Abstract:
The influence of peak-dose drug-induced dyskinesia (DID) on manual tracking
(MT) was examined in 10 dyskinetic patients (OPO), and compared to 10 age/gendermatched
non-dyskinetic patients (NDPD) and 10 healthy controls. Whole body movement
(WBM) and MT were recorded with a 6-degrees of freedom magnetic motion tracker and
forearm rotation sensors, respectively. Subjects were asked to match the length of a
computer-generated line with a line controlled via wrist rotation. Results show that OPO
patients had greater WBM displacement and velocity than other groups. All groups
displayed increased WBM from rest to MT, but only DPD and NDPO patients
demonstrated a significant increase in WBM displacement and velocity. In addition, OPO
patients exhibited excessive increase in WBM suggesting overflow DID. When two distinct
target pace segments were examined (FAST/SLOW), all groups had slight increases in
WBM displacement and velocity from SLOW to FAST, but only OPO patients showed
significantly increased WBM displacement and velocity from SLOW to FAST. Therefore,
it can be suggested that overflow DID was further increased with increased task speed.
OPO patients also showed significantly greater ERROR matching target velocity, but no
significant difference in ERROR in displacement, indicating that significantly greater
WBM displacement in the OPO group did not have a direct influence on tracking
performance. Individual target and performance traces demonstrated this relatively good
tracking performance with the exception of distinct deviations from the target trace that
occurred suddenly, followed by quick returns to the target coherent in time with increased
performance velocity. In addition, performance hand velocity was not correlated with
WBM velocity in DPO patients, suggesting that increased ERROR in velocity was not a
direct result of WBM velocity. In conclusion, we propose that over-excitation of motor
cortical areas, reported to be present in DPO patients, resulted in overflow DID during
voluntary movement. Furthermore, we propose that the increased ERROR in velocity was
the result of hypermetric voluntary movements also originating from the over-excitation of
motor cortical areas.
