H. Poizner et al., The timing of arm-trunk coordination is deficient and vision-dependent in Parkinson's patients during reaching movements, EXP BRAIN R, 133(3), 2000, pp. 279-292
The role of the basal ganglia in the coordination of different body segment
s and utilization of motor synergies was investigated by analyzing reaching
movements to remembered three-dimensional (3D) targets in patients with Pa
rkinson's disease (PD). Arm movements were produced alone or in combination
with a forward bending of the trunk, with or without visual feedback. Move
ments in PD patients were more temporally segmented, as evidenced by irregu
lar changes in tangential velocity profiles. In addition, the relative timi
ng in the onsets and offsets of fingertip and trunk motions were substantia
lly different in PD patients than in control subjects. While the control su
bjects synchronized both onsets and offsets, the PD patients had large mean
intervals between the onsets and offsets of the fingertip and trunk motion
s. Moreover, PD patients showed substantially larger trial-to-trial variabi
lity in these intervals. The degree of synchronization in PD patients gradu
ally increased during the movement under the influence of visual feedback.
The mean and variability of the intersegmental intervals decreased as the f
ingertip approached the target, This improvement in timing occurred even th
ough the separate variability in the timing of arm and trunk motions was no
t reduced by vision. In combined movements, even without vision, the PD pat
ients were able to achieve normal accuracy, suggesting they were able to us
e the same movement synergies as normals to control the multiple degrees of
freedom involved in the movements and to compensate for the added trunk mo
vement. However, they were unable to reemit these synergies in the stereoty
ped manner characteristic of healthy subjects. These results suggest that t
he basal ganglia are involved in the temporal coordination of movement of d
ifferent body segments and that related timing abnormalities may be partly
compensated by vision. Abnormal intersegmental timing may be a highly sensi
tive indicator of a deficient ability to assemble complex movements in pati
ents with basal-ganglia dysfunction. This abnormality may be apparent even
when the overall movement goal of reaching a target is preserved and normal
movement synergies appear to be largely intact.