Interaction of afferent and efferent signals underlying joint position sense: empirical and theoretical approaches

A model of joint position sense is considered based on the concept that central motor commands are adequately expressed in terms of shifts of the so-called invariant length-tension characteristics for agonist and antagonist muscles. The main points of this concept are discussed to clarify them and to prevent misunderstanding. The basic idea of the model is that the efferent copy of the central motor commands plays the role of a reference frame for evaluation of afferent proprioceptive discharges. An experiment with reproduction of constrained movements was performed in order to investigate the influence of voluntary flexor or extensor muscle tension on position sense in the elbow joint. The results demonstrate adequate perception of joint position on the background of voluntary muscle tension and thus are quite consistent with the model. The role of afferent and efferent signals in position sense is discussed with special reference to views expressed recently by different authors. The interrelation between position sense and sense of effort is considered, based on a concept of senso-motor space.