IMPAIRED SENSORY-MOTOR INTEGRATION DURING GRASPING IN WRITERS CRAMP

Six subjects with writer's cramp and six healthy control subjects were examined while lifting a small instrumented object with variable weig ht and friction using the precision grip. The isometric grip and load forces were sampled at 400 Hz and stored in a flexible laboratory comp uter system for Inter analysis. Quantitative measurement of vibration and temperature sensibility showed normal sensory perception in the wr iter's cramp subjects. They exhibited an impaired programming of the g rip-lift force co-ordination, while the ability to generate unimodal f orce-rate trajectories and to characterize the pattern of the force ou tput according to memory representations of weight and friction of the object were intact The capacity to terminate quickly the programmed g rip force in lifts erroneously programmed too high was impaired Writer 's cramp subjects also employed excessive grip force during the static phase of the lift, and some patients had a short grip force latency a fter sudden unpredicted load increases, indicating a disinhibited spin al reflex response. The results indicate an impaired capacity in write r's cramp subjects to integrate sensory information in the motor progr amming and force regulation during precision grip tasks, despite a nor mal sensibility.