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Reduced short term adaptation to robot generated dynamic environment in children affected by Cerebral Palsy.

Masia L, Frascarelli F, Morasso P, Di Rosa G, Petrarca M, Castelli E, Cappa P - J Neuroeng Rehabil (2011)

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Robotics Brain and Cognitive Sciences Dept,, Italian Institute of Technology, Genoa, Italy. lorenzo.masia@iit.it

ABSTRACT

Background: 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.

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Polar plot of lateral deviation (top) and peak of acceleration (bottom) for a representative subject (subj_1) from CP group. Red lines along the different directions are the average of the lateral deviation and peak acceleration values. Green lines represent the standard error and red dot is the centre of the interpolating ellipse. The blue ellipse is an interpolation of the average values over the different directions.
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Figure 6: Polar plot of lateral deviation (top) and peak of acceleration (bottom) for a representative subject (subj_1) from CP group. Red lines along the different directions are the average of the lateral deviation and peak acceleration values. Green lines represent the standard error and red dot is the centre of the interpolating ellipse. The blue ellipse is an interpolation of the average values over the different directions.

Mentions: Movement anisotropy of the human arm is responsible for directional variability of movement kinematics [36], therefore a directional distribution of acceleration peaks while moving along the targets may help in comprehending how inertial anisotropy plays an important role in the adaptation performance to the robot generated force field. Figure 6 (referred to S1 of the CP group) shows the polar plots of the lateral deviation and the acceleration peak, i.e. the distribution along the different target directions of the two indicators. As shown in figure 6 the kinematic error is distributed towards those geometrical configurations in which the arm and the robot together may result more difficult to control by the subject. Observing the average of acceleration peaks along the different directions (bottom figure 6), one can realize how the orientation of the major axes of the interpolating ellipses seems to be concordant with the ones interpolating the lateral deviations, over the three different phases of the experiment; we may hypothesize that the higher is the lateral deviation over a certain direction and the higher is the correspondent acceleration peak due to the trajectory correction operated by the subject. The directional distribution of the kinematic variables seems to shed some light on how the subjects try to master the interaction with the generated external environment by taking into account the anisotropy of the arm.


Reduced short term adaptation to robot generated dynamic environment in children affected by Cerebral Palsy.

Masia L, Frascarelli F, Morasso P, Di Rosa G, Petrarca M, Castelli E, Cappa P - J Neuroeng Rehabil (2011)

Polar plot of lateral deviation (top) and peak of acceleration (bottom) for a representative subject (subj_1) from CP group. Red lines along the different directions are the average of the lateral deviation and peak acceleration values. Green lines represent the standard error and red dot is the centre of the interpolating ellipse. The blue ellipse is an interpolation of the average values over the different directions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3117777&req=5

Figure 6: Polar plot of lateral deviation (top) and peak of acceleration (bottom) for a representative subject (subj_1) from CP group. Red lines along the different directions are the average of the lateral deviation and peak acceleration values. Green lines represent the standard error and red dot is the centre of the interpolating ellipse. The blue ellipse is an interpolation of the average values over the different directions.
Mentions: Movement anisotropy of the human arm is responsible for directional variability of movement kinematics [36], therefore a directional distribution of acceleration peaks while moving along the targets may help in comprehending how inertial anisotropy plays an important role in the adaptation performance to the robot generated force field. Figure 6 (referred to S1 of the CP group) shows the polar plots of the lateral deviation and the acceleration peak, i.e. the distribution along the different target directions of the two indicators. As shown in figure 6 the kinematic error is distributed towards those geometrical configurations in which the arm and the robot together may result more difficult to control by the subject. Observing the average of acceleration peaks along the different directions (bottom figure 6), one can realize how the orientation of the major axes of the interpolating ellipses seems to be concordant with the ones interpolating the lateral deviations, over the three different phases of the experiment; we may hypothesize that the higher is the lateral deviation over a certain direction and the higher is the correspondent acceleration peak due to the trajectory correction operated by the subject. The directional distribution of the kinematic variables seems to shed some light on how the subjects try to master the interaction with the generated external environment by taking into account the anisotropy of the arm.

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Robotics Brain and Cognitive Sciences Dept,, Italian Institute of Technology, Genoa, Italy. lorenzo.masia@iit.it

ABSTRACT

Background: 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.

Show MeSH
Related in: MedlinePlus