The organization of prehension movements has been studied in man and primates. Initial studies were on the kinematic aspects of reach and grasp movements. Transport and manipulation components of arm movement in reaching and grasping an object appeared to act through independent channels. In perturbution experiments, where the location of the object was changed at the beginning of arm movement, it was found that different times were required by the 2 components to reorganize movement. The time required to generate a motor response on changing object size or position was measured. There was a slower motor response to size changes, suggesting the visuomotor pathways involved cortical mechanisms in processing information for object identification. Vocal responses to changes were longer than motor correction times suggesting the neural pathways involved in awareness are distinct from these involved in sensorimotor processing.
Prehension movements were studied in a patient with a right parietal lesion. When a distractor object was presented to the ipsilateral side of the target, hand trajectory deviated towards the distractor, but grasp kinematics were unaffected. The shift to the ipsilesional side demonstrated a dissociation in motor control.
Neurophysiological studies were carried out in monkeys. Single neuron recording in the rostral part of the agranular frontal cortex (area 6ab) showed that the neurons were activated during arm reaching and grasping movements. Results from inferior area 6 visual neurons suggest these are responsible for the stable frame of reference necessary for programming visually guided movements. Neurons of the rostal part of the inferior premotor cortex discharged during hand movements and also while the monkey observed specific hand movements performed by experimenters. There was a link between observed movement and that performed by the monkey suggesting these neurons can retrieve movements on the basis of observed actions.
The aim of this project is the study of the kinematics and the neurophysiological mechanisms of reaching and grasping movements in normal subjects and conditioned monkeys. Movements will be analyzed by using a computerized system recognizing the position of passive markers applied to the limbs. The following issues will be addressed : a) Coordinates used by normal subjects for planning grasping movements; b) Relations between transportation and manipulation components of reaching; c) Organization of the peripersonal space; d) Correlation between the kinematics of monkey's arm movements and neuronal discharge in the premotor areas. The combined effort of the two groups of Lyon and Parma should provoide new theoretical insight in the organization of goal-directed movements an establish a standardized set data on reaching-grasping kinematics useful for the assessment of motor disorders.
Funding SchemeCSC - Cost-sharing contracts