An experimental simulation method for iterative and interactive reconstruction of unknown (fusimotor) inputs contributing to known (spindle afferent) responses.

A simulation technique, combining chronic recordings in freely moving alert cats with acute experiments on a nerve muscle preparation, has been designed to estimate fusimotor activity profiles underlying chronically recorded muscle spindle afferent responses to movements. Fusimotor stimulation patterns are iteratively generated and tested for their ability to simulate a target response during reproduction of the movement. The error between a simulated and the target response is incorporated into the current stimulation pattern, to generate the stimulation profile for the next cycle of iteration. The procedure is semi-automatic and offers a number of interactive features. For instance, the user has the choice to redraw manually critical segments of a given stimulation profile. The procedure converges rapidly, and solutions are unique, since target responses (first produced with known inputs) could be reconstructed by virtually identical, iterated, profiles. The method opens up the possibility of investigating complex transient adjustments of fusimotor drive, e.g. during adaptive motor performance.