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Error Correction Strategies Used By Hemiparetic Subjets: Short-term Learning Processes.

Dancause, N (Neurological Sciences Research Centre and School of Rehabilitation, University of Montreal, Canada)
Levin, M. F. (Neurological Sciences Research Centre and School of Rehabilitation, University of Montreal, Canada)

Contact Person: Numa Dancause (dancausn@magellan.umontreal.ca)


Sensorimotor problems following central nervous system lesions resulting in hemiplegia include spasticity and movement deficits of the upper limb. The rehabilitation of these patients is broadly based on movement repetition in order to learn new motor patterns. Two processes may be involved in motor learning: the ability to modify the motor command as a function of variations in the external environment and, the capacity to integrate previously acquired skills into motor performance. These may be expressed by the specification of an adequate central command and by the use of short-term memory. The process of motor recovery and the acquisition of new motor skills in hemiparetic patients is poorly understood. It is not known, for example, how sensorimotor recovery may be optimized to improve the efficiency of rehabilitation services. The goal of this study was to identify the correction stategies used by hemiparetic subjects to procuce precise elbow flexion movements. Ten hemiparetic subjects (aged less than 70 years old, Chedoke-McMaster Arm Function Score > 3, between 3 months and 3 years post CVA) made 'as fast as possible' one degree-of-freedom movements to a 6 wide target. They were instructed not to correct (control trials) or to correct (experimental trials) their movement errors resulting from the sudden introduction of an external load produced by a torque motor. The appropriate load was chosen as a function of the patient's maximal strength. It was applied for a series of 5 to 10 trials and then removed for the next series of 5 to 10 trials. The number of trials for each condition was chosen randomly to prevent subjects from anticipating the change in load and making preparatory adjustments. The total number of trials was 120. For movements with the load, the load was zero at the initial position and increased as a linear function of displacement to the target (spring like load). Angular position and velocity data along with torque and electromyographic activity from 4 muscles ( 2 elbow flexors and 2 elbow extensors) were recorded. Movement precision, movement duration and velocities were calculated. Data analysis was based on the hpothesis that voluntary movement are associated with shifts in the net joint torque/angle characteristic. Error patterns were identified by analyzing angular positions and torques before and after correction. Since hemiparetic patients move their arms considerably slower than healthy subjects, we recorded movements from healthy subjects moving at comparably slow velocities. We found that healthy subjects use the same strategies of correction at slower speeds than those observed when moving as fast as possible which confirmed that movement speed was not responsible for the observed differences in correction patterns between healthy and hemiparetic subjects. Results showed that even those subjects with high levels of spasticity and low motor functional ability were able to produce appropriate motor command since the estimated final elbow positions and corrections were accurate even if, visually, the movement appeared erratic and incorrect. For subjects with only mild hemiparesis (Fugl-Meyer score 50-60), correction strategies were similar to those observed in healthy subjects. These subjects showed the ability to correct their movement after only one trial (one-trial learning). They also showed an increasing precision and ability over the 120 trials. These subjects would be fully capable of improving their motor skills after treatments based on movement repetition. Subjects with moderate motor disability (Fugl-Meyer score 25-40) often needed two, three or even four trials to correct movemetn errors. However, during the course of repetition, there was an improvement in the numberof trials needed for correction and an increase in the movement precision. These subjects would fall into an 'intermediate' category of hemiparetic patients who could benefit from movement repetion but, who would require a great deal of time and effort to learn these new tasks. A third category of subjects who were more severely affected (Fugl-Meyer score 10-15) did not show any correction strategy nor improvement in performance even after 120 trials. For these subjects, repetitive movement treatment approaches may not be appropriate.

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Poster Number PAdancause0805
Keywords: Hemiparetic, movement, control, rehabilitation, treatment

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Dancause, N; Levin, M. F.; (1998). Error Correction Strategies Used By Hemiparetic Subjets: Short-term Learning Processes.. Presented at INABIS '98 - 5th Internet World Congress on Biomedical Sciences at McMaster University, Canada, Dec 7-16th. Available at URL http://www.mcmaster.ca/inabis98/neuroscience/dancause0805/index.html
© 1998 Author(s) Hold Copyright