COORDINATION OF MANIPULATIVE FORCES IN PARKINSONS-DISEASE

The coordination of manipulative forces was examined in 10 subjects wi th Parkinson's disease (PD) both OFF and ON medication while they gras ped and lifted a small object using the precision grip. The developmen t of grip (squeeze) force and load (vertical lifting) force was record ed and compared to a group of age-matched control subjects. Subjects w ith PD often exhibited a prolonged delay between the first digit conta ct with the object and initiation of the lifting drive. These subjects also exhibited stepwise increases in force, with regular oscillations in the force rates. However, once the vertical drive began, the main increase in grip and load force generally was in parallel and most oth er temporal aspects of the force coordination were similar to those of the control subjects. The extent to which the movement initiation was delayed was related to the stage of the disease, and most subjects im proved ON medication. When the object was held in the air, subjects wi th PD used a grip force level which was similar to that of the control subjects, and all subjects adjusted their grip force according to the surface texture. Furthermore, they exhibited proper reflexive correct ions to sudden changes in load (object perturbations), suggesting inta ct sensorimotor integration. We conclude that the most obvious impairm ents in the coordination of this task were delayed initiation of the g rip-lift sequence and tremor-like oscillations superimposed on otherwi se normal force. (C) 1997 Academic Press.