Motor control and position sense: action-perception coupling.

This chapter focuses on the relationship between motor control and position sense (PS) defined as the ability of humans to recognize the position of body segments under different conditions. Studies showed that afferent signals from proprioceptive and cutaneous and, to a lesser degree, articular receptors satisfactorily reflect passive changes in the position of body segments (Matthews 1972; Edin and Johansson 1995). In contrast, afferent signals deliver ambiguous positional information during intentional motor actions. For example, the activity of a major contributor to PS— muscle spindle afferents—increases with increasing isometric muscle torque (Vallbo 1974) whereas the arm position at which the torque is produced is perceived as unchanged. During slow intentional finger motion in isotonic conditions, discharges of spindle afferents virtually remain constant (Hulliger et al. 1982) and thus do not reflect the perceived changes in the finger position. These and other examples, justified the conclusion that afferent signals are somehow integrated with central control signals underlying motor actions to form PS (von Holst 1954; McCloskey 1981; Feldman and Latash 1982a; Proske and Gandevia 2012). The nature of this integration in PS remains unclear. This situation results, in particular, from controversies in the understanding of how motor actions are controlled.