The effects of semantic category and knowledge type on lexical-semantic access: a PET study

Hemispheric annealing and lateralization under psychedelics (HEALS): A novel hypothesis of psychedelic action in the brain

Current models of psychedelic action in the brain propose changes along the dorsal-ventral and anterior-posterior axes but neglect to address the lateral axis. This article proposes a novel model of psychedelic action called HEALS (Hemispheric Annealing and Lateralization Under Psychedelics) which involves the reversal of the typical hierarchical relationship between the two hemispheres of the brain. In typical modes of consciousness, the hemispheres act in parallel process with the left predominating. Under psychedelics, as well as in other altered states of consciousness (ASCs), this hierarchy is reversed, with the right hemisphere released from inhibition by the left. In support of this model, the available neuroimaging evidence for lateralization under psychedelics is reviewed. Then, various cognitive and emotional changes observed under psychedelics are contrasted with those same functions in each hemisphere. These include attention; social and emotional intelligence; creativity and insight; and language. The article concludes with a review of laterality in other ASCs, such as meditative and trance states, and suggests that many phenomena associated with psychedelics, and other ASCs, might be explained by an atypical annealing between the hemispheres toward right hemisphere predominance.

Why are human animacy judgments continuous rather than categorical? A computational modeling approach

Introduction

The concept of animacy is often taken as a basic natural concept, in part I because most cases seem unambiguous. Most entities either are or are not animate. However, human animacy judgments do not reflect this binary classification. They suggest that there are borderline cases, such as virus, amoeba, fly, and imaginary beings (giant, dragon, god). Moreover, human roles (professor, mother, girlfriend) are consistently recognized as animate by far less than 100% of human judges.

Method

In this paper, I use computational modeling to identify features associated with human animacy judgments, modeling human animacy and living/non-living judgments using both bottom-up predictors (the principal components from a word embedding model) and top-down predictors (cosine distances from the names of animate categories).

Results

The results suggest that human animacy judgments may be relying on information obtained from imperfect estimates of category membership that are reflected in the word embedding models. Models using cosine distance from category names mirror human judgments in distinguishing strongly between humans (estimated lower animacy by the measure) and other animals (estimated higher animacy by the measure).

Discussion

These results are consistent with a family resemblance approach to the apparently categorical concept of animacy.

Meta-analytic evidence for a novel hierarchical model of conceptual processing

Conceptual knowledge plays a pivotal role in human cognition. Grounded cognition theories propose that concepts consist of perceptual-motor features represented in modality-specific perceptual-motor cortices. However, it is unclear whether conceptual processing consistently engages modality-specific areas. Here, we performed an activation likelihood estimation (ALE) meta-analysis across 212 neuroimaging experiments on conceptual processing related to 7 perceptual-motor modalities (action, sound, visual shape, motion, color, olfaction-gustation, and emotion). We found that conceptual processing consistently engages brain regions also activated during real perceptual-motor experience of the same modalities. In addition, we identified multimodal convergence zones that are recruited for multiple modalities. In particular, the left inferior parietal lobe (IPL) and posterior middle temporal gyrus (pMTG) are engaged for three modalities: action, motion, and sound. These "trimodal" regions are surrounded by "bimodal" regions engaged for two modalities. Our findings support a novel model of the conceptual system, according to which conceptual processing relies on a hierarchical neural architecture from modality-specific to multimodal areas up to an amodal hub.

Neuroanatomical correlates of screening for aphasia in NeuroDegeneration (SAND) battery in non-fluent/agrammatic variant of primary progressive aphasia

Background

Non-fluent/agrammatic variant of Primary Progressive Aphasia (avPPA) is primarily characterized by language impairment due to atrophy of the inferior frontal gyrus and the insula cortex in the dominant hemisphere. The Screening for Aphasia in NeuroDegeneration (SAND) battery has been recently proposed as a screening tool for PPA, with several tasks designed to be specific for different language features. Applying multivariate approaches to neuroimaging data and verbal fluency tasks, Aachener Aphasie Test (AAT) naming subtest and SAND data may help in elucidating the neuroanatomical correlates of language deficits in avPPA.

Objective

To investigate the neuroanatomical correlates of language deficits in avPPA using verbal fluency tasks, AAT naming subtest and SAND scores as proxies of brain structural imaging abnormalities.

Methods

Thirty-one avPPA patients were consecutively enrolled and underwent extensive neuropsychological assessment and MRI scan. Raw scores of verbal fluency tasks, AAT naming subtest, and SAND subtests, namely living and non-living picture naming, auditory sentence comprehension, single-word comprehension, words and non-words repetition and sentence repetition, were used as proxies to explore structural (gray matter volume) neuroanatomical correlates. We assessed univariate (voxel-based morphometry, VBM) as well as multivariate (source-based morphometry, SBM) approaches. Age, gender, educational level, and disease severity were considered nuisance variables.

Results

SAND picture naming (total, living and non-living scores) and AAT naming scores showed a direct correlation with the left temporal network derived from SBM. At univariate analysis, the left middle temporal gyrus was directly correlated with SAND picture naming (total and non-living scores) and AAT naming score. When words and non-words repetition (total score) was considered, a direct correlation with the left temporal network (SBM) and with the left fusiform gyrus (VBM) was also evident.

Conclusion

Naming impairments that characterize avPPA are related to specific network-based involvement of the left temporal network, potentially expanding our knowledge on the neuroanatomical basis of this neurodegenerative condition.

Duality of Function: Activation for Meaningless Nonwords and Semantic Codes in the Same Brain Areas

Studies of the neural substrates of semantic (word meaning) processing have typically focused on semantic manipulations, with less consideration for potential differences in difficulty across conditions. While the idea that particular brain regions can support multiple functions is widely accepted, studies of specific cognitive domains rarely test for co-location with other functions. Here we start with standard univariate analyses comparing words to meaningless nonwords, replicating our recent finding that this contrast can activate task-positive regions for words, and default-mode regions in the putative semantic network for nonwords, pointing to difficulty effects. Critically, this was followed up with a multivariate analysis to test whether the same areas activated for meaningless nonwords contained semantic information sufficient to distinguish high- from low-imageability words. Indeed, this classification was performed reliably better than chance at 75% accuracy. This is compatible with two non-exclusive interpretations. Numerous areas in the default-mode network are task-negative in the sense of activating for less demanding conditions, and the same areas contain information supporting semantic cognition. Therefore, while areas of the default mode network have been hypothesized to support semantic cognition, we offer evidence that these areas can respond to both domain-general difficulty effects, and to specific aspects of semantics.

Why do herpes simplex encephalitis and semantic dementia show a different pattern of semantic impairment in spite of their main common involvement within the anterior temporal lobes?

A very challenging problem in the domain of the cognitive neurosciences is to explain why herpes simplex encephalitis and semantic dementia show, respectively, a category-specific semantic disorder for biological entities and an across-categories semantic disruption, despite highly overlapping areas of anterior temporal lobe damage. The aim of the present review consisted in trying to make a separate survey of anatomo-clinical investigations (single-case studies and group studies) and of activation studies, in order to analyse the factors that could explain these different patterns of semantic disruption. Factors taken into account in this review were laterality of lesions, disease aetiology, kind of brain pathology and locus of damage within the temporal lobes. Locus of damage within the temporal lobes and kind of brain pathology seemed to play the most important role, because in patients with herpes simplex encephalitis and category-specific semantic disorder for biological entities the lesions prevailed in the anteromedial temporal lobes. Furthermore, the neuropathology concerned both the anterior temporal cortices and the white matter pathways connecting these areas with the posterior visual areas, whereas in semantic dementia the inferior longitudinal fasciculus involvement was restricted to the rostral temporal lobe and did not extend into the cortically uninvolved occipital lobe.

In defense of abstract conceptual representations

An extensive program of research in the past 2 decades has focused on the role of modal sensory, motor, and affective brain systems in storing and retrieving concept knowledge. This focus has led in some circles to an underestimation of the need for more abstract, supramodal conceptual representations in semantic cognition. Evidence for supramodal processing comes from neuroimaging work documenting a large, well-defined cortical network that responds to meaningful stimuli regardless of modal content. The nodes in this network correspond to high-level "convergence zones" that receive broadly crossmodal input and presumably process crossmodal conjunctions. It is proposed that highly conjunctive representations are needed for several critical functions, including capturing conceptual similarity structure, enabling thematic associative relationships independent of conceptual similarity, and providing efficient "chunking" of concept representations for a range of higher order tasks that require concepts to be configured as situations. These hypothesized functions account for a wide range of neuroimaging results showing modulation of the supramodal convergence zone network by associative strength, lexicality, familiarity, imageability, frequency, and semantic compositionality. The evidence supports a hierarchical model of knowledge representation in which modal systems provide a mechanism for concept acquisition and serve to ground individual concepts in external reality, whereas broadly conjunctive, supramodal representations play an equally important role in concept association and situation knowledge.

For a cognitive neuroscience of concepts: Moving beyond the grounding issue

Cognitive neuroscience research on conceptual knowledge often is discussed with respect to "embodiment" or "grounding." We tried to disentangle at least three distinct claims made using these terms. One of these, the view that concepts are entirely reducible to sensory-motor representations, is untenable and diminishing in the literature. A second is the view that concepts and sensory-motor representations "interact," and a third view addresses the question of how concepts are neurally organized-the neural partitions among concepts of different kinds, and where these partitions are localized in cortex. We argue that towards the second and third issues, much fruitful research can be pursued, but that no position on them is specifically related to "grounding." Furthermore, to move forward on them, it is important to precisely distinguish different kinds of representations-conceptual vs. sensory-motor-from each other theoretically and empirically. Neuroimaging evidence often lacks such specificity. We take an approach that distinguishes conceptual from sensory-motor representations by virtue of two properties: broad generality and tolerance to the absence of sensory-motor associations. We review three of our recent experiments that employ these criteria in order to localize neural representations of several specific kinds of nonsensory attributes: functions, intentions, and belief traits. Building on past work, we find that neuroimaging evidence can be used fruitfully to distinguish interesting hypotheses about neural organization. On the other hand, most such evidence does not speak to any clear notion of "grounding" or "embodiment," because these terms do not make clear, specific, empirical predictions. We argue that cognitive neuroscience will proceed most fruitfully by relinquishing these terms.

Semantic and Phonological Encoding in Adults Who Stutter: Silent Responses to Pictorial Stimuli

PURPOSE

Research on language planning in adult stuttering is relatively sparse and offers diverging arguments about a potential causative relationship between semantic and phonological encoding and fluency breakdowns. This study further investigated semantic and phonological encoding efficiency in adults who stutter (AWS) by means of silent category and phoneme identification, respectively.

METHOD

Fifteen AWS and 15 age- and sex-matched adults who do not stutter (ANS) participated. The groups were compared on the basis of the accuracy and speed of superordinate category (animal vs. object) and initial phoneme (vowel vs. consonant) decisions, which were indicated manually during silent viewing of pictorial stimuli. Movement execution latency was accounted for, and no other cognitive, linguistic, or motor demands were posed on participants' responses. Therefore, category identification accuracy and speed were considered indirect measures of semantic encoding efficiency and phoneme identification accuracy and speed of phonological encoding efficiency.

RESULTS

For category decisions, AWS were slower but not less accurate than ANS, with objects eliciting more errors and slower responses than animals in both groups. For phoneme decisions, the groups did not differ in accuracy, with consonant errors outnumbering vowel errors in both groups, and AWS were slower than ANS in consonant but not vowel identification, with consonant response time lagging behind vowel response time in AWS only.

CONCLUSIONS

AWS were less efficient than ANS in semantic encoding, and they might harbor a consonant-specific phonological encoding weakness. Future independent studies are warranted to discover if these positive findings are replicable and a marker for persistent stuttering.

Differing Time of Onset of Concurrent TMS-fMRI during Associative Memory Encoding: A Measure of Dynamic Connectivity

There has been a distinct shift in neuroimaging from localization of function into a more network based approach focused on connectivity. While fMRI has proven very fruitful for this, the hemodynamic signal is inherently slow which limits the temporal resolution of fMRI-only connectivity measures. The brain, however, works on a time scale of milliseconds. This study utilized concurrent transcranial magnetic stimulation (TMS)-fMRI in a novel way to obtain measures of dynamic connectivity by measuring changes in fMRI signal amplitude in regions distal to the site of stimulation following differing TMS onset times. Seventeen healthy subjects completed an associative memory encoding task known to involve the DLPFC, viewing pairs of objects which could be semantically related or unrelated. Three pulses of 10 Hz repetitive TMS were applied over the left DLPFC starting either at 200, 600, or 1000 ms after stimulus onset. Associations for related pairs were better remembered than unrelated pairs in a post-scan cued recall test. Differences in neural activity were assessed across different TMS onsets, separately for related and unrelated pairs. Time specific TMS effects were observed in several regions, including those associated with higher-level processing (lateral frontal, anterior cingulate), visual areas (occipital), and regions involved in semantic processing (e.g., left mid-temporal and medial frontal). Activity in the frontal cortex was decreased at 200 ms post-stimulus for unrelated pairs, and 1000 ms post-stimulus for related pairs. This suggests differences in the timing across conditions in which the DLFPC interacts with other PFC regions, consistent with the notion that the DLPFC is facilitating extended semantic processing for related items. This study demonstrates that time-varying TMS onset inside the MRI can be used to reliably measure fast dynamic connectivity with a temporal resolution in the hundreds of milliseconds.

A unified model of human semantic knowledge and its disorders

How is knowledge about the meanings of words and objects represented in the human brain? Current theories embrace two radically different proposals: either distinct cortical systems have evolved to represent different kinds of things, or knowledge for all kinds is encoded within a single domain-general network. Neither view explains the full scope of relevant evidence from neuroimaging and neuropsychology. Here we propose that graded category-specificity emerges in some components of the semantic network through joint effects of learning and network connectivity. We test the proposal by measuring connectivity amongst cortical regions implicated in semantic representation, then simulating healthy and disordered semantic processing in a deep neural network whose architecture mirrors this structure. The resulting neuro-computational model explains the full complement of neuroimaging and patient evidence adduced in support of both domain-specific and domain-general approaches, reconciling long-standing disputes about the nature and origins of this uniquely human cognitive faculty.

Framing effects reveal discrete lexical-semantic and sublexical procedures in reading: an fMRI study

According to the dual-route model, a printed string of letters can be processed by either a grapheme-to-phoneme conversion (GPC) route or a lexical-semantic route. Although meta-analyses of the imaging literature support the existence of distinct but interacting reading procedures, individual neuroimaging studies that explored neural correlates of reading yielded inconclusive results. We used a list-manipulation paradigm to provide a fresh empirical look at this issue and to isolate specific areas that underlie the two reading procedures. In a lexical condition, we embedded disyllabic Italian words (target stimuli) in lists of either loanwords or trisyllabic Italian words with unpredictable stress position. In a GPC condition, similar target stimuli were included within lists of pseudowords. The procedure was designed to induce participants to emphasize either the lexical-semantic or the GPC reading procedure, while controlling for possible linguistic confounds and keeping the reading task requirements stable across the two conditions. Thirty-three adults participated in the behavioral study, and 20 further adult participants were included in the fMRI study. At the behavioral level, we found sizeable effects of the framing manipulations that included slower voice onset times for stimuli in the pseudoword frames. At the functional anatomical level, the occipital and temporal regions, and the intraparietal sulcus were specifically activated when subjects were reading target words in a lexical frame. The inferior parietal and anterior fusiform cortex were specifically activated in the GPC condition. These patterns of activation represented a valid classifying model of fMRI images associated with target reading in both frames in the multi-voxel pattern analyses. Further activations were shared by the two procedures in the occipital and inferior parietal areas, in the premotor cortex, in the frontal regions and the left supplementary motor area. These regions are most likely involved in either early input or late output processes.

The neural correlates of semantic richness: evidence from an fMRI study of word learning

We investigated the neural correlates of concrete nouns with either many or few semantic features. A group of 21 participants underwent two days of training and were then asked to categorize 40 newly learned words and a set of matched familiar words as living or nonliving in an MRI scanner. Our results showed that the most reliable effects of semantic richness were located in the left angular gyrus (AG) and middle temporal gyrus (MTG), where activation was higher for semantically rich than poor words. Other areas showing the same pattern included bilateral precuneus and posterior cingulate gyrus. Our findings support the view that AG and anterior MTG, as part of the multimodal network, play a significant role in representing and integrating semantic features from different input modalities. We propose that activation in bilateral precuneus and posterior cingulate gyrus reflects interplay between AG and episodic memory systems during semantic retrieval.

ERP signs of categorical and supra-categorical processing of visual information

BACKGROUND

The aim of the present study was to investigate to what extent shared and distinct brain mechanisms are possibly subserving the processing of visual supra-categorical and categorical knowledge as observed with event-related potentials of the brain. Access time to these knowledge types was also investigated. Picture pairs of animals, objects, and mixed types were presented. Participants were asked to decide whether each pair contained pictures belonging to the same category (either animals or man-made objects) or to different categories by pressing one of two buttons. Response accuracy and reaction times (RTs) were also recorded.

RESULTS

Both ERPs and RTs were grand-averaged separately for the same-different supra-categories and the animal-object categories. Behavioral performance was faster for more endomorphic pairs, i.e., animals vs. objects and same vs. different category pairs. For ERPs, a modulation of the earliest C1 and subsequent P1 responses to the same vs. different supra-category pairs, but not to the animal vs. object category pairs, was found. This finding supports the view that early afferent processing in the striate cortex can be boosted as a by-product of attention allocated to the processing of shapes and basic features that are mismatched, but not to their semantic quintessence, during same-different supra-categorical judgment. Most importantly, the fact that this processing accrual occurred independent of a traditional experimental condition requiring selective attention to a stimulus source out of the various sources addressed makes it conceivable that this processing accrual may arise from the attentional demand deriving from the alternate focusing of visual attention within and across stimulus categorical pairs' basic structural features. Additional posterior ERP reflections of the brain more prominently processing animal category and same-category pairs were observed at the N1 and N2 levels, respectively, as well as at a late positive complex level, overall most likely related to different stages of analysis of the greater endomorphy of these shape groups. Conversely, an enhanced fronto-central and fronto-lateral N2 as well as a centro-parietal N400 to man-made objects and different-category pairs were found, possibly indexing processing of these entities' lower endomorphy and isomorphy at the basic features and semantic levels, respectively.

CONCLUSION

Overall, the present ERP results revealed shared and distinct mechanisms of access to supra-categorical and categorical knowledge in the same way in which shared and distinct neural representations underlie the processing of diverse semantic categories. Additionally, they outlined the serial nature of categorical and supra-categorical representations, indicating the sequential steps of access to these separate knowledge types.

Repetitive deep transcranial magnetic stimulation improves verbal fluency and written language in a patient with primary progressive aphasia-logopenic variant (LPPA)

BACKGROUND

To date, no therapies are available for the logopenic variant of primary progressive aphasia (LPPA). Even though deep repetitive transcranial magnetic stimulation (rTMS) may improve cognitive functions in some neurodegenerative disorders, no previous studies investigated its effects in patients with LPPA.

OBJECTIVE

Our aim was to investigate the effects on cognitive function of high frequency rTMS (hf-rTMS) delivered over the left dorso-lateral prefrontal cortex (DLPFC) through a coil designed for deep rTMS, compared to a SHAM stimulation, in a right-handed patient with LPPA.

METHODS

The patient presented a progressive language impairment (phonological errors in speech and naming, impaired single word retrieval and sentences repetition) and predominant left perisylvian atrophy and hypoperfusion. He received four stimulation cycles (two REAL and two SHAM) each of whom lasted 20 min for 5 consecutive days. Patient's performances in frontal, visuo-spatial and linguistic tasks were evaluated before and after each stimulation session. Test scores after REAL were compared with those obtained at baseline and after SHAM.

RESULTS

We found a temporary and highly significant improvement in the linguistic skills (both oral and written tasks) but not in the other cognitive domains tested, after REAL, but not SHAM stimulations.

DISCUSSION

Hf-rTMS delivered over the DLPFC could improve language in LPPA by enhancing long-term potentiation and synaptic plasticity within the stimulated and interconnected areas involved in language network. Our findings might prompt future researches into the feasibility and efficacy of deep hf-rTMS as a therapeutic tool in progressive aphasia syndromes and other neurodegenerative disorders.

The selective impairment of fruit and vegetable knowledge:amultiple processing channels account of fine-grain category specificity

We report the case of a gentleman, FAV, who developed a grave anomia and selective comprehension deficit following a left temporo-occipital infarction. His word retrieval abilities were significantly more impaired for living things than for man-made artefacts. There was no difference between his performance when naming to confrontation and naming to verbal description. However, further assessment revealed a more fine-grain deficit at the level of comprehension. FAV had significantly more difficulty with fruit and vegetables than animals or nonliving foods on a number of tests probing semantic knowledge. These results are discussed within the context of current theories of the organisation of conceptual knowledge. We conclude that this pattern of performance and other fine-grain category effects within the realms of living and nonliving things are best explained by a multiple processing pathways account.

Do semantic categories activate distinct cortical regions? Evidence for a distributed neural semantic system

A key issue in cognitive neuroscience concerns the neural representation of conceptual knowledge. Currently, debate focuses around the issue of whether there are neural regions specialised for the processing of specific semantic attributes or categories, or whether concepts are represented in an undifferentiated neural system. Neuropsychological studies of patients with selective semantic deficits and previous neuroimaging studies do not unequivocally support either account. We carried out a PET study to determine whether there is any regional specialisation for the processing of concepts from different semantic categories using picture stimuli and a semantic categorisation task. We found robust activation of a large semantic network extending from left inferior frontal cortex into the inferior temporal lobe and including occipital cortex and the fusiform gyrus. The only category effect that we found was additional activation for animals in the right occipital cortex, which we interpret as being due to the extra visual processing demands required in order to differentiate one animal from another. We also carried out analyses in specific cortical regions that have been claimed to be preferentially activated for various categories, but found no evidence of any differential activation as a function of category. We interpret these data within the framework of cognitive accounts in which conceptual knowledge is represented within a nondifferentiated distributed system.

Neural correlates of conceptual knowledge for actions

The neural correlates of conceptual knowledge for actions are not well understood. To begin to address this knowledge gap, we tested the hypothesis that the retrieval of conceptual knowledge for actions depends on neural systems located in higher-order association cortices of left premotor/prefrontal, parietal, and posterior middle temporal regions. The investigation used the lesion method and involved 90 subjects with damage to various regions of the left or right hemisphere. The experimental tasks measured retrieval of knowledge for actions, in a nonverbal format: Subjects evaluated attributes of pictured actions, and compared and matched pictures of actions. In support of our hypothesis, we found that the regions of highest lesion overlap in subjects with impaired retrieval of conceptual knowledge for actions were in the left premotor/prefrontal sector, the left parietal region, and in the white matter underneath the left posterior middle temporal region. These sites are partially distinct from those identified previously as being important for the retrieval of words for actions. We propose that a key function of the sites is to operate as two-way intermediaries between perception and concept retrieval, to promote the retrieval of the multidimensional aspects of knowledge that are necessary and sufficient for the mental representation of a concept of a given action.

Action-related semantic content and negation polarity modulate motor areas during sentence reading: an event-related desynchronization study

Our study evaluated motor cortex involvement during silent reading of sentences referring to hand actions. We aimed at defining whether sentential polarity (affirmative vs. negative) would modulate motor cortex activation using the event-related desynchronization (ERD) analysis of the mu rhythm. Eleven healthy volunteers performed a reading task involving 160 sentences (80 affirmative: 40 hand-related, 40 abstract; 80 negative: 40 hand-related, 40 abstract). After reading each sentence, subjects had to decide whether the verb was high or low frequency in Italian. Electroencephalographic (EEG) activity was recorded with 32 surface electrodes and mu ERD analyses were performed for each subject. Hand-action related sentences induced a greater mu ERD over the left premotor and motor hand areas compared to abstract sentences. Mu ERD was greater and temporally delayed when the hand-related verbs were presented in the negative versus affirmative form. As predicted by the "embodied semantic" theory of language understanding, motor areas were activated during sentences referring to hand actions. In addition, motor cortex activation was larger for negative than affirmative motor sentences, a finding compatible with the hypothesis that comprehension is more demanding in the specific case of motor content negation.

Similar or different? The role of the ventrolateral prefrontal cortex in similarity detection

Patients with frontal lobe syndrome can exhibit two types of abnormal behaviour when asked to place a banana and an orange in a single category: some patients categorize them at a concrete level (e.g., “both have peel”), while others continue to look for differences between these objects (e.g., “one is yellow, the other is orange”). These observations raise the question of whether abstraction and similarity detection are distinct processes involved in abstract categorization, and that depend on separate areas of the prefrontal cortex (PFC). We designed an original experimental paradigm for a functional magnetic resonance imaging (fMRI) study involving healthy subjects, confirming the existence of two distinct processes relying on different prefrontal areas, and thus explaining the behavioural dissociation in frontal lesion patients. We showed that: 1) Similarity detection involves the anterior ventrolateral PFC bilaterally with a right-left asymmetry: the right anterior ventrolateral PFC is only engaged in detecting physical similarities; 2) Abstraction per se activates the left dorsolateral PFC.

The neural manifestation of the word concreteness effect: an electrical neuroimaging study

Previous studies have provided controversial evidence about the way in which words with different degrees of concreteness are represented in the brain. The aim of the present study was to investigate whether the processing of abstract vs. concrete words differently affected the timing and topographical distribution of ERP components. Participants were engaged in a lexical decision task (word/non-word discrimination) while EEG was recorded from 128 scalp sites. Reaction times (RTs) to words were faster than RTs to pseudowords. Words were discriminated from pseudowords since larger N2 responses to words than to pseudowords were observed over the left occipito-temporal areas at 300 ms post-stimulus. Concrete words and abstract words were discriminated as early as 350 ms post-stimulus, with larger responses to concrete than to abstract words over the mesial occipital regions. Concreteness-related ERP differences were also observed in the amplitudes of the later anterior LP component (between 370 and 570 ms), with larger responses to abstract words than to concrete words. The LORETA source localization technique was also applied to identify the intra-cranial generators of surface potentials reflecting lexico-semantic processing. Results showed that words (both abstract and concrete) were associated with a stronger activation of the left fusiform gyrus and the left temporal cortex, as compared to pseudowords. Concrete word processing was associated with a stronger activation of the left extrastriate visual areas (namely BA 18 and BA 19) as compared to abstract word processing. By revealing the neural markers of the concreteness effect, our study contributes to the understanding of the neurogenesis of verbal semantic knowledge impairments and the incidence of these impairments in clinical populations.

Right hemispheric participation in semantic decision improves performance

Functional neuroimaging studies in healthy adults demonstrate involvement of a left-lateralized network of frontal, temporal, and parietal regions during a variety of semantic processing tasks. While these areas are believed to be fundamental to semantic processing, it is unclear if task performance is correlated with differential recruitment of these or other brain regions. The objective of this study was to identify the structures underlying improved accuracy on a semantic decision task. We also investigated whether extra-scanner performance on the Boston Naming Test (BNT) and Semantic Fluency Test (SFT), neuropsychological measures of semantic retrieval, is correlated with specific areas of activation during the semantic decision/tone decision (SDTD) fMRI task. Fifty-two healthy, right-handed individuals performed a block-design SDTD task. Regression analyses revealed that increased performance on this task was associated with activation in the right inferior parietal lobule. Higher SFT performance resulted in greater recruitment of right frontal regions; improved performance on BNT was associated with more widespread activation in prefrontal, temporal, and parietal cortex bilaterally, although this activation appeared to be stronger in the right hemisphere. Overall, our results suggest that improved performance on both intra- and extra-scanner measures of semantic processing are associated with increased recruitment of right hemispheric regions.

Deconstructing events: the neural bases for space, time, and causality

Space, time, and causality provide a natural structure for organizing our experience. These abstract categories allow us to think relationally in the most basic sense; understanding simple events requires one to represent the spatial relations among objects, the relative durations of actions or movements, and the links between causes and effects. The present fMRI study investigates the extent to which the brain distinguishes between these fundamental conceptual domains. Participants performed a 1-back task with three conditions of interest (space, time, and causality). Each condition required comparing relations between events in a simple verbal narrative. Depending on the condition, participants were instructed to either attend to the spatial, temporal, or causal characteristics of events, but between participants each particular event relation appeared in all three conditions. Contrasts compared neural activity during each condition against the remaining two and revealed how thinking about events is deconstructed neurally. Space trials recruited neural areas traditionally associated with visuospatial processing, primarily bilateral frontal and occipitoparietal networks. Causality trials activated areas previously found to underlie causal thinking and thematic role assignment, such as left medial frontal and left middle temporal gyri, respectively. Causality trials also produced activations in SMA, caudate, and cerebellum; cortical and subcortical regions associated with the perception of time at different timescales. The time contrast, however, produced no significant effects. This pattern, indicating negative results for time trials but positive effects for causality trials in areas important for time perception, motivated additional overlap analyses to further probe relations between domains. The results of these analyses suggest a closer correspondence between time and causality than between time and space.

Is the semantic category effect in the lateral temporal cortex due to motion property differences?

Two specific areas within the posterior lateral temporal cortex (PLTC), the posterior superior temporal sulcus (pSTS) and the posterior middle temporal gyrus (pMTG), have been proposed to store different types of conceptual properties of motion: the pSTS encodes knowledge of articulated, biological motion, and the pMTG encodes knowledge about unarticulated, mechanical motion. We examined this hypothesis by comparing activation patterns evoked by verbs denoting biological motion (e.g., walk), mechanical motion (e.g., rotate), and low-motion events (e.g., ferment). Classical noun categories with different motion types (animals, tools, and buildings) were also tested and compared with previous findings of the categorical effects in PLTC. Replicating previous findings of different types of nouns, we observed stronger activation for animals than tools in the pSTS and stronger activation for tools compared to other types of nouns in the pMTG. However, such motion-type specific activation patterns only partly extended to verbs. Whereas the pSTS showed preferences for biological-motion verbs, no region within the pMTG was sensitive to verbs denoting mechanical motion. We speculate that the pMTG preference for tools is driven by properties other than mechanical motion, such as strong mappings between the visual form and motor-related representations.

Visual and semantic processing of living things and artifacts: an FMRI study

We carried out an fMRI study with a twofold purpose: to investigate the relationship between networks dedicated to semantic and visual processing and to address the issue of whether semantic memory is subserved by a unique network or by different subsystems, according to semantic category or feature type. To achieve our goals, we administered a word-picture matching task, with within-category foils, to 15 healthy subjects during scanning. Semantic distance between the target and the foil and semantic domain of the target-foil pairs were varied orthogonally. Our results suggest that an amodal, undifferentiated network for the semantic processing of living things and artifacts is located in the anterolateral aspects of the temporal lobes; in fact, activity in this substrate was driven by semantic distance, not by semantic category. By contrast, activity in ventral occipito-temporal cortex was driven by category, not by semantic distance. We interpret the latter finding as the effect exerted by systematic differences between living things and artifacts at the level of their structural representations and possibly of their lower-level visual features. Finally, we attempt to reconcile contrasting data in the neuropsychological and functional imaging literature on semantic substrate and category specificity.

Cortical representation of verbs with optional complements: the theoretical contribution of fMRI

Verbs like "eat" are special in that they can appear both with a complement (e.g., "John ate ice-cream") and without a complement ("John ate"). How are such verbs with optional complements represented? This fMRI study attempted to provide neurally based constraints for the linguistic theory of the representation of verbs with optional complements. One linguistic approach suggests that the representation of these verbs in the lexicon includes two complementation frames (one with and one without the complement), similarly to verbs that allow two different types of complements (e.g., discover). Another approach assumes that only one frame is represented (with a complement) and, when the complement is omitted, the relevant thematic role is saturated, either lexically or syntactically. We compared the patterns of cortical activation of verbs with optional complements to verbs that take either one or two frames and to verbs with one or two complements. These comparisons--together with prior findings regarding the cortical activation related to the number of complementation frames and the number of complements--were used to decide between the theoretical approaches. We found support for the idea that verbs with optional complements have only one frame and that a lexical operation enables complement omission. We also used fMRI in the traditional manner and identified the fusiform gyrus and the temporo-parieto-occipital junction as the regions that participate in the execution of the omission and saturation of optional complements.

The orthography-specific functions of the left fusiform gyrus: evidence of modality and category specificity

We report on an investigation of the cognitive functions of an individual with a resection of the left fusiform gyrus. This individual and a group of control participants underwent testing to examine the question of whether or not there are neural substrates within the left fusiform gyrus that are dedicated to orthographic processing. We evaluated the modality specificity (written vs spoken language) and the category specificity (written language vs other visual categories) of this individual's impairments. The results clearly reveal deficits affecting lexical processes in both reading and spelling. Specifically, we find disruption of normal, rapid access to meaning from print in reading and of accurate retrieval of the spellings of words from their meaning in writing. These deficits stand in striking contrast with intact processing of spoken language and categories of visual stimuli such as line drawings of objects and faces. The modality and category specificity of the deficits provide clear evidence of neural substrates within the left-mid-fusiform gyrus that are specialized and necessary for normal orthographic processing.

Where is the semantic system? A critical review and meta-analysis of 120 functional neuroimaging studies

Semantic memory refers to knowledge about people, objects, actions, relations, self, and culture acquired through experience. The neural systems that store and retrieve this information have been studied for many years, but a consensus regarding their identity has not been reached. Using strict inclusion criteria, we analyzed 120 functional neuroimaging studies focusing on semantic processing. Reliable areas of activation in these studies were identified using the activation likelihood estimate (ALE) technique. These activations formed a distinct, left-lateralized network comprised of 7 regions: posterior inferior parietal lobe, middle temporal gyrus, fusiform and parahippocampal gyri, dorsomedial prefrontal cortex, inferior frontal gyrus, ventromedial prefrontal cortex, and posterior cingulate gyrus. Secondary analyses showed specific subregions of this network associated with knowledge of actions, manipulable artifacts, abstract concepts, and concrete concepts. The cortical regions involved in semantic processing can be grouped into 3 broad categories: posterior multimodal and heteromodal association cortex, heteromodal prefrontal cortex, and medial limbic regions. The expansion of these regions in the human relative to the nonhuman primate brain may explain uniquely human capacities to use language productively, plan, solve problems, and create cultural and technological artifacts, all of which depend on the fluid and efficient retrieval and manipulation of semantic knowledge.

New insights into name category-related effects: is the Age of Acquisition a possible factor?

BACKGROUND

Electrophysiological, hemodynamic and neuropsychological studies have provided evidence of dissociation in the way words belonging to different semantic categories (e.g., animals, tools, actions) are represented in the brain. The aim of the present study was to investigate whether a word's semantic domain may affect the amplitude and latency of ERP components, independently of any other factor.

METHODS

EEGs were recorded from 16 volunteers engaged in a lexical decision task (word/non-word discrimination) involving 100 words (flora and fauna names). This task allowed us to evaluate differences in processing between words belonging to different categories (fauna vs. flora) independently of task demands. All stimuli were balanced in terms of length, frequency of occurrence, familiarity and imageability. Low Resolution Electromagnetic Tomography (LORETA) was performed on ERP difference waves of interest.

RESULTS

Our findings showed that the two categories were discriminated as early as 200 ms post-stimulus, with larger responses to flora names over the left occipito-temporal areas, namely BA37 and BA20. Category-related ERP differences were also observed in the amplitudes of the later centro-parietal N400, posterior P300 and anterior LP components. Behavioral responses to words denoting fauna were more accurate than to words denoting flora.

CONCLUSION

Overall, it seems that it was easier to access the lexical properties of fauna, probably because of their biologically relevant status. The results are discussed in the light of the possible role played by different factors.

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

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

Processing the universal quantifier during sentence comprehension: ERP evidence

This study investigates the temporal neural dynamics of processing the Chinese universal quantifier dou during Chinese sentence comprehension using the event-related potential (ERP) technique. Universal quantifier violations were created when the universal quantifier dou (all, every) was misplaced either after a singular object noun phrase (NP) in a Subject-Object-Verb (SOV) sentence (Experiments 1 and 3) or after a singular subject NP in a SVO sentence (Experiment 2). Participants were asked to make semantic plausibility judgment (Experiments 1 and 2) or to comprehend sentences real time followed by a sentence recognition test at the end of the experiment (Experiment 3). Experiment 1 found that quantifier violations elicited a sustained positivity from 400 to 1100ms post-onset of the quantifier and a sustained negativity from 300 to 800ms post-onset of the following verb. Experiment 2 varied the distance between dou and the following verb by the presence or absence of an adverb between them. Again, the sustained positivity was observed on the mismatching quantifier; in addition, a sustained negativity was observed on the word immediately following the quantifier, regardless of whether this word was a verb or adverb. Experiment 3 used the same stimuli as Experiment 1 but with a different task. The quantifier violation elicited anteriorly distributed negativities over different time intervals post-onset of the quantifier. The sustained positivity is interpreted as being associated with an integration process that links the universal quantifier with the preceding entity. The sustained negativity is attributed to a second-pass process to reinterpret the sentence. Other functional interpretations of the ERP components were discussed and ruled out.

A comparison of five fMRI protocols for mapping speech comprehension systems

AIMS

Many fMRI protocols for localizing speech comprehension have been described, but there has been little quantitative comparison of these methods. We compared five such protocols in terms of areas activated, extent of activation, and lateralization.

METHODS

fMRI BOLD signals were measured in 26 healthy adults during passive listening and active tasks using words and tones. Contrasts were designed to identify speech perception and semantic processing systems. Activation extent and lateralization were quantified by counting activated voxels in each hemisphere for each participant.

RESULTS

Passive listening to words produced bilateral superior temporal activation. After controlling for prelinguistic auditory processing, only a small area in the left superior temporal sulcus responded selectively to speech. Active tasks engaged an extensive, bilateral attention, and executive processing network. Optimal results (consistent activation and strongly lateralized pattern) were obtained by contrasting an active semantic decision task with a tone decision task. There was striking similarity between the network of brain regions activated by the semantic task and the network of brain regions that showed task-induced deactivation, suggesting that semantic processing occurs during the resting state.

CONCLUSIONS

fMRI protocols for mapping speech comprehension systems differ dramatically in pattern, extent, and lateralization of activation. Brain regions involved in semantic processing were identified only when an active, nonlinguistic task was used as a baseline, supporting the notion that semantic processing occurs whenever attentional resources are not controlled. Identification of these lexical-semantic regions is particularly important for predicting language outcome in patients undergoing temporal lobe surgery.

The neural systems of tool and action semantics: a perspective from functional imaging

This review discusses the contributions of functional imaging (fMRI/PET) to our understanding of how action and tool concepts are represented and processed in the human brain. Category-selective deficits in neuropsychological patients have suggested a fine-grained functional specialization within the neural systems of semantics. However, the underlying principles of semantic organization remain controversial. The feature-based account of semantic memory (or 'sensory-motor theory') predicates category-selective effects (e.g. tool vs. animals) on anatomical segregation for different semantic features (e.g. action vs. visual). Within this framework, we will review functional imaging evidence that semantic processing of tools and actions may rely on activations within the visuo-motor system.

Conceptual knowledge in the brain: fMRI evidence for a featural organization

The organization and representation of conceptual knowledge in the brain remains a controversial issue in terms of both neuropsychological and imaging evidence. We report the results of a functional magnetic resonance study in which the role of the most debated dimensions (domain and feature type) was evaluated through a concept-feature verification task. The scope of the task was to eliminate serious methodological concerns that weighed down previous imaging research in this area, and to allow more definitive conclusions regarding the specific contribution of these dimensions. The results show differential patterns of brain activity according to feature type (both motion and visual form/surface features) but not according to concept domain (living vs. nonliving things). These findings are in accord with a modality-specific account of conceptual knowledge organization in the brain, in which specific kinds of features (e.g. form, color, motion, etc) have differential importance for representing different concepts.