[Abstract Title]. - Society for Neuroscience

abnormal postures.
It is often hypothesized that a lack of inhibition results in hyperreflexia (exaggerated reflexes),
effectively causing dystonia. Humans control their movements using proprioceptive feedback
from muscle afferents: muscle force by Golgi tendon organs and muscle stretch by muscle
spindles. To assess whether proprioceptive reflexes can explain the features of dystonia a
neuromusculoskeletal model was developed.
The model describes the human wrist joint with an antagonistic muscle pair and proprioceptive
reflexes originating from Ia, II and Ib afferents: muscle stretch, stretch velocity and force.
Various scenarios were tested and the results were rated to criteria based on characteristic
features of dystonia: abnormal posture, sustained muscle contraction, increased stiffness, activity
dependent rigidity and loss of supraspinal control.
The reflex mechanisms were investigated in three scenarios: 1) hyperreflexia, overexaggerated
reflex sensitivity in both antagonists; 2) biased imbalance, a constant bias to the reflex output of
one of the antagonists; and 3) strength imbalance, increased reflex sensitivity in only one of the
antagonists.
With hyperreflexia, the model shows that despite distinct motor dysfunction, none of the reflex
pathways can fully account for dystonia, since none of them result in an abnormal posture. The
imbalance in the other two scenarios was introduced to provoke an abnormal posture. Although
biased imbalance does result in an abnormal posture, again it can not fully account for dystonia,
since other criteria are no longer satisfied. Nevertheless, strength imbalance closely resembles
the features of dystonia: effectively satisfying all criteria.
In conclusion dystonia may be explained by an imbalance in excitatory muscle force feedback.
The other reflex pathways did not satisfy the criteria for dystonia, but based on the oscillatory
characteristics may explain features in clonus, tremor, etc.
This study shows that dystonia may be explained by proprioceptive reflexes, however it does not
rule out other candidates like hyperactive pain withdrawal reflexes. More research is needed to
elucidate the cause of dystonia.
Disclosures: W. Mugge, None; A.C. Schouten, None; F.C.T. van der Helm, None.
Poster
248. Dystonia
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 248.18/U17
Topic: C.03.j. Dystonia
Support: NIH Grant