Action verbs and the primary motor cortex: A comparative TMS study of silent reading, frequency judgments, and motor imagery

Contribution of motor representations to action verb processing

Electrophysiological and brain imaging studies show a somatotopic activation of the premotor cortex while subjects process action verbs. This somatotopic motor activation has been taken as an indication that the meaning of action verbs is embedded in motor representations. However, discrepancies in the literature led to the alternative hypothesis that motor representations are activated during the course of a mental imagery process emerging only after the meaning of the action has been accessed. In order to address this issue, we asked participants to decide whether a visually presented verb was concrete or abstract by pressing a button or a pedal (primary task) and then to provide a distinct vocal response to low and high sounds played soon after the verb display (secondary task). Manipulations of the visual display (lower vs. uppercase), verb imageability (concrete vs. abstract), verb meaning (hand vs. foot-related), and response effector (hand vs. foot) allowed us to trace the perceptual, semantic and response stages of verb processing. We capitalized on the psychological refractory period (PRP), which implies that the initiation of the secondary task should be delayed only by those factors that slow down the central decision process in the primary task. In line with this prediction, our results showed that the time cost resulting from the processing of abstract verbs, when compared to concrete verbs, was still observed in the subsequent response to the sounds, whereas the overall advantage of hand over foot responses did not influence sound judgments. Crucially, we also observed a verb-effector compatibility effect (i.e., foot-related verbs are responded faster with the foot and hand-related verbs with the hand) that contaminated the performance of the secondary task, providing clear evidence that motor interference from verb meaning occurred during the central decision stage. These results cannot be explained by a mental imagery process that would deploy only during the execution of the response to verb judgments. They rather indicate that the motor activation induced by action verbs accompanies the lexico-semantic processes leading to response selection.

Differentiating Semantic Categories during the Acquisition of Novel Words: Correspondence Analysis Applied to Event-related Potentials

Growing evidence suggests that semantic knowledge is represented in distributed neural networks that include modality-specific structures. Here, we examined the processes underlying the acquisition of words from different semantic categories to determine whether the emergence of visual- and action-based categories could be tracked back to their acquisition. For this, we applied correspondence analysis (CA) to ERPs recorded at various moments during acquisition. CA is a multivariate statistical technique typically used to reveal distance relationships between words of a corpus. Applied to ERPs, it allows isolating factors that best explain variations in the data across time and electrodes. Participants were asked to learn new action and visual words by associating novel pseudowords with the execution of hand movements or the observation of visual images. Words were probed before and after training on two consecutive days. To capture processes that unfold during lexical access, CA was applied on the 100–400 msec post-word onset interval. CA isolated two factors that organized the data as a function of test sessions and word categories. Conventional ERP analyses further revealed a category-specific increase in the negativity of the ERPs to action and visual words at the frontal and occipital electrodes, respectively. The distinct neural processes underlying action and visual words can thus be tracked back to the acquisition of word-referent relationships and may have its origin in association learning. Given current evidence for the flexibility of language-induced sensory-motor activity, we argue that these associative links may serve functions beyond word understanding, that is, the elaboration of situation models.

Action Sentences Activate Sensory Motor Regions in the Brain Independently of Their Status of Reality

Some studies have reported that understanding concrete action-related words and sentences elicits activations of motor areas in the brain. The present fMRI study goes one step further by testing whether this is also the case for comprehension of nonfactual statements. Three linguistic structures were used (factuals, counterfactuals, and negations), referring either to actions or, as a control condition, to visual events. The results showed that action sentences elicited stronger activations than visual sentences in the SMA, extending to the primary motor area, as well as in regions generally associated with the planning and understanding of actions (left superior temporal gyrus, left and right supramarginal gyri). Also, we found stronger activations for action sentences than for visual sentences in the extrastriate body area, a region involved in the visual processing of human body movements. These action-related effects occurred not only in factuals but also in negations and counterfactuals, suggesting that brain regions involved in action understanding and planning are activated by default even when the actions are described as hypothetical or as not happening. Moreover, some of these regions overlapped with those activated during the observation of action videos, indicating that the act of understanding action language and that of observing real actions share neural networks. These results support the claim that embodied representations of linguistic meaning are important even in abstract linguistic contexts.

Motor-Language Coupling in Huntington's Disease Families

Traditionally, Huntington’s disease (HD) has been known as a movement disorder, characterized by motor, psychiatric, and cognitive impairments. Recent studies have shown that motor and action–language processes are neurally associated. The cognitive mechanisms underlying this interaction have been investigated through the action compatibility effect (ACE) paradigm, which induces a contextual coupling of ongoing motor actions and verbal processing. The present study is the first to use the ACE paradigm to evaluate action–word processing in HD patients (HDP) and their families. Specifically, we tested three groups: HDP, healthy first-degree relatives (HDR), and non-relative healthy controls. The results showed that ACE was abolished in HDP as well as HDR, but not in controls. Furthermore, we found that the processing deficits were primarily linguistic, given that they did not correlate executive function measurements. Our overall results underscore the role of cortico-basal ganglia circuits in action–word processing and indicate that the ACE task is a sensitive and robust early biomarker of HD and familial vulnerability.

Empirically grounding grounded cognition: the case of color

Grounded cognition theories hold that the neural states involved in experiencing objects play a direct functional role in representing and accessing object knowledge from memory. However, extant data marshaled to support this view are also consistent with an opposing view that perceptuo-motor activations occur only following access to knowledge from amodal memory systems. We provide novel discriminating evidence for the functional involvement of visuo-perceptual states specifically in accessing knowledge about an object's color. We recorded event-related brain potentials (ERPs) while manipulating the visual contrast of monochromatic words ("lime") in a semantic decision task: responses were made for valid colors ("green") and locations ("kitchen") and withheld for invalid colors and locations. Low contrast delayed perceptual processing for both color and location. Critically, low contrast slowed access to color knowledge only. This finding reveals that the visual system plays a functional role in accessing object knowledge and uniquely supports grounded views of cognition.

Passive reading and motor imagery about hand actions and tool-use actions: an fMRI study

Recent studies have shown that motor activations in action verb comprehension can be modulated by task demands (e.g., motor imagery vs. passive reading) and the specificity of action verb meaning. However, how the two factors work together to influence the involvement of the motor system during action verb comprehension is still unclear. To address the issue, the current study investigated the brain activations in motor imagery and passive reading of verbs about hand actions and tool-use actions. Three types of Chinese verbs were used, including hand-action verbs and two types of tool-use verbs emphasizing either the hand or tools information. Results indicated that all three types of verbs elicited common activations in hand motor areas during passive reading and motor imagery. Contrast analyses showed that in the hand verbs and the tool verbs where the hand information was emphasized, motor imagery elicited stronger effects than passive reading in the superior frontal gyrus, supplemental motor area and cingulate cortex that are related to motor control and regulation. For tool-use verbs emphasizing tools information, the motor imagery task elicited stronger activity than passive reading in occipital regions related to visual imagery. These results suggest that motor activations during action verb comprehension can be modulated by task demands and semantic features of action verbs. The sensorimotor simulation during language comprehension is flexible and determined by the interactions between linguistic and extralinguistic contexts.

Parkinson's disease disrupts both automatic and controlled processing of action verbs

The problem of how word meaning is processed in the brain has been a topic of intense investigation in cognitive neuroscience. While considerable correlational evidence exists for the involvement of sensory-motor systems in conceptual processing, it is still unclear whether they play a causal role. We investigated this issue by comparing the performance of patients with Parkinson's disease (PD) with that of age-matched controls when processing action and abstract verbs. To examine the effects of task demands, we used tasks in which semantic demands were either implicit (lexical decision and priming) or explicit (semantic similarity judgment). In both tasks, PD patients' performance was selectively impaired for action verbs (relative to controls), indicating that the motor system plays a more central role in the processing of action verbs than in the processing of abstract verbs. These results argue for a causal role of sensory-motor systems in semantic processing.

Semantic embodiment, disembodiment or misembodiment? In search of meaning in modules and neuron circuits

"Embodied" proposals claim that the meaning of at least some words, concepts and constructions is grounded in knowledge about actions and objects. An alternative "disembodied" position locates semantics in a symbolic system functionally detached from sensorimotor modules. This latter view is not tenable theoretically and has been empirically falsified by neuroscience research. A minimally-embodied approach now claims that action-perception systems may "color", but not represent, meaning; however, such minimal embodiment (misembodiment?) still fails to explain why action and perception systems exert causal effects on the processing of symbols from specific semantic classes. Action perception theory (APT) offers neurobiological mechanisms for "embodied" referential, affective and action semantics along with "disembodied" mechanisms of semantic abstraction, generalization and symbol combination, which draw upon multimodal brain systems. In this sense, APT suggests integrative-neuromechanistic explanations of why both sensorimotor and multimodal areas of the human brain differentially contribute to specific facets of meaning and concepts.

Dissociable somatotopic representations of Chinese action verbs in the motor and premotor cortex

The embodied view of language processing holds that language comprehension involves the recruitment of sensorimotor information, as evidenced by the somatotopic representation of action verbs in the motor system. However, this review has not yet been examined in logographic scripts such as Chinese, in which action verbs can provide explicit linguistic cues to the effectors (arm, leg, mouth) that conduct the action (hit, jump, drink). We compared the somatotopic representation of Chinese verbs that contain such effector cues and those that do not. The results showed that uncued verbs elicited similar somatotopic representation in the motor and premotor cortex as found in alphabetic scripts. However, effector-cued verbs demonstrated an inverse somatotopic pattern by showing reduced activation in corresponding motor areas, despite that effector-cued verbs actually are rated higher in imageability than uncued verbs. Our results support the universality of somatotopic representation of action verbs in the motor system.

Seeking a bridge between language and motor cortices: a PPI study

The relation between the sensorimotor cortex and the language network has been widely discussed but still remains controversial. Two independent theories compete to explain how this area is involved during action-related verbs processing. The embodied view assumes that action word representations activate sensorimotor representations which are accessed when an action word is processed or when an action is observed. The abstract hypothesis states that the mental representations of words are abstract and independent of the objects' sensorimotor properties they refer to. We combined neuropsychological and fMRI-PPI connectivity data, to address action-related verbs processing in neurosurgical patients with lesions involving (N = 5) or sparing (N = 5) the primary motor cortex and healthy controls (N = 12). A lack of significant changes in the functional coupling between the left M1 cortex and functional nodes of the linguistic network during the verb generation task was found for all the groups. In addition, we found that the ability to perform an action verb naming task was not related to a damaged M1. These data showed that there was not a task-specific functional interaction active between M1 and the inferior frontal gyrus. We will discuss how these findings indicate that action words do not automatically activate the M1 cortex; we suggest rather that its enrolment could be related to other not strictly linguistic processing.

Disrupting the brain to validate hypotheses on the neurobiology of language

Comprehension of words is an important part of the language faculty, involving the joint activity of frontal and temporo-parietal brain regions. Transcranial Magnetic Stimulation (TMS) enables the controlled perturbation of brain activity, and thus offers a unique tool to test specific predictions about the causal relationship between brain regions and language understanding. This potential has been exploited to better define the role of regions that are classically accepted as part of the language-semantic network. For instance, TMS has contributed to establish the semantic relevance of the left anterior temporal lobe, or to solve the ambiguity between the semantic vs. phonological function assigned to the left inferior frontal gyrus (LIFG). We consider, more closely, the results from studies where the same technique, similar paradigms (lexical-semantic tasks) and materials (words) have been used to assess the relevance of regions outside the classically-defined language-semantic network—i.e., precentral motor regions—for the semantic analysis of words. This research shows that different aspects of the left precentral gyrus (primary motor and premotor sites) are sensitive to the action-non action distinction of words' meanings. However, the behavioral changes due to TMS over these sites are incongruent with what is expected after perturbation of a task-relevant brain region. Thus, the relationship between motor activity and language-semantic behavior remains far from clear. A better understanding of this issue could be guaranteed by investigating functional interactions between motor sites and semantically-relevant regions.

Sentential context modulates the involvement of the motor cortex in action language processing: an FMRI study

Theories of embodied cognition propose that language comprehension is based on perceptual and motor processes. More specifically, it is hypothesized that neurons processing verbs describing bodily actions, and those that process the corresponding physical actions, fire simultaneously during action verb learning. Thus the concept and motor activation become strongly linked. According to this view, the language-induced activation of the neural substrates for action is automatic. By contrast, a weak view of embodied cognition proposes that activation of these motor regions is modulated by context. In recent studies it was found that action verbs in literal sentences activate the motor system, while mixed results were observed for action verbs in non-literal sentences. Thus, whether the recruitment of motor regions is automatic or context dependent remains a question. We investigated functional magnetic resonance imaging activation in response to non-literal and literal sentences including arm and leg related actions. The sentence structure was such that the action verb was the last word in the subordinate clause. Thus, the constraining context was presented well before the verb. Region of interest analyses showed that action verbs in literal context engage the motor regions to a greater extent than non-literal action verbs. There was no evidence for a semantic somatotopic organization of the motor cortex. Taken together, these results indicate that during comprehension, the degree to which motor regions are recruited is context dependent, supporting the weak view of embodied cognition.

The Body of Evidence: What Can Neuroscience Tell Us about Embodied Semantics?

Semantic knowledge is based on the way we perceive and interact with the world. However, the jury is still out on the question: to what degree are neuronal systems that subserve acquisition of semantic knowledge, such as sensory-motor networks, involved in its representation and processing? We will begin with a critical evaluation of the main behavioral and neuroimaging methods with respect to their capability to define the functional roles of specific brain areas. Any behavioral or neuroscientific measure is a conflation of representations and processes. Hence, a combination of behavioral and neurophysiological interactions as well as time-course information is required to define the functional roles of brain areas. This will guide our review of the empirical literature. Most research in this area has been done on semantics of concrete words, where clear theoretical frameworks for an involvement of sensory-motor systems in semantics exist. Most of this evidence still stems from correlational studies that are ambiguous with respect to the behavioral relevance of effects. Evidence for causal effects of sensory-motor systems on semantic processes is still scarce but evolving. Relatively few neuroscientific studies so far have investigated the embodiment of abstract semantics for words, numbers, and arithmetic facts. Here, some correlational evidence exists, but data on causality are mostly absent. We conclude that neuroimaging data, just as behavioral data, have so far not disentangled the fundamental link between process and representation. Future studies should therefore put more emphasis on the effects of task and context on semantic processing. Strong conclusions can only be drawn from a combination of methods that provide time-course information, determine the connectivity among poly- or amodal and sensory-motor areas, link behavioral with neuroimaging measures, and allow causal inferences. We will conclude with suggestions on how this could be accomplished in future research.

At the mercy of strategies: the role of motor representations in language understanding

Classical cognitive theories hold that word representations in the brain are abstract and amodal, and are independent of the objects’ sensorimotor properties they refer to. An alternative hypothesis emphasizes the importance of bodily processes in cognition: the representation of a concept appears to be crucially dependent upon perceptual-motor processes that relate to it. Thus, understanding action-related words would rely upon the same motor structures that also support the execution of the same actions. In this context, motor simulation represents a key component. Our approach is to draw parallels between the literature on mental rotation and the literature on action verb/sentence processing. Here we will discuss recent studies on mental imagery, mental rotation, and language that clearly demonstrate how motor simulation is neither automatic nor necessary to language understanding. These studies have shown that motor representations can or cannot be activated depending on the type of strategy the participants adopt to perform tasks involving motor phrases. On the one hand, participants may imagine the movement with the body parts used to carry out the actions described by the verbs (i.e., motor strategy); on the other, individuals may solve the task without simulating the corresponding movements (i.e., visual strategy). While it is not surprising that the motor strategy is at work when participants process action-related verbs, it is however striking that sensorimotor activation has been reported also for imageable concrete words with no motor content, for “non-words” with regular phonology, for pseudo-verb stimuli, and also for negations. Based on the extant literature, we will argue that implicit motor imagery is not uniquely used when a body-related stimulus is encountered, and that it is not the type of stimulus that automatically triggers the motor simulation but the type of strategy. Finally, we will also comment on the view that sensorimotor activations are subjected to a top-down modulation.

No specific role for the manual motor system in processing the meanings of words related to the hand

The present study explored whether semantic and motor systems are functionally interwoven via the use of a dual-task paradigm. According to embodied language accounts that propose an automatic and necessary involvement of the motor system in conceptual processing, concurrent processing of hand-related information should interfere more with hand movements than processing of unrelated body-part (i.e., foot, mouth) information. Across three experiments, 100 right-handed participants performed left- or right-hand tapping movements while repeatedly reading action words related to different body-parts, or different body-part names, in both aloud and silent conditions. Concurrent reading of single words related to specific body-parts, or the same words embedded in sentences differing in syntactic and phonological complexity (to manipulate context-relevant processing), and reading while viewing videos of the actions and body-parts described by the target words (to elicit visuomotor associations) all interfered with right-hand but not left-hand tapping rate. However, this motor interference was not affected differentially by hand-related stimuli. Thus, the results provide no support for proposals that body-part specific resources in cortical motor systems are shared between overt manual movements and meaning-related processing of words related to the hand.

Learning by doing? The effect of gestures on implicit retrieval of newly acquired words

Meaningful gestures enhance speech comprehensibility. However, their role during novel-word acquisition remains elusive. Here we investigate how meaningful versus meaningless gestures impact on novel-word learning and contrast these conditions to a purely verbal training. After training, neuronal processing of the novel words was assessed by blood-oxygen-level-dependent functional magnetic resonance imaging (BOLD-fMRI), disclosing that networks affording retrieval differ depending on the training condition. Over 3 days participants learned pseudowords for common objects (e.g., /klira/ -cap). For training they repeated the novel word while performing (i) an iconic, (ii) a grooming or (iii) no gesture. For the two conditions involving gestures, these were either actively repeated or passively observed during training. Behaviorally no substantial differences between the five different training conditions were found while fMRI disclosed differential networks affording implicit retrieval of the learned pseudowords depending on the training procedure. Most notably training with actively performed iconic gestures yielded larger activation in a semantic network comprising left inferior frontal (BA47) and inferior temporal gyri. Additionally hippocampal activation was stronger for all trained compared to unknown pseudowords of identical structure. The behavioral results challenge the generality of an 'enactment-effect' for single word learning. Imaging results, however, suggest that actively performed meaningful gestures lead to a deeper semantic encoding of novel words. The findings are discussed regarding their implications for theoretical accounts and for empirical approaches of gesture-based strategies in language (re)learning.

The effects of rTMS over the primary motor cortex: the link between action and language

Is the primary motor cortex (M1) necessary for language comprehension? The present study investigates the role of the primary motor cortex during verbs comprehension, within the framework of the embodied theories of language. We applied rTMS over the right and left hand portion of M1 and tested the effects of the stimulation toward the processing of hand-related action verbs versus abstract verbs. Results underlined a specific inhibition effect following left stimulation, only with hand-related action verbs. These findings seem to corroborate the hypothesis of a functional role of M1 in action verbs comprehension.

On-line changing of thinking about words: the effect of cognitive context on neural responses to verb reading

Activity in frontocentral motor regions is routinely reported when individuals process action words and is often interpreted as the implicit simulation of the word content. We hypothesized that these neural responses are not invariant components of action word processing but are modulated by the context in which they are evoked. Using fMRI, we assessed the relative weight of stimulus features (i.e., the intrinsic semantics of words) and contextual factors, in eliciting word-related sensorimotor activity. Participants silently read action-related and state verbs after performing a mental rotation task engaging either a motor strategy (i.e., referring visual stimuli to their own bodily movements) or a visuospatial strategy. The mental rotation tasks were used to induce, respectively, a motor and a nonmotor "cognitive context" into the following silent reading. Irrespective of the verb category, reading in the motor context, compared with reading in the nonmotor context, increased the activity in the left primary motor cortex, the bilateral premotor cortex, and the right somatosensory cortex. Thus, the cognitive context induced by the preceding motor strategy-based mental rotation modulated word-related sensorimotor responses, possibly reflecting the strategy of referring a word meaning to one's own bodily activity. This pattern, common to action and state verbs, suggests that the context in which words are encountered prevails over the intrinsic semantics of the stimuli in mediating the recruitment of sensorimotor regions.

Behavioral patterns and lesion sites associated with impaired processing of lexical and conceptual knowledge of actions

To further investigate the neural substrates of lexical and conceptual knowledge of actions, we administered a battery of six tasks to 226 brain-damaged patients with widely distributed lesions in the left and right cerebral hemispheres. The tasks probed lexical and conceptual knowledge of actions in a variety of verbal and non-verbal ways, including naming, word-picture matching, attribute judgments involving both words and pictures, and associative comparisons involving both words and pictures. Of the 226 patients who were studied, 61 failed one or more of the six tasks, with four patients being impaired on the entire battery, and varied numbers of patients being impaired on varied combinations of tasks. Overall, the 61 patients manifested a complex array of associations and dissociations across the six tasks. The lesion sites of 147 of the 226 patients were also investigated, using formal methods for lesion-deficit statistical mapping and power analysis of lesion overlap maps. Significant effects for all six tasks were found in the following left-hemisphere regions: the inferior frontal gyrus; the ventral precentral gyrus, extending superiorly into what are likely to be hand-related primary motor and premotor areas; and the anterior insula. In addition, significant effects for 4-5 tasks were found in not only the regions just mentioned, but also in several other left-hemisphere areas: the ventral postcentral gyrus; the supramarginal gyrus; and the posterior middle temporal gyrus. These results converge with previous research on the neural underpinnings of action words and concepts. However, the current study goes considerably beyond most previous investigations by providing extensive behavioral and lesion data for an unusually large and diverse sample of brain-damaged patients, and by incorporating multiple measures of verb comprehension. Regarding theoretical implications, the study provides new support for the Embodied Cognition Framework, which maintains that conceptual knowledge is grounded in sensorimotor systems.

Motor performance may be improved by kinesthetic imagery, specific action verb production, and mental calculation

Several results in the literature show that motor imagery, language production, mental calculation, and motor execution share the same or closely related brain motor cortical areas. The present study aimed at investigating the possible influence of specific action verb (AV) pronunciation and mental calculus upon motor performance compared with kinesthetic imagery (KI). Participants, novice in mental imagery, performed a vertical jump after a cognitive task (AV, silent AV, mental subtraction, meaningless verb, and KI). The results show that specific lower limbs AV, mental calculation, and KI improved the vertical jump in male, but not in female participants.

The role of volleyball expertise in motor simulation

We explored the impact of motor experience on the interaction between implicit motor simulation and language-processing. In an action familiarity judgment task, expert volleyball players, fans and novices were presented with semantically correct sentences describing possible and not possible motor actions, all as negative or positive contexts, e.g., "Don't shank!" or "Assist!". As processing negated action-phrases is known to reduce simulation states, exposure to negative or positive contexts was used here to test how simulation varies according to motor feasibility (possible, impossible) and experience (experts and fans). A significant group×stimulus×context interaction showed that athletes and fans, took longer to process negative than positive contexts for possible actions, compared to action-impossible sentences. In addition, experts were significantly faster and more accurate than fans and, in turn, they were both more accurate than novices. Thus, implicit motor simulation impacts on action-verb processing depending on (i) the domain-relevant expertise, (ii) the feasibility of the actions, and (iii) on whether scenes are presented in a negated context. These results suggest that the implicit triggering of motor representations is modulated by the context and it is tuned to people's motor repertoire, even when actions are described linguistically.

“She” Is Not Like “I”: The Tie between Language and Action Is in Our Imagination

Embodied theories hold that understanding what another person is doing requires the observer to map that action directly onto his or her own motor representation and simulate it internally. The human motor system may, thus, be endowed with a “mirror matching” device through which the same motor representation is activated, when the subject is either the performer or the observer of another's action (“self-other shared representation”). It is suggested that understanding action verbs relies upon the same mechanism; this implies that motor responses to these words are automatic and independent of the subject of the verb. In the current study, participants were requested to read silently and decide on the syntactic subject of action and nonaction verbs, presented in first (1P) or third (3P) person, while TMS was applied to the left hand primary motor cortex (M1). TMS-induced motor-evoked potentials were recorded from hand muscles as a measure of cortico-spinal excitability. Motor-evoked potentials increased for 1P, but not for 3P, action verbs or 1P and 3P nonaction verbs. We provide novel demonstration that the motor simulation is triggered only when the conceptual representation of a word integrates the action with the self as the agent of that action. This questions the core principle of “mirror matching” and opens to alternative interpretations of the relationship between conceptual and sensorimotor processes.

The lateralization of motor cortex activation to action-words

What determines the laterality of activation in motor cortex for words whose meaning is related to bodily actions? It has been suggested that the neuronal representation of the meaning of action-words is shaped by individual experience. However, core language functions are left-lateralized in the majority of both right- and left-handers. It is still an open question to what degree connections between left-hemispheric core language areas and right-hemispheric motor areas can play a role in semantics. We investigated laterality of brain activation using fMRI in right- and left-handed participants in response to visually presented hand-related action-words, namely uni- and bi-manual actions (such as "throw" and "clap"). These stimulus groups were matched with respect to general (hand-) action-relatedness, but differed with respect to whether they are usually performed with the dominant hand or both hands. We may expect generally more left-hemispheric motor cortex activation for hand-related words in both handedness groups, with possibly more bilateral activation for left-handers compared to right-handers. In our study, both participant groups activated motor cortex bilaterally for bi-manual words. Interestingly, both groups also showed a left-lateralized activation pattern to uni-manual words. We argue that this reflects the effect of left-hemispheric language dominance on the formation of semantic brain circuits on the basis of Hebbian correlation learning.

Motor simulation during action word processing in neurosurgical patients

The role that human motor areas play in linguistic processing is the subject of a stimulating debate. Data from nine neurosurgical patients with selective lesions of the precentral and postcentral sulcus could provide a direct answer as to whether motor area activation is necessary for action word processing. Action-related verbs (face-, hand-, and feet-related verbs plus neutral verbs) silently read were processed for (i) motor imagery by vividness ratings and (ii) frequency ratings. Although no stimulus- or task-dependent modulation was found in the RTs of healthy controls, patients showed a task × stimulus interaction resulting in a stimulus-dependent somatotopic pattern of RTs for the imagery task. A lesion affecting a part of the cortex that represents a body part also led to slower RTs during the creation of mental images for verbs describing actions involving that same body part. By contrast, no category-related differences were seen in the frequency judgment task. This task-related dissociation suggests that the sensorimotor area is critically involved in processing action verbs only when subjects are simulating the corresponding movement. These findings have important implications for the ongoing discussion regarding the involvement of the sensorimotor cortex in linguistic processing.

When do you grasp the idea? MEG evidence for instantaneous idiom understanding

We investigated the time-course of cortical activation during comprehension of literal and idiomatic sentences using MEG and anatomically guided distributed source analysis. Previous fMRI work had shown that the comprehension of sentences including action-related words elicits somatotopic semantic activation along the motor strip, reflecting meaning aspects of constituent words. Furthermore, idioms more strongly activated temporal pole and prefrontal cortex than literal sentences. Here we show that, compared to literal sentences, processing of idioms in a silent reading task modulates anterior fronto-temporal activity very early-on, already 150-250 ms after the sentences' critical disambiguating words ("kick the habit"). In parallel, the meaning of action words embedded in sentences is reflected by somatotopic activation of precentral motor systems. As neural reflections of constituent parts of idiomatic sentences are manifest at the same early latencies as brain indexes of idiomatic vs. literal meaning processing, we suggest that within ¼ of a second, compositional and abstract context-driven semantic processes in parallel contribute to the understanding of idiom meaning.

Modulation of the motor system during visual and auditory language processing

Studies of embodied cognition have demonstrated the engagement of the motor system when people process action-related words and concepts. However, research using transcranial magnetic stimulation (TMS) to examine linguistic modulation in primary motor cortex has produced inconsistent results. Some studies report that action words produce an increase in corticospinal excitability; others, a decrease. Given the differences in methodology and modality, we re-examined this issue, comparing conditions in which participants either read or listened to the same set of action words. In separate blocks of trials, participants were presented with lists of words in the visual and auditory modality, and a TMS pulse was applied over left motor cortex, either 150 or 300 ms after the word onset. Motor evoked potentials (MEPs) elicited were larger following the presentation of action words compared with control words. However, this effect was only observed when the words were presented visually; no changes in MEPs were found when the words were presented auditorily. A review of the TMS literature on action word processing reveals a similar modality effect on corticospinal excitability. We discuss different hypotheses that might account for this differential modulation of action semantics by vision and audition.

Embodied language comprehension requires an enactivist paradigm of cognition

Two recurrent concerns in discussions on an embodied view of cognition are the "necessity question" (i.e., is activation in modality-specific brain areas necessary for language comprehension?) and the "simulation constraint" (i.e., how do we understand language for which we lack the relevant experiences?). In the present paper we argue that the criticisms encountered by the embodied approach hinge on a cognitivist interpretation of embodiment. We argue that the data relating sensorimotor activation to language comprehension can best be interpreted as supporting a non-representationalist, enactivist model of language comprehension, according to which language comprehension can be described as procedural knowledge - knowledge how, not knowledge that - that enables us to interact with others in a shared physical world. The enactivist view implies that the activation of modality-specific brain areas during language processing reflects the employment of sensorimotor skills and that language comprehension is a context-bound phenomenon. Importantly, an enactivist view provides an embodied approach of language, while avoiding the problems encountered by a cognitivist interpretation of embodiment.

Neural Dissociations between Action Verb Understanding and Motor Imagery

According to embodied theories of language, people understand a verb like throw, at least in part, by mentally simulating throwing. This implicit simulation is often assumed to be similar or identical to motor imagery. Here we used fMRI to test whether implicit simulations of actions during language understanding involve the same cortical motor regions as explicit motor imagery. Healthy participants were presented with verbs related to hand actions (e.g., to throw) and nonmanual actions (e.g., to kneel). They either read these verbs (lexical decision task) or actively imagined performing the actions named by the verbs (imagery task). Primary motor cortex showed effector-specific activation during imagery, but not during lexical decision. Parts of premotor cortex distinguished manual from nonmanual actions during both lexical decision and imagery, but there was no overlap or correlation between regions activated during the two tasks. These dissociations suggest that implicit simulation and explicit imagery cued by action verbs may involve different types of motor representations and that the construct of “mental simulation” should be distinguished from “mental imagery” in embodied theories of language.

Grasping language--a short story on embodiment

The new concept of embodied cognition theories has been enthusiastically studied by the cognitive sciences, by as well as such disparate disciplines as philosophy, anthropology, neuroscience, and robotics. Embodiment theory provides the framework for ongoing discussions on the linkage between "low" cognitive processes as perception and "high" cognition as language processing and comprehension, respectively. This review gives an overview along the lines of argumentation in the ongoing debate on the embodiment of language and employs an ALE meta-analysis to illustrate and weigh previous findings.The collected evidence on the somatotopic activation of motor areas, abstract and concrete word processing, as well as from reported patient and timing studies emphasizes the important role of sensorimotor areas in language processing and supports the hypothesis that the motor system is activated during language comprehension.

What do brain lesions tell us about theories of embodied semantics and the human mirror neuron system?

Recent work has been mixed with respect to the notion of embodied semantics, which suggests that processing linguistic stimuli referring to motor-related concepts recruits the same sensorimotor regions of cortex involved in the execution and observation of motor acts or the objects associated with those acts. In this study, we asked whether lesions to key sensorimotor regions would preferentially impact the comprehension of stimuli associated with the use of the hand, mouth or foot. Twenty-seven patients with left-hemisphere strokes and 10 age- and education-matched controls were presented with pictures and words representing objects and actions typically associated with the use of the hand, mouth, foot or no body part at all (i.e., neutral). Picture/sound pairs were presented simultaneously, and participants were required to press a space bar only when the item pairs matched (i.e., congruent trials). We conducted two different analyses: 1) we compared task performance of patients with and without lesions in several key areas previously implicated in the putative human mirror neuron system (i.e., Brodmann areas 4/6, 1/2/3, 21 and 44/45), and 2) we conducted Voxel-based Lesion-Symptom Mapping analyses (VLSM; Bates et al., 2003) to identify additional regions associated with the processing of effector-related versus neutral stimuli. Processing of effector-related stimuli was associated with several regions across the left hemisphere, and not solely with premotor/motor or somatosensory regions. We also did not find support for a somatotopically-organized distribution of effector-specific regions. We suggest that, rather than following the strict interpretation of homuncular somatotopy for embodied semantics, these findings support theories proposing the presence of a greater motor-language network which is associated with, but not restricted to, the network responsible for action execution and observation.

Embodied language in neuroscience and psychoanalysis

There have been relatively few discussions of systematic studies of language, including neuroscience studies, in the psychoanalytic literature. To address this dearth, a detailed review of research on embodied language in neuroscience and related disciplines is presented, after which their findings are considered in light of diverse views of language in psychoanalysis, specifically the models of the Boston Change Process Study Group, Wilma Bucci, Fonagy and Target, David Olds, and Hans Loewald. The juxtaposition of psychoanalytic models with the findings of research on embodied language shows that scientific studies can focus psychoanalytic understanding of verbal processes, and that integrations with neuroscience neither inherently threaten the traditional psychoanalytic focus on verbal meanings nor reduce the richness and complexity of psychoanalytic theory.

Body-Specific Representations of Action Verbs

According to theories of embodied cognition, understanding a verb like throw involves unconsciously simulating the action of throwing, using areas of the brain that support motor planning. If understanding action words involves mentally simulating one’s own actions, then the neurocognitive representation of word meanings should differ for people with different kinds of bodies, who perform actions in systematically different ways. In a test of the body-specificity hypothesis, we used functional magnetic resonance imaging to compare premotor activity correlated with action verb understanding in right- and left-handers. Right-handers preferentially activated the left premotor cortex during lexical decisions on manual-action verbs (compared with nonmanual-action verbs), whereas left-handers preferentially activated right premotor areas. This finding helps refine theories of embodied semantics, suggesting that implicit mental simulation during language processing is body specific: Right- and left-handers, who perform actions differently, use correspondingly different areas of the brain for representing action verb meanings.

Body-specific motor imagery of hand actions: neural evidence from right- and left-handers

If motor imagery uses neural structures involved in action execution, then the neural correlates of imagining an action should differ between individuals who tend to execute the action differently. Here we report fMRI data showing that motor imagery is influenced by the way people habitually perform motor actions with their particular bodies; that is, motor imagery is ‘body-specific’ (Casasanto, 2009). During mental imagery for complex hand actions, activation of cortical areas involved in motor planning and execution was left-lateralized in right-handers but right-lateralized in left-handers. We conclude that motor imagery involves the generation of an action plan that is grounded in the participant's motor habits, not just an abstract representation at the level of the action's goal. People with different patterns of motor experience form correspondingly different neurocognitive representations of imagined actions.

Effects of TMS on different stages of motor and non-motor verb processing in the primary motor cortex

The embodied cognition hypothesis suggests that motor and premotor areas are automatically and necessarily involved in understanding action language, as word conceptual representations are embodied. This transcranial magnetic stimulation (TMS) study explores the role of the left primary motor cortex in action-verb processing. TMS-induced motor-evoked potentials from right-hand muscles were recorded as a measure of M1 activity, while participants were asked either to judge explicitly whether a verb was action-related (semantic task) or to decide on the number of syllables in a verb (syllabic task). TMS was applied in three different experiments at 170, 350 and 500 ms post-stimulus during both tasks to identify when the enhancement of M1 activity occurred during word processing. The delays between stimulus onset and magnetic stimulation were consistent with electrophysiological studies, suggesting that word recognition can be differentiated into early (within 200 ms) and late (within 400 ms) lexical-semantic stages, and post-conceptual stages. Reaction times and accuracy were recorded to measure the extent to which the participants' linguistic performance was affected by the interference of TMS with M1 activity. No enhancement of M1 activity specific for action verbs was found at 170 and 350 ms post-stimulus, when lexical-semantic processes are presumed to occur (Experiments 1-2). When TMS was applied at 500 ms post-stimulus (Experiment 3), processing action verbs, compared with non-action verbs, increased the M1-activity in the semantic task and decreased it in the syllabic task. This effect was specific for hand-action verbs and was not observed for action-verbs related to other body parts. Neither accuracy nor RTs were affected by TMS. These findings suggest that the lexical-semantic processing of action verbs does not automatically activate the M1. This area seems to be rather involved in post-conceptual processing that follows the retrieval of motor representations, its activity being modulated (facilitated or inhibited), in a top-down manner, by the specific demand of the task.

Juggling with the brain - thought and action in the human motor system

Empirical findings from various research fields indicate that cognitive and motor processes are far less dissimilar than previously thought. The present chapter takes a neuroscientific perspective and offers evidence for similarities between cognition and action focusing on three key players of the classical motor system: the primary motor cortex, the cerebellum, and the premotor cortex. Briefly, although movement execution is apparently supported in part by the same cerebral resources engaged in cognitive processes, the three brain regions reviewed here are differentially engaged in more or less action-bound cognitive processes.