Fast adjustments of ongoing movements in hemiparetic cerebral palsy.

The present study focuses on the ability of participants with spastic hemiparesis caused by cerebral palsy to adjust an ongoing movement. Typical symptoms associated with the disorder would lead one to expect that people with spastic hemiparesis would be unable to adjust their movements quickly and proportionally to a sudden change in the environment with their spastic arm. The results of the present experiment, however, prove otherwise. Eight hemiparetic adolescents with cerebral palsy and eight healthy control participants were asked to quickly hit a target projected onto a fronto-parallel screen. The target either remained stationary or started to move immediately after hand movement onset. Participants needed to adapt the ongoing movement to hit moving targets. The task was performed with the spastic and non-spastic arm by the hemiparetic participants and with the dominant arm by the healthy participants. Kinematic analyses showed that although the spastic arm of the hemiparetic participants displayed a significant increase in spatial variability which led to more errors, they were capable of successfully adapting their movement in a qualitative manner. The latency of the response to the change in target position was longer for the hemiparetic participants compared to the healthy control participants, but only 25 ms. Surprisingly, no between arm latency difference was found in the hemiparetic participants. Given the commonly observed movement deficits of the spastic arm, these results show that participants with spastic hemiparesis displayed a remarkable ability in adjusting movements quickly.