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.     

Segregating semantic and syntactic aspects of processing in the human brain: an fMRI investigation of different word types

The processing of single words that varied in their semantic (concrete/abstract word) and syntactic (content/function word) status was investigated under different task demands (semantic/ syntactic task) in an event-related functional magnetic resonance imaging experiment. Task demands to a large degree determined which subparts of the neuronal network supporting word processing were activated. Semantic task demands selectively activated the left pars triangularis of the inferior frontal gyrus (BA 45) and the posterior part of the left middle/superior temporal gyrus (BA 21/22/37). In contrast, syntactic processing requirements led to an increased activation in the inferior tip of the left frontal operculum (BA 44) and the cortex lining the junction of the inferior frontal and inferior precentral sulcus (BA 44/6). Moreover, for these latter areas a word class by concreteness interaction was observed when a syntactic judgement was required. This interaction can be interpreted as a prototypicality effect: non-prototypical members of a word class, i.e. concrete function words and abstract content words, showed a larger activation than prototypical members, i.e. abstract function words and concrete content words. The combined data suggest that the activation pattern underlying word processing is predicted neither by syntactic class nor semantic concreteness but, rather, by task demands focusing either on semantic or syntactic aspects. Thus, our findings that semantic and syntactic aspects of processing are both functionally distinct and involve different subparts of the neuronal network underlying word processing support a domain-specific organization of the language system.     

Specific brain networks during explicit and implicit decoding of emotional prosody

To better define the underlying brain network for the decoding of emotional prosody, we recorded high-resolution brain scans during an implicit and explicit decoding task of angry and neutral prosody. Several subregions in the right superior temporal gyrus (STG) and bilateral in the inferior frontal gyrus (IFG) were sensitive to emotional prosody. Implicit processing of emotional prosody engaged regions in the posterior superior temporal gyrus (pSTG) and bilateral IFG subregions, whereas explicit processing relied more on mid STG, left IFG, amygdala, and subgenual anterior cingulate cortex. Furthermore, whereas some bilateral pSTG regions and the amygdala showed general sensitivity to prosody-specific acoustical features during implicit processing, activity in inferior frontal brain regions was insensitive to these features. Together, the data suggest a differentiated STG, IFG, and subcortical network of brain regions, which varies with the levels of processing and shows a higher specificity during explicit decoding of emotional prosody.     

The neural mechanisms of speech comprehension: fMRI studies of semantic ambiguity

A number of regions of the temporal and frontal lobes are known to be important for spoken language comprehension, yet we do not have a clear understanding of their functional role(s). In particular, there is considerable disagreement about which brain regions are involved in the semantic aspects of comprehension. Two functional magnetic resonance studies use the phenomenon of semantic ambiguity to identify regions within the fronto-temporal language network that subserve the semantic aspects of spoken language comprehension. Volunteers heard sentences containing ambiguous words (e.g. 'the shell was fired towards the tank') and well-matched low-ambiguity sentences (e.g. 'her secrets were written in her diary'). Although these sentences have similar acoustic, phonological, syntactic and prosodic properties (and were rated as being equally natural), the high-ambiguity sentences require additional processing by those brain regions involved in activating and selecting contextually appropriate word meanings. The ambiguity in these sentences goes largely unnoticed, and yet high-ambiguity sentences produced increased signal in left posterior inferior temporal cortex and inferior frontal gyri bilaterally. Given the ubiquity of semantic ambiguity, we conclude that these brain regions form an important part of the network that is involved in computing the meaning of spoken sentences.     

Idiom comprehension: a prefrontal task?

We investigated the neural correlates of idiomatic sentence processing using event-related functional magnetic resonance imaging. Twenty-two healthy subjects were presented with 62 literal sentences and 62 idiomatic sentences, each followed by a picture and were required to judge whether the sentence matched the picture or not. A common network of cortical activity was engaged by both conditions, with the nonliteral task eliciting overall greater activation, both in terms of magnitude and spatial extent. The network that was specifically activated by the nonliteral condition involved the left temporal cortex, the left superior medial frontal gyrus (Brodmann area 9), and the left inferior frontal gyrus (IFG). Activations were also present in the right superior and middle temporal gyri and temporal pole and in the right IFG. In contrast, literal sentences selectively activated the left inferior parietal lobule and the right supramarginal gyrus. An analysis of effective connectivity indicated that the medial prefrontal area significantly increased the connection between frontotemporal areas bilaterally during idiomatic processing. Overall, the present findings indicate a crucial role of the prefrontal cortex in idiom comprehension, which could reflect the selection between alternative sentence meanings.     

An event-related fMRI study of explicit syntactic processing of normal/anomalous sentences in contrast to implicit syntactic processing

Using event-related functional magnetic resonance imaging (fMRI), we examined activation of cortical language areas for explicit syntactic processing. In a syntactic decision (Syn) task, the participants judged whether the presented sentence was syntactically correct, where syntactic knowledge about the distinction between transitive and intransitive verbs was required. In a semantic decision (Sem) task, lexico-semantic knowledge about selectional restrictions was indispensable. In a phonological decision (Pho) task, phonological knowledge about accent patterns was required. The Sem and Pho tasks involved implicit syntactic processing, as well as explicit semantic and phonological processing, respectively. We also tested a voice-pitch comparison (Voi) task in which no explicit linguistic knowledge was required. In the direct comparison of Syn - (Sem + Pho + Voi), we found localized activation in the left inferior frontal gyrus (F3op/F3t), indicating that activation of the left F3op/F3t is more prominently enhanced in explicit syntactic processing than in implicit syntactic processing. Moreover, we determined that its activation is selective to syntactic judgments regarding both normal and anomalous sentences. These results suggest that explicit information processing in the syntactic domain critically involves the left F3op/F3t, which is functionally separable from other regions.     

Category-specific conceptual processing of color and form in left fronto-temporal cortex

To investigate the cortical basis of color and form concepts, we examined event-related functional magnetic resonance imaging (fMRI) responses to matched words related to abstract color and form information. Silent word reading elicited activity in left temporal and frontal cortex, where category-specific activity differences were also observed. Whereas color words preferentially activated anterior parahippocampal gyrus, form words evoked category-specific activity in fusiform and middle temporal gyrus as well as premotor and dorsolateral prefrontal areas in inferior and middle frontal gyri. These results demonstrate that word meanings and concepts are not processed by a unique cortical area, but by different sets of areas, each of which may contribute differentially to conceptual semantic processing. We hypothesize that the anterior parahippocampal activation to color words indexes computation of the visual feature conjunctions and disjunctions necessary for classifying visual stimuli under a color concept. The predominant premotor and prefrontal activation to form words suggests action-related information processing and may reflect the involvement of neuronal elements responding in an either-or fashion to mirror neurons related to adumbrating shapes.     

Sound to language: different cortical processing for first and second languages in elementary school children as revealed by a large-scale study using fNIRS

A large-scale study of 484 elementary school children (6-10 years) performing word repetition tasks in their native language (L1-Japanese) and a second language (L2-English) was conducted using functional near-infrared spectroscopy. Three factors presumably associated with cortical activation, language (L1/L2), word frequency (high/low), and hemisphere (left/right), were investigated. L1 words elicited significantly greater brain activation than L2 words, regardless of semantic knowledge, particularly in the superior/middle temporal and inferior parietal regions (angular/supramarginal gyri). The greater L1-elicited activation in these regions suggests that they are phonological loci, reflecting processes tuned to the phonology of the native language, while phonologically unfamiliar L2 words were processed like nonword auditory stimuli. The activation was bilateral in the auditory and superior/middle temporal regions. Hemispheric asymmetry was observed in the inferior frontal region (right dominant), and in the inferior parietal region with interactions: low-frequency words elicited more right-hemispheric activation (particularly in the supramarginal gyrus), while high-frequency words elicited more left-hemispheric activation (particularly in the angular gyrus). The present results reveal the strong involvement of a bilateral language network in children's brains depending more on right-hemispheric processing while acquiring unfamiliar/low-frequency words. A right-to-left shift in laterality should occur in the inferior parietal region, as lexical knowledge increases irrespective of language.     

Functional MRI of sentence comprehension in children with dyslexia: beyond word recognition

Sentence comprehension (SC) studies in typical and impaired readers suggest that reading for meaning involves more extensive brain activation than reading isolated words. Thus far, no reading disability/dyslexia (RD) studies have directly controlled for the word recognition (WR) components of SC tasks, which is central for understanding comprehension processes beyond WR. This experiment compared SC to WR in 29, 9-14 year olds (15 typical and 14 impaired readers). The SC-WR contrast for each group showed activation in left inferior frontal and extrastriate regions, but the RD group showed significantly more activation than Controls in areas associated with linguistic processing (left middle/superior temporal gyri), and attention and response selection (bilateral insula, right cingulate gyrus, right superior frontal gyrus, and right parietal lobe). Further analyses revealed this overactivation was driven by the RD group's response to incongruous sentences. Correlations with out-of-scanner measures showed that better word- and text-level reading fluency was associated with greater left occipitotemporal activation, whereas worse performance on WR, fluency, and comprehension (reading and oral) were associated with greater right hemisphere activation in a variety of areas, including supramarginal and superior temporal gyri. Results provide initial foundations for understanding the neurobiological correlates of higher-level processes associated with reading comprehension.     

Dissociating frontotemporal contributions to semantic ambiguity resolution in spoken sentences

Comprehension of sentences containing semantically ambiguous words requires listeners to select appropriate interpretations, maintain linguistic material in working memory, and to reinterpret sentences that have been misinterpreted. All these functions appear to involve frontal cortical regions. Here, we attempt to differentiate these functions by varying the relative timing of an ambiguous word and disambiguating information in spoken sentences. We compare the location, magnitude, and timing of evoked activity using a fast-acquisition semisparse functional magnetic resonance imaging sequence. The left inferior frontal gyrus (LIFG) shows a strong response to sentences that are initially ambiguous (disambiguated by information that occurs either soon after the ambiguity or that is delayed until the end of the sentence). Response profiles indicate that activity, in both anterior and posterior LIFG regions, is triggered both by the ambiguous word and by the subsequent disambiguating information. The LIFG also responds to ambiguities that are preceded by disambiguating context. These results suggest that the LIFG subserves multiple cognitive processes including selecting an appropriate meaning and reinterpreting sentences that have been misparsed. In contrast, the left inferior temporal gyrus responds to the disambiguating information but not to the ambiguous word itself and may be involved in reprocessing sentences that were initially misinterpreted.     

Human neural systems for conceptual knowledge of proper object use: a functional magnetic resonance imaging study

Ideational apraxia is characterized by impaired knowledge of action concepts and proper object usage. The present functional magnetic resonance imaging study aimed at investigating the neural system underlying conceptual knowledge for proper object use in healthy subjects, when the effects of visuospatial properties and perceptual modality were taken into account. Subjects performed semantic decision tasks requiring retrieval of knowledge about either object functional purposes (functional task) or visuospatial object properties (visuospatial task) and perceptual control tasks. The semantic tasks were performed with pairs of either written object names or object drawings. Activation for the functional task in common for words and pictures, compared with the visuospatial and control tasks, was found in left parietal-temporal-occipital (PTO) junction, inferior frontal, anterior dorsal premotor, and presupplementary motor areas. Ventral inferior frontal cortex activation correlated negatively with reaction time in the functional condition. No specific activation characterized the visuospatial task compared with the functional task. The conceptual tasks, compared with the control tasks, demonstrated overlapping activation in left PTO junction, prefrontal, dorsal premotor, cuneus, and inferior temporal areas. These results outline the neural processes underlying conceptual knowledge for proper object use. The left ventral inferior frontal gyrus might facilitate behavioral decisions regarding functional/pragmatical object properties.     

When that tune runs through your head: a PET investigation of auditory imagery for familiar melodies.

The present study used positron emission tomography (PET) to examine the cerebral activity pattern associated with auditory imagery for familiar tunes. Subjects either imagined the continuation of nonverbal tunes cued by their first few notes, listened to a short sequence of notes as a control task, or listened and then reimagined that short sequence. Subtraction of the activation in the control task from that in the real-tune imagery task revealed primarily right-sided activation in frontal and superior temporal regions, plus supplementary motor area (SMA). Isolating retrieval of the real tunes by subtracting activation in the reimagine task from that in the real-tune imagery task revealed activation primarily in right frontal areas and right superior temporal gyrus. Subtraction of activation in the control condition from that in the reimagine condition, intended to capture imagery of unfamiliar sequences, revealed activation in SMA, plus some left frontal regions. We conclude that areas of right auditory association cortex, together with right and left frontal cortices, are implicated in imagery for familiar tunes, in accord with previous behavioral, lesion and PET data. Retrieval from musical semantic memory is mediated by structures in the right frontal lobe, in contrast to results from previous studies implicating left frontal areas for all semantic retrieval. The SMA seems to be involved specifically in image generation, implicating a motor code in this process.     

FMRI study of emotional speech comprehension

Little is known about the neural correlates of affective prosody in the context of affective semantic discourse. We used functional magnetic resonance imaging to investigate this issue while subjects performed 1) affective classification of sentences having an affective semantic content and 2) grammatical classification of sentences with neutral semantic content. Sentences of each type were produced half by actors and half by a text-to-speech software lacking affective prosody. Compared with neutral sentences processing, sentences with affective semantic content--with or without affective prosody--led to an increase in activation of a left inferior frontal area involved in the retrieval of semantic knowledge. In addition, the posterior part of the left superior temporal sulcus (STS) together with the medial prefrontal cortex were recruited, although not activated by neutral sentences classification. Interestingly, these areas have been described as implicated during self-reflection or other's mental state inference that possibly occurred during the affective classification task. When affective prosody was present, additional rightward activations of the human-selective voice area and the posterior part of STS were observed, corresponding to the processing of speaker's voice emotional content. Accurate affective communication, central to social interactions, requires the cooperation of semantics, affective prosody, and mind-reading neural networks.     

Distinct frontal regions subserve evaluation of linguistic and emotional aspects of speech intonation

In addition to the propositional content of verbal utterances, significant linguistic and emotional information is conveyed by the tone of speech. To differentiate brain regions subserving processing of linguistic and affective aspects of intonation, discrimination of sentences differing in linguistic accentuation and emotional expressiveness was evaluated by functional magnetic resonance imaging. Both tasks yielded rightward lateralization of hemodynamic responses at the level of the dorsolateral frontal cortex as well as bilateral thalamic and temporal activation. Processing of linguistic and affective intonation, thus, seems to be supported by overlapping neural networks comprising partially right-sided brain regions. Comparison of hemodynamic activation during the two different tasks, however, revealed bilateral orbito-frontal responses restricted to the affective condition as opposed to activation of the left lateral inferior frontal gyrus confined to evaluation of linguistic intonation. These findings indicate that distinct frontal regions contribute to higher level processing of intonational information depending on its communicational function. In line with other components of language processing, discrimination of linguistic accentuation seems to be lateralized to the left inferior-lateral frontal region whereas bilateral orbito-frontal areas subserve evaluation of emotional expressiveness.     

Common and dissociable activation patterns associated with controlled semantic and phonological processing: evidence from FMRI adaptation

Recent evidence suggests specialization of anterior left inferior prefrontal cortex (aLIPC; approximately BA 45/47) for controlled semantics and of posterior LIPC (pLIPC; approximately BA 44/6) for controlled phonology. However, the more automated phonological tasks commonly used raise the possibility that some of the typically extensive aLIPC activation during semantic tasks may relate to controlled language processing beyond the semantic domain. In the present study, an event-related fMRI adaptation paradigm was employed that used a standard controlled semantic task and a phonological task that also emphasized controlled processing. When compared with letter (baseline) processing, significant fMRI task and adaptation effects in the aLIPC and pLIPC regions ( approximately BA 45/47, approximately BA 44) were observed during both semantic and phonological processing, with aLIPC showing the strongest effects during semantic processing. A left frontal region ( approximately BA 6) showed task and relative adaptation effects preferential for phonological processing, and a left temporal region ( approximately BA 21) showed task and relative adaptation effects preferential for semantic processing. Our results demonstrate that aLIPC and pLIPC regions are involved in controlled processing across multiple language domains, arguing against a domain-specific LIPC model and for domain-preferentiality in left posterior frontal and temporal regions.     

Cerebral blood flow relationships associated with a difficult tone recognition task in trained normal volunteers

Tone recognition is partially subserved by neural activity in the right frontal and primary auditory cortices. First we determined the brain areas associated with tone perception and recognition. This study then examined how regional cerebral blood flow (rCBF) in these and other brain regions correlates with the behavioral characteristics of a difficult tone recognition task. rCBF changes were assessed using H2(15)O positron emission tomography. Subtraction procedures were used to localize significant change regions and correlational analyses were applied to determine how response times (RT) predicted rCBF patterns. Twelve trained normal volunteers were studied in three conditions: REST, sensory motor control (SMC) and decision (DEC). The SMC-REST contrast revealed bilateral activation of primary auditory cortices, cerebellum and bilateral inferior frontal gyri. DEC-SMC produced significant clusters in the right middle and inferior frontal gyri, insula and claustrum; the anterior cingulate gyrus and supplementary motor area; the left insula/claustrum; and the left cerebellum. Correlational analyses, RT versus rCBF from DEC scans, showed a positive correlation in right inferior and middle frontal cortex; rCBF in bilateral auditory cortices and cerebellum exhibited significant negative correlations with RT These changes suggest that neural activity in the right frontal, superior temporal and cerebellar regions shifts back and forth in magnitude depending on whether tone recognition RT is relatively fast or slow, during a difficult, accurate assessment.      

Reading salt activates gustatory brain regions: FMRI evidence for semantic grounding in a novel sensory modality

Because many words are typically used in the context of their referent objects and actions, distributed cortical circuits for these words may bind information about their form with perceptual and motor aspects of their meaning. Previous work has demonstrated such semantic grounding for sensorimotor, visual, auditory, and olfactory knowledge linked to words, which is manifest in activation of the corresponding areas of the cortex. Here, we explore the brain basis of gustatory semantic links of words whose meaning is primarily related to taste. In a blocked functional magnetic resonance imaging design, Spanish taste words and control words matched for a range of factors (including valence, arousal, imageability, frequency of use, number of letters and syllables) were presented to 59 right-handed participants in a passive reading task. Whereas all the words activated the left inferior frontal (BA44/45) and the posterior middle and superior temporal gyri (BA21/22), taste-related words produced a significantly stronger activation in these same areas and also in the anterior insula, frontal operculum, lateral orbitofrontal gyrus, and thalamus among others. As these areas comprise primary and secondary gustatory cortices, we conclude that the meaning of taste words is grounded in distributed cortical circuits reaching into areas that process taste sensations.     

Propofol and memory: a study using a process dissociation procedure and functional magnetic resonance imaging

Thirty volunteers randomly received either mild or deep propofol sedation, to assess its effect on explicit and implicit memory. Blood oxygen level‐dependent functional magnetic resonance during sedation examined brain activation by auditory word stimulus and a process dissociation procedure was performed 4 h after scanning. Explicit memory formation did not occur in either group. Implicit memories were formed during mild but not deep sedation (p = 0.04). Mild propofol sedation inhibited superior temporal gyrus activation (Z value 4.37, voxel 167). Deep propofol sedation inhibited superior temporal gyrus (Z value 4.25, voxel 351), middle temporal gyrus (Z value 4.39, voxel 351) and inferior parietal lobule (Z value 5.06, voxel 239) activation. Propofol only abolishes implicit memory during deep sedation. The superior temporal gyrus is associated with explicit memory processing, while the formation of both implicit and explicit memories is associated with superior and middle temporal gyri and inferior parietal lobule activation.     

Neural substrates for processing task-irrelevant emotional distracters in maltreated adolescents with depressive disorders: a pilot study

In this pilot study, neural systems related to cognitive and emotional processing were examined using event-related functional magnetic resonance imaging in 5 maltreated youth with depressive disorders and 11 nonmaltreated healthy participants. Subjects underwent an emotional oddball task, where they detected infrequent ovals (targets) within a continual stream of phase-scrambled images (standards). Sad and neutral images were intermittently presented as task-irrelevant distracters. The maltreated youth revealed significantly decreased activation in the left middle frontal gyrus and right precentral gyrus to target stimuli and significantly increased activation to sad stimuli in bilateral amygdala, left subgenual cingulate, left inferior frontal gyrus, and right middle temporal cortex compared to nonmaltreated subjects. Additionally, the maltreated youth showed significantly decreased activation to both attentional targets and sad distracters in the left posterior middle frontal gyrus compared to nonmaltreated subjects. In this exploratory study of dorsal control and ventral emotional circuits, we found that maltreated youth with distress disorders demonstrated dysfunction of neural systems related to cognitive control and emotional processing.