Plenary Lecture

Plenary Lecture

Hand Reaching Adaptive and Online
Motor Control Processes

Dr. Claude Prablanc
Directeur de Recherche at Unit 864 Espace et Action (INSERM-Bron)

Several sensori-motor processes are devoted to error reduction for the production of purposeful actions. When motor responses deviate from their goal, online corrections can be performed either under voluntary control with time consuming additional sub-movements or under fast automatic smooth control. When errors cannot be corrected online and are repeated over trials, subsequent responses can be improved iteratively through adaptation, a progressive adjustment of motor commands that acts to reduce the magnitude of error. The sources of these errors may result from an erroneous evaluation of the goal, from unexpected perturbations of the goal itself , or from a patient’s inability to both plan and correct a movement after prefrontal, frontal, parietal, cerebellar or vestibular lesions from vascular or neurodegenerative origin.
Although long term natural sensorimotor recovery is not necessarily the same process as short term adaptation that can be studied experimentally, more knowledge about the latter helps improving the former, illustrated by the attentional and perceptual rehabilitation obtained through sensorimotor prism exposure in neglect patients.
As prism adaptation is rather complex, involving many sensorimotor loops along the eye head hand system connecting reciprocally the perception-action cycle, it is necessary to disentangle some of the major error signals acting upon adaptation.
It has been argued that reaching adaptation results essentially from a conflict between actual sensory feedback and expected sensory feedback. In order to show that such a mechanism is unlikely to be responsible for most of the adaptive process, we have developed two reaching paradigms that provide the subject with undistorted hand visual feedback. Both paradigms induce motor planning errors unknown to the subjects and allow an efficiency assessment of the many feedback loops through real time a control of the oculomotor and upper limb sensorimotor loops.
The first one yields continuous retinal and visuomotor feedback, allowing fast and complete automatic online corrections. It suggests that the same online corrective processes are carried out under natural conditions without awareness. In addition despite a reiterated motor planning error and an automatic online correction of the whole error, this paradigm shows a complete lack of adaptation.
The second paradigm allows an investigation of the role of terminal error feedback only, where all visual feedback is eliminated during movement execution.. In contrast to the first paradigm, it exhibits a robust and generalised adaptation, although devoid of limb inter-sensory mismatch. These results demonstrate independence between the induced motor adaptation and the automatic online correction, both characterized by the lack of any cognitive interference. A putative visuomotor cerebro-cerebellar network accounting for these results is proposed.

Brief Biography of the Speaker:
Claude Prablanc graduated from the Ecole Superieure de Marseille (Electrical Engineering) in 1966, and from the Ecole Nationale Superieure d’Electricite, d’Electronique, d’Informatique et d’Hydraulique de Toulouse in 1967. After a few years working as an engineer for the automated subway Network, he followed a training in neuropsychology and got a researcher position at the Institut National de la Sante et de la Recherche Medicale (INSERM) in 1973. He spent one year in 1981 at the Psychology Department in MIT, working on monkey motor control. His current position is Directeur de Recherche at Unit 864 Espace et Action (INSERM-Bron). His main research interests in Neuroscience are Motor Psychophysics of the eye-head-hand sensorimotor system and of its plasticity, in both normal subjects and neurological patients.

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