Ph.D Thesis

Ph.D StudentTock Yoav
SubjectInformation Theoretic Analysis of the Muscle Spindle
DepartmentDepartment of Electrical and Computer Engineering
Supervisors PROF. Yossef Steinberg
PROFESSOR EMERITUS Gideon Inbar (Deceased)


The muscle spindle (MS) is a mechanoreceptor that responds to mechanical events in skeletal muscle, and conveys this information by means of action potential sequences to the central nervous system. The MS responsiveness to mechanical events is controlled by gamma motoneurons in the spinal cord, which innervate the spindle’s muscle fibers. The information transmission properties of ensembles of MSs and the effect of the gamma system on these properties were studied by three converging lines of research: (I) Animal experiments in which the information rate was estimated and the effect of the gamma system was quantified; (II) The development of information theoretic estimation tools, and the formulation of an “operative” interpretation for the information rate; (III) Simulation of a muscle spindle model with gamma activation.

A random stimulus was applied to a muscle in the hind limb of a cat, while spike trains from several MSs were recorded. The stimulus was administered twice, with an operative and a disconnected gamma system. The information rate between the stimulus and spike trains was 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 enhances information theoretic measures quantifying the quality of the sensory neural channel. The results of the MS model simulations support this conclusion.