People
with damage to the cerebellum exhibit the neurological symptom of
ataxia (poor movement coordination). As a result, their movements are
generally characterized by directional errors, dysmetria (under- or
over-shooting), and increased variability. This project seeks to improve
our understanding of the role of the cerebellum in motor control of the
arm through behavioral studies with the KINARM exoskeleton system (BKIN
Technologies, Inc.). A better understanding of cerebellar function can
inspire new rehabilitation therapies for this patient population. |
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Cerebellar motor learning: Effect of environment dynamics vs. error size
Cerebellar damage
has been shown to impair sensorimotor adaptation, the learning of
predictable perturbations via an error-based process. We studied the
effect of specific dynamic perturbations (clockwise vs.
counter-clockwise force field) and error size (abruptly vs. gradually
introduced forces) on motor learning of a reaching movement in patients
with cerebellar damage. We also examined the coordinate system (hand vs.
joint space) in which learning generalized to different movements.
We
were surprised to find that error size did not affect patients'
adaptation (as was previously shown); instead, the direction of the
force field determined their ability to learn. Patients performed best
when the force field helped compensate for their arm dynamics during the
reach. Our results and analysis suggest that that patients use a
different mechanism than controls to improve their performance in the
presence of forces that help counteract their movement biases.
  
T. L. Gibo, S. E. Criscimagna-Hemminger, A.
M. Okamura, and A. J. Bastian.
Cerebellar motor learning: Are
environment dynamics more important than error size?
Journal of Neurophysiology, 110(2):322-333, 2013.
T. L. Gibo, A. M. Okamura, and A. J. Bastian.
Do cerebellar patients generalize after abrupt or gradual motor learning?
Program No. 825.13, 2011 Neuroscience Meeting Planner, Washington, DC: Society for Neuroscience, 2011. Online.A. M. Hadjiosif, S. E. Criscimagna-Hemminger, T. L. Gibo, A. M. Okamura, R. Shadmehr, and M. A. Smith. Cerebellar damage reduces the stability of motor memories.
Translational and Computational Motor Control, 2014
Modulation of arm stiffness during postural maintenance
Impedance control allows us to interact with our
environment during postural and movement tasks, adjusting the
mechanical behavior of our limbs to account for instability and noise.
Young, healthy individuals have been shown to selectively control the
endpoint stiffness of their arms via co-contraction, depending on the
direction of environmental disturbances. Impedance modulation is hypothesized to be distinct from the central
nervous system controller used for joint torque coordination. While the
cerebellum is thought to be involved in joint torque control, the
regions of the brain involved in impedance control are less understood.
We
had subjects perform a static postural maintenance task under two types
of directional force perturbations. We found an effect of both
cerebellar damage and age on the ability of subjects to modify their arm
stiffness between the two perturbation conditions.
Thus, the cerebellum may be involved in optimally modulating arm
impedance, although this appears to be affected by other factors such as
age. Additionally, the cerebellar patients' intact ability to alter
their limb stiffness during the postural task (albeit less than young,
healthy controls) improved their movement performance in a subsequent
tracing task. This transfer of stiffness control from a static to
movement task may be a strategy that can be used to compensate for their
motor deficits.
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T. L. Gibo, A. J. Bastian, and A.
M. Okamura.
Cerebellar ataxia impairs modulation of
arm stiffness during postural maintenance.
Journal of Neurophysiology, 110(7):1611-1620, 2013.
T. L. Gibo, A. J. Bastian, and A. M. Okamura.
Effect of age on stiffness modulation during postural maintenance of the arm.
13th International Conference on Rehabilitation Robotics, 2013.
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