Estimation of muscle spindle information rate by pattern matching and effects of the fusimotor system

The information transmission properties of ensembles of muscle spindles (MSs) and the effect of the motor muscle spindle innervation (fusimotor or gamma system) on these properties were studied. A random stimulus was applied to a muscle in the hind limb of a cat, while spike trains from several MSs were recorded simultaneously. The stimulus was administered twice, with an operative and a disconnected gamma system. The Shannon information rate between the stimulus and spike trains, as well as other information theoretic measures, were estimated. The estimation method was based upon the sliding window Lempel-Ziv algorithm with an extension to the conditional case. The information rate of ensembles of MSs increased with increasing ensemble size. However, with an operative gamma system, the "ensemble effect" was much higher. In addition, the ensemble effect was influenced by the stimulus spectrum. The results indicate that the gamma system has an important role in enhancing information transmission from ensembles of MSs to the spinal cord.