Julie Grèzes

Functional anatomy of execution, mental simulation, observation, and verb generation of actions: A meta-analysis.

There is a large body of psychological and neuroimaging experiments that have interpreted their findings in favor of a functional equivalence between action generation, action simulation, action verbalization, and perception of action. On the basis of these data, the concept of shared motor representations has been proposed. Indeed several authors have argued that our capacity to understand other peoples behavior and to attribute intention or beliefs to others is rooted in a neural, most likely distributed, execution/observation mechanism. Recent neuroimaging studies have explored the neural network engaged during motor execution, simulation, verbalization, and observation. The focus of this meta‐analysis is to evaluate in specific detail to what extent the activated foci elicited by these studies overlap. Hum. Brain Mapping 12:1–19, 2001.

Neural mechanisms subserving the perception of human actions

Our ability to generate actions and to recognize actions performed by others is the bedrock of our social life. Behavioral evidence suggests that the processes underlying perception and action might share a common representational framework. That is, observers might understand the actions of another individual in terms of the same neural code that they use to produce the same actions themselves. What neurophysiological evidence, if any, supports such a hypothesis? In this article, brain imaging studies addressing this question are reviewed and examined in the light of the functional segregation of the perceptual mechanisms subtending visual recognition and those used for action. We suggest that there are not yet conclusive arguments for a clear neurophysiological substrate supporting a common coding between perception and action.

The power of simulation : Imagining one's own and other's behavior

A large number of cognitive neuroscience studies point to the similarities in the neural circuits activated during the generation, imagination, as well as observation of ones own and others behavior. Such findings support the shared representations account of social cognition, which is suggested to provide the basic mechanism for social interaction. Mental simulation may also be a representational tool to understand the self and others. However, successfully navigating these shared representations--both within oneself and between individuals--constitutes an essential functional property of any autonomous agent. It will be argued that self-awareness and agency, mediated by the temporoparietal (TPJ) area and the prefrontal cortex, are critical aspects of the social mind. Thus, differences as well as similarities between self and other representations at the neural level may be related to the degrees of self-awareness and agency. Overall, these data support the view that social cognition draws on both domain-general mechanisms and domain-specific embodied representations.

Does visual perception of object afford action? Evidence from a neuroimaging study

Positron emission tomography (PET) was used to explore the neural correlates of a potential involvement of motor representation during the perception of visually presented objects with different tasks. The main result of this study was that the perception of objects, irrespective of the task (judgement of the vertical orientation, motor imagery, and silent generation of the noun or of the corresponding action verb), versus perception of non-objects, was associated with rCBF increases in a common set of cortical regions. The occipito-temporal junction, the inferior parietal lobule, the SMA-proper, the pars triangularis in the inferior frontal gyrus, the dorsal and ventral precentral gyrus were engaged in the left hemisphere. The ipsilateral cerebellum was also involved. These activations are congruent with the idea of an involvement of motor representation already during the perception of object and thus provide neurophysiological evidence that the perception of objects automatically affords actions that can be made toward them. Besides this common set of cortical areas, each task engaged specific regions.

A PET Exploration of the Neural Mechanisms Involved in Reciprocal Imitation

Imitation is a natural mechanism involving perception-action coupling which plays a central role in the development of understanding that other people, like the self, are mental agents. PET was used to examine the hemodynamic changes occurring in a reciprocal imitation paradigm. Eighteen subjects (a) imitated the actions of the experimenter, (b) had their actions imitated by the experimenter, (c) freely produced actions, or (d) freely produced actions while watching different actions made by the experimenter. In a baseline condition, subjects simply watched the experimenters actions. Specific increases were detected in the left STS and in the inferior parietal cortex in conditions involving imitation. The left inferior parietal is specifically involved in producing imitation, whereas the right homologous region is more activated when ones own actions are imitated by another person. This pattern of results suggests that these regions play a specific role in distinguishing internally produced actions from those generated by others.

Does Perception of Biological Motion Rely on Specific Brain Regions

Perception of biological motions plays a major adaptive role in identifying, interpreting, and predicting the actions of others. It may therefore be hypothesized that the perception of biological motions is subserved by a specific neural network. Here we used fMRI to verify this hypothesis. In a group of 10 healthy volunteers, we explored the hemodynamic responses to seven types of visual motion displays: drifting random dots, random dot cube, random dot cube with masking elements, upright point-light walker, inverted point-light walker, upright point-light walker display with masking elements, and inverted point-light walker display with masking elements. A gradient in activation was observed in the occipitotemporal junction. The responses to rigid motion were localized posteriorly to those responses elicited by nonrigid motions. Our results demonstrate that in addition to the posterior portion of superior temporal sulcus, the left intraparietal cortex is involved in the perception of nonrigid biological motions.

Objects automatically potentiate action: an fMRI study of implicit processing

Behavioural data have shown that the perception of an object automatically potentiates motor components (affordances) of possible actions toward that object, irrespective of the subjects intention. We carried out an event‐related fMRI study to investigate the influence of the intrinsic properties of an object on motor responses which were either compatible or incompatible with the action that the object affords. The subjects performed power or precision grip responses based on the categorization of objects into natural or man‐made. The objects were either ‘small’ (usually grasped with a precision grip) or ‘large’ (usually grasped with a power grip). As expected, the motor responses were fastest to objects that afforded the same grip (congruent) and slowest to objects that afforded the other grip (incongruent). Imaging revealed activations which covaried with compatibility in the parietal, dorsal premotor and inferior frontal cortex. We suggest that the greater the difference in reaction times between congruent and incongruent trials, the greater the competition between the action afforded by the object and the action specified by the task, and thus the greater the activation within this network.

Inferring false beliefs from the actions of oneself and others: an fMRI study

The ability to make judgments about mental states is critical to social interactions. Simulation theory suggests that the observer covertly mimics the activity of the observed person, leading to shared states of mind between the observer and the person observed. We tested this hypothesis by investigating the neural networks activated while subjects watched videos of themselves and of others lifting a box, and judged the beliefs of the actors about the weight of the box. A parietal premotor circuit was recruited during action perception, and the activity started earlier when making judgments about ones own actions as opposed to those of others. This earlier activity in action-related structures can be explained by simulation theory on the basis that when one observes ones own actions, there is a closer match between the simulated and perceived action than there is when one observes the actions of others. When the observers judged the actions to reflect a false belief, there was activation in the superior temporal sulcus, orbitofrontal, paracingulate cortex and cerebellum. We suggest that this reflects a mismatch between the perceived action and the predicted actions outcomes derived from simulation.

Perceiving fear in dynamic body expressions

Characteristic fear behaviour like putting the hands in front of the face and running for cover provides strong fear signals to observers who may not themselves be aware of any danger. Using event-related functional magnetic resonance imaging (fMRI) in humans, we investigated how such dynamic fear signals from the whole body are perceived. A factorial design allowed us to investigate brain activity induced by viewing bodies, bodily expressions of fear and the role of dynamic information in viewing them. Our critical findings are threefold. We find that viewing neutral and fearful body expressions enhances amygdala activity; moreover actions expressing fear activate the temporal pole and lateral orbital cortex more than neutral actions; and finally differences in activations between static and dynamic bodily expressions were larger for actions expressing fear in the STS and premotor cortex compared to neutral actions.

Emotional modulation of visual and motor areas by dynamic body expressions of anger

Abstract The ability to detect emotional meaning in others’ behavior constitutes a central component of social competence. Expressions of anger in particular present salient signals that play a major role in the regulation of social interactions. Investigations of human anger signals have to date used still pictures of facial expressions but so far the neurobiological basis of bodily communication of anger remains largely unknown. Using functional magnetic resonance imaging, the present study investigated the neural bases involved in perceiving anger signals emanating from the whole body. Our study also investigates what the presence of dynamic information adds to the perception of body expressions of anger. Participants were scanned while viewing stimuli (stills or videos) of angry and neutral whole-body expressions. Whole-body expressions of anger elicit activity in regions including the amygdala and the lateral orbitofrontal cortex, which play a role in the affective evaluation of the stimuli. Importantly, the perception of dynamic body expressions of anger additionally engages the hypothalamus, the ventromedial prefrontal cortex, the temporal pole and the premotor cortex, brain regions that are coupled with autonomic reactions and motor responses related to defensive behaviors.