Primary motor cortex functionally contributes to language comprehension: An online rTMS study

Time to Face Language: Embodied Mechanisms Underpin the Inception of Face-Related Meanings in the Human Brain

In construing meaning, the brain recruits multimodal (conceptual) systems and embodied (modality-specific) mechanisms. Yet, no consensus exists on how crucial the latter are for the inception of semantic distinctions. To address this issue, we combined electroencephalographic (EEG) and intracranial EEG (iEEG) to examine when nouns denoting facial body parts (FBPs) and nonFBPs are discriminated in face-processing and multimodal networks. First, FBP words increased N170 amplitude (a hallmark of early facial processing). Second, they triggered fast (~100 ms) activity boosts within the face-processing network, alongside later (~275 ms) effects in multimodal circuits. Third, iEEG recordings from face-processing hubs allowed decoding ~80% of items before 200 ms, while classification based on multimodal-network activity only surpassed ~70% after 250 ms. Finally, EEG and iEEG connectivity between both networks proved greater in early (0-200 ms) than later (200-400 ms) windows. Collectively, our findings indicate that, at least for some lexico-semantic categories, meaning is construed through fast reenactments of modality-specific experience.

Left posterior inferior parietal cortex causally supports the retrieval of action knowledge

Conceptual knowledge is central to human cognition. The left posterior inferior parietal lobe (pIPL) is implicated by neuroimaging studies as a multimodal hub representing conceptual knowledge related to various perceptual-motor modalities. However, the causal role of left pIPL in conceptual processing remains unclear. Here, we transiently disrupted left pIPL function with transcranial magnetic stimulation (TMS) to probe its causal relevance for the retrieval of action and sound knowledge. We compared effective TMS over left pIPL with sham TMS, while healthy participants performed three different tasks-lexical decision, action judgment, and sound judgment-on words with a high or low association to actions and sounds. We found that pIPL-TMS selectively impaired action judgments on low sound-low action words. For the first time, we directly related computational simulations of the TMS-induced electrical field to behavioral performance, which revealed that stronger stimulation of left pIPL is associated with worse performance for action but not sound judgments. These results indicate that left pIPL causally supports conceptual processing when action knowledge is task-relevant and cannot be compensated by sound knowledge. Our findings suggest that left pIPL is specialized for the retrieval of action knowledge, challenging the view of left pIPL as a multimodal conceptual hub.

Challenges and Opportunities for Grounding Cognition

According to the grounded perspective, cognition emerges from the interaction of classic cognitive processes with the modalities, the body, and the environment. Rather than being an autonomous impenetrable module, cognition incorporates these other domains intrinsically into its operation. The Situated Action Cycle offers one way of understanding how the modalities, the body, and the environment become integrated to ground cognition. Seven challenges and opportunities are raised for this perspective: (1) How does cognition emerge from the Situated Action Cycle and in turn support it? (2) How can we move beyond simply equating embodiment with action, additionally establishing how embodiment arises in the autonomic, neuroendocrine, immune, cardiovascular, respiratory, digestive, and integumentary systems? (3) How can we better understand the mechanisms underlying multimodal simulation, its functions across the Situated Action Cycle, and its integration with other representational systems? (4) How can we develop and assess theoretical accounts of symbolic processing from the grounded perspective (perhaps using the construct of simulators)? (5) How can we move beyond the simplistic distinction between concrete and abstract concepts, instead addressing how concepts about the external and internal worlds pattern to support the Situated Action Cycle? (6) How do individual differences emerge from different populations of situational memories as the Situated Action Cycle manifests itself differently across individuals? (7) How can constructs from grounded cognition provide insight into the replication and generalization crises, perhaps from a quantum perspective on mechanisms (as exemplified by simulators).

Time course of brain activity during the processing of motor- and vision-related abstract concepts: flexibility and task dependency

Grounded cognition theories assume that conceptual processing depends on modality-specific brain systems in a context-dependent fashion. Although the relation of abstract concepts to modality-specific systems is less obvious than for concrete concepts, recent behavioral and neuroimaging studies indicated a foundation of abstract concepts in vision and action. However, due to their poor temporal resolution, neuroimaging studies cannot determine whether sensorimotor activity reflects rapid access to conceptual information or later conceptual processes. The present study therefore assessed the time course of abstract concept processing using event-related potentials (ERPs) and compared ERP responses to abstract concepts with a strong relation to vision or action. We tested whether possible ERP effects to abstract word categories would emerge in early or in later time windows and whether these effects would depend on the depth of the conceptual task. In Experiment 1, a shallow lexical decision task, early feature-specific effects starting at 178 ms were revealed, but later effects beyond 300 ms were also observed. In Experiment 2, a deep conceptual decision task, feature-specific effects with an onset of 22 ms were obtained, but effects again extended beyond 300 ms. In congruency with earlier neuroimaging work, the present feature-specific ERP effects suggest a grounding of abstract concepts in modal brain systems. The presence of early and late feature-specific effects indicates that sensorimotor activity observed in neuroimaging experiments may reflect both rapid conceptual and later post-conceptual processing. Results furthermore suggest that a deep conceptual task accelerates access to conceptual sensorimotor features, thereby demonstrating conceptual flexibility.

Positive effects of grasping virtual objects on memory for novel words in a second language

Theories of embodied cognition describe language processing and representation as inherently connected to the sensorimotor experiences collected during acquisition. While children grasp their world, collect bodily experiences and name them, in second language (L2), students learn bilingual word lists. Experimental evidence shows that embodiment by mean of gestures enhances memory for words in L2. However, no study has been conducted on the effects of grasping in L2. In a virtual scenario, we trained 46 participants on 18 two- and three-syllabic words of Vimmi, an artificial corpus created for experimental purposes. The words were assigned concrete meanings of graspable objects. Six words were learned audio-visually, by reading the words projected on the wall and by hearing them. Another 6 words were trained by observation of virtual objects. Another 6 words were learned by observation and additional grasping the virtual objects. Thereafter participants were subministered free, cued recall, and reaction time tests in order to assess the word retention and the word recognition. After 30 days, the recall tests were repeated remotely to assess the memory in the long term. The results show that grasping of virtual objects can lead to superior memory performance and to lower reaction times during recognition.

Feeling better: Tactile verbs speed up tactile detection

Embodiment of action-related language into the motor system has been extensively documented. Yet the case of sensory words, especially referring to touch, remains overlooked. We investigated the influence of verbs denoting tactile sensations on tactile perception. In Experiment 1, participants detected tactile stimulations on their forearm, preceded by tactile or non-tactile verbs by one of three delays (170, 350, 500 ms) reflecting different word processing stages. Results revealed shorter reaction times to tactile stimulations following tactile than non-tactile verbs, irrespective of delay. To ensure that priming pertained to tactile, and not motor, verb properties, Experiment 2 compared the impact of tactile verbs to both action and non-tactile verbs, while stimulations were delivered on the index finger. No priming emerged following action verbs, therefore not supporting the motor-grounded interpretation. Facilitation by tactile verbs was however not observed, possibly owing to methodological changes. Experiment 3, identical to Experiment 2 except that stimulation was delivered to participants' forearm, replicated the priming effect. Importantly, tactile stimulations were detected faster after tactile than after both non-tactile and action verbs, indicating that verbs' tactile properties engaged resources shared with sensory perception. Our findings suggest that language conveying tactile information can activate somatosensory representations and subsequently promote tactile detection.

Making It Harder to "See" Meaning: The More You See Something, the More Its Conceptual Representation Is Susceptible to Visual Interference

Does the perceptual system for looking at the world overlap with the conceptual system for thinking about it? We conducted two experiments (N = 403) to investigate this question. Experiment 1 showed that when people make simple semantic judgments on words, interference from a concurrent visual task scales in proportion to how much visual experience they have with the things the words refer to. Experiment 2 showed that when people make the same judgments on the very same words, interference from a concurrent manual task scales in proportion to how much manual (but critically, not visual) experience people have with those same things. These results suggest that the meanings of frequently visually experienced things are represented (in part) in the visual system used for actually seeing them, that this visually represented information is a functional part of conceptual knowledge, and that the extent of these visual representations is influenced by visual experience.

Hand-use norms for Dutch and English manual action verbs: Implicit measures from a pantomime task

Many studies use manual action verbs to test whether people use neural systems for controlling manual actions to understand language about those actions. Yet, few of these studies empirically establish how people use their hands to perform the actions described by those verbs, relying instead on explicit self-report measures. Here, participants pantomimed the manual actions described by a large set of Dutch (N = 251) and English (N = 250) verbs, allowing us to approximate the extent to which people use each of their hands to perform these actions. After the pantomime task, participants also provided explicit ratings of each of these actions. The results from the pantomime task showed that most manual actions cannot be described accurately as either "unimanual" or "bimanual." With a few exceptions, unimanual action verbs do not describe actions that are performed with only one hand, and bimanual verbs do not describe actions that are performed by using both hands equally. Instead, individual actions vary continuously in the extent to which people use their non-dominant hand to perform them, and in the extent to which people consistently prefer one hand or the other to perform them. Finally, by comparing participants' implicit behavior to their explicit ratings, we found that participants' self-report showed only limited correspondence with their observed motor behavior. We provide all of our measures in both raw and summary format, offering researchers a precision tool for constructing stimulus sets for experiments on embodied cognition.

Degradation of Praxis Brain Networks and Impaired Comprehension of Manipulable Nouns in Stroke

Distributed brain systems contribute to representation of semantic knowledge. Whether sensory and motor systems of the brain are causally involved in representing conceptual knowledge is an especially controversial question. Here, we tested 57 chronic left-hemisphere stroke patients using a semantic similarity judgment task consisting of manipulable and nonmanipulable nouns. Three complementary methods were used to assess the neuroanatomical correlates of semantic processing: voxel-based lesion-symptom mapping, resting-state functional connectivity, and gray matter fractional anisotropy. The three measures provided converging evidence that injury to the brain networks required for action observation, execution, planning, and visuomotor coordination are associated with specific deficits in manipulable noun comprehension relative to nonmanipulable items. Damage or disrupted connectivity of areas such as the middle posterior temporal gyrus, anterior inferior parietal lobe, and premotor cortex was related specifically to the impairment of manipulable noun comprehension. These results suggest that praxis brain networks contribute especially to the comprehension of manipulable object nouns.

Perceptual Representations in L1, L2 and L3 Comprehension: Delayed Sentence-Picture Verification

We used delayed sentence-picture verification tasks to investigate multilingual perceptual representations. In experiment 1, participants listened to sentences with implied shapes. After a 10-min interval, they judged whether pictures had been mentioned in the preceding sentences or not. Results in experiment 1 showed significant match effect in L1, but not in high proficient L2 or low proficient L3. In experiment 2, Participants listened to one language block, then immediately judged one picture block, totally three language-picture blocks. Results in experiment 2 were parallel to results in experiment 1. Our study supports the view of distributed conception: L2 and L3 are associated with less perceptual symbols than L1, indicating great impact of acquisition styles on perceptual representations. Our results show little impact of language proficiency levels on perceptual representations in delayed tasks.

The role of motor system in action-related language comprehension in L1 and L2: An fMRI study

The framework of embodied cognition has challenged the modular view of a language-cognition divide by suggesting that meaning-retrieval critically involves the sensory-motor system. Despite extensive research into the neural mechanisms underlying language-motor coupling, it remains unclear how the motor system might be differentially engaged by different levels of linguistic abstraction and language proficiency. To address this issue, we used fMRI to quantify neural activations in brain regions underlying motor and language processing in Chinese-English speakers' processing of literal, metaphorical, and abstract language in their L1 and L2. Results overall revealed a response in motor ROIs gradually attenuating in intensity from literal to abstract via metaphorical language in both L1 and L2. Furthermore, contrast analyses between L1 and L2 showed overall greater activations of motor ROIs in the L2. We conclude that motor involvement in language processing is graded rather than all-or-none and that the motor system has a dual-functional role.

Somatic and visceral effects of word valence, arousal and concreteness in a continuum lexical space

Although affective and semantic word properties are known to independently influence our sensorimotor system, less is known about their interaction. We investigated this issue applying a data-driven mixed-effects regression approach, evaluating the impact of lexical-semantic properties on electrophysiological parameters, namely facial muscles activity (left corrugator supercilii, zygomaticus major, levator labii superioris) and heartbeat, during word processing. 500 Italian words were acoustically presented to 20 native-speakers, while electrophysiological signals were continuously recorded. Stimuli varied for affective properties, namely valence (the degree of word positivity), arousal (the amount of emotional activation brought by the word), and semantic ones, namely concreteness. Results showed that the three variables interacted in predicting both heartbeat and muscular activity. Specifically, valence influenced activation for lower levels of arousal. This pattern was further modulated by concreteness: the lower the word concreteness, the larger affective-variable impact. Taken together, our results provide evidence for bodily responses during word comprehension. Crucially, such responses were found not only for voluntary muscles, but also for the heartbeat, providing evidence to the idea of a common emotional motor system. The higher impact of affective properties for abstract words supports proposals suggesting that emotions play a central role in the grounding of abstract concepts.

Dissociating action and abstract verb comprehension post-stroke

The neural bases of action and abstract concept representations remain a topic of debate. While several lines of research provide evidence for grounding of action-related conceptual content into sensory-motor systems, results of traditional lesion-deficit studies have been somewhat inconsistent. Further, few studies have directly compared the neural substrates of action and relatively abstract verb comprehension post-stroke. Here, we investigated the impact of the disruption of two neural networks on comprehension of action and relatively abstract verbs in 48 unilateral left-hemisphere stroke patients using two methodologies: 1) lesion-deficit association and 2) resting-state functional connectivity (RSFC) analyses. Disruption of RSFC between the left inferior frontal gyrus and right hemisphere primary and secondary sensory-motor areas predicted greater relative impairment of action semantics. Voxel-based lesion-symptom mapping revealed that damage to frontal white matter, extending towards the inferior frontal gyrus, also predicted greater relative impairment of action semantics. On the other hand, damage to the left anterior middle temporal gyrus significantly impaired the more abstract category relative to action. These findings support the view that action and non-action/abstract semantic processing rely on partially dissociable brain networks, with action concepts relying more heavily on sensory-motor areas. The results also have wider implications for lesion-deficit association studies and show how the contralateral hemisphere can play a compensatory role following unilateral stroke.

Language, Gesture, and Emotional Communication: An Embodied View of Social Interaction

Spoken language is an innate ability of the human being and represents the most widespread mode of social communication. The ability to share concepts, intentions and feelings, and also to respond to what others are feeling/saying is crucial during social interactions. A growing body of evidence suggests that language evolved from manual gestures, gradually incorporating motor acts with vocal elements. In this evolutionary context, the human mirror mechanism (MM) would permit the passage from “doing something” to “communicating it to someone else.” In this perspective, the MM would mediate semantic processes being involved in both the execution and in the understanding of messages expressed by words or gestures. Thus, the recognition of action related words would activate somatosensory regions, reflecting the semantic grounding of these symbols in action information. Here, the role of the sensorimotor cortex and in general of the human MM on both language perception and understanding is addressed, focusing on recent studies on the integration between symbolic gestures and speech. We conclude documenting some evidence about MM in coding also the emotional aspects conveyed by manual, facial and body signals during communication, and how they act in concert with language to modulate other’s message comprehension and behavior, in line with an “embodied” and integrated view of social interaction.

Six Challenges for Embodiment Research

Twenty years after Barsalou’s seminal perceptual-symbols article, embodied cognition, the notion that cognition involves simulations of sensory, motor, or affective states, has moved from an outlandish proposal to a mainstream position adopted by many researchers in the psychological and cognitive sciences (and neurosciences). Though it has generated productive work in the cognitive sciences as a whole, it has had a particularly strong impact on research into language comprehension. The view of a mental lexicon based on symbolic word representations, which are arbitrarily linked to sensory aspects of their referents, was generally accepted since the cognitive revolution in the 1950s. This has radically changed. Given the current status of embodiment as a main theory of cognition, it is somewhat surprising that a close look at the literature reveals that the debate about the nature of the processes involved in language comprehension is far from settled, and key questions remain unanswered. We present several suggestions for a productive way forward.

Concrete vs. Abstract Semantics: From Mental Representations to Functional Brain Mapping

The nature of abstract and concrete semantics and differences between them have remained a debated issue in psycholinguistic and cognitive studies for decades. Most of the available behavioral and neuroimaging studies reveal distinctions between these two types of semantics, typically associated with a so-called “concreteness effect.” Many attempts have been made to explain these differences using various approaches, from purely theoretical linguistic and cognitive frameworks to neuroimaging experiments. In this brief overview, we will try to provide a snapshot of these diverse views and relationships between them and highlight the crucial issues preventing this problem from being solved. We will argue that one potentially beneficial way forward is to identify the neural mechanisms underpinning acquisition of the different types of semantics (e.g., by using neurostimulation techniques to establish causal relationships), which may help explain the distinctions found between the processing of concrete and abstract semantics.

Grey and white matter substrates of action naming

Despite a persistent interest in verb processing, data on the neural underpinnings of verb retrieval are fragmentary. The present study is the first to analyze the contributions of both grey and white matter damage affecting verb retrieval through action naming in stroke. We used voxel-based lesion-symptom mapping (VLSM) with an action naming task in 40 left-hemisphere stroke patients. Within the grey matter, we revealed the critical involvement of the left precentral and inferior frontal gyri, insula, and parts of basal ganglia. An overlay of white matter tract probability masks on the VLSM lesion map revealed involvement of left-hemisphere long and short association tracts with terminations in the frontal areas; and several projection tracts. The involvement of these structures is interpreted in the light of existing picture naming models, semantic control processes, and the embodiment cognition framework. Our results stress the importance of both cortico-cortical and cortico-subcortical networks of language processing.

Affordance Compatibility Effect for Word Learning in Virtual Reality

Rich sensorimotor interaction facilitates language learning and is presumed to ground conceptual representations. Yet empirical support for early stages of embodied word learning is currently lacking. Finding evidence that sensorimotor interaction shapes learned linguistic representations would provide crucial support for embodied language theories. We developed a gamified word learning experiment in virtual reality in which participants learned the names of six novel objects by grasping and manipulating objects with either their left or right hand. Participants then completed a word-color match task in which they were tested on the same six words and objects. Participants were faster to respond to stimuli in the match task when the response hand was compatible with the hand used to interact with the named object, an effect we refer to as affordance compatibility. In two follow up experiments, we found that merely observing virtual hands interact with the objects was sufficient to acquire a smaller affordance compatibility effect, and we found that the compatibility effect was driven primarily by responses with a compatible hand and not by responses in a compatible spatial location. Our results support theoretical views of language which ground word representations in sensorimotor experiences, and they suggest promising future routes to explore the sensorimotor foundations of higher cognition through immersive virtual experiments.

Embodied Semantics in a Second Language: Critical Review and Clinical Implications

The role of the sensorimotor system in second language (L2) semantic processing as well as its clinical implications for bilingual patients has hitherto been neglected. We offer an overview of the issues at stake in this under-investigated field, presenting the theoretical and clinical relevance of studying L2 embodiment and reviewing the few studies on this topic. We highlight that (a) the sensorimotor network is involved in L2 processing, and that (b) in most studies, L2 is differently embodied than L1, reflected in a lower degree or in a different pattern of L2 embodiment. Importantly, we outline critical issues to be addressed in order to guide future research. We also delineate the subsequent steps needed to confirm or dismiss the value of language therapeutic approaches based on embodiment theories as a complement of speech and language therapies in adult bilinguals.

Do Not Neglect the Body and Action: The Emergence of Embodiment Approaches to Understanding Human Development

It is becoming clear that to truly understand what it is to be human, focusing scientific efforts on the mind alone is insufficient. We are embodied minds, living and acting in a world full of meaningful things. In this article, we discuss how science has been informed by important research insights into the close relationship between the body, the mind, and the world. These interactions can be translated into embodied perspectives of human development. We provide evidence that perception, cognition, emotion, human relations, and behavior are grounded in our bodies from the beginning of our lives. From this perspective, the body cannot be assumed to be simply an effector for cognition or an instrument for collecting information for the brain. This comprehensive review and debate of embodied-related literature is accompanied by the identification of theoretical challenges and practical applications that will shape research for years to come.

Visual cortex recruitment during language processing in blind individuals is explained by Hebbian learning

In blind people, the visual cortex takes on higher cognitive functions, including language. Why this functional reorganisation mechanistically emerges at the neuronal circuit level is still unclear. Here, we use a biologically constrained network model implementing features of anatomical structure, neurophysiological function and connectivity of fronto-temporal-occipital areas to simulate word-meaning acquisition in visually deprived and undeprived brains. We observed that, only under visual deprivation, distributed word-related neural circuits 'grew into' the deprived visual areas, which therefore adopted a linguistic-semantic role. Three factors are crucial for explaining this deprivation-related growth: changes in the network's activity balance brought about by the absence of uncorrelated sensory input, the connectivity structure of the network, and Hebbian correlation learning. In addition, the blind model revealed long-lasting spiking neural activity compared to the sighted model during word recognition, which is a neural correlate of enhanced verbal working memory. The present neurocomputational model offers a neurobiological account for neural changes following sensory deprivation, thus closing the gap between cellular-level mechanisms, system-level linguistic and semantic function.

Time-Course of Motor Involvement in Literal and Metaphoric Action Sentence Processing: A TMS Study

There is evidence that the motor cortex is involved in reading sentences containing an action verb ("The spike was hammered into the ground") as well as metaphoric sentences ("The army was hammered in the battle"). Verbs such as 'hammered' may be homonyms, with separate meanings belonging to the literal action and metaphoric action, or they may be polysemous, with the metaphoric sense grounded in the literal sense. We investigated the time course of the effects of single-pulse transcranial magnetic stimulation to primary motor cortex on literal and metaphoric sentence comprehension. Stimulation 300 ms post-verb presentation impaired comprehension of both literal and metaphoric sentences, supporting a causal role of sensory-motor areas in comprehension. Results suggest that the literal meaning of an action verb remains activated during metaphor comprehension, even after the temporal window of homonym disambiguation. This suggests that such verbs are polysemous, and both senses are related and grounded in motor cortex.

Is Embodied Cognition Bilingual? Current Evidence and Perspectives of the Embodied Cognition Approach to Bilingual Language Processing

Accumulating behavioral and neurophysiological evidence supports the idea of language being grounded in sensorimotor processes, with indications of a functional role of motor, sensory and emotional systems in processing both concrete and abstract linguistic concepts. However, most of the available studies focused on native language speakers (L1), with only a limited number of investigations testing embodied language processing in the case of a second language (L2). In this paper we review the available evidence on embodied effects in L2 and discuss their possible integration into existing models of linguistic processing in L1 and L2. Finally, we discuss possible avenues for future research towards an integrated model of L1 and L2 sensorimotor and emotional grounding.

Does TMS Disruption of the Left Primary Motor Cortex Affect Verb Retrieval Following Exposure to Pantomimed Gestures?

Previous research suggests that meaning-laden gestures, even when produced in the absence of language (i.e., pantomimed gestures), influence lexical retrieval. Yet, little is known about the neural mechanisms that underlie this process. Based on embodied cognition theories, many studies have demonstrated motor cortex involvement in the representation of action verbs and in the understanding of actions. The present study aimed to investigate whether the motor system plays a critical role in the behavioral influence of pantomimed gestures on action naming. Continuous theta burst stimulation (cTBS) was applied over the hand area of the left primary motor cortex and to a control site (occipital cortex). An action-picture naming task followed cTBS. In the naming task, participants named action pictures that were preceded by videos of congruent pantomimed gestures, unrelated pantomimed gestures or a control video with no movement (as a neutral, non-gestural condition). In addition to behavioral measures of performance, cTBS-induced changes in corticospinal activity were assessed. We replicated previous finding that exposure to congruent pantomimed gestures facilitates word production, compared to unrelated or neutral primes. However, we found no evidence that the left primary motor area is crucially involved in the mechanism underlying behavioral facilitation effects of gesture on verb production. Although, at the group level, cTBS induced motor cortex suppression, at the individual level we found remarkable variability of cTBS effects on the motor cortex. We found cTBS induction of both inhibition of corticospinal activity (with slower behavioral of responses) and enhancement (with faster behavioral responses). Our findings cast doubt on assumptions that the motor cortex is causally involved in the impact of gestures on action-word processing. Our results also highlight the importance of careful consideration of interindividual variability for the interpretation of cTBS effects.

Role of Sensorimotor Cortex in Gestural-Verbal Integration

Action comprehension that is related to language or gestural integration has been shown to engage the motor system in the brain, thus providing preliminary evidence for the gestural-verbal embodiment concept. Based on the involvement of the sensorimotor cortex (M1) in language processing, we aimed to further explore its role in the cognitive embodiment necessary for gestural-verbal integration. As such, we applied anodal (excitatory) and sham transcranial direct current stimulation (tDCS) over the left M1 (with reference electrode over the contralateral supraorbital region) during a gestural-verbal integration task where subjects had to make a decision about the semantic congruency of the gesture (prime) and the word (target). We used a cross-over within-subject design in young subjects. Attentional load and simple reaction time (RT) tasks served as control conditions, applied during stimulation (order of three tasks was counterbalanced). Our results showed that anodal (atDCS) compared to sham tDCS (stDCS) reduced RTs in the gestural-verbal integration task, specifically for incongruent pairs of gestures and verbal expressions, with no effect on control task performance. Our findings provide evidence for the involvement of the sensorimotor system in gestural-verbal integration performance. Further, our results suggest that functional modulation induced by sensorimotor tDCS may be specific to gestural-verbal integration. Future studies should now evaluate the modulatory effect of tDCS on semantic congruency by using tDCS over additional brain regions and include assessments of neural connectivity.

A Neurobiologically Constrained Cortex Model of Semantic Grounding With Spiking Neurons and Brain-Like Connectivity

One of the most controversial debates in cognitive neuroscience concerns the cortical locus of semantic knowledge and processing in the human brain. Experimental data revealed the existence of various cortical regions relevant for meaning processing, ranging from semantic hubs generally involved in semantic processing to modality-preferential sensorimotor areas involved in the processing of specific conceptual categories. Why and how the brain uses such complex organization for conceptualization can be investigated using biologically constrained neurocomputational models. Here, we improve pre-existing neurocomputational models of semantics by incorporating spiking neurons and a rich connectivity structure between the model ‘areas’ to mimic important features of the underlying neural substrate. Semantic learning and symbol grounding in action and perception were simulated by associative learning between co-activated neuron populations in frontal, temporal and occipital areas. As a result of Hebbian learning of the correlation structure of symbol, perception and action information, distributed cell assembly circuits emerged across various cortices of the network. These semantic circuits showed category-specific topographical distributions, reaching into motor and visual areas for action- and visually-related words, respectively. All types of semantic circuits included large numbers of neurons in multimodal connector hub areas, which is explained by cortical connectivity structure and the resultant convergence of phonological and semantic information on these zones. Importantly, these semantic hub areas exhibited some category-specificity, which was less pronounced than that observed in primary and secondary modality-preferential cortices. The present neurocomputational model integrates seemingly divergent experimental results about conceptualization and explains both semantic hubs and category-specific areas as an emergent process causally determined by two major factors: neuroanatomical connectivity structure and correlated neuronal activation during language learning.

The role of the motor system in action understanding and communication: Evidence from human infants and non-human primates

There is growing evidence that activation of the motor system during observation of actions, a phenomenon first observed in non-human primates, underlies action understanding and even communication. This review (a) examines the evidence on motor system activity as an underlying neural correlate of action understanding; (b) reviews the theoretical and empirical work linking action understanding and the development of communication, with a specific focus on the role that gestures play as an intermediary; and (c) discusses the research on and existing opportunities for understanding the link between the motor system and communication in both humans and non-human primates, through the lens of action perception. Bringing together findings and perspectives from developmental social cognition in both humans and non-human primates and applying recent neuroscientific perspectives will help to elucidate the processes underlying the ability to understand and communicate with others.

The Semantic Content of Abstract Concepts: A Property Listing Study of 296 Abstract Words

The relation of abstract concepts to the modality-specific systems is discussed controversially. According to classical approaches, the semantic content of abstract concepts can only be coded by amodal or verbal-symbolic representations distinct from the sensory and motor systems, because abstract concepts lack a clear physical referent. Grounded cognition theories, in contrast, propose that abstract concepts do not depend only on the verbal system, but also on a variety of modal systems involving perception, action, emotion and internal states. In order to contribute to this debate, we investigated the semantic content of abstract concepts using a property generation task. Participants were asked to generate properties for 296 abstract concepts, which are relevant for constituting their meaning. These properties were categorized by a coding-scheme making a classification into modality-specific and verbal contents possible. Words were additionally rated with regard to concreteness/abstractness and familiarity. To identify possible subgroups of abstract concepts with distinct profiles of generated features, hierarchical cluster analyses were conducted. Participants generated a substantial proportion of introspective, affective, social, sensory and motor-related properties, in addition to verbal associations. Cluster analyses revealed different subcategories of abstract concepts, which can be characterized by the dominance of certain conceptual features. The present results are therefore compatible with grounded cognition theories, which emphasize the importance of linguistic, social, introspective and affective experiential information for the representation of abstract concepts. Our findings also indicate that abstract concepts are highly heterogeneous requiring the investigation of well-specified subcategories of abstract concepts, for instance as revealed by the present cluster analyses. The present study could thus guide future behavioral or imaging work further elucidating the representation of abstract concepts.

Are visual processes causally involved in "perceptual simulation" effects in the sentence-picture verification task?

Many studies have shown that sentences implying an object to have a certain shape produce a robust reaction time advantage for shape-matching pictures in the sentence-picture verification task. Typically, this finding has been interpreted as evidence for perceptual simulation, i.e., that access to implicit shape information involves the activation of modality-specific visual processes. It follows from this proposal that disrupting visual processing during sentence comprehension should interfere with perceptual simulation and obliterate the match effect. Here we directly test this hypothesis. Participants listened to sentences while seeing either visual noise that was previously shown to strongly interfere with basic visual processing or a blank screen. Experiments 1 and 2 replicated the match effect but crucially visual noise did not modulate it. When an interference technique was used that targeted high-level semantic processing (Experiment 3) however the match effect vanished. Visual noise specifically targeting high-level visual processes (Experiment 4) only had a minimal effect on the match effect. We conclude that the shape match effect in the sentence-picture verification paradigm is unlikely to rely on perceptual simulation.

Action Semantics at the Bottom of the Brain: Insights From Dysplastic Cerebellar Gangliocytoma

Recent embodied cognition research shows that access to action verbs in shallow-processing tasks becomes selectively compromised upon atrophy of the cerebellum, a critical motor region. Here we assessed whether cerebellar damage also disturbs explicit semantic processing of action pictures and its integration with ongoing motor responses. We evaluated a cognitively preserved 33-year-old man with severe dysplastic cerebellar gangliocytoma (Lhermitte-Duclos disease), encompassing most of the right cerebellum and the posterior part of the left cerebellum. The patient and eight healthy controls completed two semantic association tasks (involving pictures of objects and actions, respectively) that required motor responses. Accuracy results via Crawford’s modified t-tests revealed that the patient was selectively impaired in action association. Moreover, reaction-time analysis through Crawford’s Revised Standardized Difference Test showed that, while processing of action concepts involved slower manual responses in controls, no such effect was observed in the patient, suggesting that motor-semantic integration dynamics may be compromised following cerebellar damage. Notably, a Bayesian Test for a Deficit allowing for Covariates revealed that these patterns remained after covarying for executive performance, indicating that they were not secondary to extra-linguistic impairments. Taken together, our results extend incipient findings on the embodied functions of the cerebellum, offering unprecedented evidence of its crucial role in processing non-verbal action meanings and integrating them with concomitant movements. These findings illuminate the relatively unexplored semantic functions of this region while calling for extensions of motor cognition models.

Flexibility in Language Action Interaction: The Influence of Movement Type

Recent neuropsychological studies in neurological patients and healthy subjects suggest a close functional relationship between the brain systems for language and action. Facilitation and inhibition effects of motor system activity on language processing have been demonstrated as well as causal effects in the reverse direction, from language processes on motor excitability or performance. However, as the documented effects between motor and language systems were sometimes facilitatory and sometimes inhibitory, the “sign” of these effects still remains to be explained. In a previous study, we reported a word-category-specific differential impairment of verbal working memory for concordant arm- and leg-related action words brought about by complex sequential movements of the hands and feet. In this article, we seek to determine whether the sign of the functional interaction between language and action systems of the human brain can be changed in a predictable manner by changing movement type. We here report that the sign of the effect of motor movement on action word memory can be reversed from interference to facilitation if, instead of complex movement sequences, simple repetitive movements are performed. Specifically, when engaged in finger tapping, subjects were able to remember relatively more arm-related action words (as compared to control conditions), thus documenting an enhancement of working memory brought about by simple hand movements. In contrast, when performing complex sequences of finger movements, an effector-specific degradation of action word memory was found. By manipulating the sign of the effect in accord with theory-driven predictions, these findings provide support for shared neural bases for motor movement and verbal working memory for action-related words and strengthen the argument that motor systems play a causal and functionally relevant role in language processing semantically related to action.

The Story So Far: How Embodied Cognition Advances Our Understanding of Meaning-Making

Meaning-making in the brain has become one of the most intensely discussed topics in cognitive science. Traditional theories on cognition that emphasize abstract symbol manipulations often face a dead end: The symbol grounding problem. The embodiment idea tries to overcome this barrier by assuming that the mind is grounded in sensorimotor experiences. A recent surge in behavioral and brain-imaging studies has therefore focused on the role of the motor cortex in language processing. Concrete, action-related words have received convincing evidence to rely on sensorimotor activation. Abstract concepts, however, still pose a distinct challenge for embodied theories on cognition. Fully embodied abstraction mechanisms were formulated but sensorimotor activation alone seems unlikely to close the explanatory gap. In this respect, the idea of integration areas, such as convergence zones or the ‘hub and spoke’ model, do not only appear like the most promising candidates to account for the discrepancies between concrete and abstract concepts but could also help to unite the field of cognitive science again. The current review identifies milestones in cognitive science research and recent achievements that highlight fundamental challenges, key questions and directions for future research.

Sensorimotor experience and verb-category mapping in human sensory, motor and parietal neurons

Semantic grounding is the process of relating meaning to symbols (e.g., words). It is the foundation for creating a representational symbolic system such as language. Semantic grounding for verb meaning is hypothesized to be achieved through two mechanisms: sensorimotor mapping, i.e., directly encoding the sensorimotor experiences the verb describes, and verb-category mapping, i.e., encoding the abstract category a verb belongs to. These two mechanisms were investigated by examining neuronal-level spike (i.e. neuronal action potential) activities from the motor, somatosensory and parietal areas in two human participants. Motor and a portion of somatosensory neurons were found to be involved in primarily sensorimotor mapping, while parietal and some somatosensory neurons were found to be involved in both sensorimotor and verb-category mapping. The time course of the spike activities and the selective tuning pattern of these neurons indicate that they belong to a large neural network used for semantic processing. This study is the first step towards understanding how words are processed by neurons.