Showing papers by "Marc Jeannerod published in 1994"

The representing brain: Neural correlates of motor intention and imagery

Abstract: This paper concerns how motor actions are neurally represented and coded. Action planning and motor preparation can be studied using a specific type of representational activity, motor imagery. A close functional equivalence between motor imagery and motor preparation is suggested by the positive effects of imagining movements on motor learning, the similarity between the neural structures involved, and the similar physiological correlates observed in both imaging and preparing. The content of motor representations can be inferred from motor images at a macroscopic level, based on global aspects of the action (the duration and amount of effort involved) and the motor rules and constraints which predict the spatial path and kinematics of movements. A more microscopic neural account calls for a representation of object-oriented action. Object attributes are processed in different neural pathways depending on the kind of task the subject is performing. During object-oriented action, a pragmatic representation is activated in which object affordances are transformed into specific motor schemas (independently of other tasks such as object recognition). Animal as well as human clinical data implicate the posterior parietal and premotor cortical areas in schema instantiation. A mechanism is proposed that is able to encode the desired goal of the action and is applicable to different levels of representational organization.

Mapping motor representations with positron emission tomography

Abstract: Brain activity was mapped in normal subjects during passive observation of the movements of an 'alien' hand and while imagining grasping objects with their own hand. None of the tasks required actual movement. Shifting from one mental task to the other greatly changed the pattern of brain activation. During observation of hand movements, activation was mainly found in visual cortical areas, but also in subcortical areas involved in motor behaviour, such as the basal ganglia and the cerebellum. During motor imagery, cortical and subcortical areas related to motor preparation and programming were strongly activated. These data support the notion that motor learning during observation of movements and mental practice involves rehearsal of neural pathways related to cognitive stages of motor control.

Orienting the finger opposition space during prehension movements.

Abstract: Two experiments are reported that examined the act of prehension when subjects were asked to grasp with their thumb and index finger pads an elongated object resting horizontally on a surface and placed at different orientations with respect to the subject. In Experiment 1, the pad opposition preferences were determined for the six angles of orientation examined. For angles of 90 degrees (object parallel to frontal plane) or less, no rotation of the wrist (pronation) was used; for angles 110 degrees or greater, pronation was systematically employed to reorient the finger opposition space. Only one angle, 100 degrees , produced any evidence of ambiguity in how to grasp the object: Approximately 60% of these grasps involved pronation and 40% did not. Using the foregoing grasp preference data, in Experiment 2 we examined the kinematics of the wrist and elbow trajectories during prehension movements directed at an object in different orientations. Movement time, time to peak acceleration, velocity, and deceleration were measured. No kinematic differences were observed when the object orientation either required (110 degrees ) or did not require (80 degrees ) a pronation. By contrast, if the orientation was changed at the onset of the movement, such that an unpredicted pronation had to be introduced to achieve the grasp, kinematics were affected: Movement time was increased, and the time devoted to deceleration was lengthened. These data are interpreted as evidence that when natural prehension occurs, pronation can be included in the motor plan without affecting the movement kinematics. When constraints are imposed on the movement execution as a consequence of a perturbation, however, the introduction of a pronation component requires kinematic rearrangement.

The effect of viewing the static hand prior to movement onset on pointing kinematics and variability

Abstract: Pointing accuracy and arm movement kinematics of six human subjects were measured in three conditions where the hand was never visible during the ongoing movement: (1) in the dark; (2) the static hand was seen in peripheral vision prior to target presentation, but not during the reaction time (H−T); (3) the static hand was seen in peripheral vision until movement onset (H+T). It was shown that: (1) viewing the hand prior to movement decreased pointing variability as compared to the dark condition. (2) Viewing simultaneously hand and target (H+T) further decreased pointing variability as compared to the H−T condition. This effect was proportional to the reaction time. (3) A lengthening of the deceleration phase was observed for movements performed in the H + T condition, as compared to the other two conditions. (4) A negative correlation between variability and the first part of the deceleration phase was observed in the H + T condition, but neither in the H-T condition nor in the dark. These results suggest that the decrease in pointing variability observed in the H + T condition is due to a feedback based on kinesthetic reafference. Better encoding of the initial position of the hand relative to the target (as in H + T) would allow a calibration of arm position sense, which is used to drive the hand toward the target during the deceleration phase.

The hand and the object: the role of posterior parietal cortex in forming motor representations.

Abstract: The hypothesis of several subsystems for processing visual information is expanded to the context of visuomotor functions. It is proposed that object-oriented actions involve three main types of processing whether the object is to be localized, identified, or grasped and manipulated. Neurological evidence from patients is provided, showing that each type of processing pertains to a distinct pathway. Whereas identification is impaired by lesions affecting the occipitotemporal pathway, localization and grasping are processed in posterior patrietal cortex. A new clinical case with a parietal lesion is presented, where the grasping deficit contrasted with preservation of both identification and localization. This result suggests separate representations for localizing and grasping within parietal cortex.Key words: visuomotor coordination, hand movements, parietal cortex, neuropsychology.

Chapter 1 Object Oriented Action

Abstract: Summary This chapter reviews some of the aspects of object oriented behaviour during the action of grasping and describes the kinematic aspects of grip formation during object acquisition. It is postulated that hand shaping during grasping is largely based on a pragmatic representation of the object attributes which are relevant to action. This mode of representation is contrasted with another, semantic, mode for object recognition and categorization. A possible cortical mechanism underlying the pragmatic representation is outlined.

Dissociating visual and kinesthetic coordinates during pointing movements.

Abstract: Goal-directed movements imply that the visual coordinates in which the localisation of the goal is coded are transformed into proprioceptive coordinates in which the arm movement is coded. The two systems of coordinates are normally superimposed. Using a virtual reality device attached to the subject's head, we have created a situation where these systems were dissociated from each other. The virtual environment involved virtual visual targets and an image of the subject's hand reconstructed from the output of a data glove wore by the subject's right hand. When the subject's head was rotated, the visual targets and the image of the hand rotated by the same amount. Movements of the real hand were thus in conflict with those of the reconstructed hand, which appeared to err in the direction of head rotation. Pointing movements directed at five targets (0 degree, 26 degrees and 52 degrees on each side) were studied for five different head positions (0 degree, 45 degrees and 80 degrees to the right and to the left). The results showed a significant pointing bias towards head position, except for the left-most targets in the right head rotations. Constant errors in azimuth were proportional to the amount of head rotation. When the head was rotated to the right, constant errors in azimuth were greater during pointing towards right than left targets. Similarly, they were greater for left than for right stimuli when the head was rotated to the left. Errors in amplitude were not influenced by the direction nor the amount of head rotation.(ABSTRACT TRUNCATED AT 250 WORDS)