Competing mechanisms for mapping action-related categorical knowledge and observed actions

Does the involvement of motor cortex in embodied language comprehension stand on solid ground? A p-curve analysis and test for excess significance of the TMS and tDCS evidence

According to the embodied cognition view, comprehending action-related language requires the participation of sensorimotor processes. A now sizeable literature has tested this proposal by stimulating (with TMS or tDCS) motor brain areas during the comprehension of action language. To assess the evidential value of this body of research, we exhaustively searched the literature and submitted the relevant studies (N = 43) to p-curve analysis. While most published studies concluded in support of the embodiment hypothesis, our results suggest that we cannot yet assert beyond reasonable doubt that they explore real effects. We also found that these studies are quite underpowered (estimated power < 30%), which means that a large percentage of them would not replicate if repeated identically. Additional tests for excess significance show signs of publication bias within this literature. In sum, extant brain stimulation studies testing the grounding of action language in the motor cortex do not stand on solid ground. We provide recommendations that will be important for future research on this topic.

Sports ingroup love does not make me like the sponsor's beverage but gets me buying it

Previous literature has shown that social identity influences consumer decision-making towards branded products. However, its influence on ones' own sensory perception of an ingroup (or outgroup) associated brand's product (i.e. sponsor) is seldom documented and little understood. Here, we investigate the impact of social identity (i.e. team identification) with a football team on the sensorial experience and willingness to buy a beverage, said to be sponsoring the ingroup or the outgroup team. Ninety subjects participated in one of three sensorial experience conditions (matched identity: ingroup beverage; mismatched identity: outgroup beverage; control: no group preference). Each participant tasted the new sponsoring beverage and answered a questionnaire about their subjective sensorial experience of the beverage. EEG and BVP were synchronously collected throughout. Analyses revealed that team identification does not influence subjective responses and only slightly modulates physiological signals. All participants reported high valence and arousal values while physiological signals consistently translated negative affects across groups, which showed that participants reported to be happy/excited about trying the beverage while their physiological signals showed that they were feeling sad/depressed/angry. Crucially, despite a similar sensorial experience, and similar socially desirable report of the subjective experience, only participants in the matched identity group demonstrate higher willingness to buy, showing that the level of team identification, but not taste or beverage quality, influences willingness to buy the said sponsor's product.

Elite competitive swimmers exhibit higher motor cortical inhibition and superior sensorimotor skills in a water environment

Motor skill learning leads to task-related contextual behavioral changes that are underpinned by neuroplastic cortical reorganization. Short-term training induces environment-related contextual behavioral changes and neuroplastic changes in the primary motor cortex (M1). However, it is unclear whether environment-related contextual behavioral changes persist after long-term training and how cortical plastic changes are involved in behavior. To address these issues, we examined 14 elite competitive swimmers and 14 novices. We hypothesized that the sensorimotor skills of swimmers would be higher in a water environment than those of novices, and the recruitment of corticospinal and intracortical projections would be different between swimmers and novices. We assessed joint angle modulation performance as a behavioral measure and motor cortical excitation and inhibition using transcranial magnetic stimulation (TMS) at rest and during the tasks that were performed before, during, and after water immersion (WI). Motor cortical inhibition was measured with short-interval intracortical inhibition and long-interval intracortical inhibition by a paired-pulse TMS paradigm. We found that 1) the sensorimotor skills of swimmers who underwent long-term training in a water environment were superior and robustly unchanged compared with those of novices with respect to baseline on land, during WI, on land post-WI and 2) intracortical inhibition in water environments was increased in swimmers but was decreased in non-swimmers at rest compared to that on land; however, the latter alterations in intracortical inhibition in water environment were insufficient to account for the superior sensorimotor skills of swimmers. In conclusion, we demonstrate that environment-related contextual behavioral and neural changes occur even with long-term training experience.

Auditory prediction cues motor preparation in the absence of movements

There is increasing evidence for integrated representation of sensory and motor information in the brain, and that seeing or hearing action-related stimuli may automatically cue the movements required to respond to or produce them. In this study we tested whether anticipation of tones in a known melody automatically activates corresponding motor representations in a predictive way, in preparation for potential upcoming movements. Therefore, we trained 20 non-musicians (8 men, 12 women) to play a simple melody. Then, while they passively listened to the learned or unlearned melodies, we applied single pulse transcranial magnetic stimulation (TMS) over M1 to measure motor evoked potentials from the associated finger muscle either preceding or following the onset of individual tones. Our results show that listening to the learned melody increased corticospinal excitability for specific finger muscles before tone onset. This demonstrates that predictable auditory information can activate motor representations in an anticipatory muscle-specific manner, even in the absence of intention to move. This suggests that the motor system is involved in the prediction of sensory events, likely based on auditory-parietal-prefrontal feedforward/feedback loops that automatically prepare predictable sound-related actions independent of actual execution and the associated auditory feedback. Overall, we propose that multimodal forward models of upcoming sounds and actions support motor preparation, facilitate error detection and correction, and guide perception.

Semantic discrimination impacts tDCS modulation of verb processing

Motor cortex activation observed during body-related verb processing hints at simulation accompanying linguistic understanding. By exploiting the up- and down-regulation that anodal and cathodal transcranial direct current stimulation (tDCS) exert on motor cortical excitability, we aimed at further characterizing the functional contribution of the motor system to linguistic processing. In a double-blind sham-controlled within-subjects design, online stimulation was applied to the left hemispheric hand-related motor cortex of 20 healthy subjects. A dual, double-dissociation task required participants to semantically discriminate concrete (hand/foot) from abstract verb primes as well as to respond with the hand or with the foot to verb-unrelated geometric targets. Analyses were conducted with linear mixed models. Semantic priming was confirmed by faster and more accurate reactions when the response effector was congruent with the verb's body part. Cathodal stimulation induced faster responses for hand verb primes thus indicating a somatotopical distribution of cortical activation as induced by body-related verbs. Importantly, this effect depended on performance in semantic discrimination. The current results point to verb processing being selectively modifiable by neuromodulation and at the same time to a dependence of tDCS effects on enhanced simulation. We discuss putative mechanisms operating in this reciprocal dependence of neuromodulation and motor resonance.

Pictures of disgusting foods and disgusted facial expressions suppress the tongue motor cortex

The tongue holds a unique role in gustatory disgust. However, it is unclear whether the tongue representation in the motor cortex (tM1) is affected by the sight of distaste-related stimuli. Using transcranial magnetic stimulation (TMS) in healthy humans, we recorded tongue motor-evoked potentials (MEPs) as an index of tM1 cortico-hypoglossal excitability. MEPs were recorded while participants viewed pictures associated with gustatory disgust and revulsion (i.e. rotten foods and faces expressing distaste), non-oral-related disgusting stimuli (i.e. invertebrates like worms) and control stimuli. We found that oral-related disgust pictures suppressed tM1 cortico-hypoglossal output. This tM1 suppression was predicted by interindividual differences in disgust sensitivity. No similar suppression was found for disgusting invertebrates or when MEPs were recorded from a control muscle. These findings suggest that revulsion-eliciting food pictures trigger anticipatory inhibition mechanisms, possibly preventing toxin swallowing and contamination. A similar suppression is elicited when viewing distaste expressions, suggesting vicarious motor inhibition during social perception of disgust. Our study suggests an avoidant-defensive mechanism in human cortico-hypoglossal circuits and its ‘resonant’ activation in the vicarious experience of others’ distaste. These findings support a role for the motor system in emotion-driven motor anticipation and social cognition.

Relationship between blood lactate and cortical excitability between taekwondo athletes and non-athletes after hand-grip exercise

OBJECTIVES

In taekwondo competitions, fatigue has a large influence on performance. Recent studies have reported that the excitability in the primary hand motor cortex, investigated with transcranial magnetic stimulation (TMS), is enhanced at the end of a maximal exercise and that this improvement correlates with blood lactate. The aim of the present study was to investigate the relationship between blood lactate and cortical excitability in taekwondo athletes and non-athletes.

METHODS

The excitability of the primary motor cortex was measured before and after fatiguing hand-grip exercise by TMS. Capillary blood lactate was measured at rest (pre-test), at the end (0 min), and at 3 and 10 min after the exercise by using a "Lactate Pro" portable lactate analyzer.

RESULTS

Significant differences in cortical excitability between the two groups were found after the exercise (p < 0.05). Furthermore, we found a significant relationship between cortical excitability and blood lactate (p < 0.01).

CONCLUSION

The present findings showed changes in the excitability in the athletes group and also in the non-athletes group. However, blood lactate seems to have the greater effect in trained subjects compared to untrained subjects. In fact, it appears that, during extremely intensive exercise in taekwondo athletes, lactate may delay the onset of fatigue not only by maintaining the excitability of muscle, but also by increasing the excitability of the primary motor cortex more than in non-athletes.

Visual and Sensorimotor Contributions to the Esthetic Appraisal of Body Form, Motion, and Emotion

Recent neuroscience studies indicate that the visual processing of human bodies relies on a cortical network comprising different sensorimotor regions (extrastriate body area [EBA], superior temporal sulcus [STS], parietal cortex [PC], and premotor cortex [PM]). These regions seem to be specifically involved in the processing of morphological (form) and dynamic (movement) cues of the body. Importantly, the integrated activity within the network dedicated to body processing seems to underpin the unified perception of the body and its movements via simulation-like mechanisms (“cold embodiment”). Studies also suggest that regions within the body-related network are involved in the esthetic appreciation of human bodies together with a variety of cortical and subcortical regions associated to the emotional reward coding of stimuli (e.g., the amygdala for fear/disgust and the nucleus accumbens, the insula, and the cingulate cortex for pleasure reward), which may drive a form of “hot embodiment.” Thus, the esthetic evaluation of human bodies may rely upon a large cortico-subcortical network. Here we review evidence concerning the role of specific sensorimotor cortical and subcortical regions in the perception of beauty and attractiveness of the body. We conclude that exploring the way in which visual, sensorimotor, affective, and multisensory information in art and ecological life in general perturb our body representations is crucial for understanding the neural foundations of esthetic body appreciation.

Excitability of the primary motor cortex increases more strongly with slow- than with normal-speed presentation of actions

Introduction

The aim of the present study was to investigate how the speed of observed action affects the excitability of the primary motor cortex (M1), as assessed by the size of motor evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS).

Methods

Eighteen healthy subjects watched a video clip of a person catching a ball, played at three different speeds (normal-, half-, and quarter-speed). MEPs were induced by TMS when the model's hand had opened to the widest extent just before catching the ball (“open”) and when the model had just caught the ball (“catch”). These two events were locked to specific frames of the video clip (“phases”), rather than occurring at specific absolute times, so that they could easily be compared across different speeds. MEPs were recorded from the thenar (TH) and abductor digiti minimi (ADM) muscles of the right hand.

Results

The MEP amplitudes were higher when the subjects watched the video clip at low speed than when they watched the clip at normal speed. A repeated-measures ANOVA, with the factor VIDEO-SPEED, showed significant main effects. Bonferroni's post hoc test showed that the following MEP amplitude differences were significant: TH, normal vs. quarter; ADM, normal vs. half; and ADM, normal vs. quarter. Paired t-tests showed that the significant MEP amplitude differences between TMS phases under each speed condition were TH, “catch” higher than “open” at quarter speed; ADM, “catch” higher than “open” at half speed.

Conclusions

These results indicate that the excitability of M1 was higher when the observed action was played at low speed. Our findings suggest that the action observation system became more active when the subjects observed the video clip at low speed, because the subjects could then recognize the elements of action and intention in others.

Weight dependent modulation of motor resonance induced by weight estimation during observation of partially occluded lifting actions

Seeing others performing an action induces the observers' motor cortex to "resonate" with the observed action. Transcranial magnetic stimulation (TMS) studies suggest that such motor resonance reflects the encoding of various motor features of the observed action, including the apparent motor effort. However, it is unclear whether such encoding requires direct observation or whether force requirements can be inferred when the moving body part is partially occluded. To address this issue, we presented participants with videos of a right hand lifting a box of three different weights and asked them to estimate its weight. During each trial we delivered one transcranial magnetic stimulation (TMS) pulse over the left primary motor cortex of the observer and recorded the motor evoked potentials (MEPs) from three muscles of the right hand (first dorsal interosseous, FDI, abductor digiti minimi, ADM, and brachioradialis, BR). Importantly, because the hand shown in the videos was hidden behind a screen, only the contractions in the actor's BR muscle under the bare skin were observable during the entire videos, while the contractions in the actor's FDI and ADM muscles were hidden during the grasp and actual lift. The amplitudes of the MEPs recorded from the BR (observable) and FDI (hidden) muscle increased with the weight of the box. These findings indicate that the modulation of motor excitability induced by action observation extends to the cortical representation of muscles with contractions that could not be observed. Thus, motor resonance appears to reflect force requirements of observed lifting actions even when the moving body part is occluded from view.

Transcranial magnetic stimulation reveals two functionally distinct stages of motor cortex involvement during perception of emotional body language

Studies indicate that perceiving emotional body language recruits fronto-parietal regions involved in action execution. However, the nature of such motor activation is unclear. Using transcranial magnetic stimulation (TMS) we provide correlational and causative evidence of two distinct stages of motor cortex engagement during emotion perception. Participants observed pictures of body expressions and categorized them as happy, fearful or neutral while receiving TMS over the left or right motor cortex at 150 and 300 ms after picture onset. In the early phase (150 ms), we observed a reduction of excitability for happy and fearful emotional bodies that was specific to the right hemisphere and correlated with participants’ disposition to feel personal distress. This ‘orienting’ inhibitory response to emotional bodies was also paralleled by a general drop in categorization accuracy when stimulating the right but not the left motor cortex. Conversely, at 300 ms, greater excitability for negative, positive and neutral movements was found in both hemispheres. This later motor facilitation marginally correlated with participants’ tendency to assume the psychological perspectives of others and reflected simulation of the movement implied in the neutral and emotional body expressions. These findings highlight the motor system’s involvement during perception of emotional bodies. They suggest that fast orienting reactions to emotional cues—reflecting neural processing necessary for visual perception—occur before motor features of the observed emotional expression are simulated in the motor system and that distinct empathic dispositions influence these two neural motor phenomena. Implications for theories of embodied simulation are discussed.

Enhanced corticobulbar excitability in chronic smokers during visual exposure to cigarette smoking cues

BACKGROUND

Neuroimaging studies of chronic smokers report altered activity of several neural regions involved in the processing of rewarding outcomes. Neuroanatomical evidence suggests that these regions are directly connected to the tongue muscle through the corticobulbar pathways. Accordingly, we examined whether corticobulbar excitability might be considered a somatic marker for nicotine craving.

METHODS

We compared motor-evoked potential (MEP) amplitudes recorded from the tongue and the extensor carpi radialis (control muscle) of chronic smokers under drug withdrawal and intake conditions as well as a nonsmoker group. All participants were tested during passive exposure to pictures showing a smoking cue or a meaningless stimulus. In the intake condition, chronic smokers were asked to smoke a real cigarette (CSn: group 1) or a placebo (CSp: group 2).

RESULTS

Results show that MEP amplitudes recorded from the tongues of participants in the CSn and CSp groups under the withdrawal condition were selectively enhanced during exposure to a smoking cue. However, this effect on tongue MEP amplitudes disappeared in the intake condition for both the CSn and CSp groups.

LIMITATIONS

Limitations include the fact that the study was conducted in 2 different laboratories, the small sample size, the absence of data on chronic smoker craving strength and the different tastes of the real and placebo cigarettes.

CONCLUSION

These results suggest that, in chronic smokers, tongue muscle MEP amplitudes are sensitive to neural processes active under the physiological status of nicotine craving. This finding implicates a possible functional link between neural excitability of the corticobulbar pathway and the reward system in chronic smokers.

Neuroanatomical substrates of action perception and understanding: an anatomic likelihood estimation meta-analysis of lesion-symptom mapping studies in brain injured patients

Several neurophysiologic and neuroimaging studies suggested that motor and perceptual systems are tightly linked along a continuum rather than providing segregated mechanisms supporting different functions. Using correlational approaches, these studies demonstrated that action observation activates not only visual but also motor brain regions. On the other hand, brain stimulation and brain lesion evidence allows tackling the critical question of whether our action representations are necessary to perceive and understand others’ actions. In particular, recent neuropsychological studies have shown that patients with temporal, parietal, and frontal lesions exhibit a number of possible deficits in the visual perception and the understanding of others’ actions. The specific anatomical substrates of such neuropsychological deficits however, are still a matter of debate. Here we review the existing literature on this issue and perform an anatomic likelihood estimation meta-analysis of studies using lesion-symptom mapping methods on the causal relation between brain lesions and non-linguistic action perception and understanding deficits. The meta-analysis encompassed data from 361 patients tested in 11 studies and identified regions in the inferior frontal cortex, the inferior parietal cortex and the middle/superior temporal cortex, whose damage is consistently associated with poor performance in action perception and understanding tasks across studies. Interestingly, these areas correspond to the three nodes of the action observation network that are strongly activated in response to visual action perception in neuroimaging research and that have been targeted in previous brain stimulation studies. Thus, brain lesion mapping research provides converging causal evidence that premotor, parietal and temporal regions play a crucial role in action recognition and understanding.

Harm avoiders suppress motor resonance to observed immoral actions

Motor resonance (MR) contingent upon action observation is thought to occur largely automatically. Although recent studies suggest that this process is not completely impervious to top-down modulations, much less is known on the possible role of the moral connotation of observed action goal in modulating MR. Here, we explored whether observing actions with different moral connotations modulates MR and whether any modulation depends on the onlookers' personality. To this aim, we recorded motor potentials evoked by single-pulse transcranial magnetic stimulation from hand muscles of participants who were watching images of a model performing hand actions with the same postures and low-level goals (i.e. grasping an object) but with different moral connotations ('stealing a wallet' vs 'picking up a notepaper'). Participants' personality traits were measured using the temperament and character inventory. Results show a selective suppression of corticospinal excitability during observation of immoral actions in individuals with high scores in harm avoidance, a personality trait characterized by excessive worrying and fearfulness. Thus, a combination of dispositional (personality traits) and situational (morality of an action) variables appears to influence MR with the observed actions.

Emotions affect the recognition of hand gestures

The body is closely tied to the processing of social and emotional information. The purpose of this study was to determine whether a relationship between emotions and social attitudes conveyed through gestures exists. Thus, we tested the effect of pro-social (i.e., happy face) and anti-social (i.e., angry face) emotional primes on the ability to detect socially relevant hand postures (i.e., pictures depicting an open/closed hand). In particular, participants were required to establish, as quickly as possible, if the test stimulus (i.e., a hand posture) was the same or different, compared to the reference stimulus (i.e., a hand posture) previously displayed in the computer screen. Results show that facial primes, displayed between the reference and the test stimuli, influence the recognition of hand postures, according to the social attitude implicitly related to the stimulus. We found that perception of pro-social (i.e., happy face) primes resulted in slower RTs in detecting the open hand posture as compared to the closed hand posture. Vice-versa, perception of the anti-social (i.e., angry face) prime resulted in slower RTs in detecting the closed hand posture compared to the open hand posture. These results suggest that the social attitude implicitly conveyed by the displayed stimuli might represent the conceptual link between emotions and gestures.

Cortico-spinal embodiment of newly acquired, action-related semantic associations

BACKGROUND

Behavioral and neurophysiological studies indicate that the semantic derivation of the motor skills of a given model (e.g., famous tennis or soccer athlete) modulates the reactivity of arm and leg cortico-spinal representations of an onlooker who performs a categorization task. Information on the possible plastic nature of the sensorimotor mapping of action-related knowledge is still lacking.

OBJECTIVE/HYPOTHESIS

Here we explored the time course of any cortico-spinal excitability modulation induced by the creation of arbitrary associations between a personal name and tennis- or soccer-related motor skills.

METHODS

We recorded the amplitude of Transcranial Magnetic Stimulation (TMS) Motor Evoked Potentials (MEPs) from arm and leg muscles during a categorization task concerning names that were learned in association with either soccer players, tennis players or control, non-motor, identities (actors). We stimulated the cortico-spinal system and recorded the MEPs at three different time points (0-24-72 h) after the association learning.

RESULTS

Coherently with previous literature we found a relative dissociation of leg muscles MEPs during reading of soccer-associated personal names with respect to tennis ones. Importantly this modulation was measured only 72 h after having learned the association. This effect was not found in the arm muscle.

CONCLUSION

The results suggest that for the process of embodying semantic associations in the motor system to take place, the strength of the association itself needs to rise above some level of consolidation.

Vicarious motor activation during action perception: beyond correlational evidence

Neurophysiological and imaging studies have shown that seeing the actions of other individuals brings about the vicarious activation of motor regions involved in performing the same actions. While this suggests a simulative mechanism mediating the perception of others' actions, one cannot use such evidence to make inferences about the functional significance of vicarious activations. Indeed, a central aim in social neuroscience is to comprehend how vicarious activations allow the understanding of other people's behavior, and this requires to use stimulation or lesion methods to establish causal links from brain activity to cognitive functions. In the present work, we review studies investigating the effects of transient manipulations of brain activity or stable lesions in the motor system on individuals' ability to perceive and understand the actions of others. We conclude there is now compelling evidence that neural activity in the motor system is critical for such cognitive ability. More research using causal methods, however, is needed in order to disclose the limits and the conditions under which vicarious activations are required to perceive and understand actions of others as well as their emotions and somatic feelings.

Fooling the kickers but not the goalkeepers: behavioral and neurophysiological correlates of fake action detection in soccer

Studies demonstrate that elite athletes are able to extract kinematic information of observed domain-specific actions to predict their future course. Little is known, however, on the perceptuo-motor processes and neural correlates of the athletes' ability to predict fooling actions. Combining psychophysics and transcranial magnetic stimulation, we explored the impact of motor and perceptual expertise on the ability to predict the fate of observed actual or fake soccer penalty kicks. We manipulated the congruence between the model's body kinematics and the subsequent ball trajectory and investigated the prediction performance and cortico-spinal reactivity of expert kickers, goalkeepers, and novices. Kickers and goalkeepers outperformed novices by anticipating the actual kick direction from the model's initial body movements. However, kickers were more often fooled than goalkeepers and novices in cases of incongruent actions. Congruent and incongruent actions engendered a comparable facilitation of kickers' lower limb motor representation, but their neurophysiological response was correlated with their greater susceptibility to be fooled. Moreover, when compared with actual actions, motor facilitation for incongruent actions was lower among goalkeepers and higher among novices. Thus, responding to fooling actions requires updation of simulative motor representations of others' actions and is facilitated by visual rather than by motor expertise.

tDCS of the primary motor cortex improves the detection of semantic dissonance

Increasing evidences show that the linguistic representation of motor activities induces simulative processes that involve motor neural systems normally engaged in actual execution of movements. However, other researches suggest that the motor cortex is not an integral part of the network for action-word representation but is recruited only to execute tasks that critically require the retrieval of sensorimotor attributes associated with words. In order to enlighten this controversial literature, three groups of healthy participants were submitted to transcranial direct current stimulation (tDCS) (cathodal, anodal and sham stimulations) of the left primary motor cortex during the execution of a picture recognition task. Results show that cathodal stimulation improves the participants' ability to detect either mismatching motor vs. no motor sentence-drawing associations, while no significant difference has not been reported for compatible associations. The current result is in line with the suggestion that motor regions play a critical role in detecting dissonant outcomes.

Embodiment of motor skills when observing expert and novice athletes

If people are shown a dynamic movie of an action such as kicking a soccer ball or hitting a tennis ball, they will respond to it faster if it requires the same effector. This standard congruency effect was reported to reverse when participants viewed static images of famous athletes not actually performing an action. It was suggested that the congruent response was inhibited because of a social contrast effect, based on an implied action, whereby responders viewed themselves as comparatively worse than the professional athlete. The present study recorded hand and foot responses when identifying static images of both famous and novice athletes in soccer and tennis. The action was either explicit or implied. In Experiment 1, a standard congruency effect was found for all images. In Experiment 2, when a response was based on the identity of the athlete rather than their expertise, the standard congruency effect was enhanced for images of novice athletes, but was eliminated for experts, suggesting a social contrast effect. Our study is the first to show that embodiment effects can be seen for implied and explicit action images of both novices and experts, and that static images are capable of eliciting priming effects associated with sport-relevant effector pairings.

Do not resonate with actions: sentence polarity modulates cortico-spinal excitability during action-related sentence reading

Background

Theories of embodied language suggest that the motor system is differentially called into action when processing motor-related versus abstract content words or sentences. It has been recently shown that processing negative polarity action-related sentences modulates neural activity of premotor and motor cortices.

Methods and Findings

We sought to determine whether reading negative polarity sentences brought about differential modulation of cortico-spinal motor excitability depending on processing hand-action related or abstract sentences. Facilitatory paired-pulses Transcranial Magnetic Stimulation (pp-TMS) was applied to the primary motor representation of the right-hand and the recorded amplitude of induced motor-evoked potentials (MEP) was used to index M1 activity during passive reading of either hand-action related or abstract content sentences presented in both negative and affirmative polarity. Results showed that the cortico-spinal excitability was affected by sentence polarity only in the hand-action related condition. Indeed, in keeping with previous TMS studies, reading positive polarity, hand action-related sentences suppressed cortico-spinal reactivity. This effect was absent when reading hand action-related negative polarity sentences. Moreover, no modulation of cortico-spinal reactivity was associated with either negative or positive polarity abstract sentences.

Conclusions

Our results indicate that grammatical cues prompting motor negation reduce the cortico-spinal suppression associated with affirmative action sentences reading and thus suggest that motor simulative processes underlying the embodiment may involve even syntactic features of language.

Gesturing Meaning: Non-action Words Activate the Motor System

Across cultures, speakers produce iconic gestures, which add – through the movement of the speakers’ hands – a pictorial dimension to the speakers’ message. These gestures capture not only the motor content but also the visuospatial content of the message. Here, we provide first evidence for a direct link between the representation of perceptual information and the motor system that can account for these observations. Across four experiments, participants’ hand movements captured both shapes that were directly perceived, and shapes that were only implicitly activated by unrelated semantic judgments of object words. These results were obtained even though the objects were not associated with any motor behaviors that would match the gestures the participants had to produce. Moreover, implied shape affected not only gesture selection processes but also their actual execution – as measured by the shape of hand motion through space – revealing intimate links between implied shape representation and motor output. The results are discussed in terms of ideomotor theories of action and perception, and provide one avenue for explaining the ubiquitous phenomenon of iconic gestures.