Speaker: Dr. Terence D. Sanger, (MD PhD)
Provost Associate Professor, University of Southern California
Departments of Biomedical Engineering, Neurology, and Biokinesiology.
Childrens Hospital of Los Angeles, Department of Neurology.
Title: What dystonia tells us about the motor function of the basal ganglia
Dystonia is a disorder that distorts voluntary movements. Since there
is no weakness, dystonia is fundamentally a failure of motor control.
Therefore we can learn about both normal and abnormal biological
motor control by understanding the mechanisms of failure and recovery
from dystonia. In this lecture, I will present current models of
basal ganglia and thalamus functional anatomy, including the way that
the dynamics of movement can be represented and controlled. I will
then show recent data from multi-electrode recordings in children with
dystonia. The most salient feature of these data is the reversal of
the normal function of basal ganglia: instead of normal inhibition of
unwanted activity in thalamus, only the desired activity is inhibited
while undesired activity is permitted. Therefore attempts at
voluntary movement are met with muscle activation that is the opposite
of the desired movement. Furthermore, lack of inhibition leads to
very high gain in the thalamic feedback pathway which results in
overdriven or oscillatory muscle activity. I will argue that the sign
reversal in the output of basal ganglia is equivalent to a 180-degree
phase shift in a feedback controller that leads to unrecoverable
instability. Finally, I will show how deep-brain stimulation can be a
partially effective treatment that works by reducing the feedback gain
sufficiently that the phase shift no longer produces instability.
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