Neural Systems Underlying Observation of Humanly Impossible Movements: An fMRI Study

Voxelwise encoding models of body stimuli reveal a representational gradient from low-level visual features to postural features in occipitotemporal cortex

Research on body representation in the brain has focused on category-specific representation, using fMRI to investigate the response pattern to body stimuli in occipitotemporal cortex without so far addressing the issue of the specific computations involved in body selective regions, only defined by higher order category selectivity. This study used ultra-high field fMRI and banded ridge regression to investigate the coding of body images, by comparing the performance of three encoding models in predicting brain activity in occipitotemporal cortex and specifically the extrastriate body area (EBA). Our results suggest that bodies are encoded in occipitotemporal cortex and in the EBA according to a combination of low-level visual features and postural features.

Evaluation of abstract rule-based associations in the human premotor cortex during passive observation

Decision-making often manifests in behavior, typically yielding overt motor actions. This complex process requires the registration of sensory information with one's internal representation of the current context, before a categorical judgment of the most appropriate motor behavior can be issued. The construct concept of embodied decision-making encapsulates this sequence of complex processes, whereby behaviorally salient information from the environment is represented in an abstracted space of potential motor actions rather than only in an abstract cognitive "decision" space. Theoretical foundations and some empirical evidence account for support the involvement of premotor cortical circuits in embodied cognitive functions. Animal models show that premotor circuits participate in the registration and evaluation of actions performed by peers in social situations, that is, prior to controlling one's voluntary movements guided by arbitrary stimulus-response rules. However, such evidence from human data is currently limited. Here we used time-resolved magnetoencephalography imaging to characterize activations of the premotor cortex as human participants observed arbitrary, non-biological visual stimuli that either respected or violated a simple stimulus-response association rule. The participants had learned this rule previously, either actively, by performing a motor task (active learning), or passively, by observing a computer perform the same task (passive learning). We discovered that the human premotor cortex is activated during the passive observation of the correct execution of a sequence of events according to a rule learned previously. Premotor activation also differs when the subjects observe incorrect stimulus sequences. These premotor effects are present even when the observed events are of a non-motor, abstract nature, and even when the stimulus-response association rule was learned via passive observations of a computer agent performing the task, without requiring overt motor actions from the human participant. We found evidence of these phenomena by tracking cortical beta-band signaling in temporal alignment with the observation of task events and behavior. We conclude that premotor cortical circuits that are typically engaged during voluntary motor behavior are also involved in the interpretation of events of a non-ecological, unfamiliar nature but related to a learned abstract rule. As such, the present study provides the first evidence of neurophysiological processes of embodied decision-making in human premotor circuits when the observed events do not involve motor actions of a third party.

Multimodal processing in face-to-face interactions: A bridging link between psycholinguistics and sensory neuroscience

In face-to-face communication, humans are faced with multiple layers of discontinuous multimodal signals, such as head, face, hand gestures, speech and non-speech sounds, which need to be interpreted as coherent and unified communicative actions. This implies a fundamental computational challenge: optimally binding only signals belonging to the same communicative action while segregating signals that are not connected by the communicative content. How do we achieve such an extraordinary feat, reliably, and efficiently? To address this question, we need to further move the study of human communication beyond speech-centred perspectives and promote a multimodal approach combined with interdisciplinary cooperation. Accordingly, we seek to reconcile two explanatory frameworks recently proposed in psycholinguistics and sensory neuroscience into a neurocognitive model of multimodal face-to-face communication. First, we introduce a psycholinguistic framework that characterises face-to-face communication at three parallel processing levels: multiplex signals, multimodal gestalts and multilevel predictions. Second, we consider the recent proposal of a lateral neural visual pathway specifically dedicated to the dynamic aspects of social perception and reconceive it from a multimodal perspective ("lateral processing pathway"). Third, we reconcile the two frameworks into a neurocognitive model that proposes how multiplex signals, multimodal gestalts, and multilevel predictions may be implemented along the lateral processing pathway. Finally, we advocate a multimodal and multidisciplinary research approach, combining state-of-the-art imaging techniques, computational modelling and artificial intelligence for future empirical testing of our model.

Mu-desynchronization, N400 and corticospinal excitability during observation of natural and anatomically unnatural finger movements

The action observation networks (AON) (or the mirror neuron system) are the neural underpinnings of visuomotor integration and play an important role in motor control. Besides, one of the main functions of the human mirror neuron system is recognition of observed actions and the prediction of its outcome through the comparison with the internal mental motor representation. Previous studies focused on the human mirror neurons (MNs) activation during object-oriented movements observation, therefore intransitive movements observation effects on MNs activity remains relatively little-studied. Moreover, the dependence of MNs activation on the biomechanical characteristics of observed movement and their biological plausibility remained highly underexplored. In this study we proposed that naturalness of observed intransitive movement can modulate the MNs activity. Event-related desynchronization (ERD) of sensorimotor electroencephalography (EEG) rhythms, N400 event-related potentials (ERPs) component and corticospinal excitability were investigated in twenty healthy volunteers during observation of simple non-transitive finger flexion that might be either biomechanically natural or unnatural when finger wriggled out toward the dorsal side of palm. We showed that both natural and unnatural movements caused mu/beta-desynchronization, which gradually increased during the flexion phase and returned to baseline while observation of extension. Desynchronization of the mu-rhythm was significantly higher during observation of the natural movements. At the same time, beta-rhythm was not found to be sensitive to the action naturalness. Also, observation of unnatural movements caused an increased amplitude of the N400 component registered in the centro-parietal regions. We suggest that the sensitivity of N400 to intransitive action observation with no explicit semantic context might imply the broader role of N400 sources within AON. Surprisingly, no changes in corticospinal excitability were found. This lack of excitability modulation by action observation could be related with dependence of the M1 activity on the observed movement phase.

Decoding the difference between explicit and implicit body expression representation in high level visual, prefrontal and inferior parietal cortex

Recent studies provide an increasing understanding of how visual objects categories like faces or bodies are represented in the brain and also raised the question whether a category based or more dynamic network inspired models are more powerful. Two important and so far sidestepped issues in this debate are, first, how major category attributes like the emotional expression directly influence category representation and second, whether category and attribute representation are sensitive to task demands. This study investigated the impact of a crucial category attribute like emotional expression on category area activity and whether this varies with the participants' task. Using (fMRI) we measured BOLD responses while participants viewed whole body expressions and performed either an explicit (emotion) or an implicit (shape) recognition task. Our results based on multivariate methods show that the type of task is the strongest determinant of brain activity and can be decoded in EBA, VLPFC and IPL. Brain activity was higher for the explicit task condition in VLPFC and was not emotion specific. This pattern suggests that during explicit recognition of the body expression, body category representation may be strengthened, and emotion and action related activity suppressed. Taken together these results stress the importance of the task and of the role of category attributes for understanding the functional organization of high level visual cortex.

What modulates the Mirror Neuron System during action observation?: Multiple factors involving the action, the actor, the observer, the relationship between actor and observer, and the context

Seeing an agent perform an action typically triggers a motor simulation of that action in the observer's Mirror Neuron System (MNS). Over the past few years, it has become increasingly clear that during action observation the patterns and strengths of responses in the MNS are modulated by multiple factors. The first aim of this paper is therefore to provide the most comprehensive survey to date of these factors. To that end, 22 distinct factors are described, broken down into the following sets: six involving the action; two involving the actor; nine involving the observer; four involving the relationship between actor and observer; and one involving the context. The second aim is to consider the implications of these findings for four prominent theoretical models of the MNS: the Direct Matching Model; the Predictive Coding Model; the Value-Driven Model; and the Associative Model. These assessments suggest that although each model is supported by a wide range of findings, each one is also challenged by other findings and relatively unaffected by still others. Hence, there is now a pressing need for a richer, more inclusive model that is better able to account for all of the modulatory factors that have been identified so far.

Great apes' understanding of biomechanics: eye-tracking experiments using three-dimensional computer-generated animations

Visual processing of the body movements of other animals is important for adaptive animal behaviors. It is widely known that animals can distinguish articulated animal movements even when they are just represented by points of light such that only information about biological motion is retained. However, the extent to which nonhuman great apes comprehend the underlying structural and physiological constraints affecting each moving body part, i.e., biomechanics, is still unclear. To address this, we examined the understanding of biomechanics in bonobos (Pan paniscus) and chimpanzees (Pan troglodytes), following a previous study on humans (Homo sapiens). Apes underwent eye tracking while viewing three-dimensional computer-generated (CG) animations of biomechanically possible or impossible elbow movements performed by a human, robot, or nonhuman ape. Overall, apes did not differentiate their gaze between possible and impossible movements of elbows. However, some apes looked at elbows for longer when viewing impossible vs. possible robot movements, which indicates that they may have had knowledge of biomechanics and that this knowledge could be extended to a novel agent. These mixed results make it difficult to draw a firm conclusion regarding the extent to which apes understand biomechanics. We discuss some methodological features that may be responsible for the results, as well as implications for future nonhuman animal studies involving the presentation of CG animations or measurement of gaze behaviors.

Visuo-motor and interoceptive influences on peripersonal space representation following spinal cord injury

Peripersonal space (PPS) representation is modulated by information coming from the body. In paraplegic individuals, whose lower limb sensory-motor functions are impaired or completely lost, the representation of PPS around the feet is reduced. However, passive motion can have short-term restorative effects. What remains unclear is the mechanisms underlying this recovery, in particular with regard to the contribution of visual and motor feedback and of interoception. Using virtual reality technology, we dissociated the motor and visual feedback during passive motion in paraplegics with complete and incomplete lesions and in healthy controls. The results show that in the case of paraplegics, the presence of motor feedback was necessary for the recovery of PPS representation, both when the motor feedback was congruent and when it was incongruent with the visual feedback. In contrast, visuo-motor incongruence led to an inhibition of PPS representation in the control group. There were no differences in sympathetic responses between the three groups. Nevertheless, in individuals with incomplete lesions, greater interoceptive sensitivity was associated with a better representation of PPS around the feet in the visuo-motor incongruent conditions. These results shed new light on the modulation of PPS representation, and demonstrate the importance of residual motor feedback and its integration with other bodily information in maintaining space representation.

Neural processing of social interaction: Coordinate-based meta-analytic evidence from human neuroimaging studies

While the action observation and mentalizing networks are considered to play complementary roles in understanding others' goals and intentions, they might be concurrently engaged when processing social interactions. We assessed this hypothesis via three activation-likelihood-estimation meta-analyses of neuroimaging studies on the neural processing of: (a) social interactions, (b) individual actions by the action observation network, and (c) mental states by the mentalizing network. Conjunction analyses and direct comparisons unveiled overlapping and specific regions among the resulting maps. We report quantitative meta-analytic evidence for a "social interaction network" including key nodes of the action observation and mentalizing networks. An action-social interaction-mentalizing gradient of activity along the posterior temporal cortex highlighted a hierarchical processing of interactions, from visuomotor analyses decoding individual and shared intentions to in-depth inferences on actors' intentional states. The medial prefrontal cortex, possibly in conjunction with the amygdala, might provide additional information concerning the affective valence of the interaction. This evidence suggests that the functional architecture underlying the neural processing of interactions involves the joint involvement of the action observation and mentalizing networks. These data might inform the design of rehabilitative treatments for social cognition disorders in pathological conditions, and the assessment of their outcome in randomized controlled trials.

Mirror Neuron System Activation in Children With Unilateral Cerebral Palsy During Observation of Actions Performed by a Pathological Model

Background. Recent evidence suggested that Action Observation Therapy (AOT), based on observation of actions followed by immediate reproduction, could be a useful rehabilitative strategy for promoting functional recovery of children affected by unilateral cerebral palsy (UCP). AOT most likely exploits properties of the parieto-premotor mirror neuron system (MNS). This is more intensely activated when participants observe actions belonging to their own motor repertoire. Objective. The aim of the present study was to investigate the issue of whether MNS of UCP children is better activated by actions performed by a paretic hand rather than a healthy one. Methods. Using functional magnetic resonance imaging, we assessed brain activation in a homogeneous group of 10 right UCP children compared with that of 10 right-handed typically developing (TD) children, during observation of grasping actions performed by a healthy or a paretic hand. Results. The results revealed a significant activation within the MNS in both UCP and TD children, more lateralized to the left hemisphere in the TD group. Most important, region of interest (ROI) analysis on parietal and premotor regions showed that, in UCP, the MNS was more strongly activated by observation of actions performed by the paretic hand, a motor model more similar to the observer’s motor repertoire. Conclusions. This study shows that children affected by spastic UCP exhibit enhanced activation of the MNS during observation of goal-directed actions performed by a pathological model with respect to a healthy one.

Reduced Motor Interference in Preschoolers with Autism Spectrum Disorder and Williams Syndrome

Motor interference occurs when action execution is hindered by the observation of an incongruent action. The present study used a novel eye-tracking paradigm to test the motor interference effect in 22 preschoolers with autism spectrum disorder (ASD), 14 preschoolers with Williams syndrome (WS), and 18 typically developing (TD) peers. In TD children, performance of a pre-determined action was slower after the observation of an incongruent motor action and faster following observation of a congruent motor action, indicating a motor interference effect. In both the ASD and WS groups, performance was unaffected by the congruent versus incongruent nature of the observed motor action.

Understanding Activation Patterns in Shared Circuits: Toward a Value Driven Model

Over the past decade many studies indicate that we utilize our own motor system to understand the actions of other people. This mirror neuron system (MNS) has been proposed to be involved in social cognition and motor learning. However, conflicting findings regarding the underlying mechanisms that drive these shared circuits make it difficult to decipher a common model of their function. Here we propose adapting a “value-driven” model to explain discrepancies in the human mirror system literature and to incorporate this model with existing models. We will use this model to explain discrepant activation patterns in multiple shared circuits in the human data, such that a unified model may explain reported activation patterns from previous studies as a function of value.

Seeing More Than Human: Autism and Anthropomorphic Theory of Mind

Theory of mind (ToM) is defined as the process of taking another's perspective. Anthropomorphism can be seen as the extension of ToM to non-human entities. This review examines the literature concerning ToM and anthropomorphism in relation to individuals with Autism Spectrum Disorder (ASD), specifically addressing the questions of how and why those on the spectrum both show an increased interest for anthropomorphism and may even show improved ToM abilities when judging the mental states of anthropomorphic characters. This review highlights that while individuals with ASD traditionally show deficits on a wide range of ToM tests, such as recognizing facial emotions, such ToM deficits may be ameliorated if the stimuli presented is cartoon or animal-like rather than in human form. Individuals with ASD show a greater interest in anthropomorphic characters and process the features of these characters using methods typically reserved for human stimuli. Personal accounts of individuals with ASD also suggest they may identify more closely with animals than other humans. It is shown how the social motivations hypothesized to underlie the anthropomorphizing of non-human targets may lead those on the spectrum to seek social connections and therefore gain ToM experience and expertise amongst unlikely sources.

Early modulation of intra-cortical inhibition during the observation of action mistakes

Errors while performing an action are fundamental for learning. During interaction others' errors must be monitored and taken into account to allow joint action coordination and imitation learning. This monitoring relies on an action observation network (AON) mainly based on parietofrontal recurrent circuits. Although different studies suggest that inappropriate actions may rapidly be inhibited during execution, little is known about the modulation of the AON when an action misstep is shown. Here we used single and paired pulse transcranial magnetic stimulation to assess corticospinal excitability, intracortical facilitation and intracortical inhibition at different time intervals (120, 180, 240 ms) after the visual presentation of a motor execution error. Results show a specific and early (120 ms) decrease of intracortical inhibition likely because of a significant mismatch between the observed erroneous action and observer's expectations. Indeed, as proposed by the top-down predictive framework, the motor system may be involved in the generation of these error signals and our data show that this mechanism could rely on the early decrease of intracortical inhibition within the corticomotor system.

Fronto-parietal coding of goal-directed actions performed by artificial agents

With advances in technology, artificial agents such as humanoid robots will soon become a part of our daily lives. For safe and intuitive collaboration, it is important to understand the goals behind their motor actions. In humans, this process is mediated by changes in activity in fronto-parietal brain areas. The extent to which these areas are activated when observing artificial agents indicates the naturalness and easiness of interaction. Previous studies indicated that fronto-parietal activity does not depend on whether the agent is human or artificial. However, it is unknown whether this activity is modulated by observing grasping (self-related action) and pointing actions (other-related action) performed by an artificial agent depending on the action goal. Therefore, we designed an experiment in which subjects observed human and artificial agents perform pointing and grasping actions aimed at two different object categories suggesting different goals. We found a signal increase in the bilateral inferior parietal lobule and the premotor cortex when tool versus food items were pointed to or grasped by both agents, probably reflecting the association of hand actions with the functional use of tools. Our results show that goal attribution engages the fronto-parietal network not only for observing a human but also a robotic agent for both self-related and social actions. The debriefing after the experiment has shown that actions of human-like artificial agents can be perceived as being goal-directed. Therefore, humans will be able to interact with service robots intuitively in various domains such as education, healthcare, public service, and entertainment.

Lateralized occipito-temporal N1 responses to images of salient distorted finger postures

For humans as social beings, other people’s hands are highly visually conspicuous. Exceptionally striking are hands in other than natural configuration which have been found to elicit distinct brain activation. Here we studied response strength and lateralization of this activation using event-related potentials (ERPs), in particular, occipito-temporal N1 responses as correlates of activation in extrastriate body area. Participants viewed computer-generated images of hands, half of them showing distorted fingers, the other half showing natural fingers. As control stimuli of similar geometric complexity, images of chairs were shown, half of them with distorted legs, half with standard legs. The contrast of interest was between distorted and natural/standard stimuli. For hands, stronger N1 responses were observed for distorted (vs natural) stimuli from 170 ms post stimulus. Such stronger N1 responses were found for distorted hands and absent for distorted chairs, therefore likely unrelated to visuospatial processing of the unusual distorted shapes. Rather, N1 modulation over both hemispheres – but robustly right-lateralized – could reflect distorted hands as emotionally laden stimuli. The results are in line with privileged visual processing of hands as highly salient body parts, with distortions engaging neural resources that are especially activated for biological stimuli in social perception.

Gravity Cues Embedded in the Kinematics of Human Motion Are Detected in Form-from-Motion Areas of the Visual System and in Motor-Related Areas

The present study investigated the cortical areas engaged in the perception of graviceptive information embedded in biological motion (BM). To this end, functional magnetic resonance imaging was used to assess the cortical areas active during the observation of human movements performed under normogravity and microgravity (parabolic flight). Movements were defined by motion cues alone using point-light displays. We found that gravity modulated the activation of a restricted set of regions of the network subtending BM perception, including form-from-motion areas of the visual system (kinetic occipital region, lingual gyrus, cuneus) and motor-related areas (primary motor and somatosensory cortices). These findings suggest that compliance of observed movements with normal gravity was carried out by mapping them onto the observer's motor system and by extracting their overall form from local motion of the moving light points. We propose that judgment on graviceptive information embedded in BM can be established based on motor resonance and visual familiarity mechanisms and not necessarily by accessing the internal model of gravitational motion stored in the vestibular cortex.

Primary somatosensory cortex necessary for the perception of weight from other people's action: A continuous theta-burst TMS experiment

The presence of a network of areas in the parietal and premotor cortices, which are active both during action execution and observation, suggests that we might understand the actions of other people by activating those motor programs for making similar actions. Although neurophysiological and imaging studies show an involvement of the somatosensory cortex (SI) during action observation and execution, it is unclear whether SI is essential for understanding the somatosensory aspects of observed actions. To address this issue, we used off-line transcranial magnetic continuous theta-burst stimulation (cTBS) just before a weight judgment task. Participants observed the right hand of an actor lifting a box and estimated its relative weight. In counterbalanced sessions, we delivered sham and active cTBS over the hand region of the left SI and, to test anatomical specificity, over the left motor cortex (M1) and the left superior parietal lobule (SPL). Active cTBS over SI, but not over M1 or SPL, impaired task performance relative to sham cTBS. Moreover, active cTBS delivered over SI just before participants were asked to evaluate the weight of a bouncing ball did not alter performance compared to sham cTBS. These findings indicate that SI is critical for extracting somatosensory features (heavy/light) from observed action kinematics and suggest a prominent role of SI in action understanding.

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TMS over the somatosensory cortex disrupts performance on a weight judgment task.

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Disruption is specific for judgements based on observed human actions.

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No TMS effect is found for judgements based on observed non-human motion.

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No effect is found when TMS is administered over nearby frontal and parietal region.

Monitoring Different Phonological Parameters of Sign Language Engages the Same Cortical Language Network but Distinctive Perceptual Ones

The study of signed languages allows the dissociation of sensorimotor and cognitive neural components of the language signal. Here we investigated the neurocognitive processes underlying the monitoring of two phonological parameters of sign languages: handshape and location. Our goal was to determine if brain regions processing sensorimotor characteristics of different phonological parameters of sign languages were also involved in phonological processing, with their activity being modulated by the linguistic content of manual actions. We conducted an fMRI experiment using manual actions varying in phonological structure and semantics: (1) signs of a familiar sign language (British Sign Language), (2) signs of an unfamiliar sign language (Swedish Sign Language), and (3) invented nonsigns that violate the phonological rules of British Sign Language and Swedish Sign Language or consist of nonoccurring combinations of phonological parameters. Three groups of participants were tested: deaf native signers, deaf nonsigners, and hearing nonsigners. Results show that the linguistic processing of different phonological parameters of sign language is independent of the sensorimotor characteristics of the language signal. Handshape and location were processed by different perceptual and task-related brain networks but recruited the same language areas. The semantic content of the stimuli did not influence this process, but phonological structure did, with nonsigns being associated with longer RTs and stronger activations in an action observation network in all participants and in the supramarginal gyrus exclusively in deaf signers. These results suggest higher processing demands for stimuli that contravene the phonological rules of a signed language, independently of previous knowledge of signed languages. We suggest that the phonological characteristics of a language may arise as a consequence of more efficient neural processing for its perception and production.

The Processing of Biologically Plausible and Implausible forms in American Sign Language: Evidence for Perceptual Tuning

The human auditory system distinguishes speech-like information from general auditory signals in a remarkably fast and efficient way. Combining psychophysics and neurophysiology (MEG), we demonstrate a similar result for the processing of visual information used for language communication in users of sign languages. We demonstrate that the earliest visual cortical responses in deaf signers viewing American Sign Language (ASL) signs show specific modulations to violations of anatomic constraints that would make the sign either possible or impossible to articulate. These neural data are accompanied with a significantly increased perceptual sensitivity to the anatomical incongruity. The differential effects in the early visual evoked potentials arguably reflect an expectation-driven assessment of somatic representational integrity, suggesting that language experience and/or auditory deprivation may shape the neuronal mechanisms underlying the analysis of complex human form. The data demonstrate that the perceptual tuning that underlies the discrimination of language and non-language information is not limited to spoken languages but extends to languages expressed in the visual modality.

Vivid Mental Imagery of Biomechanically Impossible Movements Elicited by Cortical Electrostimulation of the Central Region in an Awake Patient

BACKGROUND

The perception we have of our own body, called 'body image,' is crucial for self-awareness. Here, we evoked reproducible mental imagery of a postural illusion by intrasurgical electrostimulation of the central cortex.

CASE REPORT

A 24-year-old patient experienced seizures involving vivid mental imagery of biomechanically impossible movements of the upper limb. A right precentral low-grade glioma was diagnosed. Awake surgery with intraoperative electrostimulation sensorimotor mapping was performed. Remarkably, the same mental representations of biomechanically impossible movements of the left upper limb were repeatedly elicited during stimulation of the central cortex. These eloquent areas were preserved, even though the precentral part of the knob of the hand was removed. After a transient monoplegia, the patient recovered and resumed a normal life which included playing the guitar.

CONCLUSION

These mental experiences of a postural illusion generated by intraoperative stimulation could be related to neuroplasticity mechanisms induced by the slow growth of low-grade glioma within the knob of the hand. Such a functional reorganization may explain why this area was removed without permanent deficits. This perception of biomechanically impossible movements during surgery might be due to a transient disruption by stimulating the frontoparietal network involved in the coding of the body image.

Alpha and beta band event-related desynchronization reflects kinematic regularities

The short-lasting attenuation of brain oscillations is termed event-related desynchronization (ERD). It is frequently found in the alpha and beta bands in humans during generation, observation, and imagery of movement and is considered to reflect cortical motor activity and action-perception coupling. The shared information driving ERD in all these motor-related behaviors is unknown. We investigated whether particular laws governing production and perception of curved movement may account for the attenuation of alpha and beta rhythms. Human movement appears to be governed by relatively few kinematic laws of motion. One dominant law in biological motion kinematics is the 2/3 power law (PL), which imposes a strong dependency of movement speed on curvature and is prominent in action-perception coupling. Here we directly examined whether the 2/3 PL elicits ERD during motion observation by characterizing the spatiotemporal signature of ERD. ERDs were measured while human subjects observed a cloud of dots moving along elliptical trajectories either complying with or violating the 2/3 PL. We found that ERD within both frequency bands was consistently stronger, arose faster, and was more widespread while observing motion obeying the 2/3 PL. An activity pattern showing clear 2/3 PL preference and lying within the alpha band was observed exclusively above central motor areas, whereas 2/3 PL preference in the beta band was observed in additional prefrontal-central cortical sites. Our findings reveal that compliance with the 2/3 PL is sufficient to elicit a selective ERD response in the human brain.

Self-recognition of one's own fall recruits the genuine bodily crisis-related brain activity

While bipedalism is a fundamental evolutionary adaptation thought to be essential for the development of the human brain, the erect body is always an inch or two away from falling. Although the neural mechanism for automatically detecting one's own body instability is an important consideration, there have thus far been few functional neuroimaging studies because of the restrictions placed on participants' movements. Here, we used functional magnetic resonance imaging to investigate the neural substrate underlying whole body instability, based on the self-recognition paradigm that uses video stimuli consisting of one's own and others' whole bodies depicted in stable and unstable states. Analyses revealed significant activity in the regions which would be activated during genuine unstable bodily states: The right parieto-insular vestibular cortex, inferior frontal junction, posterior insula and parabrachial nucleus. We argue that these right-lateralized cortical and brainstem regions mediate vestibular information processing for detection of vestibular anomalies, defensive motor responding in which the necessary motor responses are automatically prepared/simulated to protect one's own body, and sympathetic activity as a form of alarm response during whole body instability.

Increased Visual Stimulation Systematically Decreases Activity in Lateral Intermediate Cortex

Previous studies have attributed multiple diverse roles to the posterior superior temporal cortex (STC), both visually driven and cognitive, including part of the default mode network (DMN). Here, we demonstrate a unifying property across this multimodal region. Specifically, the lateral intermediate (LIM) portion of STC showed an unexpected feature: a progressively decreasing fMRI response to increases in visual stimulus size (or number). Such responses are reversed in sign, relative to well-known responses in classic occipital temporal visual cortex. In LIM, this "reversed" size function was present across multiple object categories and retinotopic eccentricities. Moreover, we found a significant interaction between the LIM size function and the distribution of subjects' attention. These findings suggest that LIM serves as a part of the DMN. Further analysis of functional connectivity, plus a meta-analysis of previous fMRI results, suggests that LIM is a heterogeneous area including different subdivisions. Surprisingly, analogous fMRI tests in macaque monkeys did not reveal a clear homolog of LIM. This interspecies discrepancy supports the idea that self-referential thinking and theory of mind are more prominent in humans, compared with monkeys.

Hand specific representations in language comprehension

Theories of embodied cognition argue that language comprehension involves sensory-motor re-enactments of the actions described. However, the degree of specificity of these re-enactments as well as the relationship between action and language remains a matter of debate. Here we investigate these issues by examining how hand-specific information (left or right hand) is recruited in language comprehension and action execution. An fMRI study tested self-reported right-handed participants in two separate tasks that were designed to be as similar as possible to increase sensitivity of the comparison across task: an action execution go/no-go task where participants performed right or left hand actions, and a language task where participants read sentences describing the same left or right handed actions as in the execution task. We found that language-induced activity did not match the hand-specific patterns of activity found for action execution in primary somatosensory and motor cortex, but it overlapped with pre-motor and parietal regions associated with action planning. Within these pre-motor regions, both right hand actions and sentences elicited stronger activity than left hand actions and sentences—a dominant hand effect. Importantly, both dorsal and ventral sections of the left pre-central gyrus were recruited by both tasks, suggesting different action features being recruited. These results suggest that (a) language comprehension elicits motor representations that are hand-specific and akin to multimodal action plans, rather than full action re-enactments; and (b) language comprehension and action execution share schematic hand-specific representations that are richer for the dominant hand, and thus linked to previous motor experience.

The affordance-matching hypothesis: how objects guide action understanding and prediction

Action understanding lies at the heart of social interaction. Prior research has often conceptualized this capacity in terms of a motoric matching of observed actions to an action in one's motor repertoire, but has ignored the role of object information. In this manuscript, we set out an alternative conception of intention understanding, which places the role of objects as central to our observation and comprehension of the actions of others. We outline the current understanding of the interconnectedness of action and object knowledge, demonstrating how both rely heavily on the other. We then propose a novel framework, the affordance-matching hypothesis, which incorporates these findings into a simple model of action understanding, in which object knowledge-what an object is for and how it is used-can inform and constrain both action interpretation and prediction. We will review recent empirical evidence that supports such an object-based view of action understanding and we relate the affordance matching hypothesis to recent proposals that have re-conceptualized the role of mirror neurons in action understanding.

Interference effect of body shadow in action control

Observing actions performed by other persons can subsequently influence our own motor behaviours. However, it is unknown whether the shadows cast by such actions can also have an impact on the observers' actions. Here we show that the mere observation of a cast shadow can influence imitative behaviours. Specifically, participants were shown a hand picture and its associated cast shadow in a neutral position. In a 'compatible trial' the hand and the shadow that followed were turned in the same open or closed direction, whereas in an 'incompatible trial' the hand and the shadow were turned in different directions. We contrasted two experimental conditions: (i) 'hand-shadow' in which participants observed a hand and its cast shadow (the hand covered the shadow); (ii) 'hand-hand' in which participants observed a hand and another black hand (the shadow covered the hand). The participants' task was to imitate (ie by closing or opening their own hands) the hand or the cast shadow of an action. For both conditions results revealed interference (ie longer response latencies) for incompatible trials. This suggests for the first time that the mere observation of a cast shadow of a hand can influence imitative behaviours. However, time courses of the response latencies revealed that imitative effect in the hand-shadow condition was different than the imitative effect in the hand-hand condition. Therefore, we suggest considering the cast shadow of an action as an important feature during motor control for humans.

Exploring the development of the mirror neuron system: finding the right paradigm

Due to its ability to map an observed action onto the observer's own cortical motor circuits, the mirror neuron system (MNS) has been implicated in many facets of social cognition. As such, achieving an understanding of the typical development of this intriguing brain system seems obvious. Only now, however, are studies attempting to explore the processes and principles behind the emergence of the MNS. This article critically reviews a number of experimental paradigms employed in this endeavor. We conclude by suggesting that future neuroscientific investigations should incorporate a response-stimulus procedure, whereby action execution results in, not from, novel sensory stimuli.

Theory of mind: a neural prediction problem

Predictive coding posits that neural systems make forward-looking predictions about incoming information. Neural signals contain information not about the currently perceived stimulus, but about the difference between the observed and the predicted stimulus. We propose to extend the predictive coding framework from high-level sensory processing to the more abstract domain of theory of mind; that is, to inferences about others' goals, thoughts, and personalities. We review evidence that, across brain regions, neural responses to depictions of human behavior, from biological motion to trait descriptions, exhibit a key signature of predictive coding: reduced activity to predictable stimuli. We discuss how future experiments could distinguish predictive coding from alternative explanations of this response profile. This framework may provide an important new window on the neural computations underlying theory of mind.

How are the motor system activity and functional connectivity between the cognitive and sensorimotor systems modulated by athletic expertise?

Expertise offers a unique insight into how our brain functions. The purpose of this experiment was to determine if motor system activity and functional connectivity between the cognitive system and sensorimotor system is differentially modulated by an individual's level of expertise. This goal was achieved through the acquisition of functional neuroimaging data in 10 expert volleyball players and 10 novice individuals who were presented with a series of sentences describing possible technical volleyball-specific motor acts and acts that cannot be performed as positive ("Do …!") or negative ("Don't …") commands, while they were silently reading them and deciding whether the actions were technically feasible or not. Compared with novices, experts' activity in the left primary motor cortex hand area (M1) and in the left premotor cortex (Pm) was decreased by impossible actions presented as positive commands. Sensorimotor activation in response to action-related stimuli is not that automatic as held since we found that these areas were deactivated during the task, and their functional connectivity to the primary visual cortex was strengthened for possible actions presented as positive commands, reflecting the neural processes underlying the interaction between motor and visual imagery. These results suggest that the neural activity within the key areas implicitly triggered by motor simulation is a function of the expertise, action feasibility, and context.

Perturbing the action observation network during perception and categorization of actions' goals and grips: state-dependency and virtual lesion TMS effects

Watching others grasping and using objects activates an action observation network (AON), including inferior frontal (IFC), anterior intraparietal (AIP), and somatosensory cortices (S1). Yet, causal evidence of the differential involvement of such AON sensorimotor nodes in representing high- and low-level action components (i.e., end-goals and grip type) is meager. To address this issue, we used transcranial magnetic stimulation-adaptation (TMS-A) during 2 novel action perception tasks. Participants were shown adapting movies displaying a demonstrator performing goal-directed actions with a tool, using either power or precision grips. They were then asked to match the end-goal (Goal-recognition task) or the grip (Grip-recognition task) of actions shown in test pictures to the adapting movies. TMS was administered over IFC, AIP, or S1 during presentation of test pictures. Virtual lesion-like effects were found in the Grip-recognition task where IFC stimulation induced a general performance decrease, suggesting a critical role of IFC in perceiving grips. In the Goal-recognition task, IFC and S1 stimulation differently affected the processing of "adapted" and "nonadapted" goals. These "state-dependent" effects suggest that the overall goal of seen actions is encoded into functionally distinct and spatially overlapping neural populations in IFC-S1 and such encoding is critical for recognizing and understanding end-goals.

Social cognition and the cerebellum: a meta-analysis of over 350 fMRI studies

This meta-analysis explores the role of the cerebellum in social cognition. Recent meta-analyses of neuroimaging studies since 2008 demonstrate that the cerebellum is only marginally involved in social cognition and emotionality, with a few meta-analyses pointing to an involvement of at most 54% of the individual studies. In this study, novel meta-analyses of over 350 fMRI studies, dividing up the domain of social cognition in homogeneous subdomains, confirmed this low involvement of the cerebellum in conditions that trigger the mirror network (e.g., when familiar movements of body parts are observed) and the mentalizing network (when no moving body parts or unfamiliar movements are present). There is, however, one set of mentalizing conditions that strongly involve the cerebellum in 50-100% of the individual studies. In particular, when the level of abstraction is high, such as when behaviors are described in terms of traits or permanent characteristics, in terms of groups rather than individuals, in terms of the past (episodic autobiographic memory) or the future rather than the present, or in terms of hypothetical events that may happen. An activation likelihood estimation (ALE) meta-analysis conducted in this study reveals that the cerebellum is critically implicated in social cognition and that the areas of the cerebellum which are consistently involved in social cognitive processes show extensive overlap with the areas involved in sensorimotor (during mirror and self-judgments tasks) as well as in executive functioning (across all tasks). We discuss the role of the cerebellum in social cognition in general and in higher abstraction mentalizing in particular. We also point out a number of methodological limitations of some available studies on the social brain that hamper the detection of cerebellar activity.

Action prediction in younger versus older adults: neural correlates of motor familiarity

Generating predictions during action observation is essential for efficient navigation through our social environment. With age, the sensitivity in action prediction declines. In younger adults, the action observation network (AON), consisting of premotor, parietal and occipitotemporal cortices, has been implicated in transforming executed and observed actions into a common code. Much less is known about age-related changes in the neural representation of observed actions. Using fMRI, the present study measured brain activity in younger and older adults during the prediction of temporarily occluded actions (figure skating elements and simple movement exercises). All participants were highly familiar with the movement exercises whereas only some participants were experienced figure skaters. With respect to the AON, the results confirm that this network was preferentially engaged for the more familiar movement exercises. Compared to younger adults, older adults recruited visual regions to perform the task and, additionally, the hippocampus and caudate when the observed actions were familiar to them. Thus, instead of effectively exploiting the sensorimotor matching properties of the AON, older adults seemed to rely predominantly on the visual dynamics of the observed actions to perform the task. Our data further suggest that the caudate played an important role during the prediction of the less familiar figure skating elements in better-performing groups. Together, these findings show that action prediction engages a distributed network in the brain, which is modulated by the content of the observed actions and the age and experience of the observer.

Time perception during apparent biological motion reflects subjective speed of movement, not objective rate of visual stimulation

We have investigated links between biological motion perception and time perception. Participants compared the durations of two paired visual frames, inside which task-irrelevant sequences of static body postures were presented. The sequences produced apparent movements of shorter and longer path lengths, depending on the sequential order of body postures (ABC or ACB). Shorter and longer path lengths were paired with shorter and longer interstimulus intervals (ISIs) to produce path/ISI congruent sequences with intermediate subjective speeds and path/ISI incongruent sequences with slowest and fastest subjective speeds. Participants compared the duration of the visual frames surrounding these sequences; body postures and biological motion were irrelevant. The ability to discriminate the duration of the frames (as measured by the just noticeable difference, JND) was reduced for pairs of path/ISI congruent sequences as compared to pairs of path/ISI incongruent sequences. That is, duration discrimination improved when implied speed differed between the two sequences of a pair compared to when the implied speed was the same. Since stimuli showed no actual movement and were fully matched for lower-level visual input and objective stimulus durations, our findings suggest an involvement of higher-order visual or even motor areas in temporal biases during apparent biological motion perception. We show that apparent speed is the primary dimension of such percepts consistent with a dominant role of movement dynamics in the perception of other people's actions. Our results also confirm an intimate relation between time perception and processing of human movement.

Action simulation plays a critical role in deceptive action recognition

The ability to infer deceptive intents from nonverbal behavior is critical for social interactions. By combining single-pulse and repetitive transcranial magnetic stimulation (TMS) in healthy humans, we provide both correlational and causative evidence that action simulation is actively involved in the ability to recognize deceptive body movements. We recorded motor-evoked potentials during a faked-action discrimination (FAD) task: participants watched videos of actors lifting a cube and judged whether the actors were trying to deceive them concerning the real weight of the cube. Seeing faked actions facilitated the observers' motor system more than truthful actions in a body-part-specific manner, suggesting that motor resonance was sensitive to deceptive movements. Furthermore, we found that TMS virtual lesion to the anterior node of the action observation network, namely the left inferior frontal cortex (IFC), reduced perceptual sensitivity in the FAD task. In contrast, no change in FAD task performance was found after virtual lesions to the left temporoparietal junction (control site). Moreover, virtual lesion to the IFC failed to affect performance in a difficulty-matched spatial-control task that did not require processing of spatiotemporal (acceleration) and configurational (limb displacement) features of seen actions, which are critical to detecting deceptive intent in the actions of others. These findings indicate that the human IFC is critical for recognizing deceptive body movements and suggest that FAD relies on the simulation of subtle changes in action kinematics within the motor system.