The role of the right hemisphere in the interpretation of figurative aspects of language. A positron emission tomography activation study

Neural activity when people solve verbal problems with insight

People sometimes solve problems with a unique process called insight, accompanied by an “Aha!” experience. It has long been unclear whether different cognitive and neural processes lead to insight versus noninsight solutions, or if solutions differ only in subsequent subjective feeling. Recent behavioral studies indicate distinct patterns of performance and suggest differential hemispheric involvement for insight and noninsight solutions. Subjects solved verbal problems, and after each correct solution indicated whether they solved with or without insight. We observed two objective neural correlates of insight. Functional magnetic resonance imaging (Experiment 1) revealed increased activity in the right hemisphere anterior superior temporal gyrus for insight relative to noninsight solutions. The same region was active during initial solving efforts. Scalp electroencephalogram recordings (Experiment 2) revealed a sudden burst of high-frequency (gamma-band) neural activity in the same area beginning 0.3 s prior to insight solutions. This right anterior temporal area is associated with making connections across distantly related information during comprehension. Although all problem solving relies on a largely shared cortical network, the sudden flash of insight occurs when solvers engage distinct neural and cognitive processes that allow them to see connections that previously eluded them.

Functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) are used to study neural activity in subjects during a verbal task for which they report solutions achieved by insight

Temporal lobe abnormalities in semantic processing by criminal psychopaths as revealed by functional magnetic resonance imaging

We tested the hypothesis that psychopathy is associated with abnormalities in semantic processing of linguistic information. Functional magnetic resonance imaging (fMRI) was used to elucidate and characterize the neural architecture underlying lexico-semantic processes in criminal psychopathic individuals and in a group of matched control participants. Participants performed a lexical decision task in which blocks of linguistic stimuli alternated with a resting baseline condition. In each lexical decision block, the stimuli were either concrete words and pseudowords or abstract words and pseudowords. Consistent with our hypothesis, psychopathic individuals, relative to controls, showed poorer behavioral performance for processing abstract words. Analysis of the fMRI data for both groups indicated that processing of word stimuli, compared with the resting baseline condition, was associated with neural activation in bilateral fusiform gyrus, anterior cingulate, left middle temporal gyrus, right posterior superior temporal gyrus, and left and right inferior frontal gyrus. Analyses confirmed our prediction that psychopathic individuals would fail to show the appropriate neural differentiation between abstract and concrete stimuli in the right anterior temporal gyrus and surrounding cortex. The results are consistent with other studies of semantic processing in psychopathy and support the theory that psychopathy is associated with right hemisphere abnormalities for processing conceptually abstract material.

Metaphor Comprehension in Right Brain-Damaged Patients with Visuo-Verbal and Verbal Material: A Dissociation (RE)Considered

Metaphor comprehension was investigated in 50 right-hemisphere damaged (RHD) patients and 38 control subjects in two experimental conditions: a visuo-verbal and a verbal test. In the visuo-verbal test, subjects had to match a metaphorical sentence with one of four pictures representing the correct metaphorical meaning, the literal meaning, a control metaphor and a control literal meaning. In the verbal test, a metaphorical sentence had to be matched to a correct written metaphorical interpretation, a literal or a control interpretation. On both tests, the number of correct metaphorical responses in the RHD group was lower than in the control group. However, RHD patients performed more poorly in the visuo-verbal than in the verbal condition. Interestingly, when they selected the wrong response, the RHD patients tended to select the literal one only in the visuo-verbal condition. Context does not seem to be responsible for the dissociation between the two tests. The influence of the RHD patients' major visuo-spatial deficits was also checked, to exclude their role in the tendency to be literal with visuo-verbal material. Results are discussed in the perspective of an integration deficit.

Neural correlates of implicit object identification

The present study sought to assess neural correlates of implicit identification of objects by means of fMRI, using tasks that require matching of the physical properties of objects. Behavioural data suggests that there is automatic access to object identity when observers attend to a physical property of the form of an object (e.g. the object's orientation) and no evidence for semantic processing when subjects attend to colour. We evaluated whether, in addition to neural areas associated with decisions to specific perceptual properties, areas associated with access to semantic information were activated when tasks demanded processing of the global configuration of pictures. We used two perceptual matching tasks based on the global orientation or on the colour of line drawings. Our results confirmed behavioural data. Activations in the inferior occipital cortex, fusiform and inferior temporal gyri in both tasks (orientation and colour) account for perceptual and structural processing involved in each task. In contrast, activations in the posterior and medial parts of the fusiform gyrus, shown to be involved in explicit semantic judgements, were more pronounced in the orientation-matching task, suggesting that semantic information from the pictures is processed in an implicit way even when not required by the task. Thus, this study suggests that cortical regions usually involved in explicit semantic processing are also activated when implicit processing of objects occurs.

Interindividual variability in the hemispheric organization for speech

A PET activation study was designed to investigate hemispheric specialization during speech comprehension and production in right- and left-handed subjects. Normalized regional cerebral blood flow (NrCBF) was repeatedly monitored while subjects either listened to factual stories (Story) or covertly generated verbs semantically related to heard nouns (Gener), using silent resting (Rest) as a common control condition. NrCBF variations in each task, as compared to Rest, as well as functional asymmetry indices (FAI = right minus left NrCBF variations), were computed in anatomical regions of interest (AROIs) defined on the single-subject MNI template. FAIs were predominantly leftward in all regions during both tasks, although larger FAIs were observed during Gener. Subjects were declared "typical" for language hemispheric specialization based on the presence of significant leftward asymmetries (FAI < 0) in the pars triangularis and opercularis of the inferior frontal gyrus during Gener, and in the middle and inferior temporal AROIs during Story. Six subjects (including five LH) showed an atypical language representation. Among them, one presented a right hemisphere specialization during both tasks, another a shift in hemispheric specialization from production to comprehension (left during Gener, right during Story). The group of 14 typical subjects showed significant positive correlation between homologous left and right AROIs NrCBF variations in temporal areas during Story, and in temporal and inferior frontal areas during Gener, almost all regions presenting a leftward FAI. Such correlations were also present in deactivated areas with strong leftward asymmetry (supramarginalis gyrus, inferior parietal region). These results suggest that entry into a language task translates into a hemispheric reconfiguration of lateral cortical areas with global NrCBF increase in the dominant hemisphere and decrease in the minor hemisphere. This can be considered as the setting up of a "language mode", under the control of a mechanism that operates at a perisylvian level. On top of this global organization, regional variations carry on the performance of the cognitive operations specific to the language task to be performed. Hemispheric relationships could be different in atypical subjects, with either between task hemispheric regulation differences or differences in regional specialization.

N400 during lexical decision tasks: a current source localization study

OBJECTIVE

Our primary aim in the present study was to establish the anatomic and psychophysiological correlates of automatic and controlled semantic priming.

METHODS

Current sources were calculated on N400 component data from a previous study on lexical decision tasks [Clin Neurophysiol 1999;110:813] using the variable resolution electromagnetic tomography method (VARETA). In this study, two experiments were carried out, one using directly related pairs and the other one using mediated related pairs. Each experiment consisted of 3 tasks that required different levels of contribution from controlled processes.

RESULTS

Average source localization images showed the brain structures involved in lexical decision tasks. The automatic component of the N400 effect was related to activation of occipitotemporal and parahippocampal gyri and anterior temporal lobes bilaterally. The expectancy strategy was related to activation of the right posterior temporal and right frontal areas. The postlexical strategy was associated with activation of right frontal, anterior cingulate and bilateral superior parietal areas.

CONCLUSIONS

The findings indicated that the current sources of the N400 varied according to the relative contributions of automatic and controlled mechanisms. Moreover, the sources of the N400 effect depended on the type of strategy used.

Processing of metaphoric and non-metaphoric alternative meanings of words after right- and left-hemispheric lesion

This study examines the specificity of the contribution of the right hemisphere to the processing of metaphoric meaning of words. Ten right- and 10 left-hemisphere-damaged subjects, and 20 normal control subjects were submitted to: (1) a word-triad task where they had to associate alternative metaphoric and non-metaphoric words to a target word, and to (2) a word-dyad task where they had to decide whether or not there was a semantic relationship between two words. The two tasks aimed at differentiating between the subjects' preference for a given semantic meaning versus a genuine semantic deficit for a particular meaning. Results revealed that both right- and left-hemisphere-damaged groups presented a genuine semantic deficit for the processing of metaphoric meaning. The absence of a double dissociation between the two brain-damaged groups does not support the hypothesis of a specific contribution of the right-hemisphere to the processing of metaphoric meaning of words.

The neural substrate of analogical reasoning: an fMRI study

This study investigated the anatomical substrate of analogical reasoning using functional magnetic resonance imaging. In the study, subjects performed a verbal analogy task (e.g., soldier is to army as drummer is to band) and, to control for activation caused by purely semantic access, a semantic judgment task. Significant activation differences between the verbal analogy and the semantic judgment task were found bilaterally in the prefrontal cortex (right BA 11/BA 47 and left BA45), the fusiform gyrus, and the basal ganglia; left lateralized in the postero-superior temporal gyrus (BA 22) and the (para) hippocampal region; and right lateralized in the anterior cingulate. The role of these areas in analogical reasoning is discussed.

Age-related differences in the functional connectivity of the hippocampus during memory encoding

The purpose of the current experiment was to examine the functional connectivity of the hippocampus during encoding in young and old adults, and the way in which this connectivity was related to recognition performance. Functional connectivity was defined as the correlation between activity in the hippocampus and activity in the rest of the brain, as measured by neuroimaging. During encoding of words and pictures of objects in young adults, hippocampal activity was correlated with activity in the ventral prefrontal and extrastriate regions, and increased activity in all these regions was associated with better recognition. In contrast, older adults showed correlations between hippocampal activity and the dorsolateral prefrontal and parietal regions, and positive correlations between activity in these regions and better memory performance. This ventral/dorsal distinction suggests a shift in the cognitive resources used with age from more perceptually based processes to those involved in executive and organizational functions. The results of this study provide evidence that aging is associated with alterations in hippocampal function, including how it is functionally connected with prefrontal cortex, and that these alterations have an impact on memory performance.

Aha! Insight experience correlates with solution activation in the right hemisphere

In one experiment, we tested for an association between semantic activation in the right hemisphere (RH) and left hemisphere (LH) and the Aha! experience when people recognize solutions to insight-like problems. The compound remote associate problems used in this experiment sometimes evoke an Aha! experience and sometimes do not. On each trial, participants (N = 44) attempted to solve these problems and, after 7 sec, named a target word, made a solution decision, and rated their insight experience of recognizing the solution. As in prior studies, the participants demonstrated more solution priming for solutions presented to the left visual field-RH (lvf-RH) than for solutions presented to the right visual field-LH (rvf-LH). As was predicted, following unsolved problems the participants showed greater priming for solutions that they rated as evoking an insight experience on the subsequent solution decision than for solutions that did not evoke an insight experience. This association was stronger for solutions presented to the lvf-RH than for those presented to the rvf-LH. These results tie the subjective experience of insight to an objective measure--semantic priming--and suggest that people have an Aha! experience in part because they already had semantic activation that could lead them to recognize the solution quickly. We believe semantic activation in both hemispheres cooperatively contributes to problem solving, but weak solution activation that contributes to the Aha! experience is more likely to occur in the RH than in the LH.

The neural response to emotional prosody, as revealed by functional magnetic resonance imaging

Prosody is an important feature of language, comprising intonation, loudness, and tempo. Emotional prosodic processing forms an integral part of our social interactions. The main aim of this study was to use bold contrast fMRI to clarify the normal functional neuroanatomy of emotional prosody, in passive and active contexts. Subjects performed six separate scanning studies, within which two different conditions were contrasted: (1) "pure" emotional prosody versus rest; (2) congruent emotional prosody versus 'neutral' sentences; (3) congruent emotional prosody versus rest; (4) incongruent emotional prosody versus rest; (5) congruent versus incongruent emotional prosody; and (6) an active experiment in which subjects were instructed to either attend to the emotion conveyed by semantic content or that conveyed by tone of voice. Data resulting from these contrasts were analysed using SPM99. Passive listening to emotional prosody consistently activated the lateral temporal lobe (superior and/or middle temporal gyri). This temporal lobe response was relatively right-lateralised with or without semantic information. Both the separate and direct comparisons of congruent and incongruent emotional prosody revealed that subjects used fewer brain regions to process incongruent emotional prosody than congruent. The neural response to attention to semantics, was left lateralised, and recruited an extensive network not activated by attention to emotional prosody. Attention to emotional prosody modulated the response to speech, and induced right-lateralised activity, including the middle temporal gyrus. In confirming the results of lesion and neuropsychological studies, the current study emphasises the importance of the right hemisphere in the processing of emotional prosody, specifically the lateral temporal lobes.

Going beyond the information given: a neural system supporting semantic interpretation

Relating the meaning of a word to the context in which it is encountered is central to comprehension. We investigated the neural basis of this process. Subjects made decisions based on a semantic property of single nouns. The lack of sentence context created ambiguity, as nouns may have several, unrelated semantic identities. Contrasted with unambiguous decisions about each noun's sound structure, the semantic task resulted in activity in the left superior frontal gyrus (SFG), activity that was dependent on choice reaction time. This identified the left SFG as an executive component of a distributed cognitive system that relates a word's meaning to its semantic context to facilitate comprehension.

ERP and behavioral evidence of individual differences in metaphor comprehension

In two experiments, we examined individual differences in metaphor processing. In Experiment 1, the subjects judged the literal truth of literal, metaphorical, and scrambled sentences. Overall, metaphors were more difficult to judge as false, in comparison with scrambled controls, suggesting that the metaphorical meaning was being processed automatically. However, there were individual differences in that high-IQ subjects showed more interference. These effects were reflected in ERP amplitude differences at the onset of N400 and after the response. In Experiment 2, the subjects completed IQ tests and a series of working memory tests and then rated and interpreted the same set of metaphors. The results showed that IQ was correlated with working memory capacity and that low-IQ subjects had similar ratings but poorer quality interpretations than did high-IQ subjects. The results were most consistent with a constraint satisfaction approach to metaphor comprehension.

Top-down and bottom-up modulation of language related areas--an fMRI study

BACKGROUND

One major problem for cognitive neuroscience is to describe the interaction between stimulus and task driven neural modulation. We used fMRI to investigate this interaction in the human brain. Ten male subjects performed a passive listening and a semantic categorization task in a factorial design. In both tasks, words were presented auditorily at three different rates.

RESULTS

We found: (i) as word presentation rate increased hemodynamic responses increased bilaterally in the superior temporal gyrus including Heschl's gyrus (HG), the planum temporale (PT), and the planum polare (PP); (ii) compared to passive listening, semantic categorization produced increased bilateral activations in the ventral inferior frontal gyrus (IFG) and middle frontal gyrus (MFG); (iii) hemodynamic responses in the left dorsal IFG increased linearly with increasing word presentation rate only during the semantic categorization task; (iv) in the semantic task hemodynamic responses decreased bilaterally in the insula with increasing word presentation rates; and (v) in parts of the HG the hemodynamic response increased with increasing word presentation rates during passive listening more strongly.

CONCLUSION

The observed "rate effect" in primary and secondary auditory cortex is in accord with previous findings and suggests that these areas are driven by low-level stimulus attributes. The bilateral effect of semantic categorization is also in accord with previous studies and emphasizes the role of these areas in semantic operations. The interaction between semantic categorization and word presentation in the left IFG indicates that this area has linguistic functions not present in the right IFG. Finally, we speculate that the interaction between semantic categorization and word presentation rates in HG and the insula might reflect an inhibition of the transfer of unnecessary information from the temporal to frontal regions of the brain.

Cortical morphology associated with language function in neurofibromatosis, type I

Neurofibromatosis, type I (NF-I) is associated with verbal and nonverbal neuropsychological deficits and neuroanatomical anomalies. Few relationships between CNS abnormalities and cognitive function in this population, however, have been found. Reading disabilities and developmental language impairments in the general population have been associated with particular morphologic features in inferior frontal gyrus (IFG) and Heschl's gyrus (HG). We compared the morphology of these regions in children with NF-I and controls. Verbal skills in NF-I were related to IFG morphology, such that individuals with NF-I who showed "typical" gyral patterns in the right hemisphere performed worse across language measures than those showing an extra "atypical" gyrus. A doubling of HG in the left and right hemispheres was also significantly associated with performance on several neuropsychological measures. This is the first study to link regional gyral morphology with language function in NF-I. A possible molecular basis for the observed relationships is discussed.

Development and neurophysiology of mentalizing

The mentalizing (theory of mind) system of the brain is probably in operation from ca. 18 months of age, allowing implicit attribution of intentions and other mental states. Between the ages of 4 and 6 years explicit mentalizing becomes possible, and from this age children are able to explain the misleading reasons that have given rise to a false belief. Neuroimaging studies of mentalizing have so far only been carried out in adults. They reveal a system with three components consistently activated during both implicit and explicit mentalizing tasks: medial prefrontal cortex (MPFC), temporal poles and posterior superior temporal sulcus (STS). The functions of these components can be elucidated, to some extent, from their role in other tasks used in neuroimaging studies. Thus, the MPFC region is probably the basis of the decoupling mechanism that distinguishes mental state representations from physical state representations; the STS region is probably the basis of the detection of agency, and the temporal poles might be involved in access to social knowledge in the form of scripts. The activation of these components in concert appears to be critical to mentalizing.

Distinct patterns of neural modulation during the processing of conceptual and syntactic anomalies

The aim of this study was to gain further insights into how the brain distinguishes between meaning and syntax during language comprehension. Participants read and made plausibility judgments on sentences that were plausible, morphosyntactically anomalous, or pragmatically anomalous. In an event-related potential (ERP) experiment, morphosyntactic and pragmatic violations elicited significant P600 and N400 effects, respectively, replicating previous ERP studies that have established qualitative differences in processing conceptually and syntactic anomalies. Our main focus was a functional magnetic resonance imaging (fMRI) study in which the same subjects read the same sentences presented in the same pseudorandomized sequence while performing the same task as in the ERP experiment. Rapid-presentation event-related fMRI methods allowed us to estimate the hemodynamic response at successive temporal windows as the sentences unfolded word by word, without assumptions about the shape of the underlying response function. Relative to nonviolated sentences, the pragmatic anomalies were associated with an increased hemodynamic response in left temporal and inferior frontal regions and a decreased response in the right medial parietal cortex. Relative to nonviolated sentences, the morphosyntactic anomalies were associated with an increased response in bilateral medial and lateral parietal regions and a decreased response in left temporal and inferior frontal regions. Thus, overlapping neural networks were modulated in opposite directions to the two types of anomaly. These fMRI findings document both qualitative and quantitative differences in how the brain distinguishes between these two types of anomalies. This suggests that morphosyntactic and pragmatic information can be processed in different ways but by the same neural systems.

Age, working memory, figurative language type, and reading ability: influencing factors in African American adults' comprehension of figurative language

This study investigated the cognitive and linguistic factors presumed to be associated with adult comprehension of figurative language, including age, working memory (WM), figurative language type, and reading comprehension (RC). Forty younger (M = 22 years) and 40 older (M = 63 years) healthy African American adults completed WM and reading tasks, and the 60-item forced-choice multiple-category (20 idioms, 20 metaphors, and 20 metonyms) Figurative Language Comprehension Test. After controlling for WM and RC, the older adults outperformed the younger adults on idioms and metonyms. Metaphor comprehension was comparable between the groups. Findings demonstrate that WM and RC underlie adults' comprehension of figurative language and should be considered when interpreting performance on tests assessing figurative language competence in this population.

Age effects on the neural correlates of successful memory encoding

Event-related functional MRI (fMRI) was used to investigate the neural correlates of memory encoding as a function of age. While fMRI data were obtained, 14 younger (mean age 21 years) and 14 older subjects (mean age 68 years) made animacy decisions about words. Recognition memory for these words was tested at two delays such that older subjects' performance at the short delay was comparable to that of the young subjects at the long delay. This allowed age-associated changes in the neural correlates of encoding to be dissociated from the correlates of differential recognition performance. Activity in left inferior prefrontal cortex and the left hippocampal formation was greater for subsequently recognized words in both age groups, consistent with the findings of previous studies in young adults. In the prefrontal cortex, these 'subsequent memory effects' were, however, left-lateralized in the younger group but bilateral in the older subjects. In addition, for the younger group only, greater activity for remembered words was observed in anterior inferior temporal cortex, as were reversed effects ('subsequent forgetting' effects) in anterior prefrontal regions. The data indicate that older subjects engage much of the same neural circuitry as younger subjects when encoding new memories. However, the findings also point to age-related differences in both prefrontal and temporal activity during successful episodic encoding.

Neuroimaging studies of language production and comprehension

The 1990s were dubbed the "Decade of the Brain." During this time there was a marked increase in the amount of neuroimaging work observing how the brain accomplishes many tasks, including the processing of language. In this chapter we review the past 15 years of neuroimaging research on language production and comprehension. The findings of these studies indicate that the processing involved in language use occurs in diffuse brain regions. These regions include Broca's and Wernicke's areas, primary auditory and visual cortex, and frontal regions in the left hemisphere, as well as in the right hemisphere homologues to these regions. We conclude the chapter by discussing the future of neuroimaging research into language production and comprehension.

What does the frontomedian cortex contribute to language processing: coherence or theory of mind?

The frontomedian cortex (FMC) has been shown to be important for coherence processes in language comprehension, i.e., for establishing the pragmatic connection between successively presented sentences. The same brain region has a role during theory-of-mind processes, i.e., during the attribution of other people's actions to their motivations, beliefs, or emotions. In this study, we used event-related functional magnetic resonance imaging at 3 T to disentangle the relative contributions of the FMC to theory-of-mind (ToM) and coherence processes, respectively. The BOLD response of nine participants was recorded while they listened to pragmatically coherent or unrelated sentence pairs. Using a logic instruction for inanimate sentence pairs, ToM processing was discouraged during the first part of the experiment. Using explicit ToM instructions for sentence pairs mentioning human protagonists, ToM processing was induced during the second part. In three of the resulting four conditions a significant increase in the BOLD response was observed in FMC: when ToM instructions were given, both coherent and incoherent trials elicited frontomedian activation, in replication of previous results showing involvement of the FMC during ToM tasks. When logic instructions were given, the coherent trials, but not the incoherent trials, activated the FMC. These results clearly show that the FMC plays a role in coherence processes even in the absence of concomitant ToM processes. The findings support the view of this cortex having a domain-independent functionality related to volitional aspects of the initiation and maintenance of nonautomatic cognitive processes.

Functional MRI of language: new approaches to understanding the cortical organization of semantic processing

Until recently, our understanding of how language is organized in the brain depended on analysis of behavioral deficits in patients with fortuitously placed lesions. The availability of functional magnetic resonance imaging (fMRI) for in vivo analysis of the normal brain has revolutionized the study of language. This review discusses three lines of fMRI research into how the semantic system is organized in the adult brain. These are (a) the role of the left inferior frontal lobe in semantic processing and dissociations from other frontal lobe language functions, (b) the organization of categories of objects and concepts in the temporal lobe, and (c) the role of the right hemisphere in comprehending contextual and figurative meaning. Together, these lines of research broaden our understanding of how the brain stores, retrieves, and makes sense of semantic information, and they challenge some commonly held notions of functional modularity in the language system.

Asperger syndrome: tests of right hemisphere functioning and interhemispheric communication

The primary aim of this investigation was to assess to what extent Rourke's (1989, 1995) nonverbal learning disabilities syndrome (NLD) model resembles the pattern of assets and deficits seen in people with Asperger syndrome (AS). NLD can be characterized by a cluster of deficits primarily affecting nonverbal aspects of functioning, in the presence of proficiency in single word reading and a superior verbal memory. The neurological underpinnings of this syndrome may be dysfunction of white matter affecting right hemisphere functioning and interhemispheric communication. To explore this hypothesis, eight participants with AS (ages 10 to 41 years) were assessed in the following areas: the pragmatics of language and communication, verbal and visual memory, visual-spatial abilities, and bimanual motor skills. Results confirmed the close similarity in the neuropsychologic profiles of NLD and AS.

The brain circuitry of syntactic comprehension

Syntactic comprehension is a fundamental aspect of human language, and has distinct properties from other aspects of language (e.g. semantics). In this article, we aim to identify if there is a specific locus of syntax in the brain by reviewing imaging studies on syntactic processing. We conclude that results from neuroimaging support evidence from neuropsychology that syntactic processing does not recruit one specific area. Instead a network of areas including Broca's area and anterior, middle and superior areas of the temporal lobes is involved. However, none of these areas appears to be syntax specific.

Degree of language lateralization determines susceptibility to unilateral brain lesions

Language is considered a function of either the left or, in exceptional cases, the right side of the brain. Functional imaging studies show, however, that in the general population a graded continuum from left hemispheric to right hemispheric language lateralization exists. To determine the functional relevance of lateralization differences, we suppressed language regions using transcranial magnetic stimulation (TMS) in healthy human subjects who differed in lateralization of language-related brain activation. Language disruption correlated with both the degree and side of lateralization. Subjects with weak lateralization (more bilaterality) were less affected by either left- or right-side TMS than were subjects with strong lateralization to one hemisphere. Thus in some people, language processing seems to be distributed evenly between the hemispheres, allowing for ready compensation after a unilateral lesion.

Functional networks in emotional moral and nonmoral social judgments

Reading daily newspaper articles often evokes opinions and social judgments about the characters and stories. Social and moral judgments rely on the proper functioning of neural circuits concerned with complex cognitive and emotional processes. To examine whether dissociable neural systems mediate emotionally charged moral and nonmoral social judgments, we used a visual sentence verification task in conjunction with functional magnetic resonance imaging (fMRI). We found that a network comprising the medial orbitofrontal cortex, the temporal pole and the superior temporal sulcus of the left hemisphere was specifically activated by moral judgments. In contrast, judgment of emotionally evocative, but non-moral statements activated the left amygdala, lingual gyri, and the lateral orbital gyrus. These findings provide new evidence that the orbitofrontal cortex has dedicated subregions specialized in processing specific forms of social behavior.

The response of left temporal cortex to sentences

The meaning of a sentence differs from the sum of the meanings of its constituents. Left anterior temporal cortex responds to sentences more strongly than to unconnected words. We hypothesized that the anterior temporal response to sentences is due to this difference in meaning (compositional semantics). Using positron emission tomography (PET), we studied four experimental conditions (2 x 2 factorial design): In one condition, subjects read normal sentences. In a second condition, they read grammatically correct sentences containing numerous semantic violations (semantically random sentences). In a third condition, we scrambled the word order within the normal sentences, and, in a fourth condition, the word order was scrambled within the semantically random sentences. The left anterior temporal pole responded strongly to sentences compared to scrambled versions of sentences. A similar although weaker response occurred in the left anterior superior temporal sulcus and the left posterior middle temporal gyrus. A subset of voxels within the left anterior temporal pole responded more to semantically random sentences and their scrambled versions than to normal sentences and the corresponding scrambled versions (main effect of semantic randomness). Finally, the grammatical and the semantic factor interacted in a subset of voxels within the anterior temporal pole: Activity was higher when subjects read normal sentences compared to their scrambled versions but not for semantically random sentences compared to their corresponding scrambled versions. The effects of grammar and meaning and, most importantly, the interaction between grammatical and semantic factors are compatible with the hypothesis that the left anterior temporal pole contributes to the composition of sentence meaning.

A PET study of stimulus- and task-induced semantic processing

To investigate the neural correlates of semantic processing, previous functional imaging studies have used semantic decision and generation tasks. However, in addition to activating semantic associations these tasks also involve executive functions that are not specific to semantics. The study reported in this paper aims to dissociate brain activity due to stimulus-driven semantic associations and task-induced semantic and executive processing by using repetition and semantic decision on auditorily presented words in a cognitive conjunction design. The left posterior inferior temporal, inferior frontal (BA 44/45), and medial orbital gyri were activated by both tasks, suggesting a general role in stimulus-driven semantic and phonological processing. In addition, semantic decision increased activation in (i) left ventral inferior frontal cortex (BA 47), right cerebellum, and paracingulate, which have all previously been implicated in executive functions, and (ii) a ventral region in the left anterior temporal pole which is commonly affected in patients with semantic impairments. We attribute activation in this area to the effortful linkage of semantic features. Thus, our study replicated the functional dissociation between dorsal and ventral regions of the left inferior frontal cortex. Moreover, it also dissociated the semantic functions of the left posterior inferior temporal gyrus and anterior temporal pole: The posterior region subserves stimulus-driven activation of semantic associations and the left anterior region is involved in task-induced association of semantic information.

Story processing in patients with damage to the prefrontal cortex

The prefrontal cortex is known to be involved in performing complex cognitive tasks requiring reasoning, planning and decision-making. Neuropsychological evidence also supports the idea that the prefrontal cortex is generally involved in encoding and retrieving complex events, such as action and narrative knowledge. Patients with frontal lobe damage are reported to have difficulty in processing different aspects of narrative representations, such as the figurative moral meaning, syntactic features, and inference generation. In the present study, we examined story processing in 17 patients with frontal lobe lesions and compared their performance to 7 amnesic patients and 17 normal controls. Two stories were presented by using two slightly different processing demands in order to assess the subject's ability to draw inferences on-line during the course of comprehension or later retrieval. Although all patients had impaired story memory, patients with frontal lobe lesions showed a pattern of deficit at an early stage of story comprehension that specifically involved the ability to reconstruct the sequential links among events and to extract inferential knowledge from the text during encoding. Amnesic patients were severely impaired in recalling story semantic units, including single events and larger narrative constituents, as well as in the event recognition task. Consequently, they were unable to establish inferential relations among the events and, thus, the global sequential structure of the stories during retrieval. In contrast, they had no difficulty in extracting inferential knowledge during story comprehension on the basis of readily available information. This study shows that damage to different cortical regions may induce impairments at various levels of story processing.

Sentence processing strategies in healthy seniors with poor comprehension: an fMRI study

We used fMRI to examine patterns of brain recruitment in 22 healthy seniors, half of whom had selective comprehension difficulty for grammatically complex sentences. We found significantly reduced recruitment of left posterolateral temporal [Brodmann area (BA) 22/21] and left inferior frontal (BA 44/6) cortex in poor comprehenders compared to the healthy seniors with good sentence comprehension, cortical regions previously associated with language comprehension and verbal working memory, respectively. The poor comprehenders demonstrated increased activation of left prefrontal (BA 9/46), right dorsal inferior frontal (BA 44/6), and left posterior cingulate (BA 31/23) cortices for the grammatically simpler sentences that they understood. We hypothesize that these brain regions support an alternate, nongrammatical strategy for processing complex configurations of symbolic information. Moreover, these observations emphasize the crucial role of the left perisylvian network for grammatically guided sentence processing in subjects with good comprehension.

Making sense during conversation: an fMRI study

Although language is thought of as a left hemisphere function, there is increasing evidence that the right hemisphere contributes to language processing by identifying the theme of spoken and written language. Using fMRI, we examined the role played by the right and left hemispheres in making sense of a conversation. When this process involves implicit appraisal of changes in the conversation's topic, the neural network has a right hemisphere bias and includes Broca's and Wernicke's areas, their right hemisphere homologues, right dorsolateral prefrontal cortex, and the cerebellum. When making sense of conversation involves appraisal of the conversation's reasoning, however, the network includes Broca's and Wernicke's areas. Thus, right and left hemisphere systems contribute uniquely to the linguistic skills involved in making sense of a conversation.

Brain activation during automatic and controlled processing of semantic relations: a priming experiment using lexical-decision

Semantic relations may be studied using the experimental technique known as semantic priming, in which a word 'primes' the processing of a related target (e.g. lion-tiger), following a short delay. Priming may be automatic or, with longer delays, under more controlled processing. This study used functional magnetic resonance imaging (fMRI) to examine the cerebral activation during two lexical-decision semantic priming experiments, with a short and long delay, representing automatic and controlled processing, respectively. A further two un-primed lexical-decision tasks were performed to distinguish cerebral activation specific to semantic priming itself from those utilised during lexical-decision processes. Distinct regions of anterior cingulate cortex (ACC) were critical to automatic and controlled semantic priming, whilst the putamen and hippocampal complex responded differently to unrelated and semantically related prime-target pairs. Lexical-decision alone revealed activation in posterior temporal cortex especially on the left, in agreement with previous neuroimaging studies. The results provide a plausible neural substrate for common semantic relations independent of task demands and further emphasise the regional functional specialisation of the ACC.

Functional MRI of language processing: dependence on input modality and temporal lobe epilepsy

PURPOSE

Functional magnetic resonance imaging (MRI) using two language-comprehension tasks was evaluated to determine its ability to lateralize language processing and identify regions that must be spared in surgery.

METHODS

Two parallel cognitive language tasks, one using auditory input and the other visual input, were tested in a group of control subjects and in temporal lobe epilepsy patients who were candidates for surgical intervention. The patient studies provide an opportunity to compare functional MRI language localization with that obtained using Wada testing and electrocorticography. All of the patients in this study underwent all three procedures and a battery of neuropsychological testing. Such studies provide an opportunity not only to validate the fMRI findings but also, by comparing the patient results with those obtained in control subjects, to provide insight into the impact of a pathology such as epilepsy on cortical organization or functional patterns of activation.

RESULTS

The results reveal both modality-dependent and modality-independent language-processing patterns for visual versus auditory task presentation. The visual language task activated distinct sites in Broca's area, BA (Brodmann area) 44 that were not activated in the auditory language task. The auditory language task strongly activated contralateral right BA22-21 area (homologous to Wernicke's area on the left). Language lateralization scores were significantly stronger for visual than for auditory task presentation. The conjunction of activation from the two different input modalities (modality-independent areas) likely highlights regions that perform more abstract computations (e.g., syntactic or pragmatic processing) in language processing. Modality-specific areas (e.g., right Wernicke, left fusiform gyrus, Broca BA44, supramarginal gyrus), appear to cope with the computations relevant to making contact with these more abstract dimensions. Patients showed recruitment of contralateral homologous language areas (p < 0.005) that was significantly above that found in a normal control group. Extra- and intraoperative cortical stimulations were concordant with the fMRI data in eight of 10 cases. The fMRI lateralization scores were also consistent with the Wada testing in 8/10 patients.

CONCLUSIONS

The fMRI results demonstrate that the epileptic brain may be a progressive model for cortical plasticity.

Frontopolar and anterior temporal cortex activation in a moral judgment task: preliminary functional MRI results in normal subjects

OBJECTIVE

To study the brain areas which are activated when normal subjects make moral judgments.

METHOD

Ten normal adults underwent BOLD functional magnetic resonance imaging (fMRI) during the auditory presentation of sentences that they were instructed to silently judge as either "right" or "wrong". Half of the sentences had an explicit moral content ("We break the law when necessary"), the other half comprised factual statements devoid of moral connotation ("Stones are made of water"). After scanning, each subject rated the moral content, emotional valence, and judgment difficulty of each sentence on Likert-like scales. To exclude the effect of emotion on the activation results, individual responses were hemodynamically modeled for event-related fMRI analysis. The general linear model was used to evaluate the brain areas activated by moral judgment.

RESULTS

Regions activated during moral judgment included the frontopolar cortex (FPC), medial frontal gyrus, right anterior temporal cortex, lenticular nucleus, and cerebellum. Activation of FPC and medial frontal gyrus (BA 10/46 and 9) were largely independent of emotional experience and represented the largest areas of activation.

CONCLUSIONS

These results concur with clinical observations assigning a critical role for the frontal poles and right anterior temporal cortex in the mediation of complex judgment processes according to moral constraints. The FPC may work in concert with the orbitofrontal and dorsolateral cortex in the regulation of human social conduct.

The effects of case mixing on word recognition: evidence from a PET study

The early stages of visual word recognition were investigated by scanning participants using PET as they took part in implicit and explicit reading tasks with visually disrupted stimuli. CaSe MiXiNg has been shown in behavioral studies to increase reaction times (RTs) in naming and other word recognition tasks. In this study, we found that during both an implicit (feature detection) task and an explicit word-naming task, mixed-case words compared to same-case words produced increased activation in an area of the right parietal cortex previously associated with visual attention. No effect of case was found in this area for pseudowords or consonant strings. Further, lowering the contrast of the stimuli slowed RTs as much as case mixing, but did not lead to the same increase in right parietal activation. No significant effect of case mixing was observed in left-hemisphere language areas. The results suggest that reading mixed-case words requires increased attentional processing. However, later word recognition processes may be relatively unaffected by the disruption in presentation.

Mind reading: neural mechanisms of theory of mind and self-perspective

Human self-consciousness as the metarepresentation of ones own mental states and the so-called theory of mind (TOM) capacity, which requires the ability to model the mental states of others, are closely related higher cognitive functions. We address here the issue of whether taking the self-perspective (SELF) or modeling the mind of someone else (TOM) employ the same or differential neural mechanisms. A TOM paradigm was used and extended to include stimulus material that involved TOM and SELF capacities in a two-way factorial design. A behavioral study in 42 healthy volunteers showed that TOM and SELF induced differential states of mind: subjects assigned correctly first or third person pronouns when providing responses to the stimuli. Following the behavioral study, we used functional magnetic resonance imaging (fMRI) in eight healthy, right-handed males to study the common and differential neural mechanisms underlying TOM and SELF. The main factor TOM led to increased neural activity in the anterior cingulate cortex and left temporopolar cortex. The main factor SELF led to increased neural activity in the right temporoparietal junction and in the anterior cingulate cortex. A significant interaction of both factors TOM and SELF was observed in the right prefrontal cortex. These divergent neural activations in response to TOM and SELF suggest that these important differential mental capacities of human self-consciousness are implemented at least in part in distinct brain regions. Press

The role of coherence and cohesion in text comprehension: an event-related fMRI study

Text processing requires inferences for establishing coherence between successive sentences. In neuropsychological studies and brain imaging studies, these coherence-building processes have been ascribed to the right hemisphere. On the other hand, there is evidence for prefrontal brain damage causing non-aphasic language disorders, in which text level processes are impaired. In this study, we used an event-related, whole-head fMRI methodology to evaluate the contributions of prefrontal areas and the right hemisphere to coherence building. We scanned 12 participants while they read 120 sentence pairs and judged their coherence. Four conditions were used, resulting from crossing coherence and cohesion (i.e. the presence of a lexical connection). A behavioral pretest confirmed that cohesion aided establishing coherence, whereas it hindered the detection of coherence breaks. In the fMRI study, all language conditions yielded activation in left frontolateral and temporolateral regions, when compared to a physical control task. The differences due to coherence of the sentence pairs were most evident in larger activation for coherent as compared to incoherent sentence pairs in the left frontomedian wall, but also in posterior cingulate and precuneal regions. Finally, a left inferior prefrontal area was sensitive to the difficulty of the task, and in particular to the increase in processing costs when cohesion falsely indicated coherence. These results could not provide evidence for a special involvement of the right hemisphere during inferencing. Rather, they suggest that the left frontomedian cortex plays an important role in coherence building.

Differential activation of temporal cortex during sentence completion in schizophrenic patients with and without formal thought disorder

The neural correlates of processing linguistic context in schizophrenic patients with formal thought disorder (FTD) were examined. Six right-handed male patients with prominent 'positive' FTD were compared with six schizophrenic patients without FTD and seven volunteers, matched for cognitive and demographic variables. Functional magnetic resonance imaging (IMRI) was used to measure cerebral activation while subjects read and completed sentence stems out loud. During a GENERATION condition, subjects were required to generate a word which completed the sentence stem appropriately. During a DECISION condition, subjects selected and articulated one of two presented terminal words. A READING condition served as baseline. The three conditions were compared with each other. Regions activated were identified in each group, and between-group differences were detected using an ANCOVA. When GENERATION was compared with READING, FTD patients showed less activation in the right superior temporal gyrus than patients without FTD or controls, but greater activation in the left inferior frontal, inferior temporal and fusiform gyri. FTD patients also showed an attenuated right temporal response when GENERATION was compared with DECISION. This differential engagement of the right temporal cortex was independent of differences in the speed or accuracy of responses, whereas the left fronto-temporal differences in activation were not evident after covarying for task errors. The attenuated engagement of right temporal cortex, which is implicated in language comprehension at the discourse level, is consistent with neuropsychological evidence linking thought disorder with deficits in processing linguistic context.

Memory and encoding of spoken discourse following right hemisphere damage: evidence from the Auditory Moving Window (AMW) technique

We investigated the hypotheses that impaired discourse processing following right hemisphere damage is mediated by task difficulty and is associated with deficits in discourse encoding. Spoken discourse passages differing in contextual predictability were presented to right hemisphere-damaged (RHD) patients and to non-brain-damaged (NBD) controls for subsequent recall using the Auditory Moving Window paradigm. To manipulate processing difficulty, speech segments were of normal or accelerated speech rates. The recall results showed that RHD adults recalled less than NBD controls overall and failed to recall major idea units better than minor idea units for high predictability passages presented at accelerated speech rates. Both RHD patients and NBD controls failed to recall major idea units better than minor idea units for low predictability passages, regardless of speech rate. The encoding results showed that RHD adults were both slower overall and differentially slower than NBD controls when listening to accelerated passage segments. Taken together, the encoding and recall results are consistent with the view that extracting passage gist under difficult listening conditions is especially vulnerable for patients with right hemisphere strokes.

The effect of stimulus-response compatibility on cortical motor activation

Stimulus-response compatibility (SRC) is a general term describing the relationship between a triggering stimulus and its associated motor response. The relationship between stimulus and response can be manipulated at the level of the set of stimulus and response characteristics (set-level) or at the level of the mapping between the individual elements of the stimulus and response sets (element-level). We used functional magnetic resonance imaging (fMRI) to investigate the effects of SRC on functional activation in cortical motor areas. Using behavioral tasks to separately evaluate set- and element-level compatibility, and their interaction, we measured the volume of functional activation in 11 cortical motor areas, in the anterior frontal cortex, and in the superior temporal lobe. Element-level compatibility effects were associated with significant activation in the pre-supplementary motor area (preSMA), the dorsal (PMd) and ventral (PMv) premotor areas, and the parietal areas (inferior, superior, intraparietal sulcus, precuneus). The activation was lateralized to the right hemisphere for most of the areas. Set-level compatibility effects resulted in significant activation in the inferior frontal gyri, anterior cingulate and cingulate motor areas, the PMd, PMv, preSMA, the parietal areas (inferior, superior, intraparietal sulcus, precuneus), and in the superior temporal lobe. Activation in the majority of these areas was lateralized to the left hemisphere. Finally, there was an interaction between set and element-level compatibility in the middle and superior frontal gyri, in an area co-extensive with the dorsolateral prefrontal cortex, suggesting that this area provided the neural substrate for common processing stages, such as working memory and attention, which are engaged when both levels of SRC are manipulated at once.

Engagement of right temporal cortex during processing of linguistic context

Language processing involves the interplay of areas in both cerebral hemispheres. Whereas the left temporal lobe is necessary for most language tasks, the right hemisphere seems to be additionally activated during processing of paragraphs and metaphors. We studied the neural correlates of word generation and selection in a sentence context, using functional magnetic resonance imaging (fMRI). Cerebral activation was measured while seven healthy, right handed volunteers read and completed sentence stems, with relatively low Cloze frequency, out loud. During a GENERATION condition, subjects were required to generate a word which completed a sentence stem appropriately. During a DECISION condition, subjects selected and articulated one of two presented terminal words. A READING condition in which subjects read an appropriate completion aloud, served as baseline. When GENERATION was compared to READING or DECISION, the left middle frontal, anterior cingulate, precuneus and right lateral temporal cortex were activated. During DECISION relative to READING, the left inferior frontal and middle/superior temporal cortex bilaterally were activated. The prominent engagement of the right lateral temporal cortex during the GENERATION conditions may reflect the processing of linguistic context, and particularly the activation of multiple meanings in the course of producing an appropriate completion.

The anatomy of language: contributions from functional neuroimaging

This article illustrates how functional neuroimaging can be used to test the validity of neurological and cognitive models of language. Three models of language are described: the 19th Century neurological model which describes both the anatomy and cognitive components of auditory and visual word processing, and 2 20th Century cognitive models that are not constrained by anatomy but emphasise 2 different routes to reading that are not present in the neurological model. A series of functional imaging studies are then presented which show that, as predicted by the 19th Century neurologists, auditory and visual word repetition engage the left posterior superior temporal and posterior inferior frontal cortices. More specifically, the roles Wernicke and Broca assigned to these regions lie respectively in the posterior superior temporal sulcus and the anterior insula. In addition, a region in the left posterior inferior temporal cortex is activated for word retrieval, thereby providing a second route to reading, as predicted by the 20th Century cognitive models. This region and its function may have been missed by the 19th Century neurologists because selective damage is rare. The angular gyrus, previously linked to the visual word form system, is shown to be part of a distributed semantic system that can be accessed by objects and faces as well as speech. Other components of the semantic system include several regions in the inferior and middle temporal lobes. From these functional imaging results, a new anatomically constrained model of word processing is proposed which reconciles the anatomical ambitions of the 19th Century neurologists and the cognitive finesse of the 20th Century cognitive models. The review focuses on single word processing and does not attempt to discuss how words are combined to generate sentences or how several languages are learned and interchanged. Progress in unravelling these and other related issues will depend on the integration of behavioural, computational and neurophysiological approaches, including neuroimaging.

The right hemisphere maintains solution-related activation for yet-to-be-solved problems

In five experiments, we examined the time course of hemispheric differences in solution activation for insight-like problems. We propose that solving insight problems requires retrieval of unusual interpretations of problem elements, and that right-hemisphere (RH) coarse semantic coding is more likely than left-hemisphere (LH) fine semantic coding to maintain semantic activation of such interpretations. In four experiments, participants attempted word problems for 7 sec (Experiments 1A and 1B) or 2 sec (Experiments 2A and 2B), and 750 msec later responded to lateralized target words. After 7 sec of solving effort, Experiment 1A participants showed greater solution-related priming (i.e., they named solutions faster than unrelated words) for left visual field-RH (lvf-RH) targets than for right visual field-LH (rvf-LH) targets, and Experiment 1B participants made faster solution decisions on target words presented to the RH, as previously demonstrated following 15 sec of effort. After 2 sec of solving effort in Experiment 2A, women showed symmetric solution-related priming, although men showed a slight lvf-RH advantage in priming; and in Experiment 2B participants made equally quick solution decisions for targets presented to the LH and to the RH. In Experiment 3, participants viewed the problems for 1,250 msec then named lateralized target words; they showed symmetric solution-related priming. These experiments demonstrate solution activation initially in both hemispheres, but maintained solution activation only in the RH.

Movement and mind: a functional imaging study of perception and interpretation of complex intentional movement patterns

We report a functional neuroimaging study with positron emission tomography (PET) in which six healthy adult volunteers were scanned while watching silent computer-presented animations. The characters in the animations were simple geometrical shapes whose movement patterns selectively evoked mental state attribution or simple action description. Results showed increased activation in association with mental state attribution in four main regions: medial prefrontal cortex, temporoparietal junction (superior temporal sulcus), basal temporal regions (fusiform gyrus and temporal poles adjacent to the amygdala), and extrastriate cortex (occipital gyrus). Previous imaging studies have implicated these regions in self-monitoring, in the perception of biological motion, and in the attribution of mental states using verbal stimuli or visual depictions of the human form. We suggest that these regions form a network for processing information about intentions, and speculate that the ability to make inferences about other people's mental states evolved from the ability to make inferences about other creatures' actions.

Interhemispheric inhibition, intrahemispheric activation, and lexical capacities of the right hemisphere: a tachistoscopic, divided visual-field study in normal subjects

This study proposes that the lexical-semantic capacities of the right hemisphere (RH) are underestimated in normal subjects and reexamines them in a "dynamic model" framework. As expected, overloading the left hemisphere by combining a lexical-decision task presented in divided visual field with a concurrent heavy verbal memory load, and activating the RH by combining the lexical-decision task with a concurrent visuo-imaged memory load, lead to enhanced left visual field-RH lexical performance. The RH appears to support a larger lexical-semantic network than suggested in the literature, including representations for long and nonimageable words, and the accessibility threshold for the representations stored therein is modulated by hemispheric activation-inhibition mechanisms.

Recognition of emotional prosody and verbal components of spoken language: an fMRI study

This study examined the neural areas involved in the recognition of both emotional prosody and phonemic components of words expressed in spoken language using echo-planar, functional magnetic resonance imaging (fMRI). Ten right-handed males were asked to discriminate words based on either expressed emotional tone (angry, happy, sad, or neutral) or phonemic characteristics, specifically, initial consonant sound (bower, dower, power, or tower). Significant bilateral activity was observed in the detection of both emotional and verbal aspects of language when compared to baseline activity. We found that the detection of emotion compared with verbal detection resulted in significant activity in the right inferior frontal lobe. Conversely, the detection of verbal stimuli compared with the detection of emotion activated left inferior frontal lobe regions most significantly. Specific analysis of the anterior auditory cortex revealed increased right hemisphere activity during the detection of emotion compared to activity during verbal detection. These findings illustrate bilateral involvement in the detection of emotion in language while concomitantly showing significantly lateralized activity in both emotional and verbal detection, in both the temporal and frontal lobes.

Functional neuroanatomy of the cognitive process of mapping during discourse comprehension

We used functional magnetic resonance imaging (fMRI) to identify brain regions involved in the process of mapping coherent discourse onto a developing mental representation. We manipulated discourse coherence by presenting sentences with definite articles (which lead to more coherent discourse) or indefinite articles (which lead to less coherent discourse). Comprehending connected discourse, compared with reading unrelated sentences, produced more neural activity in the right than left hemisphere of the frontal lobe. Thus, the right hemisphere of the frontal lobe is involved in some of the processes underlying mapping. In contrast, left-hemisphere structures were associated with lower-level processes in reading (such as word recognition and syntactic processing). Our results demonstrate the utility of using fMRI to investigate the neural substrates of higher-level cognitive processes such as discourse comprehension.

Common and distinct neural substrates for pragmatic, semantic, and syntactic processing of spoken sentences: an fMRI study

Extracting meaning from speech requires the use of pragmatic, semantic, and syntactic information. A central question is: Does the processing of these different types of linguistic information have common or distinct neuroanatomical substrates? We addressed this issue using functional magnetic resonance imaging (fMRI) to measure neural activity when subjects listened to spoken normal sentences contrasted with sentences that had either (A) pragmatical, (B) semantic (selection restriction), or (C) syntactic (subcategorical) violations sentences. All three contrasts revealed robust activation of the left-inferior-temporal/fusiform gyrus. Activity in this area was also observed in a combined analysis of all three experiments, suggesting that it was modulated by all three types of linguistic violation. Planned statistical comparisons between the three experiments revealed (1) a greater difference between conditions in activation of the left-superior-temporal gyrus for the pragmatic experiment than the semantic/syntactic experiments; (2) a greater difference between conditions in activation of the right-superior and middle-temporal gyrus in the semantic experiment than in the syntactic experiment; and (3) no regions activated to a greater degree in the syntactic experiment than in the semantic experiment. These data show that, while left- and right-superior-temporal regions may be differentially involved in processing pragmatic and lexico-semantic information within sentences, the left-inferior-temporal/fusiform gyrus is involved in processing all three types of linguistic information. We suggest that this region may play a key role in using pragmatic, semantic (selection restriction), and subcategorical information to construct a higher representation of meaning of sentences.