Biomedical subjects

J Grèzes

Publications and source records attributed to J Grèzes.

9 recordsLinked to original sources

PubMed2003

Activations related to "mirror" and "canonical" neurones in the human brain: an fMRI study.

In the macaque monkey ventral premotor cortex (F5), "canonical neurones" are active when the monkey observes an object and when the monkey grasps that object. In the same area, "mirror neurones" fire both when the monkey observes another monkey grasping an object and when the monkey grasps that object. We used event-related fMRI to investigate where in the human brain activation can be found that reflects both canonical and mirror neuronal activity. There was activation in the intraparietal and ventral limbs of the precentral sulcus when subjects observed objects and when they executed movements in response to the objects (canonical neurones). There was activation in the dorsal premotor cortex, the intraparietal cortex, the parietal operculum (SII), and the superior temporal sulcus when subjects observed gestures (mirror neurones). Finally, activations in the ventral premotor cortex and inferior frontal gyrus (area 44) were found when subjects imitated gestures and executed movements in response to objects. We suggest that in the human brain, the ventral limb of the precentral sulcus may form part of the area designated F5 in the macaque monkey. It is possible that area 44 forms an anterior part of F5, though anatomical studies suggest that it may be a transitional area between the premotor and prefrontal cortices.

Adult↗

PubMed2003

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 subject's 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.

Adult↗

PubMed2002

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 experimenter's 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 one's 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.

Adult↗

PubMed2002

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.

Adult↗

PubMed2001

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 people's 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 metaanalysis is to evaluate in specific detail to what extent the activated foci elicited by these studies overlap.

Brain Mapping↗

PubMed2001

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.

Adult↗

PubMed1999

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.

Journal Article↗

PubMed1999

The effects of learning and intention on the neural network involved in the perception of meaningless actions.

PET was used to explore the neural network involved in the perception of meaningless action. In two conditions, subjects observed learned and unknown meaningless actions without any purpose. In two other conditions, subjects observed the same type of stimuli for later imitation. The control condition, which consisted of the presention of stationary hands, served as a baseline. Unsurprisingly, a common network that forms part of the dorsal pathway was engaged in all conditions when compared with stationary hands, and this was interpreted as being devoted to the analysis of hand movements. One of the most striking results of the present study was that some brain areas were strongly modulated by the learning level, independent of the subject's intention. Two different effects were observed: a reduced activity in posterior regions within the common network, which correlated with specific increases in the frontopolar area 10 and in the angular gyrus during the perception of learned meaningless actions compared with the perception of unknown actions. Finally, the major effect of the subject's intention to imitate was a strong increase in the dorsal pathway extending to the lateral premotor cortex and to the dorsolateral prefrontal cortex, which reflects the information processing needed for prospective action. Overall, our results provide evidence for both an effect of the visuomotor learning level and of the subject's intention on the neural network involved during the perception of human meaningless actions.

Adult↗

PubMed1997

Brain activity during observation of actions. Influence of action content and subject's strategy.

PET was used to map brain regions that are associated with the observation of meaningful and meaningless hand actions. Subjects were scanned under four conditions which consisted of visually presented actions. In each of the four experimental conditions, they were instructed to watch the actions with one of two aims: to be able to recognize or to imitate them later. We found that differences in the meaning of the action, irrespective of the strategy used during observation, lead to different patterns of brain activity and clear left/right asymmetries. Meaningful actions strongly engaged the left hemisphere in frontal and temporal regions while meaningless actions involved mainly the right occipitoparietal pathway. Observing with the intent to recognize activated memory-encoding structures. In contrast, observation with the intent to imitate was associated with activation in the regions involved in the planning and in the generation of actions. Thus, the pattern of brain activation during observation of actions is dependent both on the nature of the required executive processing and the type of the extrinsic properties of the action presented.

Adult↗