Thomas Eggert (Neurology, LMU-Munich, Munich, Germany) "Patients with cerebral infarcts reduce the degrees of freedom of the arm position by visual control

Abstract :

We investigated the degrees of freedom (DGF) of all joints of the arm position. We compared 10 normals and 5 patients with slight arm paresis due to cerebral infarcts in a repetitive pointing task with open and closed eyes. Subjects were instructed to point always to the same location in space. We analysed the standard deviation of the final hand position (STD_HP) and estimated the dependence of the 7 joint angles on the horizontal and vertical final hand position by means of a multiple quadratic regression. A principle component analysis of the residual error was used to compute the DGF, defined as the number of principle components that covered 90% of the residual error.
The average DGF in normals was 2.6. The standard deviation of the final hand position was 15 mm. Controls were compared with patients when pointing with the affected arm. An ANOVA with the within-subjects factor Vision (with/without) and the between-subjects factor Group (controls/patients) was used. On the DGF both main effects and the interaction were significant showing a smaller DGF in patients (2.1) than in the control group (2.6). The DGF was smaller with (2.4) than without (2.6) vision. The difference between the groups was more pronounced with vision (controls: 2.7; patients: 1.7) than without (controls: 2.6; patients: 2.5). The STD_HP was smaller with (13 mm) than without vision (18 mm). This effect was stronger in the patients (with: 12; without: 22 mm) than in the controls (with: 14; without: 17 mm).
These results suggest that the patients use vision to restrict the DGF of the arm in order to reduce the variability of their final hand position.

Contacts :

Zoï KAPOULA, Tél. 01 44 27 16 35
Maria Pia BUCCI, Tél. 01 44 27 16 36
Françoise VITU, Tél. 01 55 20 58 64