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First published online on August 26, 2004.
Copyright © 2004 by The Physiological Society
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jphysiol.2004.068668v1
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Received May 24, 2004
Revised July 1, 2004
Accepted after revision August 25, 2004

Coding of position by simultaneously recorded sensory neurons in the cat dorsal root ganglion

Richard B Stein1*, Douglas J Weber1, Yoichiro Aoyagi2, Arthur Prochazka1, Joost Wagenaar3, Shy Shoham4, and Richard A Normann5

1 University of Alberta
2 Kawasaki Medical School
3 University of Twente
4 Princeton University
5 University of Utah

* To whom correspondence should be addressed. E-mail: richard.stein{at}ualberta.ca.

Muscle, cutaneous and joint afferents continuously signal information about the position and movement of individual joints. How does the nervous system extract more global information, for example about the position of the foot in space? To study this question we used microelectrode arrays to record impulses from up to 100 discriminable, nerve cells simultaneously in the L6 and L7 dorsal root ganglia (DRG) of the anesthetized cat. When the limb was displaced passively with a random trajectory, the firing rate of the neurons could be predicted from a linear sum of positions and velocities in Cartesian (x, y), polar or joint angular coordinates. The process could also be reversed to predict the kinematics of the limb from the firing rates of the neurons with an accuracy of 1-2 cm. Predictions of position and velocity could be combined to give an improved fit to limb position. Decoders trained using random movements successfully predicted cyclic movements and movements in which the limb was displaced from a central point to various positions in the periphery. A small number of highly informative neurons (6-8) could account for over 80% of the variance in position and a similar result was obtained in a realistic limb model. In conclusion, this work illustrates how populations of sensory receptors may encode a sense of limb position and how the firing of even a small number of neurons can be used to decode the position of the limb in space.


Key words: Cat • Dorsal root ganglion • Proprioception







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