Article

It is known that healthy adults can quickly adapt to a novel dynamic
environment, generated by a robotic manipulandum as a structured disturbing force
field. We suggest that it may be of clinical interest to evaluate to which extent
this kind of motor learning capability is impaired in children affected by
cerebal palsy. METHODS: We adapted the protocol already used with adults, which
employs a velocity dependant viscous field, and compared the performance of a
group of subjects affected by Cerebral Palsy (CP group, 7 subjects) with a
Control group of unimpaired age-matched children. The protocol included a
familiarization phase (FA), during which no force was applied, a force field
adaptation phase (CF), and a wash-out phase (WO) in which the field was removed.
During the CF phase the field was shut down in a number of randomly selected
"catch" trials, which were used in order to evaluate the "learning index" for
each single subject and the two groups. Lateral deviation, speed and acceleration
peaks and average speed were evaluated for each trajectory; a directional
analysis was performed in order to inspect the role of the limb's inertial
anisotropy in the different experimental phases. RESULTS: During the FA phase the
movements of the CP subjects were more curved, displaying greater and variable
directional error; over the course of the CF phase both groups showed a
decreasing trend in the lateral error and an after-effect at the beginning of the
wash-out, but the CP group had a non significant adaptation rate and a lower
learning index, suggesting that CP subjects have reduced ability to learn to
compensate external force. Moreover, a directional analysis of trajectories
confirms that the control group is able to better predict the force field by
tuning the kinematic features of the movements along different directions in
order to account for the inertial anisotropy of arm. CONCLUSIONS: Spatial
abnormalities in children affected by cerebral palsy may be related not only to
disturbance in motor control signals generating weakness and spasticity, but also
to an inefficient control strategy which is not based on a robust knowledge of
the dynamical features of their upper limb. This lack of information could be
related to the congenital nature of the brain damage and may contribute to a
better delineation of therapeutic intervention.

Langue : ANGLAIS