tDCS of right-hemispheric Wernicke's area homologue affects contextual learning of novel lexicon.

Numerous studies have shown robust evidence of the right hemisphere's involvement in the language function, for instance in the processing of intonation, grammar, word meanings, metaphors, etc. However, its role in lexicon acquisition remains obscure. We applied transcranial direct current stimulation (tDCS) over the right-hemispheric homologue of Wernicke's area to assess its putative involvement in the processing of different types of novel semantics. After receiving 15 min of anodal, cathodal, or sham (placebo) tDCS, three groups of healthy participants learnt novel concrete and abstract words in the context of short stories. Learning outcomes were assessed using a battery of tests immediately after this contextual learning session and 24 h later. As a result, an inhibitory effect of cathodal tDCS and a facilitatory effect of anodal tDCS were found for abstract word acquisition only. We also found a significant drop in task performance on the second day of the assessment for both word types in all the stimulation groups, suggesting no significant influence of tDCS on the post-learning consolidation of new memory traces. The results suggest an involvement of Wernicke's right-hemispheric counterpart in initial encoding (but not consolidation) of abstract semantics, which may be explained either by the right hemispheres direct role in processing lexical semantics or by an indirect impact of tDCS on contralateral (left-hemispheric) cortical areas through cross-callosal connections.

Rapid microstructural plasticity in the cortical semantic network following a short language learning session.

Despite the clear importance of language in our life, our vital ability to quickly and effectively learn new words and meanings is neurobiologically poorly understood. Conventional knowledge maintains that language learning-especially in adulthood-is slow and laborious. Furthermore, its structural basis remains unclear. Even though behavioural manifestations of learning are evident near instantly, previous neuroimaging work across a range of semantic categories has largely studied neural changes associated with months or years of practice. Here, we address rapid neuroanatomical plasticity accompanying new lexicon acquisition, specifically focussing on the learning of action-related language, which has been linked to the brain's motor systems. Our results show that it is possible to measure and to externally modulate (using transcranial magnetic stimulation (TMS) of motor cortex) cortical microanatomic reorganisation after mere minutes of new word learning. Learning-induced microstructural changes, as measured by diffusion kurtosis imaging (DKI) and machine learning-based analysis, were evident in prefrontal, temporal, and parietal neocortical sites, likely reflecting integrative lexico-semantic processing and formation of new memory circuits immediately during the learning tasks. These results suggest a structural basis for the rapid neocortical word encoding mechanism and reveal the causally interactive relationship of modal and associative brain regions in supporting learning and word acquisition.

Keeping track of time: Horizontal spatial biases for hours, days, and months.

In many Western cultures, the processing of temporal words related to the past and to the future is associated with left and right space, respectively - a phenomenon known as the horizontal Mental Time Line (MTL). While this mapping is apparently quite ubiquitous, its regularity and consistency across different types of temporal concepts remain to be determined. Moreover, it is unclear whether such spatial mappings are an essential and early constituent of concept activation. In the present study, we used words denoting time units at different scales (hours of the day, days of the week, months of the year) associated with either left space (e.g., 9 a.m., Monday, February) or right space (e.g., 8 p.m., Saturday, November) as cues in a line bisection task. Fifty-seven healthy adults listened to temporal words and then moved a mouse cursor to the perceived midpoint of a horizontally presented line. We measured movement trajectories, initial line intersection coordinates, and final bisection response coordinates. We found movement trajectory displacements for left- vs. right-biasing hour and day cues. Initial line intersections were biased specifically by month cues, while final bisection responses were biased specifically by hour cues. Our findings offer general support to the notion of horizontal space-time associations and suggest further investigation of the exact chronometry and strength of this association across individual time units.

Broca's area involvement in abstract and concrete word acquisition: tDCS evidence.

Broca's area in the left hemisphere of the human neocortex has been suggested as a major hub for acquisition, storage, and access of linguistic information, abstract words in particular. Direct causal evidence for the latter, however, is still scarce; filling this gap was the goal of the present study. Using transcranial direct current stimulation (tDCS) of Broca's region, we aimed to delineate the involvement of this area in abstract and concrete word acquisition. The experiment used a between-subject design and involved 15 min of anodal or cathodal tDCS over Broca's area, or a sham/placebo control condition. The stimulation procedure was followed by a contextual learning session, in which participants were exposed to new concrete and abstract words embedded into short five-sentence texts. Finally, a set of behavioural assessment tasks was run to assess the learning outcomes immediately after the training (Day 1) and with a 24-hour delay (Day 2). The results showed that participants recognised novel abstract words more accurately after both anodal and cathodal tDCS in comparison with the sham condition on Day 1, which was also accompanied by longer recognition times (presumably due to deeper lexico-semantic processing), supporting the role of Broca's region in acquisition of abstract semantics. They were also more successful when recalling concrete words after cathodal tDCS, which indicates a degree of Broca's area involvement in forming memory circuits for concrete words as well. A decrease in the accuracy of recall of word forms and their meanings, as well as in recognition, was observed for all stimulation groups and both types of semantics on Day 2. The results suggest that both anodal and cathodal tDCS of Broca's area improves immediate contextual learning of novel vocabulary, predominantly affecting abstract semantics.

Biliteracy and acquisition of novel written words: the impact of phonological conflict between L1 and L2 scripts.

The acquisition of new orthographic representations is a rapid and accurate process in proficient monolingual readers. The present study used biliterate and bialphabetic population to address the impact of phonological inconsistencies across the native (L1) and second (L2) alphabets. Naming latencies were collected from 50 Russian-English biliterates through a reading-aloud task with familiar and novel word forms repeated across 10 blocks. There were three Script conditions: (1) native Cyrillic, (2) non-native Roman, and (3) Ambiguous (with graphically identical, but phonologically inconsistent graphemes shared by both alphabets). Our analysis revealed the main effect of Script on both reading and orthographic learning: naming latencies during training were longer for the ambiguous stimuli, particularly for the novel ones. Nonetheless, novel word forms in the ambiguous condition approached the latencies for the familiar words along the exposures, although this effect was faster in the phonologically consistent trials. Post-training tests revealed similarly successful performance patterns for previously familiar and newly trained forms, indicating successful rapid acquisition of the latter. Furthermore, we found the highest free recall rates for the ambiguous stimuli. Overall, our results indicate that phonological inconsistency initially interferes with the efficiency of novel word encoding. Nevertheless, it does not prevent efficient attribution of orthographic representations; instead, the knowledge of two distinct alphabets supports a more efficient learning and a better memory for ambiguous stimuli via enhancing their encoding and retrieval.

STN-DBS affects language processing differentially in Parkinson's disease: Multiple-case MEG study.

OBJECTIVES: In this study, we investigated the effects of bilateral and unilateral deep brain stimulation of the subthalamic nucleus (STN-DBS) in PD patients on neural responses associated with two aspects of spoken language processing: semantics of action-related verbs and morphosyntactic processing. MATERIALS AND METHODS: Using a passive unattended paradigm to present spoken linguistic stimuli, we recorded magnetoencephalographic (MEG) responses in three PD patients in four DBS conditions: left unilateral STN-DBS, right unilateral STN-DBS, bilateral STN-DBS, and no STN-DBS. To ensure that any observed effects of DBS on the neuromagnetic responses could be attributed to the linguistic context per se and were not merely induced by the electrical stimulation, we assessed the effects of STN-DBS on linguistic contrasts within each stimulation condition. Hence, we contrasted the processing of action vs. abstract verbs as well as the processing of correct vs. incorrect morphosyntactic inflections within each DBS condition. RESULTS: The results revealed that, compared to the DBS-off state, both bilateral and right unilateral stimulation of the STN yielded significant dissociations in the processing of action and abstract verbs, with greater neuromagnetic responses for action verbs compared to abstract verbs. For morphosyntax processing, only left unilateral stimulation yielded significant dissociations (relative to the DBS-off state), with greater neuromagnetic responses to the incorrect inflections compared to the correct inflections. CONCLUSION: The results reflect differential effects of unilateral and bilateral STN-DBS on neuromagnetic responses associated with the processing of spoken language. They suggest that different specific aspects of linguistic information processing in PD are affected differently by STN-DBS.

Rapid acquisition of novel written word-forms: ERP evidence.

BACKGROUND: Novel word acquisition is generally believed to be a rapid process, essential for ensuring a flexible and efficient communication system; at least in spoken language, learners are able to construct memory traces for new linguistic stimuli after just a few exposures. However, such rapid word learning has not been systematically found in visual domain, with different confounding factors obscuring the orthographic learning of novel words. This study explored the changes in human brain activity occurring online, during a brief training with novel written word-forms using a silent reading task RESULTS: Single-trial, cluster-based random permutation analysis revealed that training caused an extremely fast (after just one repetition) and stable facilitation in novel word processing, reflected in the modulation of P200 and N400 components, possibly indicating rapid dynamics at early and late stages of the lexical processing. Furthermore, neural source estimation of these effects revealed the recruitment of brain areas involved in orthographic and lexico-semantic processing, respectively. CONCLUSIONS: These results suggest the formation of neural memory traces for novel written word-forms after a minimal exposure to them even in the absence of a semantic reference, resembling the rapid learning processes known to occur in spoken language.

Referent's Lexical Frequency Predicts Mismatch Negativity Responses to New Words Following Semantic Training.

Lexical ERPs (event-related potentials) obtained in an oddball paradigm were suggested to be an index of the formation of new word representations in the brain in the learning process: with increased exposure to new lexemes, the ERP amplitude grows, which is interpreted as a signature of a new memory-trace build-up and activation. Previous learning studies using this approach have, however, mostly used meaningless novel word forms; it therefore remains uncertain whether the increased amplitude simply reflects increased familiarity with the new stimulus or is indeed a reflection of a complete word representation. Here, we used the oddball paradigm to measure the mismatch negativity (MMN) responses to novel word forms before and after semantic training, during which they were associated with previously familiar words of either high or low frequency of occurrence. Following training, the amplitude of the MMN to novel words was enhanced. Furthermore, these changes were dependent on the frequency of the reference which novel items became associated with: namely, the MMN amplitude became greater and the latency shorter for the item which was assigned the high-frequency meaning. Even though the amount of training was the same for both types of items, the low-frequency stimulus did not achieve similar significant changes. Our results suggest that the new surface form becomes linked to the existing representation, which then automatically activates in full when the respective stimulus is present at the input. This finding indicates that the learning-related MMN dynamics, manifest as a response increase after learning, likely reflects the formation and activation of a complete lexicosemantic memory circuits for words.

Learning with the wave of the hand: Kinematic and TMS evidence of primary motor cortex role in category-specific encoding of word meaning.

Language processing recruits a core fronto-temporal cortical network, which is complemented by a distributed network of modality-specific areas (such as the motor cortex) to encode referential aspects of meaning. Since most studies typically focus on already fully-formed adult vocabulary, it remains unclear how and when exactly modality-specific areas become involved in language processing. Here, we addressed this question using a 3D virtual environment game to teach adult participants new action verbs and object nouns. To test the role of primary motor cortex (M1) in selectively encoding aspects of action verb meaning early on in the process of word learning, we delivered theta-burst stimulation to three groups of participants prior to learning: M1 TMS, active control TMS, and sham TMS. Our results show that TMS of M1 (but not active or sham controls) interferes with the learning process, as indexed by measures of movement kinematics and a higher number of errors during training. Thus, TMS disruption of M1 degrades learning outcomes when motor information is an integral part of lexico-semantic encoding. This effect was corroborated in a subsequent lexical decision task, which showed significant group- and word-category RT differences, suggesting category-specific effects of TMS on word learning. Overall, our study demonstrates the M1's causal involvement in the earliest phases of word learning and rapid encoding of semantic motor information.

Different answers to different audiences: effects of social context on the accuracy-informativeness trade-off.

Research on conversational exchanges shows that people attempt to optimise their responses' relevance when they definitely know the correct answer (e.g., "What time is it?"). However, such certainty is often unavailable while speakers may still be under social pressure to provide an answer. We investigated how social context influences the informativeness level when answering questions under uncertainty. In three experiments, participants answered difficult general-knowledge questions placed in different social contexts (formal vs. informal). Participants generated their answers, then they were presented with a given context, and decided on the number of alternative responses they wanted to provide (single, with one alternative vs. plural, with several alternatives) and whether the answer should be reported or withheld (report option). Participants reported more answers in the informal context. In the formal context, single answers were preferred, and they were more frequently reported. We conclude that social context influences the level of informativeness in a conversation, affecting achievable accuracy. Our results also show the joint influence of the confidence and the social context on willingness to share information.

Silent Expectations: Dynamic Causal Modeling of Cortical Prediction and Attention to Sounds That Weren't.

UNLABELLED: There is increasing evidence that human perception is realized by a hierarchy of neural processes in which predictions sent backward from higher levels result in prediction errors that are fed forward from lower levels, to update the current model of the environment. Moreover, the precision of prediction errors is thought to be modulated by attention. Much of this evidence comes from paradigms in which a stimulus differs from that predicted by the recent history of other stimuli (generating a so-called "mismatch response"). There is less evidence from situations where a prediction is not fulfilled by any sensory input (an "omission" response). This situation arguably provides a more direct measure of "top-down" predictions in the absence of confounding "bottom-up" input. We applied Dynamic Causal Modeling of evoked electromagnetic responses recorded by EEG and MEG to an auditory paradigm in which we factorially crossed the presence versus absence of "bottom-up" stimuli with the presence versus absence of "top-down" attention. Model comparison revealed that both mismatch and omission responses were mediated by increased forward and backward connections, differing primarily in the driving input. In both responses, modeling results suggested that the presence of attention selectively modulated backward "prediction" connections. Our results provide new model-driven evidence of the pure top-down prediction signal posited in theories of hierarchical perception, and highlight the role of attentional precision in strengthening this prediction. SIGNIFICANCE STATEMENT: Human auditory perception is thought to be realized by a network of neurons that maintain a model of and predict future stimuli. Much of the evidence for this comes from experiments where a stimulus unexpectedly differs from previous ones, which generates a well-known "mismatch response." But what happens when a stimulus is unexpectedly omitted altogether? By measuring the brain's electromagnetic activity, we show that it also generates an "omission response" that is contingent on the presence of attention. We model these responses computationally, revealing that mismatch and omission responses only differ in the location of inputs into the same underlying neuronal network. In both cases, we show that attention selectively strengthens the brain's prediction of the future.

Cortical networks for reference-frame processing are shared by language and spatial navigation systems.

To help us live in the three-dimensional world, our brain integrates incoming spatial information into reference frames, which are based either on our own body (egocentric) or independent from it (allocentric). Such frames, however, may be crucial not only when interacting with the visual world, but also in language comprehension, since even the simplest utterance can be understood from different perspectives. While significant progress has been made in elucidating how linguistic factors, such as pronouns, influence reference frame adoption, the neural underpinnings of this ability are largely unknown. Building on the neural reuse framework, this study tested the hypothesis that reference frame processing in language comprehension involves mechanisms used in navigation and spatial cognition. We recorded EEG activity in 28 healthy volunteers to identify spatiotemporal dynamics in (1) spatial navigation, and (2) a language comprehension task (sentence-picture matching). By decomposing the EEG signal into a set of maximally independent activity patterns, we localised and identified a subset of components which best characterised perspective-taking in both domains. Remarkably, we find individual co-variability across these tasks: people's strategies in spatial navigation are also reflected in their construction of sentential perspective. Furthermore, a distributed network of cortical generators of such strategy-dependent activity responded not only in navigation, but in sentence comprehension. Thus we report, for the first time, evidence for shared brain mechanisms across these two domains - advancing our understanding of language's interaction with other cognitive systems, and the individual differences shaping comprehension.

Flexible, rapid and automatic neocortical word form acquisition mechanism in children as revealed by neuromagnetic brain response dynamics.

Children learn new words and word forms with ease, often acquiring a new word after very few repetitions. Recent neurophysiological research on word form acquisition in adults indicates that novel words can be acquired within minutes of repetitive exposure to them, regardless of the individual's focused attention on the speech input. Although it is well-known that children surpass adults in language acquisition, the developmental aspects of such rapid and automatic neural acquisition mechanisms remain unexplored. To address this open question, we used magnetoencephalography (MEG) to scrutinise brain dynamics elicited by spoken words and word-like sounds in healthy monolingual (Danish) children throughout a 20-min repetitive passive exposure session. We found rapid neural dynamics manifested as an enhancement of early (~100ms) brain activity over the short exposure session, with distinct spatiotemporal patterns for different novel sounds. For novel Danish word forms, signs of such enhancement were seen in the left temporal regions only, suggesting reliance on pre-existing language circuits for acquisition of novel word forms with native phonology. In contrast, exposure both to novel word forms with non-native phonology and to novel non-speech sounds led to activity enhancement in both left and right hemispheres, suggesting that more wide-spread cortical networks contribute to the build-up of memory traces for non-native and non-speech sounds. Similar studies in adults have previously reported more sluggish (~15-25min, as opposed to 4min in the present study) or non-existent neural dynamics for non-native sound acquisition, which might be indicative of a higher degree of plasticity in the children's brain. Overall, the results indicate a rapid and highly plastic mechanism for a dynamic build-up of memory traces for novel acoustic information in the children's brain that operates automatically and recruits bilateral temporal cortical circuits.

The role of executive control in the activation of manual affordances.

We investigated the role of executive control processes in the activation of manual affordances in two experiments combining stimulus-response compatibility (SRC) and dual-task paradigms. We registered an inverse SRC effect in the presence of a parallel backward-counting task in Experiment 1, and a cancellation of the SRC effect in Experiment 2 when a parallel Stroop-like task was used. We interpret our data as supporting a self-inhibition account of the affordance activation control. Accordingly, the role of executive processes is to prevent self-inhibition in supraliminal conditions: when cognitive resources are depleted by a parallel task, the self-inhibition mechanism becomes active and irrelevantly potentiated affordances are inhibited, leading to the emergence of an inverse SRC effect. In addition, the difference between data patterns observed in the two experiments suggests that the exact roles of the executive processes involved during the activation of affordances may differ. The results suggest a mechanism for action-related activation monitoring based on a flexible control over automatically potentiated actions. The paper discusses the proposed mechanism in detail and outlines further research directions.

Automatic ultrarapid activation and inhibition of cortical motor systems in spoken word comprehension.

To address the hotly debated question of motor system involvement in language comprehension, we recorded neuromagnetic responses elicited in the human brain by unattended action-related spoken verbs and nouns and scrutinized their timecourse and neuroanatomical substrates. We found that already very early on, from ∼80 ms after disambiguation point when the words could be identified from the available acoustic information, both verbs and nouns produced characteristic somatotopic activations in the motor strip, with words related to different body parts activating the corresponding body representations. Strikingly, along with this category-specific activation, we observed suppression of motor-cortex activation by competitor words with incompatible semantics, documenting operation of the neurophysiological principles of lateral/surround inhibition in neural word processing. The extremely early onset of these activations and deactivations, their emergence in the absence of attention, and their similar presence for words of different lexical classes strongly suggest automatic involvement of motor-specific circuits in the perception of action-related language.

Brain basis of communicative actions in language.

Although language is a key tool for communication in social interaction, most studies in the neuroscience of language have focused on language structures such as words and sentences. Here, the neural correlates of speech acts, that is, the actions performed by using language, were investigated with functional magnetic resonance imaging (fMRI). Participants were shown videos, in which the same critical utterances were used in different communicative contexts, to Name objects, or to Request them from communication partners. Understanding of critical utterances as Requests was accompanied by activation in bilateral premotor, left inferior frontal and temporo-parietal cortical areas known to support action-related and social interactive knowledge. Naming, however, activated the left angular gyrus implicated in linking information about word forms and related reference objects mentioned in critical utterances. These findings show that understanding of utterances as different communicative actions is reflected in distinct brain activation patterns, and thus suggest different neural substrates for different speech act types.

Two distinct auditory-motor circuits for monitoring speech production as revealed by content-specific suppression of auditory cortex.

Speech production, both overt and covert, down-regulates the activation of auditory cortex. This is thought to be due to forward prediction of the sensory consequences of speech, contributing to a feedback control mechanism for speech production. Critically, however, these regulatory effects should be specific to speech content to enable accurate speech monitoring. To determine the extent to which such forward prediction is content-specific, we recorded the brain's neuromagnetic responses to heard multisyllabic pseudowords during covert rehearsal in working memory, contrasted with a control task. The cortical auditory processing of target syllables was significantly suppressed during rehearsal compared with control, but only when they matched the rehearsed items. This critical specificity to speech content enables accurate speech monitoring by forward prediction, as proposed by current models of speech production. The one-to-one phonological motor-to-auditory mappings also appear to serve the maintenance of information in phonological working memory. Further findings of right-hemispheric suppression in the case of whole-item matches and left-hemispheric enhancement for last-syllable mismatches suggest that speech production is monitored by 2 auditory-motor circuits operating on different timescales: Finer grain in the left versus coarser grain in the right hemisphere. Taken together, our findings provide hemisphere-specific evidence of the interface between inner and heard speech.

Real-time functional architecture of visual word recognition.

Despite a century of research into visual word recognition, basic questions remain unresolved about the functional architecture of the process that maps visual inputs from orthographic analysis onto lexical form and meaning and about the units of analysis in terms of which these processes are conducted. Here we use magnetoencephalography, supported by a masked priming behavioral study, to address these questions using contrasting sets of simple (walk), complex (swimmer), and pseudo-complex (corner) forms. Early analyses of orthographic structure, detectable in bilateral posterior temporal regions within a 150-230 msec time frame, are shown to segment the visual input into linguistic substrings (words and morphemes) that trigger lexical access in left middle temporal locations from 300 msec. These are primarily feedforward processes and are not initially constrained by lexical-level variables. Lexical constraints become significant from 390 msec, in both simple and complex words, with increased processing of pseudowords and pseudo-complex forms. These results, consistent with morpho-orthographic models based on masked priming data, map out the real-time functional architecture of visual word recognition, establishing basic feedforward processing relationships between orthographic form, morphological structure, and lexical meaning.

Rapid and automatic speech-specific learning mechanism in human neocortex.

A unique feature of human communication system is our ability to rapidly acquire new words and build large vocabularies. However, its neurobiological foundations remain largely unknown. In an electrophysiological study optimally designed to probe this rapid formation of new word memory circuits, we employed acoustically controlled novel word-forms incorporating native and non-native speech sounds, while manipulating the subjects' attention on the input. We found a robust index of neurolexical memory-trace formation: a rapid enhancement of the brain's activation elicited by novel words during a short (~30min) perceptual exposure, underpinned by fronto-temporal cortical networks, and, importantly, correlated with behavioural learning outcomes. Crucially, this neural memory trace build-up took place regardless of focused attention on the input or any pre-existing or learnt semantics. Furthermore, it was found only for stimuli with native-language phonology, but not for acoustically closely matching non-native words. These findings demonstrate a specialised cortical mechanism for rapid, automatic and phonology-dependent formation of neural word memory circuits.

Lost for emotion words: what motor and limbic brain activity reveals about autism and semantic theory.

Autism spectrum conditions (ASC) are characterised by deficits in understanding and expressing emotions and are frequently accompanied by alexithymia, a difficulty in understanding and expressing emotion words. Words are differentially represented in the brain according to their semantic category and these difficulties in ASC predict reduced activation to emotion-related words in limbic structures crucial for affective processing. Semantic theories view 'emotion actions' as critical for learning the semantic relationship between a word and the emotion it describes, such that emotion words typically activate the cortical motor systems involved in expressing emotion actions such as facial expressions. As ASC are also characterised by motor deficits and atypical brain structure and function in these regions, motor structures would also be expected to show reduced activation during emotion-semantic processing. Here we used event-related fMRI to compare passive processing of emotion words in comparison to abstract verbs and animal names in typically-developing controls and individuals with ASC. Relatively reduced brain activation in ASC for emotion words, but not matched control words, was found in motor areas and cingulate cortex specifically. The degree of activation evoked by emotion words in the motor system was also associated with the extent of autistic traits as revealed by the Autism Spectrum Quotient. We suggest that hypoactivation of motor and limbic regions for emotion word processing may underlie difficulties in processing emotional language in ASC. The role that sensorimotor systems and their connections might play in the affective and social-communication difficulties in ASC is discussed.