nonwords. Masked words, but not masked nonwords, strongly activated left hemisphere language regions, including Broca's area, the angular gyrus, and the lateral temporal lobe. Differential activation of the posterior corpus callosum was also observed.

Neural correlates of verb argument structure processing

Neuroimaging and lesion studies suggest that processing of word classes, such as verbs and nouns, is associated with distinct neural mechanisms. Such studies also suggest that subcategories within these broad word class categories are differentially processed in the brain. Within the class of verbs, argument structure provides one linguistic dimension that distinguishes among verb exemplars, with some requiring more complex argument structure entries than others. This study examined the neural instantiation of verbs by argument structure complexity: one-, two-, and three-argument verbs. Stimuli of each type, along with nouns and pseudowords, were presented for lexical decision using an event-related functional magnetic resonance imaging design. Results for 14 young normal participants indicated largely overlapping activation maps for verbs and nouns, with no areas of significant activation for verbs compared to nouns, or vice versa. Pseudowords also engaged neural tissue overlapping with that for both word classes, with more widespread activation noted in visual, motor, and peri-sylvian regions. Examination of verbs by argument structure revealed activation of the supramarginal and angular gyri, limited to the left hemisphere only when verbs with two obligatory arguments were compared to verbs with a single argument. However, bilateral activation was noted when both two- and three-argument verbs were compared to one-argument verbs. These findings suggest that posterior peri-sylvian regions are engaged for processing argument structure information associated with verbs, with increasing neural tissue in the inferior parietal region associated with increasing argument structure complexity. These findings are consistent with processing accounts, which suggest that these regions are crucial for semantic integration.

Preparatory neural activity predicts performance on a conflict task

Advance preparation has been shown to improve the efficiency of conflict resolution. Yet, with little empirical work directly linking preparatory neural activity to the performance benefits of advance cueing, it is not clear whether this relationship results from preparatory activation of task-specific networks, or from activity associated with general alerting processes. Here, fMRI data were acquired during a spatial Stroop task in which advance cues either informed subjects of the upcoming relevant feature of conflict stimuli (spatial or semantic) or were neutral. Informative cues decreased reaction time (RT) relative to neutral cues, and cues indicating that spatial information would be task-relevant elicited greater activity than neutral cues in multiple areas, including right anterior prefrontal and bilateral parietal cortex. Additionally, preparatory activation in bilateral parietal cortex and right dorsolateral prefrontal cortex predicted faster RT when subjects responded to spatial location. No regions were found to be specific to semantic cues at conventional thresholds, and lowering the threshold further revealed little overlap between activity associated with spatial and semantic cueing effects, thereby demonstrating a single dissociation between activations related to preparing a spatial versus semantic task-set. This relationship between preparatory activation of spatial processing networks and efficient conflict resolution suggests that advance information can benefit performance by leading to domain-specific biasing of task-relevant information.

The Neural Substrate of Naming Events: Effects of Processing Demands but not of Grammatical Class

Grammatical class is a fundamental property of language, and all natural languages distinguish between nouns and verbs. Brain activation studies have provided conflicting evidence concerning the neural substrates of noun and verb processing. A major limitation of many previous imaging studies is that they did not disentangle the impact of grammatical class from the differences in semantic correlates. In order to tease apart the role of semantic and grammatical factors, we performed a functional magnetic resonance imaging study presenting Italian speakers with pictures of events and asked them to name them as 1) Infinitive Verb (e.g., mangiare [to eat]); 2) Inflected Verb (e.g., mangia [she/he eats]); and 3) Action Noun (e.g., mangiata [the eating]). We did not find any verb-specific activation. However, reliable left inferior frontal gyrus (IFG) activations were found when contrasting the Action Noun with the Infinitive Verb condition. A second-level analysis indicated then that activation in left IFG was greatest for Action Nouns, intermediate for Inflected Verbs, and least for Infinitive Verbs. We conclude that, when all other factors are controlled, nouns and verbs are processed by a common neural system. In the present case, differences in left IFG activation emerge as a consequence of increasing linguistic and/or general processing demands.

Action and object processing in aphasia: from nouns and verbs to the effect of manipulability

The processing of words and pictures representing actions and objects was tested in 21 aphasic patients and 20 healthy controls across three word production tasks: picture-naming (PN), single word reading (WR) and word repetition (WRP). Analysis 1 targeted task and lexical category (noun-verb), revealing worse performance on PN and verb items for both patients and control participants. For Analysis 2 we used data collected in a concurrent gesture norming study to re-categorize the noun-verb items along hand imagery parameters (i.e., objects that can/cannot be manipulated and actions which do/do not involve fine hand movements). Here, patients displayed relative difficulty with the 'manipulable' items, while controls displayed the opposite pattern. Therefore, whereas the noun-verb distinction resulted simply in lower verb accuracy across groups, the 'manipulability' distinction revealed a 'double-dissociation' between patients and control participants. These results carry implications for theories of embodiment, lexico-semantic dissociations, and the organization of meaning in the brain.

Integration of auditory and visual communication information in the primate ventrolateral prefrontal cortex

The integration of auditory and visual stimuli is crucial for recognizing objects, communicating effectively, and navigating through our complex world. Although the frontal lobes are involved in memory, communication, and language, there has been no evidence that the integration of communication information occurs at the single-cell level in the frontal lobes. Here, we show that neurons in the macaque ventrolateral prefrontal cortex (VLPFC) integrate audiovisual communication stimuli. The multisensory interactions included both enhancement and suppression of a predominantly auditory or a predominantly visual response, although multisensory suppression was the more common mode of response. The multisensory neurons were distributed across the VLPFC and within previously identified unimodal auditory and visual regions (O'Scalaidhe et al., 1997; Romanski and Goldman-Rakic, 2002). Thus, our study demonstrates, for the first time, that single prefrontal neurons integrate communication information from the auditory and visual domains, suggesting that these neurons are an important node in the cortical network responsible for communication.

Laterality and language experience

A meta-analysis was conducted on studies that examined hemispheric functional asymmetry for language in brain-intact monolingual and bilingual adults. Data from 23 laterality studies that directly compared bilingual and monolingual speakers on the same language were analysed (n = 1234). Variables examined were language experience (monolingual, bilingual), experimental paradigm (dichotic listening, visual hemifield presentation, and dual task) and, among bilinguals, the influence of second language proficiency (proficient vs nonproficient) and onset of bilingualism (early, or before age 6; and late, or after age 6). Overall, monolinguals and late bilinguals showed reliable left hemisphere dominance, while early bilinguals showed reliable bilateral hemispheric involvement. Within bilinguals, there was no reliable effect of language proficiency when age of L2 acquisition was controlled. The findings indicate that early learning of one vs. two languages predicts divergent patterns of cerebral language lateralisation in adulthood.

Task-Guided Selection of the Dual Neural Pathways for Reading

The visual perception of words is known to activate the auditory representation of their spoken forms automatically. We examined the neural mechanism for this phonological activation using transcranial magnetic stimulation (TMS) with a masked priming paradigm. The stimulation sites (left superior temporal gyrus [L-STG] and inferior parietal lobe [L-IPL]), modality of targets (visual and auditory), and task (pronunciation and lexical decision) were manipulated independently. For both within- and cross-modal conditions, the repetition priming during pronunciation was eliminated when TMS was applied to the L-IPL, but not when applied to the L-STG, whereas the priming during lexical decision was eliminated when the L-STG, but not the L-IPL, was stimulated. The observed double dissociation suggests that the conscious task instruction modulates the stimulus-driven activation of the lateral temporal cortex for lexico-phonological activation and the inferior parietal cortex for spoken word production, and thereby engages a different neural network for generating the appropriate behavioral response.

An electrophysiological investigation of preparatory attentional control in a spatial Stroop task

Top-down attentional control is required when subjects must attend to one of multiple conflicting stimulus features, such as in the Stroop task. Performance may be improved when such control is implemented in advance of stimulus presentation, yet few studies have examined this issue. Our investigation employed a spatial Stroop task with a manual response, allowing us to focus on the effects of preparatory attention on verbal processing when it is the less automatic attribute. A letter cue (P or W) presented for 2200 msec instructed subjects to respond on the basis of the position or meaning of a word (up, down, left, right) placed in an incongruent position relative to center. Event-related potentials recorded during pre- and poststimulus periods were analyzed as a function of reaction time to the target stimulus (fast vs. slow) in order to differentiate neural activity associated with more or less successful implementation of control. During the prestimulus period, fast responses to subsequent targets were associated with enhanced slow-wave activity over right frontal and bilateral central-parietal regions. During the poststimulus period, fast word trials were uniquely associated with an enhanced inferior temporal negativity (ITN) from 200 to 600 msec. More importantly, a correlation between frontal prestimulus activity and the poststimulus ITN suggested that frontal preparatory activity played a role in facilitating conceptual processing of the verbal stimulus when it arrived, providing an important link between preparatory attention and mechanisms that improve performance in the face of conflict.

Discriminating imagined from perceived information engages brain areas implicated in schizophrenia

Some of the symptoms of schizophrenia may reflect a difficulty discriminating between information that was perceived from the outside world and information that was imagined. This study used fMRI to examine the brain regions associated with this reality monitoring ability in healthy volunteers, who recollected whether information had previously been perceived or imagined, or whether information had been presented on the left or right of a monitor screen. Recent studies have suggested that schizophrenia may be associated particularly with dysfunction in medial anterior prefrontal cortex, thalamus, and cerebellum. In our data, activation in all three of these regions of interest was significantly greater during recollection of whether stimuli had been perceived or imagined versus recollection of stimulus position. In addition, reduced prefrontal activation was associated with the same misattribution error that has been observed in schizophrenia. These results indicate a possible link between the brain areas implicated in schizophrenia and the regions supporting the ability to discriminate between perceived and imagined information.

Functional activation studies of word processing in the recovery from aphasia

Some reviews on theories of recovery in aphasia put an emphasis on neural network models based on empirical data from evoked-potentials in aphasia as an approach to mapping recovery of cognitive function to neural structure. We will focus here on what we call an "anatomical" approach to look at recovery in aphasia. "Anatomical" theories of recovery stated by classical aphasiologists have contributed to the understanding of language representations in the human brain. But many aspects of these theories can only be investigated by using modern techniques of lesion analysis, psychometric assessment and functional imaging. Whereas structure-function relations have been primarily established by looking for the association of deficit symptoms with certain lesions, functional activation methods offer a means to study more directly the functional anatomy of recovered or retained functions in neuropsychological patients. To falsify or build up anatomical theories of recovery we will propose a stepwise approach of inference. The methodological pitfalls of this approach will be discussed by focussing on anatomical hypotheses of semantic word comprehension and its impairment and recovery in aphasia.

Altered hemispheric asymmetry during word processing in dyslexic children: an event-related potential study

The present event-related potential study aimed at finding neurophysiological correlates of inadequate reading performances in developmental dyslexia. By using the same set of words in different linguistic tasks, we found variations of cortical asymmetry between dyslexic individuals and controls starting with the N420, a component supposed to index the phonological processing during reading. Whereas in controls this component was left lateralized, in disabled readers it was more distributed across hemispheres. The observed lack of lateralization in dyslexic individuals was also found in the later slow negative wave that developed in the 700 to 1500-ms time interval. We postulate that the altered asymmetry is related to an impairment of the grapheme-phoneme conversion mechanism. The findings would therefore support the hypothesis of a phonological deficit underlying this learning disability.

Polysyllabic pseudo-word processing in reading and lexical decision: Converging evidence from behavioral data, connectionist simulations and functional MRI

The cognitive mechanisms involved in polysyllabic pseudo-word processing -- and their neurobiological correlates -- were studied through the analysis of length effects on French words and pseudo-words in reading and lexical decision. Connectionist simulations conducted on the ACV98 network paralleled the behavioral data in showing a strong length effect on naming latencies for pseudo-words only and the absence of length effect for both words and pseudo-words in lexical decision. Length effects in reading were characterized at the neurobiological level by a significant and specific activity increase for pseudo-words as compared to words in the right lingual gyrus (BA 19), the left superior parietal lobule and precuneus (BA7), the left middle temporal gyrus (BA21) and the left cerebellum. The behavioral results suggest that polysyllabic pseudo-word reading mainly relies on an analytic procedure. At the biological level, additional activations in visual and visual attentional brain areas during long pseudo-word reading emphasize the role of visual and visual attentional processes in pseudo-word reading. The present findings place important constraints on theories of reading in suggesting the involvement of a serial mechanism based on visual attentional processing in pseudo-word reading.

The role of the supplementary motor area (SMA) in word production

The supplementary motor area (SMA) is a key structure for behavioral planning and execution. Recent research on motor control conducted with monkeys and humans has put to light an anatomical and functional distinction between pre-SMA and SMA-proper. According to this view, the pre-SMA would be involved in higher level processes while the SMA-proper would be more closely tied to motor output. We extended this general framework to the verbal domain, in order to investigate the role of the SMA in speech production. We conducted two speech production experiments with fMRI where we manipulated parameters such as familiarity, complexity or constraints on word selection. The results reveal a parcellation of the SMA into three distinct regions, according to their involvement in different aspects of word production. More specifically, following a rostrocaudal gradient, we observed differential activations related to lexical selection, linear sequence encoding and control of motor output. A parallel organization was observed in the dorsolateral frontal cortex. By refining its anatomical and functional parcellation, these results clarify the roles of the SMA in speech production.

The Role of Semantics and Grammatical Class in the Neural Representation of Words

On the basis of neuropsychological and functional imaging evidence, meaning and grammatical class (particularly the verb-noun distinction) have been proposed as organizational principles of linguistic knowledge in the brain. However, previous studies investigating verb and noun processing have been confounded by the presence of systematic correlations between word meaning and grammatical class. In this positron emission tomography study, we investigated implicit word processing using stimuli that allowed the effects of semantic and grammatical properties to be examined independently, without grammatical-semantic confounds. We found that left hemisphere cortical activation during single-word processing was modulated by word meaning, but not by grammatical class. Motor word processing produced significant activation in left precentral gyrus, whereas sensory word processing produced significant activation in left inferior temporal and inferior frontal regions. In contrast to previous studies, there were no effects of grammatical class in left inferior frontal gyrus (IFG). Instead, we found semantic-based differences within left IFG: anterior, but not posterior, left IFG regions responded preferentially to sensory words. These findings demonstrate that the neural substrates of implicit word processing are determined by semantic rather than grammatical properties and suggest that word comprehension involves the activation of modality-specific representations linked to word meaning.

Large-scale neural network for sentence processing

Our model of sentence comprehension includes at least grammatical processes important for structure-building, and executive resources such as working memory that support these grammatical processes. We hypothesized that a core network of brain regions supports grammatical processes, and that additional brain regions are activated depending on the working memory demands associated with processing a particular grammatical feature. We used functional magnetic resonance imaging (fMRI) to test this hypothesis by comparing cortical activation patterns during coherence judgments of sentences with three different syntactic features. We found activation of the ventral portion of left inferior frontal cortex during judgments of violations of each grammatical feature. Increased recruitment of the dorsal portion of left inferior frontal cortex was seen during judgments of violations of specific grammatical features that appear to involve a more prominent working memory component. Left posterolateral temporal cortex and anterior cingulate were also implicated in judging some of the grammatical features. Our observations are consistent with a large-scale neural network for sentence processing that includes a core set of regions for detecting and repairing several different kinds of grammatical features, and additional regions that appear to participate depending on the working memory demands associated with processing a particular grammatical feature.

Parietal rTMS distorts the mental number line: Simulating ‘spatial’ neglect in healthy subjects

Patients with left-sided visuospatial neglect, typically after damage to the right parietal lobe, show a systematic bias towards larger numbers when asked to bisect a numerical interval. This has been taken as further evidence for a spatial representation of numbers, perhaps akin to a mental number line with smaller numbers represented to the left and larger numbers to the right. Previously, contralateral neglect-like symptoms in physical line bisection have been induced in healthy subjects with repetitive transcranial magnetic stimulation (rTMS) over right posterior parietal lobe. Here we used rTMS over parietal and occipital sites in healthy subjects to investigate spatial representations in a number bisection task. Subjects were asked to name the midpoint of numerical intervals without calculating. On control trials subjects' behaviour was similar to performance reported in physical line bisection experiments. Subjects underestimated the midpoint of the numerical interval. Repetitive transcranial magnetic stimulation produced representational neglect-like symptoms in number bisection when applied over right posterior parietal cortex (right PPC). Repetitive TMS over right PPC shifted the perceived midpoint of the numerical interval significantly to the right while occipital TMS had no effect on bisection performance. Our study therefore provides further evidence that subjects use spatial representations, perhaps akin to a mental number line, in basic numerical processing tasks. Furthermore, we showed that the right posterior parietal cortex is crucially involved in spatial representation of numbers.

Neural Mechanisms of Cognitive Control: An Integrative Model of Stroop Task Performance and fMRI Data

We address the connection between conceptual knowledge and cognitive control using a neural network model. This model extends a widely held theory of cognitive control [Cohen, J. D., Dunbar, K., & McClelland, J. L. On the control of automatic processes: A parallel distributed processing model of the Stroop effect. Psychological Review, 97, 332-361, 1990] so that it can explain new empirical findings. Leveraging other computational modeling work, we hypothesize that representations used for task control are recruited from preexisting representations for categories, such as the concept of color relevant to the Stroop task we model here. This hypothesis allows the model to account for otherwise puzzling fMRI results, such as increased activity in brain regions processing to-be-ignored information. In addition, biologically motivated changes in the model's pattern of connectivity show how global competition can arise when inhibition is strictly local, as it seems to be in the cortex. We also discuss the potential for this theory to unify models of task control with other forms of attention.

Hemispheric asymmetry emerges at distinct parts of the occipitotemporal cortex for objects, logograms and phonograms: A functional MRI study

Behavioral and neuropsychological studies have suggested that the right hemisphere has a special advantage in the visual recognition of logograms. While this long-standing 'right hemisphere hypothesis' has never been investigated systematically by previous neuroimaging studies, a candidate neural substrate of such asymmetry might be found within the occipitotemporal cortex that is known to exhibit lateralized response to a certain class of stimuli, such as letters and faces. The present study examined the hemispheric specialization of brain activation during naming of objects, logograms and phonograms using functional magnetic resonance imaging. The three types of stimuli overall produced left-predominant activation of the perisylvian and inferior parietal regions relative to the resting baseline. This inter-hemispheric difference was significant irrespective of the stimuli type. In the occipitotemporal cortex, six subregions showing lateralized response were identified. That is, the three stimuli commonly produced left-lateralized response in the posterior fusiform and superior temporal gyri and right-lateralized response in the extrastriate cortex. Only logograms and objects produced a distinct cluster showing right-lateralized activation in the medial anterior fusiform gyrus associated with semantic knowledge, whereas only phonograms produced a left-lateralized activation in the posterior middle temporal cortex close to the site associated with visual perception of alphabetical letters. These findings suggest that while these stimuli similarly recruit the left perisylvian language area as a common neural component for naming, processing of objects and logograms becomes left-lateralized only in the downstream of the occipitotemporal cortex. By contrast, visual processing of phonograms is specialized to the left hemisphere in earlier stages of the area. The present data provide further evidence suggesting that both the left-right and anterior-posterior axes of the occipitotemporal cortex are differentially tuned according to the specific features of visual stimuli.

The Neurophysiology of Functionally Meaningful Categories: Macaque Ventrolateral Prefrontal Cortex Plays a Critical Role in Spontaneous Categorization of Species-Specific Vocalizations

Neurophysiological studies in nonhuman primates have demonstrated that the prefrontal cortex (PFC) plays a critical role in the acquisition of learned categories following training. What is presently unclear is whether this cortical area also plays a role in spontaneous recognition and discrimination of natural categories. Here, we explore this possibility by recording from neurons in the PFC while rhesus listen to species-specific vocalizations that vary in terms of their social function and acoustic morphology. We found that ventral prefrontal cortex (vPFC) activity, on average, did not differentiate between food calls that were associated with the same functional category, despite having different acoustic properties. In contrast, vPFC activity differentiated between food calls associated with different functional classes and specifically, information about the quality and motivational value of the food. These results suggest that the vPFC is involved in the categorization of socially meaningful signals, thereby both extending its previously conceived role in the acquisition of learned categories and showing the significance of using natural categorical distinctions in the study of neural mechanisms.

Impact of childhood epilepsy on reading and phonological processing abilities

Although children with epilepsy tend to exhibit more reading difficulties than their classmates, no systematic studies have investigated the relationship between these difficulties and epilepsy. As functional neuroimaging studies have implicated both temporal and frontal lobes in the phonological aspect of reading [K.R. Pugh, B.A. Shaywitz, S.E. Shaywitz, et al. Brain 1996;119:1221-38], seizure activity originating in either region could interfere with phonological processing, whereas generalized seizures would not disturb this function as much. To explore this hypothesis, we compared the metaphonological skills of school-aged children with either temporal lobe epilepsy (TLE), frontal lobe epilepsy (FLE), or generalized absence seizures (ABS) with those of healthy controls. While the reading ability of all epileptic children was close to 2 years behind expectations, children with TLE did not differ from the controls on phonological tasks. In contrast, children with FLE exhibited significant deficits, whereas children with ABS showed difficulties restricted to phonemic segmentation. The results suggest that FLE and, to a lesser extent, generalized seizures may interfere with phonological processing, whereas TLE may affect other aspects of reading.